Ιntra-species grafting induces epigenetic and metabolic changes accompanied by alterations in fruit size and shape of Cucurbita pepo L.

To further understand the impact of grafting on fruit characteristics and to comprehend the mechanisms involved in graft-induced changes we studied homo- and hetero- grafted Cucurbita pepo cultivars (cv.) that vary in fruit size and shape. C. pepo cv. ‘Munchkin’ and cv. ‘Big Moose’ as well as cv. ‘Round green’ and cv. ‘Princess’ were homo-grafted and reciprocally hetero-grafted. The results show significant changes in fruit size when ‘Big Moose’ was grafted onto ‘Munchkin’ rootstocks in comparison to homo-grafted controls. Statistically significant changes were also observed in fruit shape when cv. ‘Princess’ was grafted on cv. ‘Round green’. This is the first report of such phenotypic changes after intra-species/inter-cultivar grafting in Cucurbitaceae. Additionally, we found significant changes in (i) secondary metabolite profile, (ii) global DNA methylation pattern and (iii) miRNA expression patterns in grafted scions and (iv) DNA methylation on graft-induced phenotypic changes in grafted plants. Our results contribute to further understanding graft-induced effects on fruit morphology in intra-species grafting. Furthermore, our results pave the way for understanding the role of phenolic metabolites and epigenetic molecular mechanisms on the phenotypic changes recorded.