APS Abstracts of Presentations

Screening cucumber germplasm for resistance to Phytophthora capsici using a detached fruit method
Presenter: A. Gevens, Michigan State University, East Lansing, MI 48824, USA
Co-Author(s): M. Hausbeck, Michigan State University, East Lansing, MI 48824, USA; K. Lamour, University of Tennessee, Knoxville, TN 37996, USA
Phytopathology 95:S34

Phytophthora capsici causes fruit rot of cucumbers and its long-lasting oospore renders fields unsuitable for future production. Commercial hybrids (143) and plant introductory accessions (PIs) (192) were screened in the laboratory from 1999 to 2004 for resistance to P. capsici. A screening technique was developed using detached, unwounded fruit produced in fields known to have no history of P. capsici infestation. Fruit were inoculated with 7-mm plugs of mycelia and sporangia from 7-day-old cultures and incubated at 22°C under 100% relative humidity. Fruit were evaluated after 3 days for lesion diameter and pathogen sporulation. Four P. capsici isolates from different hosts were compared for virulence in 1999 and 2000. The isolates represented both compatibility types (A1 and A2) and varied in sensitivity to the fungicide mefenoxam. Significant differences among isolates were not observed (P = 0.05) and a single isolate (OP97) was used in subsequent inoculations. Although no fruit exhibited complete resistance, 31 PIs (16% of all PIs) and 14 commercial hybrids (10% of all commercial hybrids) were observed with limited pathogen sporulation. This method provided an efficient technique for screening cultigen fruit for resistance to P. capsici.

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