This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Archives of Phytopathology and Plant Protection, Dec 14, 2015
The individual and combined effects of Pseudomonas fluorescens (Pf) and salicylic acid (SA) were ... more The individual and combined effects of Pseudomonas fluorescens (Pf) and salicylic acid (SA) were investigated for control of citrus bacterial canker (CBC). Both treated plants with copper hydroxide and untreated ones were used as controls. Mexican lime (Citrus aurantifolia) seedlings were treated with SA at 10 mM, Pf and distilled water. Plants were initially inoculated with Xanthomonas citri subsp citri 72 h post treatments. Results indicated that the Pf and SA treatment controlled CBC more effectively compared to separately applying Pf or SA. The application of Pf in combination with SA significantly reduced lesion number per leaf (72%) and disease severity (84%). Significant changes in the activities of peroxidase and catalase were found. In conclusion, the integration of Pf with SA complements each other and can be applied to manage citrus canker disease in conjunction with other control programmes.
A total of 350 citrus canker bacterial isolates, representing different citrus growing regions in... more A total of 350 citrus canker bacterial isolates, representing different citrus growing regions in Saudi Arabia, were identified as Xanthomonas citri subsp. citri (Xcc). DNA alignment of the 16S-rDNA of the three citrus canker organisms (Xcc, pathotypes A, X. fuscans pv. aurantifolii, pathotype B, and C) showed that they can be distinguished by using two SNPs. All the 350 Saudi Xcc strains belonged to the 16-rDNA haplotype of Xcc-A pathotypes. Pathogenicity in leaf assays using differential citrus cultivars, grapefruit (Citrus paradisi) and Mexican lime (C. aurantifolia), divided the Saudi Arabian bacterial isolates into two groups. The first group produced typical symptoms of Xcc, including erumpent canker lesions with water-soaked margins on all hosts. However, the second group caused atypical symptoms on grapefruit leaves. REP-PCR analysis grouped Xcc strains into three clusters that were not correlated with host, pathogenicity or geographic origin. However, the Baha Xcc population had the highest genetic variability, suggesting that this region may be responsible for disseminating Xcc strains to Saudi southern citrus-growing regions through movement of contaminated planting materials. Although we were able to definitely identify the Saudi citrus canker bacteria as Xcc-A pathotypes, its pathotypes still needs more investigation to be recognized. To our knowledge, this also is the first report of occurrence of citrus canker of sweet orange in the Abha region of Saudi Arabia.
Applications of formulated bacteriophages with skim milk and sucrose or nonformulated bacteriopha... more Applications of formulated bacteriophages with skim milk and sucrose or nonformulated bacteriophages combined with acibenzolar-S-methyl (ASM) were compared with copper bactericides applications for suppressing Asiatic citrus canker (ACC) caused by Xanthomonas citri subsp. citri (Xcc) on leaves under greenhouse and field conditions in Saudi Arabia. Bacteriophages were applied one day prior to inoculation of Mexican lime (Citrus aurantifolia) plants with Xcc, then twice a week until the end of the trials. Copper hydroxide was applied once prior to inoculation and then every seven days afterward, whereas ASM was applied one week prior to inoculation and then every 21 days afterward. Under greenhouse conditions, the incidence of ACC on leaves was reduced significantly from 75.2 to 12.8% or 18.3% for plants treated with copper hydroxide or bacteriophages in combination with ASM, respectively. Applications of formulated phages in combination with ASM as soil drench under field conditions significantly decreased disease incidence by 14.8% (Trial 1) and 16.8% (Trial 2) compared with untreated control plants. Overall, the Xcc-inoculated plants treated with bacteriophages + ASM combination showed significant ACC reduction under greenhouse and field conditions. The bacteriophages + ASM combination tested in these trials can be an effective tool in the integrated management programs of Asiatic citrus canker disease.
Aedes aegypti mosquito is the principal dengue vector in the Kingdom of Saudi Arabia (KSA); howev... more Aedes aegypti mosquito is the principal dengue vector in the Kingdom of Saudi Arabia (KSA); however, no study has addressed its ecology and population structure yet. Therefore, we report on Ae. aegypti phylo- and population genetics using three DNA markers: COI, ND4, and rDNA-ITS2. Sampling the immature stages of Ae. aegypti revealed that water storage tanks (34.3% of habitats) were the most productive and contained 33% of immatures stages. Other important habitats included containers for wastewater drainage (including air-conditioning and water cooler trays) and containers associated with ornamentation. Shallow water leakage spots (2.7% of habitats, 8% of immatures) can be considered rare-but-epidemiologically-important containers. Neighbor-joining (NJ) phylogenetic analysis of Ae. aegypti identified 8, 14, and 9 haplotypes of COI, ND4, and ITS2, respectively, and revealed high levels of genetic variation in Ae. aegypti populations of KSA. Global distribution of haplotypes also indicated multiple gene introductions into these populations, with high levels of intra-population genetic variation and continuous gene exchange. The neutrality values indicated a deficiency of alleles and suggested that the KSA Ae. aegypti loci tested did not follow a neutral model of molecular evolution. Fst values and AMOVA indicated that most of the genetic variation in the KSA Ae. aegypti populations is due to intra- rather than inter-population differences. This is the first comprehensive report on the phylo- and population genetics of Ae. aegypti from the Arabian Peninsula. This information expands our understanding of the ecology and population dynamics of this important arboviral vector for informed control efforts.
