Plant-pathogen interactions

Sweet corn, silage and grain crops have been facing the threat of severe corn disease for many years, spreading to various parts of Israel. Over the past few years, we conducted a series of field experiments, with the assistance of Netafim Israel, growers' associations and farmers from the Galilee region. In 2017-2018, this research led to a historic breakthrough: for the first time, 60 years since its discovery, an economically feasible solution was found for late wilt disease of corn in Israel. The successful treatment protocol is based on changing the cultivation method, changing the traditional irrigation method used in most corn growing areas in Israel, and the sophisticated integration of pesticide mixtures in a schedule adapted to key points in the development of the disease. This method can now be widely applied in commercial fields for the protection of sensitive corn varieties.

Late wilt disease in corn is caused by the fungus Harpophora maydis, which is found in the soil and seeds. It penetrates the plant and blocks the water supply to its upper parts. The disease, considered to be the most severe corn disease in our region, was first discovered in Egypt in 1960, where it still persists and causes serious damage. The disease is now reported in 11 countries. In Israel, it has existed for 40 years in the Upper Galilee, especially in the Hula Valley, and in the past decade, has spread to the south of the country. In heavily contaminated fields and in sensitive maize cultivars, the pathogen can cause 100% infection and total yield loss. The disease is characterized by a rapid wilt of the corn plant, which usually occurs two to three weeks before harvesting. In the past, attempts had been made to control the pathogen using different methods, including agricultural (balanced soil fertility and flood fallowing), chemical, biological, physical (solar heating) and plant compounds. Despite the potential of some of these methods, the only means applied in Israel to date to restrict the disease is the use of resistant corn varieties. However, in Egypt and Spain, virulent pathogen strains that threaten resistant maize cultivars have been found.

The research team led by Dr. Ofir Degani from Migal – The Galilee Research Institute and Tel-Hai College, funded and supported by Netafim Israel, the Extension Service of the Israel Ministry of Agriculture and Rural Development, and growers' associations, has recently led to a breakthrough development of historical significance. For the first time, 60 years since the discovery of the late wilt disease, an efficient and economically feasible solution has been found that can be used on a large scale to protect sensitive corn varieties in commercial fields.

This solution, published in December 2018 in the leading scientific journal PloS ONE, saves about 40% of irrigation costs and combines antifungal mixtures with different mechanisms to prevent resistance development. The new application was tested in field trials in 2017-2018 and included the injection to the irrigation system of  the substances Difenoconazole + Azoxystrobin (of which the commercial name is 'Ortiva-Top', manufactured by Syngenta, Basel ,Switzerland, supplied by Adama Makhteshim, Airport City, Israel), at intervals of 15, 30 and 45 days from sowing, or other fungicide mixtures. Savings in the deployment of irrigation lines was acquired by using a dripline for two adjacent rows (a row spacing of 50 cm instead of 96 cm), a row space that maintains the effective concentration of the fungicide in the soil. A recently developed real-time PCR-based molecular detection system showed that following the treatment of 'Ortiva-Top', the amount of pathogen DNA in the host tissue decreased to near zero levels. The successful treatments using 'Ortiva-Top' resulted in a 100% decrease in dehydration symptoms and a 100% increase in crop yield, together with an approximately 40% increase in crop quality (the yield classified as A class that had a cob weight exceeding 250 g). These results were also obtained in an alternative protocol– the replacement of pesticides based on 'Ortiva-Top' in the first application and the application of pesticides harboring a different mechanism of action in the second and third applications. A remote sensing evaluation of the efficacy of the treatments using a quadcopter equipped with a thermal infra-red sensitive camera carried out by Dr. Assaf Chen’s research team (Migal - Galilee Research Institute) supported the results and showed its effectiveness as a research tool for diagnosing infected fields.

These results are the fruits of a decade of research (since 2008), in which a fundamental understanding of the pathogen H. maydis and the generation and development of late wilt disease in Israel was established. During this period, new research methods such as sensitive molecular tests (PCR and qPCR) were developed in order to diagnose fungal virulence and in order to detect the pathogen inside the host plant tissue. In addition, a link was found to plant hormones that regulate the development of the pathogen. Complex field trials that were carried out annually over a full growing season (about 80 days) since 2009 led to this important discovery.
However, the work on late wilt disease does not end here. In the past two years, Dr. Degani's research team identified the presence of H. maydis in secondary hosts, such as cotton, watermelon and green foxtail (Setaria viridis), which could support the survival of the pathogen, developed an environmentally friendly biological control method to control the pathogen, and established a new bio-assay for examining soils suspected of being infected with the pathogen. These new findings, which are currently in the process of being prepared for scientific publication, are encouraging the continuation and enhancement of the research.

