Systemic resistance of kidney bean plants induced by exogenous CaCl2 and western flower thrips infestation

The western flower thrips (WFT, Thysanoptera: Thripidae) is an important pest worldwide that causes serious damage to commercial crops. To assess the impact of calcium chloride (CaCl₂) application and WFT infestation on the systemic resistance of kidney bean plant, a comparison was conducted about the contents of calcium ion (Ca²⁺) and activities of defensive enzymes in the upper, middle, and lower leaves after treating the middle leaves with either CaCl₂ application or H₂O and exposing them to WFT infestation or not. The development, feeding behavior, and leaf area damaged by WFT in different leaf positions were also observed. The results showed that the Ca²⁺ content was the highest on all leaf positions under CaCl₂ treatment plus WFT infestation. The activities of lipoxygenase (LOX), allene oxide synthase (AOS), phenylalanine ammonia-lyase (PAL), and β-1, 3-glucanase had no significant differences among leaf positions without WFT infestation, but they became significant after WFT infestation, WFT infestation could enhance the CaCl₂ treatment on all indexes. The immature period of WFT infestation on the upper, middle, and lower leaves of CaCl₂-treated plants were 0.8, 1.9, and 1.2 days longer than that of WFT fed on H₂O-treated plants, respectively. Electrical penetration graphs (EPG) showed that the total duration of long-ingestion probes (LP) of WFT on the upper, middle, and lower leaves of CaCl₂-treated plants obviously decreased than that in control plants. The feeding preference and feeding areas of WFT in CaCl₂-treated plants significantly reduced at all leaf positions. These results indicated that CaCl₂ application could weaken the development, feeding behavior, and damage areas of WFT, but WFT infestation triggered exogenous CaCl₂ application in activating the systemic defense of the whole plant.