Effect of sugar spraying on host plant resistance to western flower thrips in tomato

Sugar spraying can cause induced plant resistance. In this study we investigated the effects of sugar spraying on the resistance to western flower thrips, WFT, Frankliniella occidentalis on tomato. We tested three different sugars: sucrose, fructose and glucose, at four concentrations: 0, 1, 10 and 100 ppm, to induce resistance of the cultivated tomato (var. Moneymaker). Bioassays conducted 2 weeks after sugar treatment showed significantly lower damage compared to bioassays after 24 hours, while such a difference was absent in the control. Only for fructose we detected indications that sugar-spraying may increase plant resistance to thrips. At concentrations of 1 and 10 ppm fructose plants showed less thrips damage compared to control plants. In 10 out of the 12 treatments with fructose, thrips damage was less than in the control. Although this number is significantly higher than can be expected by chance (χ2 = 5.3, df= 1 and P = 0.02), differences were generally small and not significant. Plant leaf stage at the time of sugar spraying, did not affect thrips resistance.