CREATION OF SPECIES HYBRIDS OF PHYTOPHTHORA WITH MODIFIED HOST RANGESBY ZOOSPORE FUSION

Species hybrids of the fungal plant pathogens Phytophthora capsici and P. nicotianae were created that exhibited expanded host ranges compar ed with parent organisms. One hybrid lost its ability to infect host p lants specific to either species. The hybrids were created by a novel method of fusing uninucleate zoospores of these pathogens in the prese nce of polyethylene glycol (PEG) and LiCl. Lithium ion inhibited cell wall formation and encystment of zoospores during fusion in the presen ce of PEG. After fusion, lithium ion was replaced with calcium and pot assium ions to induce encystment and spore germination. The hybrid cha racters of the fusion offspring were confirmed by detection of DNA seq uences specific to each parent organism. Repetitive DNA of P. capsici was detected readily in all species hybrids by hybridization with a sp ecies-specific DNA probe. DNA of P. nicotianae was detected in some of the hybrids after amplification of DNA from hybrids with species-spec ific primers derived from P. nicotianae. Zoospore fusion provided a me ans of generating a series of organisms with modified pathogenicity-re lated traits to be used in molecular and ecological analyses.