Occurrence, Distribution, and Pathogenicity of the Cowpea Root and Stem Rot Pathogen, Phytophthora vignae, in Soils of Sri Lanka. W. G. Dilantha Fernando, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97330. R. G. Linderman, USDA-ARS, Horticultural Crops Research Laboratory, Corvallis, OR 97330. Plant Dis. 77:1158-1164. Accepted for publication 26 June 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-1158.

A Phytophthora sp. isolated from stem and root lesions of cowpeas (Vigna unguiculata subsp. unguiculata ‘California Blackeye’) grown in a mixture of riverbank and forest soils in containers under greenhouse conditions 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 disks of tea leaves over soil. However, the root and stem disease was apparent at only one site, suggesting that some field soils might be suppressive. Among the 25 field soils tested, the disease potential index varied from 0 in many fields to 16 in one field. Among the cowpea cultivars grown in Sri Lanka, MI-35, ETA, Muttessa, and Sudumung were most resistant. The U.S. cultivars Mississippi Purple, Purple Hulk, and Hercules were resistant to most isolates but susceptible to three—P006, P007, and P009. The morphological characters and pathogenicity of these three isolates on the U.S. cultivars differed from those of the other isolates, suggesting they were of a different race(s). No other legume tested—Vigna radiata (green gram), V. mungo (black gram), Phaseolus vulgaris (cvs. Top Crop, French Bean, and Kentucky Wonder), Glycine max (soybean), Cajanus cajan (pigeon pea), Mucuna pruriens (velvetbean), and Lanka kadala—was susceptible to the cowpea pathogen.

Keyword(s): disease resistance, suppressive soils.