Mix and match to counteract virus infections in plants: results of the application of vegetable grafting

Vegetable grafting is a common practice in horticulture, used to propagate many plant species and to combine desirable traits of two different plants, such as fruit quality and crop productivity. This technique is also particularly useful in areas busted by recurrent outbreaks of emerging and re-emerging plant virus species as it might provide a rapid response based on natural resistance/tolerance traits without the need for chemical treatments. By the systematic screening of Apulian local plant varieties and ecotypes for virus resistance/tolerance, we identified a promising rootstock for sustainable crop production and management of outbreaks derived from infections of tomato spotted wilt virus Sw5 resistance-breaking strain. Using different experimental approaches, we studied and suggested possible mechanisms for the observed tolerance/resistance in grafted tomato and we tested this method to counteract infections caused by cucumber mosaic virus supporting stunting or necrotic satellite RNAs and recombinant strain of potato virus Y in tomatoes, and tomato leaf curl New Delhi virus in cucurbit varieties. We analyzed virus movement in plants, the production of endogenous virus-activated small interfering RNAs and virus genome-derived siRNAs targeting viral genome and host gene transcripts, respectively, genes and volatile organic compounds related to graft wound response, and tolerance to virus infection. Grafted plants did not show or show very mild disease symptoms suggesting the use of the selected local ecotypes as potential rootstocks to obtain suitable levels of tolerance against virus infections in commercial crops. The plant may be primed to respond to stresses by memorizing them through epigenetic modification of the genome, leading to lasting functional states of adaptive immunity, which could also be seen in a higher baseline level of alert to pathogen attack, characterized by the mild symptoms and low transcriptome modulation, compared to susceptible plants. In addition to protecting plants from virus infections, grafting can also improve plant growth, yield, and resilience to environmental stress factors.