Development of a Method to Evaluate Grapevine Anthracnose Resistance by Spraying Cuttings and Seedlings with Conidial Suspension

Abstract

Symptoms of grapevine anthracnose after spray inoculation were evaluated by imaging analysis to develop a method for anthracnose resistance evaluation. The results suggested that the lesion area could be stably evaluated with a few replicates, whereas many replicates are necessary for lesion number evaluation. Therefore, a visual rating scale on the basis of the lesion size, equivalent to the lesion area, was established for high throughput and reliable evaluation. Then, 575 seedlings in total from different hybridizations were evaluated by visual rating for three years in a greenhouse, and then they were evaluated in a fungicide-free orchard. The visual evaluation was significantly correlated with the successive evaluation in the fungicide-free orchard with Spearman’s rank correlation coefficient of 0.66 to 0.68. Seedlings evaluated as highly resistant or susceptible were observed as resistant or susceptible in the fungicide-free orchard, respectively. However, the evaluation of individuals rated as slightly resistant by the seedling visual rating highly fluctuated in the fungicide free orchard, suggesting that it is difficult to evaluate low-level resistance by visual rating. Hence, highly resistant or susceptible seedlings should be selected or discarded based on visual rating, whereas seedlings rated as partially resistant should be evaluated in detail with more replicates.