Cowpea reactions to Alectra vogelii I: effect on growth

Field trials were conducted in 1993, 1994 and 1995 wet seasons to determine the effect of Alectra vogelii on the vegetative growth of 16 cowpea variet ies. This include 11 resistant varieties: IT81D-985, IT81D-994, IT89KD-245- 1, TN93-80, TN121-80. IT90K-76. IT90K-59, IT86D-534. IT86D-843, B301 and IT 89KD-245, two tolerant varieties: KANO 1696 and VITA 3 and three susceptibl e varieties: SAMPEA 7, TVX 3236 and IT82D-849. The growth of A. vogelii on each of the cowpea varieties was also evaluated. Cowpea varieties Tvx 3236, VITA 3, SAMPEA 7, KANO 1696, IT89KD-245 and IT82D-849 had higher Alectra i nfestation than the other varieties in the study. Alectra infestation gener ally showed a high tendency to stimulate root and shoot dry matter producti on of most cowpea varieties studied at 5 WAP, especially in 1993 and 1994. Generally, more cowpea varieties had the root and shoot dry matter producti on reduced at 9 WAP, with greater reduction in the late planted crop and he avily infested cowpea plants as observed in 1993 and 1995, respectively. Th e root dry weight of varieties IT89KD-245, IT90K-76 and IT90K-59 in 1993 an d 1994 and IT81D-994 and B301 in 1994 and 1995 and TN93-80 in 1993 and 1995 was increased at 9 WAP, whereas that of SAMPEA 7 and IT86D-843 was reduced at 9 WAP in all the trials. Irrespective of sowing date and level of infes tation, the adverse effect of Alectra infestation on cowpea shoot growth wa s more apparent between 7 and 9 WAP-a period of flower initiation and first phase of pod development. Generally, Alectra infestation showed a high ten dency to reduce the leaf area of most of the cowpea varieties in at least t wo of the sampling dates. The root nodule formation in both resistant and s usceptible cowpea varieties was inhibited by Alectra infestation. It reduce d the root nodule count of varieties IT81D-985, IT89KD-245-1, IT90K-76, TN9 3-80, KANO 1696 and SAMPEA 7 in 1994 and IT82D-849 in 1995 at all the sampl ing dates in each trial. This study showed that the devastation of cowpea g rain yield by Alectra could be attributed to the reduced root nodulation, r oot and shoot growth exhibited by susceptible varieties at stages of vegeta tive growth. (C) 2001 Elsevier Science Ltd. All rights reserved.