Surface Waxes in Grapevine as Target for Resistance Breeding

Abstract

Viticulture accounts for around 80% of fungicide use in Europe, a demand which is caused by several diseases that have been introduced in the 19th century, especially Powdery Mildew (Arnold, Schnitzler, Douard, Peter, & Gillet, 2005). Owing to the structure and the location of surface wax (Collinge, 2009; L. Kunst & Samuels, 2003), maybe it can block Powdery Mildew penetrating the surface wax and cuticle as well as the adhesion at the leaf surface (Wenping Qiu, 2015). It is important consequently to find out that if there are distinct resistance to the Powdery Mildew in the grape accessions which have wax accumulation differences. Further wax biosynthesis mechanism needs to be investigated in the grapevine collection. That can provide another strategy to create new varieties. In this study, there were three types of wax morphologies discerned as long wing-like structure, small wax crystals and occurrence long wax wings with small wax crystals together in the wild ancestor of domesticated grapevine collections. Surface waxes formation and accumulation of the genotypes indicated genetic variation and wax contents stabilized at fully expanded leaves. The relationship between wax content and Powdery Mildew resistance was that varieties with low wax abundance were more susceptible to Powdery Mildew. Moreover, the higher wax accumulation of Ke114 genotype, compared with genotype of Ke35, could prevent the Powdery Mildew spores further generating the appressorium, instead, the aberrant stage ap*(only hyphae growth) appearance, thus influenced the resistance to Powdery Mildew. We found one pair of Ke114 and Ke35, which were close to each other according to the SNP polygenetic tree, that they had different wax formation and the resistance to the Powdery Mildew. Further the expression levels of MYB106 and MYB30 were also distinguished in the pair, especially MYB106 expression level in the secondary leaf. Both of them could complement the wax-lack phenotype in myb106 and myb30 Arabidopsis mutant background, respectively. MYB 106 and MYB 30 interacted with each other to regulate the wax biosynthesis in the pair. Furthermore, chitosan, as the main component of fungal cell walls could regulate the promoter activity of MYB 106 and MYB 30, further influenced the genes expression level and regulate the wax biosynthesis in the Ke114 and Ke35.