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چکیده
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We tested the extent to which resistance of common bean (Phaseolus vulgaris) cultivars to the spider mite Tetranychus urticae, parallels the extent to which these plants display indirect defenses via the induced attraction of predatory mite Phytoseiulus persimilis. First via field and greenhouse trials on 19 commercial bean cultivars, we selected two spider mite-resistant (Naz and Ks41128) and two susceptible (Akthar and G11867) cultivars and measured their spider mite-induced volatiles and the subsequent induced attraction of predatory mites via olfactory choice assays. The two major volatiles, 4,8,12-trimethyltrideca-1,3,7,11- tetraene (TMTT) and (Z)-3-hexenyl-acetate, were induced in the resistant but not in the susceptible cultivars. However, uninfested susceptible cultivars emitted these volatiles at levels similar to those of mite-infested resistant cultivars. Significant induction of several minor components was observed for all four cultivars except for the infested-susceptible cultivar G11867. Both the spider mite-resistant cultivar Naz and the susceptible cultivar G11867 attracted more predatory mites when infested. In contrast, spider mites induced increased emission of two major and five minor volatiles in Ks41128 but predatory mites did not discriminate between infested and uninfested plants. Overall, the attraction of predatory mites appeared to correlate positively with the presence of TMTT and (Z)-3-hexenyl acetate and negatively with β-caryophyllene and α-pinene in the bean headspace. Taken together, our data suggest that resistance and attraction of natural enemies via induced volatiles are separate traits. We argue that it should be possible to cross predatorattraction promoting traits into resistant cultivars that lack sufficiently inducible indirect defenses.
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