Diagnostic, caractérisation et contrôle des maladies fongiques de l'oignon (Allium cepa L.) dans les agrosystèmes maraîchers du Burkina Faso
(2017)
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- Abstract
- Onion (Allium Cepa L.) sector plays an important role in the socio-economic development of Burkina Faso. Its production is however confronted with biotic diseases which cause considerable yield losses. A lack of knowledge of the pathogens responsible for these diseases leads to inappropriate use of chemicals, the consequences of which are an unnecessary increase in production costs, important risks of water and crops contamination. The general objective of this study was to develop an integrated onion protection strategy, which application will contribute to improve sustainably, the production levels while preserving the health of producers, consumers, and environment. The achievement of this objective requires, firstly, the realization of a correct and precise diagnosis of the pathogens, the knowledge of the agricultural practices that interact with them and, finally, the development of effective, available and environmentally friendly control methods. Data from the literature reported that the major onion diseases are of fungal origin. Based on this hypothesis, 18 seed samples, 167 whole plant samples and 40 samples of preserved bulbs with various symptoms, were collected in the main basins of vegetable production of Burkina Faso and analyzed between 2013 and 2015 for fungal pathogen occurrence. According to the results of this diagnosis, six main fungal diseases of onion are present in Burkina Faso: Seedling damping-off and basal rot disease caused by Fusarium oxysporum (Schlecht.) Emend. Snyd & Hans and Fusarium solani Sacc. Seedling damping-off and black mold caused by Aspergillus niger Tiegh ; Purple blotch disease caused by Alternaria porri Ellis.; Leaf blight disease caused by Alternaria alternata (Fr.) Keyssler ; Pink rot disease caused by Phoma terrestris Hansen ; White rot disease caused by Sclerotium cepivorum Berk. The last two diseases are located in two zones and the others are present in all visited areas. The identified pathogens are seed-borne and seed-transmitted and the prevalence of Fusarium spp. and Aspergillus spp. was particularly high on locally produced seeds. Basal rot disease appears to be the most damaging because of its direct impact on yields. The disease was identified in the Sourou valley, the largest current onion production area in Burkina Faso. Through a field survey of 250 onion producers in 2015-2016, a review of agricultural practices was carried out in this zone to understand their possible role in the disease epidemiology. The results of this analysis indicate that 35% of producers use local seeds whose poor sanitary quality has also been shown. Almost 80% of producers practice a short rotation between the dry and rainy seasons and 12% practice pure monoculture. These practices do not make it possible to reduce the amount of inoculum of pathogens in the soil. The study reveals an unbalanced fertilization method that favors the use of large amounts of mineral nitrogen at the expense of organic matter. This imbalance could weaken plants and predispose them to attacks by some pathogens. The study concludes at the need to undertake awareness-raising, information and training of producers on the role of agricultural practices in the development of diseases and their management. In this context, three activities aiming at the control of the pathogens detected and transmitted by the seeds were carried out. First of all, botanical extracts of Portulaca oleracea L. and Cymbopogon citratus Stapf. have been tested in seed treatment. These two extracts significantly reduced seed infection rates by Fusarium spp. and Aspergillus niger. However, they negatively affected the germination and growth of seedlings, respectively. Subsenquently, conidial suspensions of the antagonist Trichoderma harzianum were applied to the nursery stage by seed coating and substrates spraying against seedling damping-off caused by F. oxysporum and F. solani. These two practices significantly permitted to significantly improve the emergence and growth of seedlings and protected them against damping-off. Finally, eleven onion varieties available in Burkina Faso were screened for their behavior against basal rot and purple blotch diseases under natural infection conditions in fields. The onion varieties Noflaye and Gandiol + were found to be resistant or tolerant, respectively, to basal rot and more tolerant to purple blotch disease than local varieties. All these results enabled us to develop an integrated protection strategy in 31 components based on the use of a healthy planting material and substrate through the improvement of certain agricultural practices. The strategy also includes necessary accompanying measures as well as the assumptions and risks associated with the use of each component. The implementation of these recommendations requires additional tests to optimize the strategy according to field conditions.
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Dabiré, T. G. (2017). Diagnostic, caractérisation et contrôle des maladies fongiques de l’oignon (Allium cepa L.) dans les agrosystèmes maraîchers du Burkina Faso. https://hdl.handle.net/2078.5/105502