A technique was standardized to screen for resistance to stem rot (Sclerotium rolfsii Sacc.) in groundnut (Arachis hypogaea L.). A total of seven different inoculation techniques were screened by using susceptible genotype TMV-2. The techniques involved inoculation of 10 day old groundnut plants raised in pots by spreading mycelial propagules of S. rolfsii grown on sorghum grain medium (SGM) on soil surface, Inoculum spread on the soil surface and covered with groundnut leaf debris, Inoculum placed around the collar region, Inoculum placed around the collar region and covered with groundnut leaf debris, Inoculum mixed in the soil, Inoculum mixed in the soil and covered with groundnut leaf debris, Agar disc method. Among these techniques inoculum spread on the soil surface and covered with groundnut leaf debris was found to be most efficient in getting highest per cent incidence of stem rot (84.86%) and pod rot (70.48%). How to view point the article : Poornima and Sunkad, Gururaj (2020). Standardization of inoculation technique to identify the sources of resistance against stem and pod rot of groundnut. Internat. J. Plant Protec., 13(1) : 58-61,

Spot blotch pathogen Bipolaris sorokiniana of wheat was investigated with threefold objectives: to establish a relationship between morphological and pathological variability of isolates, identify clonal genotype(s) acting as a source for the generation of new variability, and to determine the mechanism of generation of such variability in the pathogen. Isolates were collected from the leaves and seeds of field-grown wheat crop at four different sites in eastern Gangetic plains of India. Eighty-six clonal isolates derived from a single isolate (gray with white patches, Group III), which segregated in an equal proportion of parental and nonparental types, were studied. Morphological characters-i.e., colony morphology, growth rate, and sporulation-were studied along with disease-causing ability of the isolate clones. Clonal isolates were grouped into three categories. Microscopic analysis of nuclei was done to determine the causes of such variability. Morphological variability appeared to be related to the pathological variability. The isolate having epidemic potential appeared different than that acting as the reservoir for variability. The cause of such variability could be attributed either to hyphal fusion and heterokaryosis, nuclear migration and occurrence of multinucleate state, or a combination of these factors. Random Amplified Polymorphic DNA (RAPD) assay suggested that the unique fragments for different groups could be utilized as molecular markers to identify the isolates of specific groups.

Effect of nutrient media, temperature, hydrogen ion concentration, and photoperiod were studied under in vitro conditions to record the maximum colony growth and spore count. Maximum growth was recorded on 28 o C on PDA media having pH 6.5 with 16/8 light and dark period. The maximum growth on PDA was 87 mm and the spore count was 4.36 × 10 6 spores/mL while the lowest growth was observed in MEA media which was 47mm and spore was counted as 1.48 × 10 6 spores/mL. The present studies were found useful to prepare mass inoculum and also by maintain physiological factors attack of Alternaria porri can be decreased in the controlled environment.

Cocoyam (Colocasia esculenta) corms, purchased from a local barn in Awka, Anambra state, showing spoilage symptoms were examined for rot associated with fungal pathogens. The spoilage organisms were isolated from the corms by explanting the spoilt tissues obtained aseptically onto Sabouraud Dextrose Agar supplemented with chloramphenicol an antibacterial agent. The developing isolates were purified by repeated subculture and identified macroscopically and microscopically using the slide culture technique. The organisms recovered from spoilt cocoyam were Aspergillus niger, Rhizopus stolonifer, Mucor circinelloides, Penicillium cyclopium and Fusarium oxysporum. The rot due to Rhizopus, Mucor and Fusarium were extensive resulting in complete maceration of cocoyam tissues. The pathogenicity test also showed that the above organisms were responsible for cocoyam spoilage. These spoilage organisms may have had access into these cocoyam corms through air, wounds, working equipment (for harvesting) and pests. Proper care should be taken in the handling of these corms as some of these spoilage fungi are known to have negative impact on both humans and livestock because they produce mycotoxins.

Herbal extracts of 26 plants belonging to 20 different families of the plant kingdom were evaluated for antifungal
activity against Phomopsis azadirachtae, a fungus causing destructive die-back disease in neem. Test fungus was isolated from
infected neem seeds. The screening was performed by poisoned food technique. Extracts of Syzygium aromaticum, Lawsonia
inermis, Cinnamomum verum and Allium sativum exhibited significant antifungal activity in a dose-dependent manner. Relatively
potent herbal extracts were further evaluated to determine the obligate lowest concentration required to inhibit visible mycelial
growth of the pathogen. Syzygium extract exhibited 100% inhibition of the pathogen at minimum concentration of 20% then
followed by Lawsonia and Ocimum extracts thus being strongest antifungal agents. The present study revealed that, these plants
could be exploited for the possible control of deadly pathogen P. azadirachtae. Accordingly, this is an important step towards
preventing the spread of the die-back disease through a more ecofriendly approach.

Root-Knot Nematode (RKN) Meloidogyne spp. is one of the important pests in pepper plants that can cause withered. The antagonistic effect of three endophytic bacteria Pseudomonas sp. strain A175 and F23, and Micrococcus sp. strain S54 were tested against RKN under greenhouse condition. The efficacies of these endophytic bacteria were further confirmed by comparing their efficacy with synthetic nematicide. The results obtained showed that these three endophytic bacteria significantly reduce the gall formation and nematode population for >23% and >41%. These antagonistic efficacies are at par with chemical treatment with the efficacy percentage of 24% and 40.9% respectively for gall formation and nematode population reduction. This indicated that these bacterial isolates could reduce the ability of M. incognita to reproduce in soil. The greenhouse trial also revealed that the application of Pseudomonas sp. strain A175 and F23, and Micrococcus sp. strain S54  significantly increase pepper growth performance of pepper in term of plant height, number of branches number of leaves, number of segments, shoot fresh weight, shoot dry weight, root fresh weight, and dry weight. On the basis of aforementioned results, it is suggested that Pseudomonas sp. strain A175 and F23, and Micrococcus sp. strain S54 can be an effective biological control agent against pepper root knot nematode.
Keywords: culture filtrate, nematode suppression, pepper growth

