Varietal resisitance of hops, Humulus lupulus (Linn.), to the two-spotted spider mite, Tetranychus urticae (Koch) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sj139437f

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  • The purpose of this study was to determine the relative resistance of genetic lines of hops, Humulus lupulus (Linn.) to the two-spotted spider mite, Tetranychus urticae (Koch) in western Oregon. Approximately three-hundred genetic lines of hops were screened under insectory conditions during the 1965 growing season at Corvallis, Oregon. Reduction in fecundity was the basis for delineating spider mite resistance. A commercial hop variety, Fuggle, was used as a standard, and the fecundity of spider mites on this variety was arbitrarily set at 100 percent. Striking differences in fecundity was found during the screening experiments, and 24 varieties which showed 50 percent or less fecundity compared to the standard were re-screened during the 1966 season. Although the results of the 1966 re-screening program were not as striking as the data obtained during the 1965 screening experiments, six hop varieties were selected as possible resistant varieties and were compared to two commercial hop genotypes in a growth chamber under controlled environmental conditions. Several factors in the biology of the spider mite were studied in the laboratory under optimum conditions for spider mite development. The various developmental stages of the spider mite biology showed no significant differences among the eight selected hop varieties. Although the research was primarily concerned with screening of various genotypes of hops for possible resistance, it was essential in conducting the study to acquire a background on certain aspects of the biology and life history of the two-spotted spider mite on hops. Orange-colored female spider mites were found overwintering within the hop yard. Actively feeding mites were first observed in early May, 1965 and early June, 1966. The majority of spider mites confined their activities to the 4-6 foot level on the hop vines.
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