Control of Tomato Yellow Leaf Curl Disease in Tomato

A study was performed in 2011 and 2012 with the purpose of evaluating the efficacy of two products, the insecticide Cyantraniliprole and a mixture of the insecticide with the inducer of systemic acquired resistance (SAR), Acibenzolar-S-Methyl (ASM), in the control of Tomato yellow leaf curl disease in tomato. The experiment was performed in laboratory, in a thermo-conditioned greenhouse divided into separate insect-proof cages. It consisted of four treatments (Tr.): Tr. 1, ASM+Cyantraniliprole 1.56 g/hl + 12.5 ml/hl; Tr. 2 = Cyantraniliprole 12.5 ml/hl; Tr. 3 = ASM 1.56 g/hl; Tr. 4 = untreated plants (check), and two applications of each by foliar spray. Tomato seedlings of the cultivar ‘San Marzano’, indetermined and extremely susceptible to TYLCSV, were used for the test. All plants of each treatment were put in a unique flower pot saucer in order to make available the same amount of water. Each treatment was exposed to viruliferous whiteflies for 24 h (exposure time, e.t., A), 8 days (e.t. B) or 15 days (e.t. C) after the 2nd application. After that, insects were killed by treatment with Imidacloprid. Plants of each treatment were observed daily to record any symptom of leaf curling and/or of phytotoxicity. Eventual infection of the plants was verified by molecular hybridization using a probe specific for TYLCSV. It was shown that the combination of ASM and Cyantraniliprole allowed the best control of TYLCSV transmission by whiteflies and of the development of the infection in treated tomato plants, in particular when viruliferous whiteflies were introduced to healthy plants 1 day after the last treatment. In this case (only in e.t. A), a comparable result is obtained using the insecticide Cyantraniliprole alone. In contrast, ASM used alone showed less activity of control of both parameters (virus transmission and, consequently, disease development) than the former. Moreover, a lower control was also observed in all the treatments (and above all in those where ASM or the insecticide were use alone) when the viruliferous whiteflies were introduced 8 or 15 days after the last treatment: with increasing exposure time, only the combined use of ASM and Cyantraniliprole proved to be effective in the activity of control. Results suggest that the combination between an insecticide and a strong inducer of systemic acquired resistance to virus infections, such as ASM (which is also effective in inducing SAR against B. tabaci), can contribute greatly to control virus infections.