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Three-way interactions between crop plants-phytopathogenic fungi-and plants bugs( Hemiptera: Miridae): evidence from African cropping systems and management perspectives

Ratnadass A., Deguine J.P.. 2019. Abidjan : African Association of Insect Scientists, 1 p.. Réunion et conférence scientifique de l'African Association of Insect Scientists (AAIS). 23, 2019-11-18/2019-11-22, Abidjan (Côte d'Ivoire).

Contrary to a generally accepted view, unlike most Hemiptera, herbivore and omnivorous plant bugs (Miridae) are not phloem feeders, but rather either ¿lacerate & flush¿ or ¿macerate & flush¿ feeders. Plant response to damage by plant bugs and other arthropods of the same feeding guild is therefore rather via the jasmonic acid (JA) or ethylene (ET) pathways than via the salicylic acid (SA) pathway. On the other hand, regarding phytopathogenic fungi/oomycetes, a difference should also be made between biotrophic fungi (which trigger the SA pathway plant response), and necrotrophic and/or hemibiotrophic fungi (which trigger the JA/ET pathway plant response). Based on an extensive literature review, three major frameworks of interaction between plant bugs and phytopathogenic fungi were identified, namely: 1) Fungal infection of the crop plant is facilitated (mainly mechanically transmitted) or hampered following prior infestation by plant bugs; 2) Crop plant infestation by plant bugs is facilitated or hampered by prior fungal infection; 3) Fungus pathogen & herbivore bug are merely concomitant, namely favored by the same conditions, either climatic, or linked to endogenous factors in the crop plant (e.g. redox status), whether or not triggered by abiotic or biotic factors. Several instances from each framework are described, with particular emphasis on the panicle-feeding plant bug-grain mold interaction on sorghum in West and Central Africa for the first, and on the powdery mildew-plant bug interaction on mango in Reunion island for the second. Evidences are provided of cases when management of the pest solves the disease problem, or conversely increases it, or when management of the disease solves the pest problem. Several lines of research are proposed, primarily in view of managing plant bug pest¿fungal pathogen complexes on crop plants on the African continent and islands of South West Indian Ocean.

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