OCCURRENCE, DISTRIBUTION, AND PATHOGENICITY OF THE COWPEA ROOT AND STEM ROT PATHOGEN, PHYTOPHTHORA-VIGNAE, IN SOILS OF SRI-LANKA

A Phytophthora sp. isolated from stem and root lesions of cowpeas (Vig na unguiculata subsp. unguiculata 'California Blackeye') grown in a mi xture of riverbank and forest soils in containers under greenhouse con ditions was identified as P. vignae based on morphological characters and pathogenicity tests. P. vignae was isolated from soils in three of five cowpea-growing districts of Sri Lanka by baiting with plants of the susceptible cowpea cultivar California Blackeye or by floating dis ks of tea leaves over soil. However, the root and stem disease was app arent at only one site, suggesting that some field soils might be supp ressive. Among the 25 field soils tested, the disease potential index varied from 0 in many fields to 16 in one field. Among the cowpea cult ivars grown in Sri Lanka, MI-35, ETA, Muttessa, and Sudumung were most resistant. The U.S. cultivars Mississippi Purple, Purple Hulk, and He rcules were resistant to most isolates but susceptible to three-P006, P007, and P009. The morphological characters and pathogenicity of thes e three isolates on the U.S. cultivars differed from those of the othe r isolates, suggesting they were of a different race(s). No other legu me tested-Vigna radiata (green gram), V. mungo (black gram), Phaseolus vulgaris (cvs. Top Crop, French Bean, and Kentucky Wonder), Glycine m ax (soybean), Cajanus cajan (pigeon pea), Mucuna pruriens (velvetbean) , and Lanka kadala-was susceptible to the cowpea pathogen.