Assaiyng brown rot (Monilinia laxa Aderh. et Ruhl. (Honey) susceptibility in peach cultivars and progeny

Tree-ripe fruits from 27 cultivars and advanced selections, and 62 seedlings from the 'Contender' (tolerant) x 'Elegant Lady' (highly susceptible) cross were tested for tolerance to Monilinia laxa (conidia spray test). Forty-five fruits per genotype were harvested and thoroughly washed under running water to eliminate field contamination from conidia. Thirty fruits were then inoculated by spraying a 10(5) solution of conidia on the skin; fifteen were kept as control. On an additional sample of 5-20 fruits, individual weight, firmness by a 8 mm-tip penetrometer and soluble solids were measured. After seven days at 25+/-2 degrees C and 95-100% RH the 45 fruits were evaluated for brown rot infections as number of diseased fruit and percent of rotted skin. 'Glohaven' (yellow-flesh peach) was the least susceptible (50% of fruits rotted, with an average of 17.4% of skin affected), followed by 'Contender' (yellow peach),'Maria Aurelia' (yellow nectarine) and 'Maria Bianca' (white peach). While all fruits of 'Elegant Lady' rotted and 'Contender' showed only 53%, diseased fruits of their progeny varied from 0% (3 seedlings) to 100% (17 seedlings). The inoculation spray test is to be regarded as a reliable means to discriminate between low and highly susceptible peach genotypes in selecting for new cultivars or breeding parents tolerant to fruit brown rot. The possibility of increasing the general level of tolerance to brown rot by recurrent selection in progeny showing both skin and flesh resistance is also discussed.