RESISTANCE TO THE LEGUME POD BORER, MARUCA-VITRATA FABRICIUS, AND THEPROBABLE MODALITIES INVOLVED IN WILD VIGNA

A large number of accessions belonging to selected wild Vigna species namely V. unguiculata subspecies dekindtiana, V. oblongifolia, and V. vexillata were evaluated using choice (DCAT) and no-choice (NCFT) labo ratory feeding bioassays to determine their resistance to the pod bore r, Maruca vitrata Fabricius. The most resistant accessions belonged to V. vexillata, followed by those from V. oblongifolia, with a few outs tanding exceptions from V. unguiculata. Even though the latter were th e least resistant, they provided the greatest variability among the te sted accessions. In the DCAT, the cultivated cowpea line, IT84S-2246, which was used as the susceptible control was always preferred for fee ding by the larvae (feeding index [FI] of 1.10-2.60) than the V. ungui culata accessions (Fr ranged from 0-0.52). Against the resistant contr ol (itself belonging to V. vexillata), only a few accessions were less preferred, most of these being either V. vexillata or V. oblongifolia . Larvae lost weight on the most resistant from all three species, bec ause they either did not feed, or fed very little. Weight gain was pos itively correlated with seed damage (r = 0.82, P < 0.01) and the amoun t of frass produced (r = 0.91, P < 0.01). Seed damage was also positiv ely correlated with the amount of frass produced (r = 0.64, P < 0.05). On the basis of these results, we believe that both antibiosis (post- ingestive effects) and antixenosis (deterrence to boring into the pods to feed) modalities of resistance are involved. The results are discu ssed further in relation to the origin, domestication and use of these accessions in cowpea improvement. Copyright (C) 1996 Elsevier Science Ltd