GENOTYPIC VARIATION IN CONSTITUTIVE AND INDUCED RESISTANCE IN GRAPES AGAINST SPIDER-MITE (ACARI, TETRANYCHIDAE) HERBIVORES

We examined genotypic variation in constitutive and induced resistance in grapes against Willamette spider mites, Eotetranychus willametti E wing, and Pacific spider mites, Tetranychus pacificus McGregor, 2 comm on species of tetranychid mites found in California vineyards. We foun d evidence that early-season injury by Pacific mites induced resistanc e against subsequent Willamette mite populations but early-season inju ry by Willamette mites did not induce resistance against subsequent Wi llamette mite populations. Significant levels of induction were detect ed for several cultivars of the Old World species Vitis vinifera L. as well as the North American species V. californica Bentham. Phylogenet ic relationships among grape genotypes explained little of the variati on we observed in induced resistance. Phylogenetic relatedness among g rapes did help explain patterns of constitutive resistance for Pacific mites; cultivars of V, vinifera L. tended to be susceptible, whereas North American species were resistant. Willamette mites, however, perf ormed well on some Old World cultivars and 2 North American species of Vitis that are native to California. We did not and any strong eviden ce of a negative correlation between constitutive resistance and stren gth of induction for these grape genotypes. Our results show that seve ral factors contribute to variation in constitutive and induced resist ance in grapes against these 2 species of spider mites, including grap e genotype, previous history of mite injury (induction), the species o f mite causing previous injury, and to some extent, phylogenetic relat edness among grapes. We also suspect that mite genotype has important influences.