Repeatability of Laboratory Inoculation on Assessing Susceptibility of Walnut Unripe Fruits to Bacterial Blight and Relationship Between Resistance and Total Phenols

Main losses of bacterial blight caused by Xanthomonas arboricola pv. juglandis on walnuts is throught unripe fruit fall and mature fruit effects. In this research, the relative susceptibility of 72 walnut cultivars and local genotypes to bacterial blight was studied in laboratory condition in years 2012 and 2013. Additionally, the efficacy of the evaluation method and correlation of resistance with unripe fruit size and total phenol concentration were investigated. Based on combined analysis of data, 10.7% of germplasm was susceptible, 32.1% moderately susceptible and 57.1% moderately resistant. Analysis of two years data means indicated that the evaluation method was repeatable. The highest phenol concentration was detected in the Pedro resistant cultivar and the lowest in the susceptible genotype 2-1, but the relation between resistance and phenl level was not significant. No correlation was found between fruit size and resistance. Based on the results, a great variation was detected in resistance of unripr fruits of different genotypes and this variation can be evaluated by inoculation in laboratory condition, but phenolic levels is not reliable in assessing blight resistance.