The oriental red spider mite, Eutetranychus orientalis (Klein) is a major pest of citrus in many ... more The oriental red spider mite, Eutetranychus orientalis (Klein) is a major pest of citrus in many countries including Saudi Arabia (SA). The morphological variations among the different populations of E. orientalis were reported. In the present study, phenotypic variations based on 40 different morphological characteristics were evaluated in 10 E. orientalis populations collected from different hosts and regions of SA. Further, ITS2-rDNA sequences were used to confirm the identity of these phenotypically varying populations. Phenotypic variations in all populations were found in the shape and length of dorsal setae, striation pattern between setae d1 and e1, and leg chaetotaxy. The rDNA sequence analysis of these morphologically varying populations resulted in 10 different ITS2 Saudi haplotypes. The phenotypic and genetic variations were more related to the host plants rather than their geographic distribution. The E. orientalis population collected from Phoenix dactylifera was phenotypically distinct and genetically divergent. The populations collected from citrus species were also more phenotypically and genetically related to each other than to populations collected from non-citrus host plants. The haplotypes recovered from Ziziphus sp., Morus sp., and Azadirecta indica from different regions were grouped in the same sub-clade. Further, the ITS2 haplotypes of Saudi E. orientalis recovered from Citrus reticulata from Riyadh and Al Ula were 100% identical to the ITS2 haplotypes recovered from Citrus sp. from Israel. It is concluded that phenotypic variations exist among different populations of E. orientalis inhabiting different host plants. This species should be identified carefully by considering phenotypic intraspecific variations.
Ramulispora sorghi causes sooty stripe of sorghum. Disease severity in irrigated and dryland plot... more Ramulispora sorghi causes sooty stripe of sorghum. Disease severity in irrigated and dryland plots was measured for 25 susceptible sorghum genotypes during the 2007 and 2008 growing seasons using a rating scale based upon percent leaf area infected. Disease severity ratings were approximately 1.4 points higher (P < 0.0001) on the rating scale in the irrigated plots than dryland plots for 2007 and 2008. Sooty stripe lesions were collected from each sorghum genotype in irrigated plots and assessed for mean microsclerotium production within lesions, microsclerotium size, and sporogenic germination, with significant differences apparent between genotypes for microsclerotium size (P = 0.01) and sporogenic germination (P = 0.01). There was no relationship between disease severity and microsclerotium production within leaf lesions, microsclerotium size, or sporogenic germination; however, there was a positive and significant correlation between microsclerotia production within a lesion and microsclerotium size (R 2 = 0.19, P < 0.0001). Although microsclerotia from sorghum lesions varied in structural characteristics and their ability to produce spore masses, these qualities were dependent upon the sorghum genotype from which the microsclerotia were derived, because the R. sorghi population was genetically uniform as determined by internal transcribed spacer sequences and random amplified polymorphic DNA polymerase chain reaction.
The house fly Musca domestica L. (Diptera: Muscidae) is a worldwide medical and veterinary pest, ... more The house fly Musca domestica L. (Diptera: Muscidae) is a worldwide medical and veterinary pest, causing great economic losses. Organophosphate insecticides have been widely used to control house fly populations. The main objectives of the present study were to evaluate the resistance levels of M. domestica slaughterhouse populations, collected from Riyadh, Jeddah, and Taif, against the organophosphate insecticide pirimiphos-methyl and investigate the genetic mutations of the Ace gene associated with pirimiphos-methyl resistance. The obtained data showed that there were significant differences among pirimiphos-methyl LC50 values of the studied populations, where the highest LC50 was recorded for the Riyadh population (8.44 mM), followed by Jeddah and Taif populations (2.45 mM and 1.63 mM, respectively). Seven nonsynonymous SNPs were detected in the studied house flies. The Ile239Val and Glu243Lys mutations are reported for the first time, whereas Val260Leu, Ala316Ser, Gly342Ala, Gly...
Onion (Allium cepa L.) is a globally important crop worldwide including Saudi Arabia. In November... more Onion (Allium cepa L.) is a globally important crop worldwide including Saudi Arabia. In November 2020, 2-monthold onion plants (cv. Redwing) in commercial fields within the Sajir area of Riyadh region (∼ 1.4 ha), showed symptoms of yellowing, wilting, stunting, bulb discoloration, rot in the basal parts of bulb and decrease in roots. In the advanced stages, the affected plants collapsed and died. The incidence of symptomatic plants ranged from 30 to 65% in the surveyed fields. To isolate the pathogen, symptomatic onion plants (n =20) were sampled. Diseased tissues from roots and bulbs were cut into small pieces (4 × 4 mm), sanitized with 1% sodium hypochlorite solution for 2 min, submerged in 70% alcohol for 20 s, then rinsed with sterile water, before plating on potato dextrose agar (PDA) medium. The plates were incubated at 25°C for 6 days. Subcultures of the mycelia grown out of the diseased tissues produced purplish pink fungal colonies on PDA. On carnation leaf agar, cultures were characteristic of Fusarium oxysporum as described by Leslie and Summerell (2006), with the presence of unicellular microconidia (3.8 to 7.8 × 1.7 to 2.5 μm, n= 50) without septa in false heads or short monophialides and slightly curved macroconidia (16.3 to 28 × 4.2 to 6.1 μm, n= 50) with two to four septa. Older mycelia developed many chlamydospores that were single or in short chains. To further confirm the pathogen identification, DNA was extracted from single-spore cultures of three representative isolates using the DNeasy Plant Mini kit (QIAGEN, Hilden, Germany). Three different fungal nuclear regions of internal transcribed spacer (ITS), elongation factor 1-α, (TEF1-α) and the second largest subunit of DNAdirected RNA polymerase II (RPB2) DNA were amplified by PCR and sequenced with the following primers: ITS4
Charcoal rot (CR), caused by Macrophomina phaseolina, is a major disease of sunflowers in semi-ar... more Charcoal rot (CR), caused by Macrophomina phaseolina, is a major disease of sunflowers in semi-arid regions with poor soil conditions. There are fungicide-based strategies to mange this disease; however, alternative eco-friendly control approachs are needed to prevent further deterioration for the environment. This study describes CR control in sunflower grown in calcareous soil using a talc-based bioformulation containing a mixture of rhizobacterial strains (Azotobacter chroococcum, Azospirillum brasilense, and Klebsiella pneumoniae) integrated with silicon nutrition. The study was conducted under greenhouse conditions; M. phaseolina was inoculated in the soil, and rhizobacterial strains were applied as seed treatment, as well as soil drenching at 7, 30, and 45 days after planting (DAP). As the silicon source (Si), potassium silicate was added to nutrient solution at a concentration of 2 mM and applied weekly starting from 7 DAP. The plants, collected at 85 DAP, showed that applying rhizobacteria and Si individually and in combination was effective in controlling CR disease and improving plant growth. The treatment that included rhizobacterial mixture and Si nutrition had a synergistic effect and resulted in the highest reduction (P < 0.05) in the disease incidence (65.3%), root-rot index (57.8%), and stem tissue colonization (63.6%) compared to non-treated inoculated control. Also, the decrease in the growth and nutrient uptake of sunflower plants due to the pathogen-induced stress was significantly reduced. Notably, rhizobacteria + Si treated-plants exhibited less lipid peroxidation and more phenolic and lignin contents with greater defence enzyme activities due to reduced root damage during M. phaseolina infection. Therefore, the integration between rhizobacterial inoculation and Si fertilization can be a good candidate for managing CR in sunflowers in semi-arid regions.
