Tomato Yellow Leaf Curl Disease: epidemiological survey of the extant population of viral agents in Sicily

Tomato yellow leaf curl disease (TYLCD), caused by viruses belonging to the genus Begomovirus, family Geminiviridae, provokes high economic losses in tomato crops worldwide. Its rapid spread is driven by the efficient persistent transmission of the whitefly Bemisia tabaci and the dynamic nature of the geminivirus genomes, prone to a high level of mutations and recombinations. In Italy, two TYLCD-related viral species are present, tomato yellow leaf curl Sardinia virus (TYLCSV), first detected in Sardinia in 1989, and tomato yellow leaf curl virus (TYLCV), detected in Sicily in 2002. Their co-existence gave origin to different recombinants (Davino et al., 2009). Moreover, the use of tomato cultivars carrying resistance genes, generally Ty-1, contributed to shaping the population dynamics of these viruses, with the generation of resistance-breaking recombinants (Panno et al., 2017). In this work, we investigated the population of TYLCD-related viruses in 70 symptomatic plants collected from seven fields in the Ragusa province (Sicily) in 2020, using multiplex PCR analysis (Belabess et al., 2015). TYLCD-related viruses were detected in 57% of the samples. An almost complete displacement of TYLCV was manifest, in favor of TYLCSV and of TYLCV/TYLCSV recombinants. Among the different types of recombinants detected by the multiplex PCR, the prevailing ones were those of the resistance breaking IS76-type, which occurred even in single infection, i.e. in the absence of TYLCV or TYLCSV parentals. This study provides valuable epidemiological results regarding the impact of growing Ty-1 resistant cultivars in an intensive tomato growing area.