CONTROL OF VIRAL DISEASES TRANSMITTED IN A PERSISTENT MANNER BY THRIPS IN PEPPER (TOMATO SPOTTED WILT VIRUS)

Tomato spotted wilt disease is caused by Tomato Spotted Wilt Virus (TSWV) (Tospovirus, Bunyaviridae), a virus that severely damages and reduces the yield of many economically important plants worldwide and actually it is a major disease affecting the production of tomato and pepper in Italy. Due to the non-predictive nature of its outbreaks combined with the lack of forecasting, adoption of preventive measures have not always been practical, in fact the disease cycle has proven to be extremely difficult to break because of the wide and often overlapping host range of both the virus and the thrips vectors, which transmit the virus in a persistent, circulative, and propagative manner. Moreover recently, resistance breaking (RB) isolates of TSWV that overcome the resistance conferred by the Tsw gene in different pepper hybrids have been recovered in different locations in Italy and also in Brazil, USA, Spain and Australia, and this occurrence raises the question on the importance of a new approach of integrated pest management for TSWV management, including both control of its insect vector and the induction of the plant's resistance against viral infection. In this perspective, a study was performed in 2012 and 2013 with the purpose of evaluating the efficacy of the insecticide Cyantraniliprole alone or combined with Acibenzolar-S-Methyl (ASM), inducer of systemic acquired resistance, in the control of tomato spotted wilt disease in pepper. The experiment was performed in laboratory, in a thermo-conditioned greenhouse, into separate insect-proof cages and consisted of 5 treatments and 2 applications (plus a pre-transplant application for treatments were ASM was used. Variables were the mode of application of ASM in pre-transplant (by foliar or by drench) and the duration of the exposure time of the treated plants to viruliferous insects. Pepper cv. Corno di Toro, devoid of any resistance to TSWV, was used. Plants were observed daily to record any symptom induced by TSWV and/or of phytotoxicity. The possible TSWV infection was verified by DAS-ELISA using antisera supplied by Agdia Biofords. It was shown that the combination of ASM and Cyantraniliprole allowed the best control of TSWV transmission by thrips and of the development of the infection in treated pepper plants, regardless of the exposure time to thrips infestation. The application via drench of the combination seems to be the most effective. The efficacy of Cyantraniliprole used alone was comparable to that obtained with its combination with ASM only when plants were exposed to viruliferous insects for 24 h after product application, and the effectiveness of protection decreased with increasing time of exposure to viruliferous thrips. Treatment with ASM alone determined a good protection to plants regardless of the length of the exposure timing to viruliferous insects, with a smaller number of infected plants and milder symptoms compared to the check. Results of our current experiments raise the interesting possibility to combine in one product an insecticide and a non-specific (to various biotic and abiotic stresses) resistance inducer, particularly against diseases caused by viruses, and offer great opportunity for the integrated pest management (IPM) strategy for the control of pepper diseases.