Several species of Fusarium cause serious diseases in date palm worldwide. In the present work, 1... more Several species of Fusarium cause serious diseases in date palm worldwide. In the present work, 14 SSR markers were used to assess the genetic variation of Fusarium strains isolated from diseased trees in Saudi Arabia. We also studied the effect of different temperatures on mycelial growth of these strains. The pathogenicity of four strains of F. proliferatum was also evaluated on local date palm cultivars. Eleven SSR markers amplified a total of 57 scorable alleles from Fusarium strains. Phylogenetic analysis showed that F. proliferatum strains grouped in one clade with 95% bootstrap value. Within F. proliferatum clade, 14 SSR genotypes were identified, 9 of them were singleton. Four out of the five multi-individual SSR genotypes contained strains isolated from more than one location. Most F. solani strains grouped in one clade with 95% bootstrap value. Overall, the SSR markers previously developed for F. verticillioides and F. oxysporum were very useful in assessing the genetic diversity and confirming the identity of Saudi Fusarium strains. The results from the temperature study showed significant differences in mycelial growth of Fusarium strains at different temperatures tested. The highest average radial growth for Fusarium strains was observed at 25˚C, irrespective of species. The four F. proliferatum strains showed significant differences in their pathogenicity on date palm cultivars. It is anticipated that the assessment of genetic diversity, effect of temperature on hyphal growth and pathogenicity of potent pathogenic Fusarium strains recovered from date palm-growing locations in Saudi Arabia can help in effectively controlling these pathogens.
Fusarium proliferatum is one of the most pathogenic Fusarium species on date palm worldwide. We e... more Fusarium proliferatum is one of the most pathogenic Fusarium species on date palm worldwide. We evaluated the colonization ability of 42 F. proliferatum strains collected from date palm trees with disease symptoms on detached leaflets of cvs Sheeshee and Sukkary. Cell wall degrading enzyme (CWDE) production by these strains was assessed with multiple relative enzyme activity (RA) indices. The ability of F. proliferatum strains to colonize leaflet cuttings varied, and there were significant differences (P < 0.05) in susceptibility between the Sheeshee and Sukkary cvs. All F. proliferatum strains tested could hydrolyze carboxymethylcellulose (CMC), citrus pectin and starch, with different capabilities. RA indices calculated from direct assessment of halo zones were consistent with fungal strain colonization ability, but ratio-based RA indices were not. Based on RA 4 index of cellulases, F. proliferatum strains were divided into three groups. The first group (33% of strains) showed very strong reaction in hydrolysing CMC, the second group (62% of strains) showed strong reaction in hydrolysing CMC, and the third group (5%) showed moderate reaction in hydrolysing CMC. Most strains had moderate pectin-hydrolysis activities. Starch-hydrolysis activities ranged from weak to strong. Overall, there was a positive correlation between cellulase production and a strain's colonization ability. Thus, CWDEs produced by F. proliferatum play a role in the colonization of date palm leaflets and hence may be important pathogenicity factors.
Fusarium oxysporum f. sp. albedinis (FOA) is a seed-and soil-borne vascular wilt pathogen that ca... more Fusarium oxysporum f. sp. albedinis (FOA) is a seed-and soil-borne vascular wilt pathogen that causes a very serious and destructive disease of date palm (Bayoud disease). FOA is not currently known to occur in Saudi Arabia, but the disease has been moving eastward from its origin in Morocco and Algeria. The main objective of this study was to evaluate Saudi Arabian date palm germplasm at the molecular level to assess the presence of R or S plasmid. We evaluated 711 trees representing 42 date palm varieties in Saudi Arabia with a mitochondrial molecular marker and sequenced 64 of the diagnostic PCR amplicons. Most of the trees (628/711) carried the R-plasmid which is associated with Bayoud resistance against FOA fungus. The other 83 trees carried the S-plasmid and are predicted to be susceptible. All amplifications from putatively resistant trees had the same DNA sequence. Moreover, the sequence of the Saudi resistance amplicon was identical to the sequence of Moroccan resistance DNA publically available in NCBI-GenBank database. All the sensitive trees from Saudi Arabia shared a common DNA sequence. This sequence differed from the Moroccan susceptible one at seven unique mutations including five single nucleotide polymorphisms (SNPs) and two insertion/deletion (indels) regions. The uniformity of the sequences means that the introduction of new germplasm to Saudi Arabia will be easily detected. The relatively high frequency of putative resistance means that if/when this disease enters the Kingdom that most trees should be resistant.
