Abstract
Grafting is routinely implemented in modern agriculture to manage soilborne pathogens such as fungi, oomycetes, bacteria, and viruses of solanaceous crops in a sustainable and environmentally friendly approach. Some rootstock/scion combinations use specific genetic resistance mechanisms to impact also some foliar and airborne pathogens, including arthropod or contact-transmitted viruses. These approaches resulted in poor efficiency in the management of plant viruses with superior virulence such as the strains of tomato spotted wilt virus breaking the Sw5 resistance, strains of cucumber mosaic virus carrying necrogenic satellite RNAs, and necrogenic strains of potato virus Y. Three different studies from our lab documented that suitable levels of resistance/tolerance can be obtained by grafting commercial tomato varieties onto the tomato ecotype Manduria (Ma) rescued in the framework of an Apulian (southern Italy) regional program on biodiversity. Here we review the main approaches, methods, and results of the three case studies and propose some mechanisms leading to the tolerance/resistance observed in susceptible tomato varieties grafted onto Ma as well as in self-grafted plants. The proposed mechanisms include virus movement in plants, RNA interference, genes involved in graft wound response, resilience, and tolerance to virus infection.
Highlights
The tomato virome consists of at least 136 characterized virus species threatening tomato production worldwide plus a number of new viruses that are being progressively identified by next-generation sequencing [1]
The lowest levels of viral RNA were detected in Ma, Mo, and S. integrifolium, these genotypes were selected as rootstocks to prepare graft combinations
Results from hybridization of the three L, M, and S genomic RNAs of tomato spotted wilt virus (TSWV)-CiPz with radiolabeled small RNA (sRNA) probes suggested that the majority of sRNAs in the total pool corresponded to vsiRNAs produced from genomic RNA S whereas those corresponding to genomic segments L and M were apparently less represented [62]
Summary
The tomato virome consists of at least 136 characterized virus species threatening tomato production worldwide plus a number of new viruses that are being progressively identified by next-generation sequencing [1]. Suitable levels of resistance against root-knot nematodes and Phytophthora capsici were attained in sweet pepper grafted on Capsicum annuum accessions “AR96023” and “AF2638,” respectively This list could not be exhaustive without including the control of Verticillium wilts obtained by grafting seed-propagated globe artichoke hybrids onto cardoon [37] as well as the list of potential rootstocks with special characteristics to manage biotic and abiotic stresses in tomato, eggplant, chili, potato, cucumber, muskmelon, pumpkin, and wax gourd reported by Kumar et al [38].
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