Physiologie végétale

In order to know the origin of the resistance in order to develop a control strategy that respects the environment and human health, this study was initiated. More specifically, it should make it possible to determine the reaction of wild strains of Mycosphaerella fijiensis to systemic synthetic fungicides in areas of intensive cultivation of dessert bananas for export in Côte d'Ivoire. Samples of leaves from dessert and plantain banana trees affected by Black Leaf Streak Disease at stages 3 and 4 were taken at a distance of at least 10 km from the industrial plantations and then transported to the laboratory for fungicide sensitivity tests on agar medium according to the method proposed by Van Den Berg Loridat in 1989 and modified by Kobenan and al in 2008. These tests revealed remarkable efficacy of all fungicides on all wild conidia of Mycosphaerella fijiensis regardless of their origin. For the triazoles the inhibition rates ranged from 67.45% to 75% for tebuconazole, 67.34% to 79.41% for epoxyconazole, and 70% to 80.14% for tebuconazole. As for methyl thiophanate, germination rates were between 0 and 11%. For azoxystrobin, germination rates were between 0 and 20 %. However, the same tests carried out in industrial plantations revealed losses in the effectiveness of certain fungicides of the triazole family in certain areas. This loss of efficacy observed in plantations regularly treated with fungicides is due to the repeated use of these fungicides without any real alternation (of the different families of active ingredients), which would have eliminated strains sensitive to these active ingredients and facilitated the proliferation of non-sensitive strains.

Rubber production in rubber trees is affected by dry notch disease, the cause of which has unfortunately not yet been fully elucidated. This study aims to evaluate the impact of biological factors on susceptibility to disease across agro-industrial companies in the West (Zagné), SouthWest (San-Pédro) and SouthEast (Anguédédou) zones of the Côte d'Ivoire. The method used is the recording of panel sick length (PSL) of rubber trees in relation to their clonal metabolisms and the attacks of the main pests of rubber trees such as Corynespora sp, Fomes sp and Loranthaceae. The results showed that the three cultivated clonal metabolic class were all affected by dry notch of rubber but at different levels with an average of 34.65 ± 1.77 %. Regarding pests, the study revealed that they significantly influence (Pr ˂ 0.05) the sensitivity to dry notch. Rubber trees attacked by Fomes sp displayed a higher rate of diseased notch (50.56 ± 20.30 %) than that of non-attacked rubber trees (30.58 ± 20 %). Similarly, rubber trees parasitized by Loranthaceae displayed higher PSL (38.41 ± 20.55 %) than those of rubber trees free (30.16 % ± 21.62 %). Only rubber trees attacked by Corynespora sp presented lower PSL (15.61 ± 13.69 %) than those of non-attacked rubber trees (39.76 ± 20.22 %). Depending on the different production zones, Loranthaceae infested rubber plantations more than the other two pests.

Black spot, caused by Mycosphaerella fijiensis, is one of the most devastating banana diseases. In banana production systems, black spot is mainly managed using fungicides. This method of disease management using systemic fungicides with unisite action has led to the emergence of resistant strains of the pathogenic fungus. The aim of this study was to analyze the relationship between fungicide resistance and banana variety susceptibility. Nine varieties were studied: Bana Dishye, Big Ebenga, French Sombre, Orishele, 3 Verts, SACI, BITA 3, FHIA 21, PITA 3 and SH 3640. The following parameters were observed: the youngest affected leaf (PJFA) and the
youngest necrotic leaf (PJFN), the characteristics of the conidia (size and number) taken from the banana leaves attacked by the disease and an assessment of the susceptibility of these conidia. The results showed a variation in PJFA rank depending on the banana variety, ranging from 3.51 for SH 3640 to 2.47 for FHIA. In terms of PJFN, there was a variation between banana varieties ranging from 7.02 (SH3640) to 4.91 (Bana dishye). Conidia size varied between 33.65 μm for the SH3640 variety and 26.1 μm for FHIA 21. The number of conidia ranged from 34.3 (3 Vert) to 2.5 (BITA 3). However, susceptibility tests did not show any differences between varieties. This
study shows that the susceptibility of the banana variety does not influence the susceptibility of the fungus to fungicides.
Keys word: Fungicides, Mycosphaerella fijiensis, Resistance and Musa spp

6.1.2. Observation du mode d'organisation des équipes phytosanitaires et évaluation de la gestion des paramètres environnementaux dans les bananeraies industrielles............. 6.1.3. Evaluation du niveau d'attaque ou pression d'inoculum et de l'état d'évolution de la cercosporiose noire .