CREATION OF SPECIES HYBRIDS OF PHYTOPHTHORA WITH MODIFIED HOST RANGES BY ZOOSPORE FUSION

Species hybrids of the fungal plant pathogens Phytophthora capsici and P. nicotianae were created that exhibited expanded host ranges compared with parent organisms. One hybrid lost its ability to infect host plants specific to either species. The hybrids were created by a novel method of fusing uninucleate zoospores of these pathogens in the presence of polyethylene glycol (PEG) and LiCl. Lithium ion inhibited cell wall formation and encystment of zoospores during fusion in the presence of PEG. After fusion, lithium ion was replaced with calcium and potassium ions to induce encystment and spore germination. The hybrid characters of the fusion offspring were confirmed by detection of DNA sequences specific to each parent organism. Repetitive DNA of P. capsici was detected readily in all species hybrids by hybridization with a species-specific DNA probe. DNA of P. nicotianae was detected in some of the hybrids after amplification of DNA from hybrids with species-specific primers derived from P. nicotianae. Zoospore fusion provided a means of generating a series of organisms with modified pathogenicity-related traits to be used in molecular and ecological analyses.