The relationship between primary metabolites in reproductive structures of cowpea Vigna unguiculata (Fabaceae: Papilionidae) cultivars and field resistance to the flower bud thrips Megalurothrips sjostedti (Thysanoptera: Thripidae)

Preliminary screening of germplasm from the International Institute of Tropical Agriculture (IITA) showed that a number of cowpea Vigna unguiculata (L). Walp. cultivars have potential for resistance to the flower bud thrips, Megalurothrips sjostedti (Trybom). In an earlier study, 10 cultivars from this germplasm were selected and the mechanisms of resistance determined. Therefore, in this study, the basis of resistance operating in the cultivars was elucidated during the first and second planting seasons of 1998. Cowpea cultivars were analysed for primary metabolites (total protein content and glucose contents) to study their relationship with resistance parameters of M. sjostedti under field conditions. Total protein and glucose contents varied significantly (P<0.01) in floral buds and flowers of the different cultivars, while in racemes there were little or no significant differences. Highly significant negative correlation coefficients were obtained between total protein contents in reproductive structures and resistance parameters, especially during the second season, regardless of cowpea cultivar, indicating that quality of total protein content plays a significant role in cowpea resistance to M. sjostedti. Significant (P<0.05) correlation between damage indices and glucose content in Vita 7 and Kpodjiguegue is responsible for their susceptibility to M. sjostedti damage. Furthermore, presence of a unique protein band (20.1 kDa) in Moussa local, Sanzibanili and Sewe cultivars could be associated with resistance to flower bud thrips, regardless of quantity of total protein content in these and other test cultivars. Similarly, the specific band just above the 94 kDa in Vita 7 could be responsible for its susceptibility to M. sjostedti.

Un criblage pneliminaire de la collection de I'Institut International d' Agriculture Tropicale (rITA) a montre que de nombreux cultivars de ruebe Vigna unguiculata (L). Walp. presentent ill) potentiel de resistance au trips des bourgeons de £leurs Megn/urotizrips sjostedli (Trybom). Dans une etude anterieme, 10 cultivars de cette collection aValent ete selectionnes et les mecanismes de resistance identifies. Dans ceUe etude, nous nous sommes in teresses a ux facteurs responsables de cette resistance pendant les deux cycles culturaux de1998. Nous avons effectue une analyse des metabolites prim aires (teneurs en proteines totales et en glucose) des cultivars afin de determiner leurs influences sur les parametres de resistance au trips en conditions naturelJes. Les teneurs en protHnes et en glucose des bourgeons f10raux et des flems sont significativement differentes (P < 0,01) sur les differents cuJtivars, nlais il y a peu ou pas de difference au niveau des racemes. Des coefficients de correlation negatifs hautement significatils ont ete obtenus entre I.a teneur en proh~ines dans les structures reproductives et les parametres de resistance, en particulier pendant Ie second cycle cultural, quelque soit Ie cultivar, indiquant que la teneur en proteines joue un role important dans la resistance du ruebe a M. sjostedti. Une correlation significative (P < 0,05) entre I'importance des degiits et la teneur en glucose chez tous les cultivars signifie que la sensibilite du cultivar Vita 7 ii M. sjostedli est due ii tme forte teneur en glucose. Par aiHeurs, la resistance des culLivars Moussa local, Sanzibanili et Sewe semble liee it la presence d'une proteine correspondant a une bande ~e 10,1 kDa alors que la sensibilite du cultivar Vita 7 serait bee a une proteine particulire presente au dessus de 94 kDa.