Abstract
Grafting of commercial tomato varieties and hybrids on the tomato ecotype Manduria resulted in high levels of tolerance to the infection of Sw5 resistance-breaking strains of tomato spotted wilt virus and of severe cucumber mosaic virus strains supporting hypervirulent satellite RNAs that co-determine stunting and necrotic phenotypes in tomato. To decipher the basis of such tolerance, here we used a RNAseq analysis to study the transcriptome profiles of the Manduria ecotype and of the susceptible variety UC82, and of their graft combinations, exposed or not to infection of the potato virus Y recombinant strain PVYC-to. The analysis identified graft- and virus-responsive mRNAs differentially expressed in UC82 and Manduria, which led to an overall suitable level of tolerance to viral infection confirmed by the appearance of a recovery phenotype in Manduria and in all graft combinations. The transcriptome analysis suggested that graft wounding and viral infection had diverging effects on tomato transcriptome and that the Manduria ecotype was less responsive than the UC82 to both graft wounding and potyviral infection. We propose that the differential response to the two types of stress could account for the tolerance to viral infection observed in the Manduria ecotype as well as in the susceptible tomato variety UC82 self-grafted or grafted on the Manduria ecotype.
Highlights
Grafting of commercial tomato varieties and hybrids on the tomato ecotype Manduria resulted in high levels of tolerance to the infection of Sw5 resistance-breaking strains of tomato spotted wilt virus and of severe cucumber mosaic virus strains supporting hypervirulent satellite RNAs that co-determine stunting and necrotic phenotypes in tomato
The evidences provided in both the studies suggest that the Ma rootstock may induce systemic tolerance to viral infection via the adaptive defense response based on RNA interference (RNAi), which is a sequence identity-dependent RNA degradation mechanism conserved in plants, invertebrates, fungi and oomycetes[14,15,16,17]
Infection of PVYC-to in self-grafted Ma (Ma/Ma) and in UC grafted on Ma (UC/Ma) induced a mild reduction of young leaf blade and only in the UC/Ma graft combination a mild distortion of leaf margin
Summary
Grafting of commercial tomato varieties and hybrids on the tomato ecotype Manduria resulted in high levels of tolerance to the infection of Sw5 resistance-breaking strains of tomato spotted wilt virus and of severe cucumber mosaic virus strains supporting hypervirulent satellite RNAs that co-determine stunting and necrotic phenotypes in tomato. Most of the economic losses are compensated by the reduced number of plants required per cultivation area unit, noticeable increases in fruit yield, reduced use of chemical fertilizers, improved economic use of irrigation water, earliness of the produce and extension of the growing season These traits rely mostly on the rootstock genotype and on the large and vigorous root systems of grafted plants that ensure the maintenance of good plant vigor and suitable levels of disease resistance or tolerance until late in the growing season[1,2,3,4,5,6]. Grafting enables exchanges of RNA, DNA, microRNA (miRNA), plastidial genomes and entire nuclear genomes between the grafting partners, as well as differential expression of proteins involved in various molecular functional and biological processes[23,24]
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