Fusarium wilt of tomato (FW) caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a major cha... more Fusarium wilt of tomato (FW) caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a major challenge for tomato production worldwide. For sustainable management of FW, the potential of five strains of Trichoderma asperellum was evaluated under greenhouse conditions. The results indicated that FOL infected plants treated with T. asperellum strains significantly reduced disease incidence and severity compared with FOL-only infected plants. The reduction of wilt disease on plants treated with T. asperellum strains was accompanied by a significant reduction in FOL populations in tomato stems and rhizosphere. Moreover, the application of T. asperellum promoted tomato plant growth irrespective of the presence or absence of FOL. Two strains of T. asperellum (TS-12 and TS-39) that showed the best performance in minimizing disease development and increases in plant growth parameters were selected for elucidating their ability in triggering tomato defense mechanisms. The expression levels of defense-related genes, chitinase (SlChi3), β-1,3-glucanase (SlGluA) and PR-1 (SlPR-1a) were significantly increased in the stems and roots of Trichoderma treated, FOL infected plants, compared with FOL-only infected ones. These results indicate that the application of T. asperellum strains TS-12 and TS-39 can be used as an alternative strategy to manage FW through their antagonistic activities and abilities to induce systemic resistance.
Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants... more Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants, animals, and humans. Moreover, many Fusarium species secrete mycotoxins (e.g. trichothecenes and fumonisins) that are toxic to humans and animals. Fusarium isolates from date palm trees showing disease symptoms, e.g. chlorosis, necrosis and whitening, were collected from seven regions across Saudi Arabia. After single-sporing, the fungal strains were morphologically characterized. To confirm the identity of morphologically characterized Fusarium strains, three nuclear loci, two partial genes of translation elongation factor 1 α (tef1α) and β-tubulin (tub2), and the rDNA-ITS region, were amplified and sequenced. Of the 70 Fusarium strains, 70 % were identified as F. proliferatum that were recovered from six regions across Saudi Arabia. Fusarium solani (13 %), as well as one strain each of the following species: F. brachygibbosum, F. oxysporum, and F. verticillioides were also recovered. In addition, five Fusarium-like strains were recognized as Sarocladium kiliense by DNA-based data. The preliminary in vitro pathogenicity results showed that F. proliferatum had the highest colonization abilities on date palm leaflets, followed by F. solani. Although F. oxysporum f. sp. albedinis is the most serious date palm pathogen, F. proliferatum and F. solani are becoming serious pathogens and efforts should be made to restrict and control them. In addition, the potential toxin risks of strains belonging to F. proliferatum should be evaluated.
Bayoud disease, caused by Fusarium oxysporum f. sp. albedinis, is a very serious and destructive ... more Bayoud disease, caused by Fusarium oxysporum f. sp. albedinis, is a very serious and destructive disease to date palm. Screening of date palm germplasm for resistance to bayoud disease is a crucial step to avoid or alleviate the disease consequences. Fortunately, it was discovered that there are two mitochondrial plasmid-like DNA molecules associated with susceptibility or resistance to bayoud disease. In this chapter, we present a fast, simple, and reliable technique to screen date palm germplasm for the presence of these mitochondrial molecular markers associated with susceptibility or resistance to bayoud.
The association between reactive oxygen species (ROS) production and potato resistance to the hem... more The association between reactive oxygen species (ROS) production and potato resistance to the hemibiotrophic pathogen Phytophthora infestans is poorly understood. In this study, the concentrations of hydrogen peroxide (H 2 O 2), malondialdehyde (MDA), and soluble phenolics, as well as the activities of superoxide dismutase, catalase, and ascorbate peroxidase were measured during the early biotrophic and late necrotrophic stages of P. infestans infection on resistant and susceptible 'Ovatio' and 'Bintje' potato plants, respectively. Pathogen biomass was examined using semi-quantitative RT-PCR. Late blight (LB) severity was also evaluated. The LB severity in Ovatio was lower than that in Bintje, irrespective of the evaluation time. Moreover, in both cultivars, various biochemical defense responses occurred following pathogen infection. The susceptible cultivar activated defense responses at the later pathogen infection stages, resulting in higher concentrations of H 2 O 2 and greater MDA content, with lower activity of antioxidant enzymes and phenolic content. These responses were accompanied by the necrotrophic phase, leading to extensive necrotic lesions on leaves. In contrast, fast hypersensitive-like lesions, an early peak in H 2 O 2 concentration, low cell membrane integrity during the biotrophic phase, and a more efficient antioxidative system effectively restricted pathogen colonization before the transition to the necrotrophic phase in the resistant cultivar. These results suggest that LB resistance or susceptibility is regulated by a balance between the induction of ROS/antioxidants (intensity and timing) and the trophic phase of P. infestans.
International Journal of Agriculture and Biology, Jul 1, 2015
Plants have evolved different defense mechanisms to combat pathogen attacks. In this study, detac... more Plants have evolved different defense mechanisms to combat pathogen attacks. In this study, detached leaf assays were conducted to estimate the influence of leaf position (leaf age) on the development of chocolate spot disease, caused by Botrytis fabae, in the lower, middle and upper leaves of five faba bean (FB) cultivars with different levels of resistance/susceptibility. Two components of resistance in terms of lesion diameter and spores per lesion were used to evaluate the disease intensity. To evaluate plant defense response, oxidative burst and phenol-oxidizing enzymes were assayed. The results indicated that regardless of the resistance level of the FB cultivar, lower (older) leaves were more severely infected by the chocolate spot pathogen than upper (younger) ones. A comparison of the defense-response behavior of the FB leaves revealed that the chocolate spot pathogen induced lipid peroxidation and the production of reactive oxygen species, peroxidase, and polyphenol oxidase in leaf tissue during the FB-B. fabae interaction. The production of these defense compounds in leaves was not static but governed in time and extent by physiological maturity. Younger leaves exhibited significantly higher oxidizing enzyme activity and lower oxidative stress than older ones. These variations in the levels of defense compounds could explain the differences in leaf resistance. The extreme differences in disease development recorded in upper and lower leaves of all FB cultivars suggest that assessing resistance using leaves from the middle positions would be the most efficient and reliable for evaluating the resistance/susceptibility of FB plants to B. fabae.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Archives of Phytopathology and Plant Protection, Dec 14, 2015
The individual and combined effects of Pseudomonas fluorescens (Pf) and salicylic acid (SA) were ... more The individual and combined effects of Pseudomonas fluorescens (Pf) and salicylic acid (SA) were investigated for control of citrus bacterial canker (CBC). Both treated plants with copper hydroxide and untreated ones were used as controls. Mexican lime (Citrus aurantifolia) seedlings were treated with SA at 10 mM, Pf and distilled water. Plants were initially inoculated with Xanthomonas citri subsp citri 72 h post treatments. Results indicated that the Pf and SA treatment controlled CBC more effectively compared to separately applying Pf or SA. The application of Pf in combination with SA significantly reduced lesion number per leaf (72%) and disease severity (84%). Significant changes in the activities of peroxidase and catalase were found. In conclusion, the integration of Pf with SA complements each other and can be applied to manage citrus canker disease in conjunction with other control programmes.
