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.
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