Biological and Molecular Characterization of a New Isolate of Tomato Mottle Mosaic Virus Causing Severe Shoestring and Fruit Deformities in Tomato Plants in India

Abstract

Tomato (Solanum lycopersicum L.), the second most important vegetable crop globally, faces a significant threat from various viral diseases. A newly emerging disease, characterised by distinctive shoestring symptoms on leaves and the development of unripe, small, and hard fruit, poses a serious challenge to tomato cultivation in India. An initial survey in an experimental field revealed more than 50% of the plants displayed symptoms of the shoestring disease, resulting in substantial reductions in fruit yield and quality. Transmission electron microscopy (TEM) and molecular analyses identified an isolate of the tomato mottle mosaic virus (ToMMV) in the affected plants. When the partially purified virus was mechanically inoculated into tomato cv. Pusa Ruby plants, it reproduced the characteristic shoestring symptoms, confirming its causal relationship with the disease. Notably, the present shoestring isolate of ToMMV (ToMMV-Tss) was found to induce similar shoestring symptoms in most of the major commercial tomato varieties when inoculated under controlled experimental conditions in the glasshouse, indicating its aggressive nature. Host range studies demonstrated that the ToMMV-Tss can infect several solanaceous species, while cucurbitaceous hosts remained unaffected. Moreover, the virus was found to be seed-transmissible, with a small percentage of seedlings from infected plants displaying symptoms. These findings underscore the significant impact of ToMMV on tomato production in India and emphasise the need for reliable diagnostic tools and effective management strategies to curb the spread and mitigate the impact of this virus on commercial tomato cultivation.