Genotypic response of brachiaria (Urochloa spp.) to spider mite (Oligonychus trichardti ) (Acari: Tetranychidae) and adaptability to different environments

Grasses in the genus Urochloa, commonly known as brachiaria, are grown as forage crops in sub-Saharan Africa, with some genotypes being used in management of insect pests. However, spider mite, Oligonychus trichardti Meyer (Acari: Tetranychidae), has recently been reported as its major pest in the region. We evaluated 18 brachiaria genotypes to identify sources of resistance to O. trichardti, and to determine their adaptability to different environments in western Kenya. Response to artificial infestation with O. trichardti was evaluated under controlled conditions in a screenhouse while adaptability to different environments and field resistance to mites was evaluated in three locations for two cropping seasons in 2016 and 2017 under farmers’ conditions. The parameters evaluated as indicators of resistance to pest damage included leaf damage, chlorophyll content reduction, plant height, leaf area, number of tillers and shoot biomass. Rainfall played a role in reducing mite infestation and increasing biomass yield of the genotypes. Significant correlations between parameters were only observed between leaf damage and yield (r = -0.50), and leaf damage and chlorophyll loss (r = 0.85). The cultivar superiority index (Pi) ranked Xaraes, Piata, ILRI 12991 and ILRI 13810 as reliable genotypes that combined moderate resistance to the mite (Pi ≤ 48.0) and high biomass yield (Pi ≤ 8.0). Since this is the first documentation of interactions between O. trichardti and different brachiaria genotypes, we propose these genotypes as potential candidates for improved forage yields in areas prone to O. trichardti infestation in Africa