Techniques for Formation, Maturation, and Germination of Plasmopara viticola Oospores Under Controlled Conditions. Cécile Ronzon-Tran Manh Sung, Inra, Centre de Recherches de Bordeaux, Station de Pathologie Végétale, BP 131, 33140 Pont de la Maye, France. M. Clerjeau, Inra, Centre de Recherches de Bordeaux, Station de Pathologie Végétale, BP 131, 33140 Pont de la Maye, France. Plant Dis. 72:938-941. Accepted for publication 7 January 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0938.

Sexual reproduction of Plasmopara viticola was induced in detached leaves inoculated with sporangia under controlled conditions. Oogenesis was stimulated by thermal shock from 20 to 10 C. Oospore maturation in controlled conditions required incubation at low temperatures of 10 and –5 C, alternating weekly. The transfer of oospores separated from leaf tissues to water agar in petri dishes at 20 C enabled the dynamics of oospore germination to be determined. Oospores germinate within 6–10 days, but a period of at least 5 mo after inoculation was necessary for optimum germination. The technique for assessing germination of mature oospores can also be used on oospores maturing naturally, and thus allows an evaluation of primary infection risks in the spring.