Abstract

An interspecific cross was attempted between two homothallic species of Phytophthora, P. sojae and P. vignae. From 1640 single-oospore cultures isolated, DNA was extracted from 800, and two interspecific F₁ hybrids (F₁1121 and F₁1426) were putatively identified using RAPD markers. The true hybrid nature of these F₁ hybrids was confirmed using additional AFLP analysis. Single-zoospore cultures were generated for each F₁ hybrid and one single-zoospore culture of each was used in pathogenicity and virulence tests. Both F₁ hybrids were pathogenic to soybean and cowpea, causing symptoms including lesions, wilting and death of susceptible soybean and cowpea cultivars. However, the aggressiveness of the F₁ hybrids was reduced and was substantially more variable when compared with that of the parental isolates on their respective hosts. The F₁ hybrids were reisolated from infected seedlings and their hybrid nature confirmed using RAPD and AFLP analysis. These results provide a basis for further research aimed at obtaining an increased understanding of the genetics of host specificity in the Oomycetes.