Inductive effects of exogenous calcium on the defense of kidney bean plants against Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract

Calcium (Ca) is an essential macronutrient for plant growth. It can confer plants with resistance to abiotic stresses. However, little is understood about its role on biotic stresses. Frankliniella occidentalis (Thysanoptera: Thripidae) is one of the world’s most important invasive pests and poses a great threat to crops; meanwhile, it is hard to control due to its polyphagia and rapid reproduction. In order to clarify the effects of Ca on the induced defense of kidney bean plants against F. occidentalis by different application methods, we treated plants with different concentrations of CaCl2 solution using three methods, including spraying on leaf, root-irrigation, and seed soaking. The activities of defensive enzymes in leaves of kidney bean plants in response to F. occidentalis feeding as well as the developmental time of F. occidentalis were examined. The results showed that all the three treatment methods with different concentrations of CaCl2 solution could obviously induce activities of lipoxygenase (LOX), phenylalanine ammonia lyase (PAL), and β-1, 3-glucanase in leaves of kidney bean plants against F. occidentalis, while inductive effects of spraying the 10 mM CaCl2 on leaves were the best among all the treatments. Furthermore, we found that the developmental time of the whole immature stage of F. occidentalis feeding on plants sprayed with 10 mM CaCl2 was longer than those on control plants. Overall, our results indicated that the exogenous CaCl2 could enhance enzymatic activities in plants by thrips-induced effects, and spraying 10 mM CaCl2 on leaves of kidney bean plants showed the highest resistance against F. occidentalis.