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Breeding and Characterization of Thrips Resistance in Cabbage 2000

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Project Leader: Phillip D. Griffiths, 302 Hedrick Hall, Department of Horticultural Sciences, Cornell University NYSAES, Geneva NY 14456

Abstract: Onion thrips (Thrips tabaci) are a major pest of the cabbage industry in New York State and the northeast, largely due to the ineffectiveness of chemical control. Host plant resistance is the most effective defense against thrips damage, but it is difficult to evaluate even with labor-intensive screening. Recent screens for thrips damage have identified varieties with high levels of thrips resistance, this resistance needs to be characterized in order to maximize the benefit of host plant resistance in new varieties and breed this resistance into varieties of different maturities. In 1999 a total of 800 primers were used to amplify molecular regions in Fresco (a thrips resistant variety) and Bartolo (a thrips susceptible variety). When compared to three other Bejo varieties Bronco (a partially resistant half-sib of Bartolo), Brutus (partially resistant) and its susceptible half-sib Gideon, A total of 15 polymorphisms were exclusive to Fresco and were not found in the other four Bejo lines, 15 polymorphisms were observed in all other Bejo lines, but not in Fresco, other polmorphisms were present in one or more resistant varieties, but absent in the susceptible varieties. Thirty-three primers were used to amplify polymorphisms in commercial varieties based on these results. A total of 20 cabbage varieties were chosen that had been previously evaluated for thrips damage, and varied in maturity and type. The two varieties exhibiting the highest levels of resistance to thrips ‘Fresco’ (Bejo seeds) and ‘Bobcat’ (Reeds seeds) were vernalized and self-fertilizations and crosses to susceptible types are being made to generate populations for future screening. Self-fertilized ‘Fresco’ seed has been harvested and some plants screened for thrips damage during the 2000 season, although the results are somewhat erroneous due to variable type and poor weather conditions leading to low damage levels. Polymorphisms were identified that were exclusive to both ‘Fresco’ and ‘Bobcat’, polymorphisms were also identified that were present in both and types and at least one other varietal type. These polymorphisms indicate some potential similarity between thrips resistant types although no clear similarities were identified in this study.