Chickpea Blight is a devastating disease of chickpea (Cicer areitinum L.) worldwide caused by Ascochyta rabiei (Pass.) Lab. The disease is more disastrous particularly in long cool and humid environmental spells. It results in huge losses by wiping off all the crop in the desert areas whenever hit its epidemics. To manage this disease, different management strategies are practiced. However, breeding resistance to the host is the best and environmentally safe strategy. During 1970s, the loss of host resistance against the pathogen was reported, so extra ordinary efforts were started by the scientists to enhance the host tolerance towards the pathogen. In this way, relatively simple field screening techniques were followed for breeding and identification of new resistant genotypes. The review sums up the efforts regarding host breeding against chickpea blight involving large scale field screening experiments as well as recent marker assisted breeding using the molecular mapping and QTLs against the different strains of pathogen. Moreover, the important aspects covering the related knowledge of the pathogen, its biology, variability, perpetuation, characteristics and factor affecting the disease establishment have also been summarized.

Plant immune systems rely on their ability to recognize enemy molecules, carry out signal transduction, and respond defensively through pathways involving many genes and their products. This Perspective paper aims to explore current views on the vaccination (immunization) of plants against diseases caused by microorganisms and their (macro)molecular components, paying special attention to practical applications. We conclude that the technique of vaccination to control plant disease needs to be further investigated, developed, and considered for wider implementation in plant protection practice.

Different isolates of Ustilaginoidea virens showed variation in the size, colour and shape of the conidia, length
of spines and width of the hyphae. The conidia were globose, irregularly round to elliptical and warty on the surface with
diameters ranging from 4.20 to 6.54 μm. The scanning electron microscopy revealed that the conidial wall was echinulated
and ornamented with prominent spines. The spines were pointed at the apex or irregularly curved and ranged from 359.9–
994.5 nm long. Based on colony characters isolates of U. virens were grouped into three groups. The maximum colony
diameter was observed in isolate UV3 (40 mm) while minimum was in UV7 (25 mm). The width of the hyphae in different
isolates varied from 1.26-2.81 μm. The maximum width of the hypha was 2.81 μm in UV4 isolate and minimum in UV3 (1.26
μm). The genetic diversity of the eight isolates of U. virens, by random amplified polymorphic DNA (RAPD) marker using
nine primers, revealed a considerable level of genetic variation. The dendrogram showed two main clusters; cluster I
comprised of five isolates (UV1, UV5, UV8, UV6 and UV7), while Cluster II consisted of three isolates (UV2, UV3 and UV4).

Bacteria diseases are major constraints in commercial agriculture. Bacteria diseases have continuously caused huge loss to both conventional and organic farming systems globally. Bacteria leaf spot is a tomato disease of concern whose management remains a challenge across the globe. The pathogen Xanthomonas campestris pv vesicatoria the causative agent of leaf spot in tomato has been isolated and positively identified in many countries to enable control. In Kenya, tomato farmers have experienced losses associated with bacterial diseases despite using available control strategies. Application of control mechanisms by majority of farmers heavily rely on symptoms on plants other than laboratory facts on pathogen identification. As such wrong chemicals have been applied which have led to development of resistance due to pathogen evolution. Scientific identification of pathogen is necessary to enable application of accurate and effective management strategy. Nonetheless, this has scarcely been done for tomato bacteria diseases in Kenya. The objective of this study was to isolate and identify bacteria leaf spot pathogen of tomato from Wanguru area in Mwea, Kirinyaga county in Kenya using nutrient agar, differential staining and selected biochemical methods. A total of ten tomato heavily infected leaves were selected randomly from different farms. The colonies were generally yellow on the surface of nutrient agar. Results of differential staining showed gram negative rods while biochemical tests slightly varied. Based on totality of cultural, morphological and biochemical tests results, we concluded that Xanthomonas campestris pv vesicatoria is responsible for leaf spot tomato disease in Wanguru. However, we recommend the inclusion of molecular tool for proper identification.

Fungicide coated seeds are beneficial against seed or soil borne pathogens in the very initial stage to minimize the indiscriminate use of chemicals for disease control in paddy fields. The present study investigated the effectiveness of three levels of thiram fungicide coated-seeds having different pre-soaking duration on inhibition of rice seed-borne fungal pathogen Curvularia sp. and the seed vigor. Treated paddy seeds (Var. Bg-300) in four concentrations of 0 (control), 0.5, 1 and 1.5 g fungicide per kg seeds and four pre-soaking times of 5 minutes, 1, 2 and 3 days were used. Modified disk diffusion bioassay for seeds and agar well diffusion inhibition bioassay for seed soaked water (extracts) were performed using spread plates of Curvularia sp. Three days pre-soaked seeds were germinated in sterilized soil medium inoculated with Curvularia sp. to screen the plant vigor.

The fungicidal activity of seeds was significantly higher in 1 and 1.5 g kg-1 fungicide treatments (p<0.05). At a given pre-soak duration, a significantly high inhibition was observed in the soaked water of seeds treated with 1 and 1.5 g kg-1 than 0.5 g kg-1of fungicide (p<0.05). The average root height of the seeds treated with 1.5 g kg-1 fungicide concentration was significantly higher (p<0.05) than the other treatments. However, no significant difference was observed for the shoot lengths among treatments. Thus it can be concluded that 1.5 g kg-1 thiram treatment is
effective in inhibiting Curvularia sp. and improving seed vigor of Bg-300.

