Fungal and Bacterial Disease Resistance Conferred by Endogenous VvPR1 Genes in Grapevine and Tobacco Under Greenhouse and Field Conditions in Aid of Precision Breeding

In order to evaluate grapevine-derived genes for instilling disease resistance, eight unique basic Vitis vinifera pathogenesis-related protein 1 (VvPR1) genes were cloned from the disease-resistant hybrid Euvitis selection, BN5-4, and the elite cultivar, Vitis vinifera ‘Chardonnay’. These genes were then over-expressed in Vitis hybrid ‘Seyval Blanc’ to investigate their potential to confer resistance to powdery mildew (Uncinula necator) using natural inoculation in a greenhouse. During a two-month growth period in the greenhouse without chemical control, non-transformed controls developed moderate to severe powdery mildew infection, whereas over 90% of VvPR1-expressing plant lines displayed relatively little infection, suggesting a high level of resistance. Under field conditions, the selected lines containing VvPR1 also showed outstanding resistance to a range of major fungal diseases common to the Floridian environment, displaying robust growth and development. Conversely, most non-transformed control plants succumbed to fungal diseases within the same growth period. In vitro detached leaf assays to monitor hyphal growth and conidiogenesis corroborated results from the field. Tobacco plants over-expressing VvPR1 genes and non-transformed controls were cultured in a mini-hydroponic system and then challenged with the bacterial pathogen of tobacco, Pseudomonas syringae pv. tobaci. Recovery of bacteria from leaf extracts of test plants revealed that VvPR1-expressing tobacco produced no to a significantly lowered number of P. syringae colonies compared to control plants, suggesting that VvPR1 genes are also capable of conferring antibacterial activity. Our findings demonstrate the potential of this class of genes in the development of improved grapevine via Precision Breeding.