BLIGHT SENSITIVITY OF SPANISH SELECTIONS OF J. REGIA

Between 1988 and 1992, walnut seedling trees (Juglans regia L.) from Spanish wild populations were pre-selected because of their apparent tolerance to Xanthomonas arboricola pv. juglandis in their original area. They were planted in a field collection, located in an environment very favourable to bacterial disease development, together with five commercial cultivars used as reference (‘Adams-10’, ‘Amigo’, ‘Chandler’, ‘Franquette’ and ‘Vina’). The blight susceptibility of these selections was evaluated on the main vegetative organs affected by this bacterial disease. Damage to completely developed nuts (evaluated as the presence or absence of bacterial necrosis on hulls) and affected leaves, recorded following a graphic pattern scale with five levels of damage, was noted in summer under field conditions. Blight susceptibility of young nuts was determined with artificial inoculation under environment controlled conditions on fruit collected 45 days after nut set. Disease severity was evaluated by severity index (ranging from 0 to 5 depending on infection intensity) for each cultivar or clone. All field data were taken for several years, namely from 1992 to 1999. Laboratory studies on immature nuts, carried out on 24 cultivars/selected clones, indicated nine local selections with a susceptibility level similar to that of ‘Adams-10′. ‘MBPo-3’ stands out because it showed almost no damage to immature nuts, whereas ‘Chandler’ cv. showed the highest level of susceptibility. Five local selections showed little damage on fully developed nuts on the 22 different accessions considered in this evaluation. Leaf-blight incidence was studied in ten selections. Seven of them proved to be more susceptible than the five reference cultivars, which had a similar level of leaf attack. Three local selections (‘MBLu-20’, ‘MBLu-21’ and ‘MBC-45′) showed a low susceptibility to blight in nuts and the ‘MBLu-20’ clone always presented healthy foliage showing a behaviour similar to ‘Adams-10’ during the growing season.
‘Franquette’’s blight susceptibility did not differ significantly from that of ‘Adams-10′ in all vegetative organs studied under field conditions, whereas on immature nuts ‘Franquette’ was highly susceptible to blight. ‘Chandler’ has been classified as a highly susceptible cultivar with respect to its immature nut infection, while the level of susceptibility of its fully developed nuts and leaves is considered to be low.

IV International Walnut Symposium

N. Aletà, A. Ninot, C. Moragrega, I. Llorente, E. Montesinos

walnut tree, Xanthomonas arboricola pv. juglandis, walnut cultivars, bacterial diseases.

https://doi.org/10.17660/ActaHortic.2001.544.47