A total of 350 citrus canker bacterial isolates, representing different citrus growing regions in... more A total of 350 citrus canker bacterial isolates, representing different citrus growing regions in Saudi Arabia, were identified as Xanthomonas citri subsp. citri (Xcc). DNA alignment of the 16S-rDNA of the three citrus canker organisms (Xcc, pathotypes A, X. fuscans pv. aurantifolii, pathotype B, and C) showed that they can be distinguished by using two SNPs. All the 350 Saudi Xcc strains belonged to the 16-rDNA haplotype of Xcc-A pathotypes. Pathogenicity in leaf assays using differential citrus cultivars, grapefruit (Citrus paradisi) and Mexican lime (C. aurantifolia), divided the Saudi Arabian bacterial isolates into two groups. The first group produced typical symptoms of Xcc, including erumpent canker lesions with water-soaked margins on all hosts. However, the second group caused atypical symptoms on grapefruit leaves. REP-PCR analysis grouped Xcc strains into three clusters that were not correlated with host, pathogenicity or geographic origin. However, the Baha Xcc population had the highest genetic variability, suggesting that this region may be responsible for disseminating Xcc strains to Saudi southern citrus-growing regions through movement of contaminated planting materials. Although we were able to definitely identify the Saudi citrus canker bacteria as Xcc-A pathotypes, its pathotypes still needs more investigation to be recognized. To our knowledge, this also is the first report of occurrence of citrus canker of sweet orange in the Abha region of Saudi Arabia.
Applications of formulated bacteriophages with skim milk and sucrose or nonformulated bacteriopha... more Applications of formulated bacteriophages with skim milk and sucrose or nonformulated bacteriophages combined with acibenzolar-S-methyl (ASM) were compared with copper bactericides applications for suppressing Asiatic citrus canker (ACC) caused by Xanthomonas citri subsp. citri (Xcc) on leaves under greenhouse and field conditions in Saudi Arabia. Bacteriophages were applied one day prior to inoculation of Mexican lime (Citrus aurantifolia) plants with Xcc, then twice a week until the end of the trials. Copper hydroxide was applied once prior to inoculation and then every seven days afterward, whereas ASM was applied one week prior to inoculation and then every 21 days afterward. Under greenhouse conditions, the incidence of ACC on leaves was reduced significantly from 75.2 to 12.8% or 18.3% for plants treated with copper hydroxide or bacteriophages in combination with ASM, respectively. Applications of formulated phages in combination with ASM as soil drench under field conditions significantly decreased disease incidence by 14.8% (Trial 1) and 16.8% (Trial 2) compared with untreated control plants. Overall, the Xcc-inoculated plants treated with bacteriophages + ASM combination showed significant ACC reduction under greenhouse and field conditions. The bacteriophages + ASM combination tested in these trials can be an effective tool in the integrated management programs of Asiatic citrus canker disease.
Aedes aegypti mosquito is the principal dengue vector in the Kingdom of Saudi Arabia (KSA); howev... more Aedes aegypti mosquito is the principal dengue vector in the Kingdom of Saudi Arabia (KSA); however, no study has addressed its ecology and population structure yet. Therefore, we report on Ae. aegypti phylo- and population genetics using three DNA markers: COI, ND4, and rDNA-ITS2. Sampling the immature stages of Ae. aegypti revealed that water storage tanks (34.3% of habitats) were the most productive and contained 33% of immatures stages. Other important habitats included containers for wastewater drainage (including air-conditioning and water cooler trays) and containers associated with ornamentation. Shallow water leakage spots (2.7% of habitats, 8% of immatures) can be considered rare-but-epidemiologically-important containers. Neighbor-joining (NJ) phylogenetic analysis of Ae. aegypti identified 8, 14, and 9 haplotypes of COI, ND4, and ITS2, respectively, and revealed high levels of genetic variation in Ae. aegypti populations of KSA. Global distribution of haplotypes also indicated multiple gene introductions into these populations, with high levels of intra-population genetic variation and continuous gene exchange. The neutrality values indicated a deficiency of alleles and suggested that the KSA Ae. aegypti loci tested did not follow a neutral model of molecular evolution. Fst values and AMOVA indicated that most of the genetic variation in the KSA Ae. aegypti populations is due to intra- rather than inter-population differences. This is the first comprehensive report on the phylo- and population genetics of Ae. aegypti from the Arabian Peninsula. This information expands our understanding of the ecology and population dynamics of this important arboviral vector for informed control efforts.
