NEW SOURCES OF RESISTANCE OF COWPEA (VIGNA-UNGUICULATA) TO STRIGA GESNERIOIDES, A PARASITIC ANGIOSPERM

Thirty-seven accessions of cowpea and yard-long bean were assessed for resistance to Striga gesnerioides. Cowpea plants were grown using an in vitro method, then inoculated with young seedlings of S. gesnerioides produced from seed from three West African countries. Resistance was assessed by comparing the number and size of S. gesnerioides tubercles on these accessions with those on a known susceptible cowpea, cv. Blackeye. Two cowpea landraces, APL-1 and 87-2, were completely resistant to S. gesnerioides from Burkina Faso, Mall and Cameroon and partially resistant to S. gesnerioides from Niger. Complete resistance was expressed either as a hypersensitive response of infected root tissues or as a severely retarded development of successful infections. All other accessions, including three samples of yard-long bean were susceptible to S. gesnerioides. The original 87-2 plants segregated for resistance and susceptibility. However, uniformly resistant progeny were obtained by producing seed from vegetatively propagated clones of single resistant 87-2 plants. Resistance of APL-1 and 87-2 to S. gesnerioides was confirmed in pot and field trials. Neither of these cowpeas were resistant to Alectra vogelii. Varieties APL-1 and 87-2 provide additional sources of resistance to most races of S. gesnerioides, including a newly discovered virulent race from Benin.