Keywords: Coated-seeds, Curvularia sp., Inhibition, Thiram, Vigor
*Corresponding author: [email protected]

The pivotal role of cultivated grapevine (Vitis vinifera L.) in many countries economy is compromised by its high susceptibility to Plasmopara viticola, the causal agent of downy mildew disease. Recent research has identified a set of genes related to resistance which may be used to track downy mildew infection. Quantification of the expression of these resistance genes requires normalizing qPCR data using reference genes with stable expression in the system studied. In this study, a set of eleven genes (VATP16, 60 S, UQCC, SMD3, EF1a, UBQ, SAND, GAPDH, ACT, PsaB, PTB2) was evaluated to identify reference genes during the first hours of interaction (6, 12, 18 and 24 hpi) between two V. vinifera genotypes and P. viticola. Two analyses were used for the selection of reference genes: direct comparison of susceptible, Trincadeira, and resistant, Regent, V. vinifera cultivars at 0 h, 6, 12, 18 and 24 hours post inoculation with P. viticola (genotype effect); and comparison of each genotype with mock inoculated samples during inoculation time-course (biotic stress effect). Three statistical methods were used, GeNorm, NormFinder, and BestKeeper, allowing to identify UBQ, EF1a and GAPDH as the most stable genes for the genotype effect. For the biotic stress effect, EF1a, SAND and SMD3 were the most constant for the susceptible cultivar Trincadeira and EF1a, GAPDH, UBQ for the resistant cultivar Regent. In addition, the expression of three defenserelated transcripts, encoding for subtilisin-like protein, CYP and PR10, was analysed, for both datasets, during inoculation time-course. Taken together, our results provide guidelines for reference gene(s) selection towards a more accurate and widespread use of qPCR to study the first hours of interaction between different grapevine cultivars and P. viticola.

Late wilt, a severe vascular disease of maize caused by the fungus Harpophora maydis, is characterized by relatively rapid wilting of maize plants, before tasseling and until shortly before maturity. In Israel, the disease becomes a major problem in recent years. The pathogen currently controlled using varieties of maize has reduced sensitivity. In earlier work, we modified a molecular method for use as a diagnostic tool to evaluate the disease progress in field infested plants. Several fungicides suppressed H. maydis in vitro and in a detached root pathogenicity assay. Seedling pathogenicity assay enables us to identified H. maydis DNA in the host root and stem tissues 18 days after sowing in both susceptible and tolerant maize plants. Although the infested plants exhibited no wilt symptoms, their roots were significantly shorter in length. This seedling assay was used to demonstrate the suppressive effect of the fungicide Flutriafol on H. maydis virulence. The method of assaying the pathogen in a series of trials starting in a plate assay, followed by a detached root and resulting in a seedlings pathogenicity assay, using molecular and morphological approaches could be generalized to other plant pathogens.

Chickpea Blight is a devastating disease of chickpea (Cicer areitinum L.) worldwide caused by Ascochyta rabiei (Pass.) Lab. The disease is more disastrous particularly in long cool and humid environmental spells. It results in huge losses by wiping off all the crop in the desert areas whenever hit its epidemics. To manage this disease, different management strategies are practiced. However, breeding resistance to the host is the best and environmentally safe strategy. During 1970s, the loss of host resistance against the pathogen was reported, so extra ordinary efforts were started by the scientists to enhance the host tolerance towards the pathogen. In this way, relatively simple field screening techniques were followed for breeding and identification of new resistant genotypes. The review sums up the efforts regarding host breeding against chickpea blight involving large scale field screening experiments as well as recent marker assisted breeding using the molecular mapping and QT...

To optimize the number and timing of trunk injections for season-long control of apple scab (Venturia inaequalis), we evaluated 1-2 and 4 seasonal and cross-seasonal injections of potassium phosphites and synthetic fungicides and quantified residues in leaves and fruit. Phosphites accumulated in the canopy at the highest concentrations, aligned well in time with scab suppression, and gave better leaf scab control of 41.8-73.5% than propiconazole (16.9-51.5%) or difenoconazole + cyprodinil (5.4-17.4%). More injections of phosphites controlled leaf scab better than fewer (23.7% vs. 48.2%), and more fungicide injections resulted in 21.9-51.1% better leaf scab control than fewer. Leaf scab control with phosphites was 3.2-13.9% better with 4 cross-seasonal compared to 4 seasonal injections, while 1-2 seasonal compared to 1-2 cross-seasonal injections improved scab control for 4.2-22.1%. On shoots, injected phosphites provided comparable or for 4.4-10.5% and 22.3-41.4% better scab control than spray standards. On fruit, injected phosphites slightly improved control compared to sprayed phosphites or the sprayed fungicide standard (33.4-40.8%). Two seasonal injections of phosphites controlled shoot scab 5.7% better than 9 spray applications. Five sprays of difenoconazole + cyprodinil controlled scab better than their injections. Fruit residues of phosphites reached 2.8 ppm and declined in all treatments except in 2 seasonal injections and phosphite sprays. Cyprodinil and difenoconazole fruit residues reached 0.02 and 0.07 ppm and declined sharply towards the end of the season. These were far below the USA, Codex, and EU MRL-s of 1, 0.8 and 0.5 ppm for difenoconazole, and 1.7, 2 and 1 ppm for cyprodinil, respectively.