The oriental red spider mite, Eutetranychus orientalis (Klein) is a major pest of citrus in many ... more The oriental red spider mite, Eutetranychus orientalis (Klein) is a major pest of citrus in many countries including Saudi Arabia (SA). The morphological variations among the different populations of E. orientalis were reported. In the present study, phenotypic variations based on 40 different morphological characteristics were evaluated in 10 E. orientalis populations collected from different hosts and regions of SA. Further, ITS2-rDNA sequences were used to confirm the identity of these phenotypically varying populations. Phenotypic variations in all populations were found in the shape and length of dorsal setae, striation pattern between setae d1 and e1, and leg chaetotaxy. The rDNA sequence analysis of these morphologically varying populations resulted in 10 different ITS2 Saudi haplotypes. The phenotypic and genetic variations were more related to the host plants rather than their geographic distribution. The E. orientalis population collected from Phoenix dactylifera was phenotypically distinct and genetically divergent. The populations collected from citrus species were also more phenotypically and genetically related to each other than to populations collected from non-citrus host plants. The haplotypes recovered from Ziziphus sp., Morus sp., and Azadirecta indica from different regions were grouped in the same sub-clade. Further, the ITS2 haplotypes of Saudi E. orientalis recovered from Citrus reticulata from Riyadh and Al Ula were 100% identical to the ITS2 haplotypes recovered from Citrus sp. from Israel. It is concluded that phenotypic variations exist among different populations of E. orientalis inhabiting different host plants. This species should be identified carefully by considering phenotypic intraspecific variations.
Ramulispora sorghi causes sooty stripe of sorghum. Disease severity in irrigated and dryland plot... more Ramulispora sorghi causes sooty stripe of sorghum. Disease severity in irrigated and dryland plots was measured for 25 susceptible sorghum genotypes during the 2007 and 2008 growing seasons using a rating scale based upon percent leaf area infected. Disease severity ratings were approximately 1.4 points higher (P < 0.0001) on the rating scale in the irrigated plots than dryland plots for 2007 and 2008. Sooty stripe lesions were collected from each sorghum genotype in irrigated plots and assessed for mean microsclerotium production within lesions, microsclerotium size, and sporogenic germination, with significant differences apparent between genotypes for microsclerotium size (P = 0.01) and sporogenic germination (P = 0.01). There was no relationship between disease severity and microsclerotium production within leaf lesions, microsclerotium size, or sporogenic germination; however, there was a positive and significant correlation between microsclerotia production within a lesion and microsclerotium size (R 2 = 0.19, P < 0.0001). Although microsclerotia from sorghum lesions varied in structural characteristics and their ability to produce spore masses, these qualities were dependent upon the sorghum genotype from which the microsclerotia were derived, because the R. sorghi population was genetically uniform as determined by internal transcribed spacer sequences and random amplified polymorphic DNA polymerase chain reaction.
The house fly Musca domestica L. (Diptera: Muscidae) is a worldwide medical and veterinary pest, ... more The house fly Musca domestica L. (Diptera: Muscidae) is a worldwide medical and veterinary pest, causing great economic losses. Organophosphate insecticides have been widely used to control house fly populations. The main objectives of the present study were to evaluate the resistance levels of M. domestica slaughterhouse populations, collected from Riyadh, Jeddah, and Taif, against the organophosphate insecticide pirimiphos-methyl and investigate the genetic mutations of the Ace gene associated with pirimiphos-methyl resistance. The obtained data showed that there were significant differences among pirimiphos-methyl LC50 values of the studied populations, where the highest LC50 was recorded for the Riyadh population (8.44 mM), followed by Jeddah and Taif populations (2.45 mM and 1.63 mM, respectively). Seven nonsynonymous SNPs were detected in the studied house flies. The Ile239Val and Glu243Lys mutations are reported for the first time, whereas Val260Leu, Ala316Ser, Gly342Ala, Gly...
Onion (Allium cepa L.) is a globally important crop worldwide including Saudi Arabia. In November... more Onion (Allium cepa L.) is a globally important crop worldwide including Saudi Arabia. In November 2020, 2-monthold onion plants (cv. Redwing) in commercial fields within the Sajir area of Riyadh region (∼ 1.4 ha), showed symptoms of yellowing, wilting, stunting, bulb discoloration, rot in the basal parts of bulb and decrease in roots. In the advanced stages, the affected plants collapsed and died. The incidence of symptomatic plants ranged from 30 to 65% in the surveyed fields. To isolate the pathogen, symptomatic onion plants (n =20) were sampled. Diseased tissues from roots and bulbs were cut into small pieces (4 × 4 mm), sanitized with 1% sodium hypochlorite solution for 2 min, submerged in 70% alcohol for 20 s, then rinsed with sterile water, before plating on potato dextrose agar (PDA) medium. The plates were incubated at 25°C for 6 days. Subcultures of the mycelia grown out of the diseased tissues produced purplish pink fungal colonies on PDA. On carnation leaf agar, cultures were characteristic of Fusarium oxysporum as described by Leslie and Summerell (2006), with the presence of unicellular microconidia (3.8 to 7.8 × 1.7 to 2.5 μm, n= 50) without septa in false heads or short monophialides and slightly curved macroconidia (16.3 to 28 × 4.2 to 6.1 μm, n= 50) with two to four septa. Older mycelia developed many chlamydospores that were single or in short chains. To further confirm the pathogen identification, DNA was extracted from single-spore cultures of three representative isolates using the DNeasy Plant Mini kit (QIAGEN, Hilden, Germany). Three different fungal nuclear regions of internal transcribed spacer (ITS), elongation factor 1-α, (TEF1-α) and the second largest subunit of DNAdirected RNA polymerase II (RPB2) DNA were amplified by PCR and sequenced with the following primers: ITS4
Charcoal rot (CR), caused by Macrophomina phaseolina, is a major disease of sunflowers in semi-ar... more Charcoal rot (CR), caused by Macrophomina phaseolina, is a major disease of sunflowers in semi-arid regions with poor soil conditions. There are fungicide-based strategies to mange this disease; however, alternative eco-friendly control approachs are needed to prevent further deterioration for the environment. This study describes CR control in sunflower grown in calcareous soil using a talc-based bioformulation containing a mixture of rhizobacterial strains (Azotobacter chroococcum, Azospirillum brasilense, and Klebsiella pneumoniae) integrated with silicon nutrition. The study was conducted under greenhouse conditions; M. phaseolina was inoculated in the soil, and rhizobacterial strains were applied as seed treatment, as well as soil drenching at 7, 30, and 45 days after planting (DAP). As the silicon source (Si), potassium silicate was added to nutrient solution at a concentration of 2 mM and applied weekly starting from 7 DAP. The plants, collected at 85 DAP, showed that applying rhizobacteria and Si individually and in combination was effective in controlling CR disease and improving plant growth. The treatment that included rhizobacterial mixture and Si nutrition had a synergistic effect and resulted in the highest reduction (P < 0.05) in the disease incidence (65.3%), root-rot index (57.8%), and stem tissue colonization (63.6%) compared to non-treated inoculated control. Also, the decrease in the growth and nutrient uptake of sunflower plants due to the pathogen-induced stress was significantly reduced. Notably, rhizobacteria + Si treated-plants exhibited less lipid peroxidation and more phenolic and lignin contents with greater defence enzyme activities due to reduced root damage during M. phaseolina infection. Therefore, the integration between rhizobacterial inoculation and Si fertilization can be a good candidate for managing CR in sunflowers in semi-arid regions.
