EVALUATION OF BROWN-ROT RESISTANCE AND ITS RELATION TO ENZYMATIC BROWNING IN CLINGSTONE PEACH GERMPLASM

Rate of brown rot lesion development following inoculation with Monilinia fructicola (Wint.) honey varied within clingstone peach (Prunus persica (L.) Batsch) germplasm evaluated in 1990 and 1991. High levels of resistance were identified in selections derived from the Brazilian clingstone peach cultivar Bolinha. Resistance appeared to be limited to the epidermal tissue. No relation was detected between brown rot resistance and concentration of phenolic compounds or polyphenol oxidase activity in the susceptible California germplasm. An inverse relation was observed between disease severity and rating for phenolic-related discoloration when 'Bolinha' derived selections were analyzed. A moderate positive correlation was observed for all germplasm tested between genotype means for phenolic content and enzymatic browning. Any causal relationship, if it exists, between phenolic content and brown rot resistance is obscured by an array of physical and chemical changes in the maturing fruit.