Sorghum (Sorghum bicolor (L.) Moench) is a drought tolerant food crop preferred by subsistence farmers in dry areas which experience low annual rainfall. However, Turcicum Leaf Blight (TLB) caused by Exserohilum turcicum has threatened sorghum production in the world. New sorghum varieties have been introduced into the Kenyan production systems, including the drier parts of Tharaka Nithi County to boost yield and thus meet the increased demands for food and as a raw material by brewing industries. Nonetheless, challenges due to infection by TLB have negatively impacted on sorghum production resulting from damaged photosynthetic leaves. This study was conducted to determine the incidence and severity of TLB on sorghum populations in different regions of Tharaka Nithi County. Sorghum farms in eleven villages for the study were selected by multistage random sampling. The study was conducted between the month of January and June 2018. Data analysis was done by SAS software version 9.3 and significantly different means separated using LSD test at 5% probability level. There was statistically significant difference in the severity and incidence of E. Turcicum leaf blight on sorghum population from different regions in Tharaka Nithi County (P<0.05). Disease TLB occurred in all the villages surveyed though at different frequencies. The disease incidence was higher at Kithaga, and Nkairini recording 74.45% and 55.93%. and lowest at Gatuntu and Gituntu both recorded the disease incidences 12.22%. Thus, farmers should be educated on sorghum TLB management for increased sorghum production and higher income to farmers.

Cherry leaf spot disease, caused by Blumeriella jaapii (Rehm) Arx., is an increasing concern to nursery producers of ornamental cherry in the southeastern United States. Spores were trapped starting in late March before symptoms were observed in the field, which indicates that leaf debris from diseased trees are an important source of primary inoculum. Previously infected trees of six cultivars ('Kwanzan', 'Yoshino', 'Okami', 'Snowgoose', 'Autumnalis' and 'Akebono'), which were overwintered in a controlled environment protected from airborne spores, developed disease symptoms in late spring, indicating that dormant buds may also be a source of primary inoculum. Because ornamental cherry trees are propagated by budding and cuttings, disease management should incorporate cultural practices that focus on propagation from disease-free trees and fungicide applications beginning at petal drop to protect emerging leaves.

This study was aimed to study the food value, associated spoilage fungi (Biodeterioration) and possible aflatoxin contents of 'Abacha' a cheap popular food locally prepared as shredded cassava in Nigeria. Fresh and stored samples (25) were collected from different markets and analysed for nutrient, fungal components and aflatoxin concentrations; these was compared laboratory prepared samples (control). The samples contained mainly carbohydrate (96.95-97.95%), moisture (10.6-12.21%), crude protein (1.57-1.63%), fat (0.44-0.49%) and fibre (0.48-0.51%). Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Aspergillus tamarii, Aspergillus ochraceus, Fusarium oxysporium, Penicillum chrysogenum, Penicillum oxalicum, Trichoderma sp. and Rhizopus stolonifer were isolated from the samples, these are commonly reported in many food deterioration and aflatoxin production. Aflatoxin contents were higher in market samples than the control, and increased with storage time. Aflatoxin G 2 had highest concentration (0.0263-0.0388 µg/kg) followed by aflatoxin G 1 (0.0150-0.0213 µg/kg), aflatoxin B 2 (0.0048-0.0071 µg/kg) while aflatoxin B 1 had the least concentration (0.0030-0.0056 µg/kg). This study showed that fungal contamination and storage time have effect on the nutrient content and aflatoxin components of 'Abacha'. The detected aflatoxin contents of abacha were found below the tolerance limit but increase with storage time. It is therefore necessary to avoid fungal contamination of this food before and during storage period to avoid being contaminated with aflatoxins and ensuring its nutritive quality.

Fusarium is an important soil-borne fungus affecting sesame. Its control could be enhanced by plant genetic resistance, however in order to be successful in this strategy, identification of resistance sources is required to start plant breeding programs. The objective of this research was to evaluate four sesame (Sesamum indicum L.) genotypes according to fungal disease incidence and severity caused by three fungus isolates. Split-plot design with four replications was used. Inoculation was carried out in plastic boxes containing a mixture of substrate and each fungus isolates, resulting that main plots were represented by fungus isolates and sub-plot were represented by sesame genotypes. On each experimental unit was determined the disease incidence and severity indicators such as plant height, lesion length, and percentage of plant height occupied by the lesion; additionally a Disease Severity Index (DSI) was calculated. Inoculated plant height did not show variation as compared to control plants. Disease incidence, the others severity indicators and DSE showed significant interaction between sesame genotypes and fungus isolates, however, there was a trend to identify sesame genotype UCLA37 as the one which presented the highest values for both parameters.

Phomopsis azadirachtae is the causal agent of destructive die-back disease of neem. The molecular mechanism of pathogenicity is not clear. Pectinases, cellulases, hemicellulases and ligninases have been extensively studied because of their plant cell wall degrading nature. Hence, this study describes the screening and assay of extracellular enzymes produced by the pathogen. The pathogenicity enzymes screened were: laccase, polygalacturonase, xylanase, amylase, cellulase, protease and lipase. A total of fifteen isolates of Phomopsis azadirachtae were from different agroclimatic regions of Karnataka, Tamil Nadu and Andhra Pradesh from diseased samples. The isolates were subjected to screening of the above mentioned enzymes on solid media supplemented with respective substrates. All the isolates were found to produce polygalacturonase, laccase, protease and xylanase. Polygalacturonase and xylanase were further assayed in order to quantify the enzyme produced in all the isolates. In addition to pathogenicity enzymes, isolates were also found to produce some industrially important enzymes such as L-asparaginase and urease.