Several species of Fusarium cause serious diseases in date palm worldwide. In the present work, 1... more Several species of Fusarium cause serious diseases in date palm worldwide. In the present work, 14 SSR markers were used to assess the genetic variation of Fusarium strains isolated from diseased trees in Saudi Arabia. We also studied the effect of different temperatures on mycelial growth of these strains. The pathogenicity of four strains of F. proliferatum was also evaluated on local date palm cultivars. Eleven SSR markers amplified a total of 57 scorable alleles from Fusarium strains. Phylogenetic analysis showed that F. proliferatum strains grouped in one clade with 95% bootstrap value. Within F. proliferatum clade, 14 SSR genotypes were identified, 9 of them were singleton. Four out of the five multi-individual SSR genotypes contained strains isolated from more than one location. Most F. solani strains grouped in one clade with 95% bootstrap value. Overall, the SSR markers previously developed for F. verticillioides and F. oxysporum were very useful in assessing the genetic diversity and confirming the identity of Saudi Fusarium strains. The results from the temperature study showed significant differences in mycelial growth of Fusarium strains at different temperatures tested. The highest average radial growth for Fusarium strains was observed at 25˚C, irrespective of species. The four F. proliferatum strains showed significant differences in their pathogenicity on date palm cultivars. It is anticipated that the assessment of genetic diversity, effect of temperature on hyphal growth and pathogenicity of potent pathogenic Fusarium strains recovered from date palm-growing locations in Saudi Arabia can help in effectively controlling these pathogens.
Fusarium proliferatum is one of the most pathogenic Fusarium species on date palm worldwide. We e... more Fusarium proliferatum is one of the most pathogenic Fusarium species on date palm worldwide. We evaluated the colonization ability of 42 F. proliferatum strains collected from date palm trees with disease symptoms on detached leaflets of cvs Sheeshee and Sukkary. Cell wall degrading enzyme (CWDE) production by these strains was assessed with multiple relative enzyme activity (RA) indices. The ability of F. proliferatum strains to colonize leaflet cuttings varied, and there were significant differences (P < 0.05) in susceptibility between the Sheeshee and Sukkary cvs. All F. proliferatum strains tested could hydrolyze carboxymethylcellulose (CMC), citrus pectin and starch, with different capabilities. RA indices calculated from direct assessment of halo zones were consistent with fungal strain colonization ability, but ratio-based RA indices were not. Based on RA 4 index of cellulases, F. proliferatum strains were divided into three groups. The first group (33% of strains) showed very strong reaction in hydrolysing CMC, the second group (62% of strains) showed strong reaction in hydrolysing CMC, and the third group (5%) showed moderate reaction in hydrolysing CMC. Most strains had moderate pectin-hydrolysis activities. Starch-hydrolysis activities ranged from weak to strong. Overall, there was a positive correlation between cellulase production and a strain's colonization ability. Thus, CWDEs produced by F. proliferatum play a role in the colonization of date palm leaflets and hence may be important pathogenicity factors.
Fusarium oxysporum f. sp. albedinis (FOA) is a seed-and soil-borne vascular wilt pathogen that ca... more Fusarium oxysporum f. sp. albedinis (FOA) is a seed-and soil-borne vascular wilt pathogen that causes a very serious and destructive disease of date palm (Bayoud disease). FOA is not currently known to occur in Saudi Arabia, but the disease has been moving eastward from its origin in Morocco and Algeria. The main objective of this study was to evaluate Saudi Arabian date palm germplasm at the molecular level to assess the presence of R or S plasmid. We evaluated 711 trees representing 42 date palm varieties in Saudi Arabia with a mitochondrial molecular marker and sequenced 64 of the diagnostic PCR amplicons. Most of the trees (628/711) carried the R-plasmid which is associated with Bayoud resistance against FOA fungus. The other 83 trees carried the S-plasmid and are predicted to be susceptible. All amplifications from putatively resistant trees had the same DNA sequence. Moreover, the sequence of the Saudi resistance amplicon was identical to the sequence of Moroccan resistance DNA publically available in NCBI-GenBank database. All the sensitive trees from Saudi Arabia shared a common DNA sequence. This sequence differed from the Moroccan susceptible one at seven unique mutations including five single nucleotide polymorphisms (SNPs) and two insertion/deletion (indels) regions. The uniformity of the sequences means that the introduction of new germplasm to Saudi Arabia will be easily detected. The relatively high frequency of putative resistance means that if/when this disease enters the Kingdom that most trees should be resistant.
