The pathogenicity of five species of Phytophthora to English walnut was studied in a greenhouse experiment. Phytophthora cinnamomi was the most aggressive species, causing severe root rot and seedling mortality. The other species tested, P. cambivora , P. citricola , P. cactorum and P. cryptogea , did not induce visible crown symptoms on seedlings 2 months after inoculation. Some strains of P. cambivora and P. cactorum also caused taproot damage to seedlings. All except one of the tested isolates caused significant necrosis of fine roots and a significant reduction of root weight compared with noninoculated seedlings. Reduction of above-ground plant development was not statistically significant. While P. cinnamomi is well known as an aggressive primary pathogen of English walnut, the other species of Phytophthora may act as predisposing factors to walnut decline, affecting root system development and increasing host vulnerability to environmental stress.

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In 1998, a severe fruit drop was observed in Italy, principally on cv. Lara Persian (English) walnut (Juglans regia). Dropped fruit showed a brown patch at the blossom end and blackening and rot of inner tissues. The disease, called brown apical necrosis (BAN), was investigated on fruit collected in Italy and France in 1999. In 2000, studies were carried out in three walnut orchards located in Italy and in France to substantiate the etiology of BAN. Isolations performed from inner diseased fruit tissues yielded several fungi, in decreasing frequency of isolation: species of Fusarium and Alternaria, and one species each of Cladosporium, Colletotrichum, and Phomopsis. However, only Fusarium spp. were recovered from stigmas of BAN-affected fruit. The fungi associated with BAN-diseased fruit and species composition differed among locations and over time, confirming results obtained in previous investigations. The species of Fusarium used in pathogenicity tests reproduced BAN-disease symptoms when inoculated on fruit, whereas an Alternaria alternata isolate caused only limited necrosis of the style. However, the role of the other fungi commonly isolated from BAN-diseased fruit remains to be defined. The walnut blight pathogen, Xanthomonas arboricola pv. juglandis, occasionally was isolated from BAN-diseased fruit. No correlation was found between the extent of external brown patches and the size of inner lesions. Repeated isolations from and inoculations of fruit demonstrated that BAN can be considered a complex disease, and the inner infections originate from the style of the fruit.

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Of seven doubled-haploid melon lines parthenogenetically originated using irradiated pollen, two lines, Nad-1 and Nad-2, were selected for resistance to Fusarium wilt after successive inoculations with F. oxysporum f. sp. melonis race 1,2w virulent isolate. Nad-1 and Nad-2 were compared with the commercial hybrids and with the parent cvs. Isabelle and Giallo di Paceco. Evaluation of germplasm extended over a 2-year period showed a higher resistance of Nad-1 and Nad-2 plants to Fusarium oxysporum f. sp. melonis race 1,2 than other genotypes tested in this study. The resistance expressed in the two doubled-haploid lines could be due to their homozygous state that maximizes the expression of the genes for resistance already present in the parental line Isabelle. The use of this source of resistance may be exploited commercially either in rootstocks or to facilitate breeding for F1 hybrids. Future research will concentrate on the identification of genetic markers associated with resistance to race 1,2 using these doubledhaploid lines.