ABSTRACT
Postharvest rot pathogens constitute a major threat to the enormous potential of yam tuber (Dioscorea species) in enhancing food security and safety. The control of yam rot in storage has been an object of research for decades especially in Africa, Asia and certain parts of Europe where yam is produced in large quantities. Various control methods ranging from the use of synthetic chemical, bio-control agents, curing, nanobiotechnology and the use of plant extracts; have been explored to tackle the menace of post-harvest rot of yam tubers. It was discovered that even though most researchers are discouraging the use of synthetic chemicals because of the associated environmental hazards and the inducement of resistance in targeted pathogens, it is still the most effective method in controlling the rot of yam tuber in storage due to its immediate action especially when compared to the use of biological control agents which often require some days before its effect is noticed. It is necessary that curing precedes any of the control method adopted coupled with an appropriate storage structure. There is an urgent need to understand the mode of action of all the plant extracts proven by research to possess anti-rot properties so as to enhance its applicability. Standardization of plant extracts will also go a long way in enhancing their efficacy, especially at various concentrations; as it has been reported in the use of synthetic chemicals. Nanobiotechnology should be explored for possible solutions in addressing the strain of rot pathogens that have become resistant to synthetic chemicals. This review provides a critical analysis of all the control methods listed above, their strengths and weaknesses, the effect of storage techniques and structures on the microbial deterioration of yam while giving insight into ways of maximizing and improving them.

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This study reports on expression analysis associated with molecular systems biology of cacao-Moniliophthora perniciosa interaction. Gene expression data were obtained for two cacao genotypes (TSH1188, resistant; Catongo, susceptible) challenged or not with the fungus M. perniciosa and collected at three time points through disease. Using expression analysis, we identified 154 and 227 genes that are differentially expressed in TSH1188 and Catongo, respectively. The expression of some of these genes was confirmed by RT-qPCR. Physical protein-protein interaction (PPPI) networks of Arabidopsis thaliana orthologous proteins corresponding to resistant and susceptible interactions were obtained followed by cluster and gene ontology analyses. The integrated analysis of gene expression and systems biology allowed designing a general scheme of major mechanisms associated with witches' broom disease resistance/susceptibility. In this sense, the TSH1188 cultivar shows strong production of ROS and elicitors at the beginning of the interaction with M. perniciosa followed by resistance signal propagation and ROS detoxification. On the other hand, the Catongo genotype displays defense mechanisms that include the synthesis of some defense molecules but without success in regards to elimination of the fungus. This phase is followed by the activation of protein metabolism which is achieved with the production of proteasome associated with autophagy as a precursor mechanism of PCD. This work also identifies candidate genes for further functional studies and for genetic mapping and marker assisted selection.

Food security (a pressing issue for all nations) faces a threat due to population growth, land availability for growing crops, a changing climate (leading to increases in both abiotic and biotic stresses), heightened consumer awareness of the risks related to the use of agrichemicals, and also the reliance on depleting fossil fuel reserves for their production. Legislative changes in Europe mean that fewer agrichemicals will be available in the future for the control of crop pests and pathogens. The need for the implementation of a more sustainable
agricultural system globally, incorporating an integrated approach to disease management, has never been more urgent. To that end, the Valorizing Andean Microbial Diversity (VALORAM) project (http://valoram.ucc.ie), funded under FP7, examined the role of microbial
communities in crop production and protection to improve the sustainability, food security, environmental protection, and productivity for rural Andean farmers. During this work, microbial volatile organic compounds (mVOCs) of 27 rhizobacterial isolates were identified using gas chromatography/mass spectrometry (GC/MS), and their antifungal
activity against Rhizoctonia solani was determined in vitro and compared to the activity of a selection of pure volatile compounds. Five of these isolates, Pseudomonas palleroniana R43631, Bacillus sp. R47065, R47131, Paenibacillus sp. B3a R49541, and Bacillus simplex M3-4 R49538 trialled in the field in their respective countries of origin, i.e., Bolivia, Peru, and Ecuador, showed significant increase in the yield of potato. The strategy followed in the VALORAM project may offer a template for the future isolation and determination of putative biocontrol and plant growth-promoting agents, useful as part of a low-input integrated pest management system.

We studied the effects of mono-, di-, tri-, and hexamers of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) on oxidative and calcium signals in transgenic tobacco suspension culture (Nicotiana tabacum L. cv. Bright Yellow-2, cell line CST-1) expressing aequorin. Addition of (GlcN)n to the cells induced an immediate oxidative burst monitored by superoxide-specific chemiluminescence of CLA (CLA-CL). The superoxide generated by (GlcN)n was converted to hydrogen peroxide, causing a transient increase in cytosolic Ca2+ concentration ([Ca2+]c) which was monitored by ([Ca2+]c-dependent luminescence of aequorin. The longer the polymer of (GlcN)n the greater the effect. The (GlcN)n-dependent CLA-CL in the culture was inhibited by a peroxidase inhibitor, but not by a NADPH oxidase inhibitor. The (GlcN)n-dependent CLA-CL was also observed in the extracellularly excreted peroxidase preparation and also in horseradish peroxidase reaction mixture. We have previously obtained similar results using salicylic acid and aromatic amines. Addition of (GlcNAc)n also resulted in an elevation of [Ca2+]c. No superoxide generation preseding [Ca2+]c elevation was detected using CLA, but gradual accumulation of superoxide signal was detected with electron spin resonance spectroscopy using Tiron as a spin trapper. No effect of GlcNAc monomer and oligomers shorter than hexamer on [Ca2+]c elevation or superoxide generation was observed.
In various plants, generation of reactive oxygen species (ROS) is one of the important early events in the active defense against pathogens. ROS can be induced by pathogen invation or treatment with elicitors....

