Variation in disease development among persian walnut cultivars, selections and crosses when inoculated with Xanthomonas arboricola pv. juglandis in Greece.

Abstract

A total of 27 walnut (Juglans regia) cultivars (14 lateral and 13 terminal fruit fullness cultivars), 12 selections and 12 crosses were evaluated for their resistance to the walnut blight bacterium Xanthomonas arboricola pv. juglandis. Healthy nuts were inoculated with pure bacterial cultures isolated from diseased nuts. Two weeks after inoculation, the frequency of successful infections, as well as the disease severity was recorded and the index of varietal susceptibility (IVS) was calculated for each treatment. Based on these results walnut cultivars, selections and crosses were ranked in five classes of susceptibility (A to E). The experiment was repeated for two consecutive years, 2007 and 2008. Results showed that all the artificially infected nuts showed typical bacterial blight symptoms as compared to the negative control. Among the cultivars tested Amigo, Asley, Eliana, Franquette and Spurgcan were the less susceptible with average IVS ranging from 13.1 to 24.4, therefore ranked as class A. Walnut selections EK1, EH29 and FM16, as well as crosses PZ-14 and FxH5 also showed low susceptibility. In contrast, the terminal fruit fullness cv. Milotai and the cross S3/1 were highly susceptible and ranked as class E.