Effects of Bemisia tabaci feeding on nutrients and resistance-related compounds of pepper varieties with different insect resistances

Induced insect resistance is a series of defending reactions of plant under biotic and abiotic stress. In order to explore the effects of Bemisia tabaci feeding on induced insect resistance of different varieties of pepper, and illuminate the insect resistance mechanisms, we conducted an experiment in insectary. In the experiment, two insect-resistant varieties ('Xinyidai Sanying' and 'Xinsujiao 5') and two insect-susceptible varieties ('Sujiao 13' and 'Sujiao 15') of pepper were selected and infected with B. tabaci adults 0 (control), 30 (lower density), 60 (middle density) and 120 (higher density) heads per plant, respectively. The contents of chlorophyll, soluble sugar, soluble protein, phenol compound and flavonoids in pepper leaves were determined after 24 h of feeding of B. tabaci. The results showed that leaf chlorophyll content of pepper under feeding of lower density of B. tabaci was significantly increased, and the chlorophyll content decreased with the increase of population density of the insect, but was still higher than that of the control. The increase of chlorophyll content in the insect-susceptible pepper varieties was higher than that of the insect-resistant varieties. The content of soluble sugar in pepper leaves showed a decreasing trend after infected with the insects with lower and higher densities, and the decreased level of insect-resistant varieties was higher than that of insect-susceptible varieties. The content of soluble protein in pepper leaves decreased after infected by the insects with lower and middle densities, but increased when fed by high density insects. The changing range of soluble protein contents of insect-resistant pepper varieties was higher than that of insect-susceptible varieties. The contents of phonemic compounds in leaves increased significantly after B. tabaci feeding, and the increase rate of insect-susceptible varieties was higher than that of the insect-resistant cultivars. With the increased insect density, the content of phenolic compounds in pepper leaves showed a significant upward trend, but decreased obviously when the population density was 120 head per plant. We also found that the content of flavonoids in the leaves of pepper 'Sujiao 15' was significantly increased after B. tabaci feeding, and that in other varieties under middle insect density were not significantly different from that of the control. However, in the case of higher insect density, the content of flavonoids was significantly higher than that of control. Our results indicated that the feeding of B. tabaci changed contents of nutrients and resistant substances in the direction of improving insect resistance. The extents of change of different pepper varieties under different insect densities were different. The results provided a basis for further revealing the defense and anti-defense mechanisms between hos plant and B. tabaci.