MicroRNAs (miRNAs) are a class of small (20–24 nucleotides (nt) long) non-coding RNAs. One mature miRNA can be transcribed from one or more gene loci known as miRNA genes (MIRs). The transcript of a MIR forms a stem-loop structure that is processed into a 20–24-nt miRNA-5p/−3p duplex by RNase III family endoribonucleases such as Dicer-like1 (DCL1). In turn, the overhang ends of the duplex are methylated by HUA ENHANCER 1 (HEN1), generating stabilized mature miRNAs. The mature miRNAs are loaded onto ARGONAUTE (AGO) proteins, forming a miRNA-induced gene silencing complex (miRISC). Then, the miRISC binds to target sites with sequences complementary to the miRNAs, leading to either cleavage or translational inhibition of the target mRNAs, or methylation of the target sequences, resulting in post-transcriptional and transcriptional gene silencing, respectively. In the past decade, more than 700 miRNAs have been identified in rice, a subset of which have been found to be responsive to th...

Bananas (Musa spp.) are considered the most important fruit crop in Kenya, grown mostly by smallholder farmers. However, in the past two decades production has declined and has largely been attributed to plant pathogens, including plant-parasitic nematodes. To assess the understanding and awareness that banana farmers have of nematodes, a survey was conducted. The incidence, abundance and distribution of nematodes in relation to altitude were determined for different banana types on 180 farms and the pathogenicity of Pratylenchus goodeyi, originating from three different altitudinal locations, was compared on two banana cultivars. Just 2.3% of farmers were aware of nematode damage and symptoms, none of whom applied any management measures. The highest abundance of nematodes was recorded at an altitude range of 1601-2000 m a.s.l., with Pratylenchus, Meloidogyne and Helicotylenchus being the predominant genera. Across all altitudinal locations, cooking banana had higher densities of nematodes than dessert bananas. In pots, P. goodeyi populations from Embu (1300 m a.s.l.) appeared more aggressive and with higher levels of multiplication than the population from Oyugis (1100 m a.s.l.). Cooking banana ('Ng'ombe') was more susceptible than dessert banana ('Sukari Ndizi'). Nematode damage is more prominent in areas at higher altitude and on cooking banana cultivars. The findings provide key information in guiding informed and suitable management decision thresholds in relation to potential climate change.

Drought is a ubiquitous abiotic factor that severely impedes growth and development of horticulture crops. The challenge postured by global climate change is the evolution of drought-tolerant cultivars that could cope with concurrent stress. Hence, in this study, biochemical, physiological and transcriptome analysis were investigated in drought-treated grapevine leaves. The results revealed that photosynthetic activity and reducing sugars were significantly diminished which were positively correlated with low stomatal conductance and CO 2 exchange in drought-stressed leaves. Further, the activities of superoxide dismutase, peroxidase, and catalase were significantly actuated in the drought-responsive grapevine leaves. Similarly, the levels of abscisic acid and jasmonic acid were also significantly increased in the drought-stressed leaves. In transcriptome analysis, 12,451 differentially expressed genes (DEGs) were annotated, out of which 8021 DEGs were up-regulated and 4430 DEGs were down-regulated in response to drought stress. In addition, the genes encoding pathogen-associated molecular pattern (PAMP) triggered immunity (PTI), including calcium signals, protein phosphatase 2C, calcineurin B-like proteins, MAPKs, and phosphorylation (FLS2 and MEKK1) cascades were up-regulated in response to drought stress. Several genes related to plant-pathogen interaction pathway (RPM1, PBS1, RPS5, RIN4, MIN7, PR1, and WRKYs) were also found up-regulated in response to drought stress. Overall the results of present study showed the dynamic interaction of DEG in grapevine physiology which provides the premise for selection of defense-related genes against drought stress for subsequent grapevine breeding programs.

ELONGATED HYPOCOTYL5 (HY5) is a basic domain/leucine zipper (bZIP) transcription factor, central for the regulation of seedling photomorphogenesis. Here, we identified a B-BOX (BBX)-containing protein, BBX25/SALT TOLERANCE HOMOLOG, as an interacting partner of HY5, which has been previously found to physically interact with CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1). BBX25 physically interacts with HY5 both in vitro and in vivo. By physiological and genetic approaches, we showed that BBX25 is a negative regulator of seedling photomorphogenesis. BBX25 and its homolog BBX24 regulate deetiolation processes and hypocotyl shade avoidance response in an additive manner. Moreover, genetic relationships of bbx25 and bbx24 with hy5 and cop1 revealed that BBX25 and BBX24 additively enhance COP1 and suppress HY5 functions. BBX25 accumulates in a light-dependent manner and undergoes COP1-mediated degradation in dark and light conditions. Furthermore, a protoplast cotransfection assay showed that BBX24 and BBX25 repress BBX22 expression by interfering with HY5 transcriptional activity. As HY5 binds to the BBX22 promoter and promotes its expression, our results identify a direct mechanism through which the expression of BBX22 is regulated. We suggest that BBX25 and BBX24 function as transcriptional corepressors, probably by forming inactive heterodimers with HY5, downregulating BBX22 expression for the fine-tuning of light-mediated seedling development.

