Field-grown soybean induces jasmonates and defensive compounds in response to thrips feeding and solar UV-B radiation

Solar UV-B radiation has been reported to enhance constitutive and inducible plant defenses against herbivore insects in many species. However, the induction of plant defenses depends on the phytohormone profile induced by the specific herbivore feeding guild. No study has shown the impact of soybean leaf chemical defenses induced by thrips herbivory in combination with solar UV-B radiation on thrips performance. To uncover plant responses to herbivory in crop conditions, we proposed the hypothesis that solar UV-B radiation will increase constitutive and inducible defenses and phytohormones related with defenses in field-grown soybean, therefore affecting thrips performance. In this study two soybean cultivars (cv.) were grown in field conditions under attenuated or solar UV-B radiation and damaged by 6 days of herbivory of Caliothrips phaseoli. Our field experiments showed similar survivorship levels of thrips that fed on foliage grown under either attenuated or solar UV-B radiation, while survivorship of thrips that fed on cv. Williams was lower than those that fed on cv Charata. Cv Williams produced different flavonols and higher trypsin protease inhibitor (TPI) activity levels and more genistin than cv Charata. The increment of jasmonic acid (JA)-regulated defenses against insects in foliage of cv Williams was explained by the induction of JA and JA-Ile after herbivory and solar UV-B exposure. Independently of the UV-B environment herbivory induced salicylic acid (SA) and 12-oxo-phytodienoic acid (cis-OPDA) in both cvs. To our knowledge no study before has showed a complete profile of defensive hormones and defensive compounds induced by thrips feeding and solar UV-B.