Fusarium wilt of tomato (FW) caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a major cha... more Fusarium wilt of tomato (FW) caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a major challenge for tomato production worldwide. For sustainable management of FW, the potential of five strains of Trichoderma asperellum was evaluated under greenhouse conditions. The results indicated that FOL infected plants treated with T. asperellum strains significantly reduced disease incidence and severity compared with FOL-only infected plants. The reduction of wilt disease on plants treated with T. asperellum strains was accompanied by a significant reduction in FOL populations in tomato stems and rhizosphere. Moreover, the application of T. asperellum promoted tomato plant growth irrespective of the presence or absence of FOL. Two strains of T. asperellum (TS-12 and TS-39) that showed the best performance in minimizing disease development and increases in plant growth parameters were selected for elucidating their ability in triggering tomato defense mechanisms. The expression levels of defense-related genes, chitinase (SlChi3), β-1,3-glucanase (SlGluA) and PR-1 (SlPR-1a) were significantly increased in the stems and roots of Trichoderma treated, FOL infected plants, compared with FOL-only infected ones. These results indicate that the application of T. asperellum strains TS-12 and TS-39 can be used as an alternative strategy to manage FW through their antagonistic activities and abilities to induce systemic resistance.
Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants... more Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants, animals, and humans. Moreover, many Fusarium species secrete mycotoxins (e.g. trichothecenes and fumonisins) that are toxic to humans and animals. Fusarium isolates from date palm trees showing disease symptoms, e.g. chlorosis, necrosis and whitening, were collected from seven regions across Saudi Arabia. After single-sporing, the fungal strains were morphologically characterized. To confirm the identity of morphologically characterized Fusarium strains, three nuclear loci, two partial genes of translation elongation factor 1 α (tef1α) and β-tubulin (tub2), and the rDNA-ITS region, were amplified and sequenced. Of the 70 Fusarium strains, 70 % were identified as F. proliferatum that were recovered from six regions across Saudi Arabia. Fusarium solani (13 %), as well as one strain each of the following species: F. brachygibbosum, F. oxysporum, and F. verticillioides were also recovered. In addition, five Fusarium-like strains were recognized as Sarocladium kiliense by DNA-based data. The preliminary in vitro pathogenicity results showed that F. proliferatum had the highest colonization abilities on date palm leaflets, followed by F. solani. Although F. oxysporum f. sp. albedinis is the most serious date palm pathogen, F. proliferatum and F. solani are becoming serious pathogens and efforts should be made to restrict and control them. In addition, the potential toxin risks of strains belonging to F. proliferatum should be evaluated.
Bayoud disease, caused by Fusarium oxysporum f. sp. albedinis, is a very serious and destructive ... more Bayoud disease, caused by Fusarium oxysporum f. sp. albedinis, is a very serious and destructive disease to date palm. Screening of date palm germplasm for resistance to bayoud disease is a crucial step to avoid or alleviate the disease consequences. Fortunately, it was discovered that there are two mitochondrial plasmid-like DNA molecules associated with susceptibility or resistance to bayoud disease. In this chapter, we present a fast, simple, and reliable technique to screen date palm germplasm for the presence of these mitochondrial molecular markers associated with susceptibility or resistance to bayoud.
The association between reactive oxygen species (ROS) production and potato resistance to the hem... more The association between reactive oxygen species (ROS) production and potato resistance to the hemibiotrophic pathogen Phytophthora infestans is poorly understood. In this study, the concentrations of hydrogen peroxide (H 2 O 2), malondialdehyde (MDA), and soluble phenolics, as well as the activities of superoxide dismutase, catalase, and ascorbate peroxidase were measured during the early biotrophic and late necrotrophic stages of P. infestans infection on resistant and susceptible 'Ovatio' and 'Bintje' potato plants, respectively. Pathogen biomass was examined using semi-quantitative RT-PCR. Late blight (LB) severity was also evaluated. The LB severity in Ovatio was lower than that in Bintje, irrespective of the evaluation time. Moreover, in both cultivars, various biochemical defense responses occurred following pathogen infection. The susceptible cultivar activated defense responses at the later pathogen infection stages, resulting in higher concentrations of H 2 O 2 and greater MDA content, with lower activity of antioxidant enzymes and phenolic content. These responses were accompanied by the necrotrophic phase, leading to extensive necrotic lesions on leaves. In contrast, fast hypersensitive-like lesions, an early peak in H 2 O 2 concentration, low cell membrane integrity during the biotrophic phase, and a more efficient antioxidative system effectively restricted pathogen colonization before the transition to the necrotrophic phase in the resistant cultivar. These results suggest that LB resistance or susceptibility is regulated by a balance between the induction of ROS/antioxidants (intensity and timing) and the trophic phase of P. infestans.
International Journal of Agriculture and Biology, Jul 1, 2015
Plants have evolved different defense mechanisms to combat pathogen attacks. In this study, detac... more Plants have evolved different defense mechanisms to combat pathogen attacks. In this study, detached leaf assays were conducted to estimate the influence of leaf position (leaf age) on the development of chocolate spot disease, caused by Botrytis fabae, in the lower, middle and upper leaves of five faba bean (FB) cultivars with different levels of resistance/susceptibility. Two components of resistance in terms of lesion diameter and spores per lesion were used to evaluate the disease intensity. To evaluate plant defense response, oxidative burst and phenol-oxidizing enzymes were assayed. The results indicated that regardless of the resistance level of the FB cultivar, lower (older) leaves were more severely infected by the chocolate spot pathogen than upper (younger) ones. A comparison of the defense-response behavior of the FB leaves revealed that the chocolate spot pathogen induced lipid peroxidation and the production of reactive oxygen species, peroxidase, and polyphenol oxidase in leaf tissue during the FB-B. fabae interaction. The production of these defense compounds in leaves was not static but governed in time and extent by physiological maturity. Younger leaves exhibited significantly higher oxidizing enzyme activity and lower oxidative stress than older ones. These variations in the levels of defense compounds could explain the differences in leaf resistance. The extreme differences in disease development recorded in upper and lower leaves of all FB cultivars suggest that assessing resistance using leaves from the middle positions would be the most efficient and reliable for evaluating the resistance/susceptibility of FB plants to B. fabae.
Uploads
Papers by Amgad Saleh