Varieties of mechanisms have been developed by plants to adapt, cope with, defend and ward off different arrays of invasion; this includes aggressive invasions from pathogenic organisms that cause diseases. The plant upon sensing danger activates certain signaling pathways within them, this leads to the induced gene expressions with different defensive roles. Their system that activates immunity within and the ability to detect microbial pathogens will be presented. For an infection to occur there must be a close ecological relationship that will be established between the host plants and the pathogens. Attention is also drawn to how pathogens produce plant penetrating mechanisms to invade and bring down the plants defensive structures and the various types of plant pathogens that invade host plants. This paper also reviews the current knowledge of defense mechanisms in host plants among which includes cell wall fortification, defense genes and its activation, secondary metabolites synthesis and defense hormones generation. Resistance and defense can be manipulated to develop varieties of crops which easily fight and inhibit infectious pathogenic stress, as it can also be used as a part of integrated disease management for productive crop production. The knowledge derived from this work together with other research studies in this area will help to draw highlight on the major components in plant defense responses and to design strategies to enhance resistance to pathogen invasion in plants.

Citrus tristeza virus (CTV) is a member of genus Closterovirus with long flexuous virions, approximately 2000 X 11 nm and monopartite genome and is vectored by aphids. CTV spreads into new regions via movement of infected propagating materials and within a citrus growing area by aphid dispersion. Efficiency of CTV transmissibility is affected by the species of aphids, the source plant at acquisition feeding and the CTV isolate. The BrCA is the most efficient aphid vector of CTV. In areas where BrCA is not present, Aphis gossypii is the most efficient vector implicated. In major citrus growing areas of Peninsular Malaysia, all Citrus varieties and its hybrides including Fortunella sp., Citrofortunella microcarpa and Citromelo were infected with CTV in a high rate. Survey of CTV vector (s) in Peninsular Malaysia revealed that at least there is one efficient vector (A. gossypii) of CTV in citrus growing areas.

In India pea is the second greatest protein source followed by chickpea for the people of the country, over the years due to pathogen attack and climate change, the yield of pea has reduced categorically which generated great concern among scientists, policymakers, and common people thus resulting into the development of strategies to assess the impact and severity of the disease spread around the country various measures were taken into the account to find out the best method to control the disease. It has been found that pea is most susceptible to fungal pathogens. After reviewing the literature it is deduced that there are enormous species of fungi reported showing beneficial as well as harmful relationships with the pea and other crop plants worldwide. Disease in the pea plant is mainly caused by microorganisms like fungi, bacteria, and some nematodes, but much of the losses are occurred due to fungal pathogens (generally soil-borne). In the present review the most common diseases of pea caused by soil-borne fungi are Fusarium oxysporum f. sp. pisi, Fusarium solani f. sp. pisi, Rhizoctonia solani, Pythium ultimum, Aphanomyces euteiches, Thielaviopsis basicola, and Sclerotinia sclerotiorum. The present article deals with the evaluation of the aggressiveness, detrimental effect and taxonomic and symptomatic status of fungal pathogens.

Insect-borne plant viruses usually alter the interactions between host plant and insect vector in ways conducive to their transmission ('host manipulation hypothesis'). Most studies have tested this hypothesis with persistently and non-persistently transmitted viruses, while few have examined semi-persistently transmitted viruses. The crinivirus Tomato chlorosis virus (ToCV) is semi-persistently transmitted virus by white-flies, and has been recently reported infecting potato plants in Brazil, where Bemisia tabaci Middle East Asia Minor 1 (MEAM1) is a competent vector. We investigated how ToCV infection modifies the interaction between potato plants and B. tabaci in ways that increase the likelihood of ToCV transmission, in two clones, one susceptible ('Agata') and the other moderately resistant (Bach-4) to B. tabaci. Whiteflies alighted and laid more eggs on ToCV-infected plants than mock-inoculated plants of Bach-4. When non-viruliferous whiteflies were released on ToCV-infected plants near mock-inoculated plants, adults moved more intensely towards non-infected plants than in the reverse condition for both clones. Feeding on ToCV-infected plants reduced egg-incubation period in both clones, but the egg-adult cycle was similar for whiteflies fed on ToCV-infected and mock-inoculated plants. Our results demonstrated that ToCV infection in potato plants alters B. tabaci behaviour and development in distinct ways depending on the host clone, with potential implications for ToCV spread.

Two sugarcane cultivars (R570 and SP71-6163) naturally infected by Sugarcane yellow leaf virus (SCYLV) were each
imported from several geographical locations into a  sugarcane yellow leaf-free environment (Montpellier, France). Plants were grown as plant cane for 5–6 months and the experiment was repeated for three consecutive years (2003–2005) in a greenhouse. Several sugarcane-growth and disease characteristics were monitored to identify variation in pathogenicity of SCYLV. Depending on their geographical origin, sugarcane cvs R570 and SP71-6163 were infected by SCYLV genotypes BRA-PER or REU, or a mixture of the two. Severity of symptoms did not vary between plants of cv. R570, but variation in disease severity between plants of cv. SP71-6163 from different geographical locations suggested the occurrence of pathogenic variants of SCYLV. For each sugarcane cultivar, differences in stalk length, number of stalk internodes, virus titre in the top visible dewlap leaf, and percentage of infection of leaf and stalk phloem vessels were also found between plants from different geographical  origins. However, these differences were not always reproducible from one year to another, suggesting occurrence of different plant responses to SCYLV isolates under varying environmental conditions