Cowpea reactions to Striga gesnerioides I. effect on growth

Field trials were conducted in 1993, 1994 and 1995 wet seasons to determine the effect of Striga gesnerioides on the vegetative growth of 16 cowpea varieties. These included 11 resistant varieties, 2 tolerant varieties and 3 susceptible varieties. The growth of S. gesnerioides on each of the cowpea varieties was also evaluated. The highest Striga infestation was observed on several cowpea varieties notably all the susceptible and several tolerant varieties. Cowpea varieties generally had root and shoot growth stimulation at 5 and 7 WAP under low Striga infestation in the late planted trial (LPT) in 1993 and the early planted trial (EPT) in 1994. There was no clear-cut difference in the change in the root dry weight of the resistant and susceptible varieties due to Striga infestation. However, heavy Striga infestation greatly reduced the root and shoot dry weight of most varieties, between 1994 and 1995 irrespective of sowing dates. Greater reduction was observed in the leaf area and root nodules of the susceptible than resistant cowpea varieties. The susceptible varieties had conspicuous reduction in shoot dry weight at 9 WAP in each trial. The reduction in cowpea shoot dry weight due to Striga infestation was slightly greater in the LPT than EPT, and there was an increasing tendency towards greater reduction of the shoot dry weight from the trial in 1993-1995, due to increasing level of infestation. The losses usually observed in the cowpea host productivity could be due to the reduction in the root nodulation, leaf area, root and shoot growth under Striga infestation.