Peroxidase isozyme polymorphism in Cucurbita pepo cultivars with various morphotypes and different level of field resistance to powdery mildew

A set of 31 Cucurbita pepo L, commercial cultivars with different fruit sha pes (morphotypes) was evaluated for resistance to powdery mildew of cucurbi ts (Erysiphe cichoracearum and Sphaerotheca fuliginea) under field conditio ns of a natural infection. During vegetative growth, the infection degree ( ID) was assessed four times on leaves (L) and twice on stems and petioles ( S). The 'Area below the: curve' values of the disease infection progress we re calculated separately for leaves (ABC-L) and stems and petioles (ABC-S). Data were subjected to one-way analyses of variance and mean separation wa s performed using LSD multiple range tests, Significant differences in fiel d resistance were found between morphotypes. Cultivars with scallop and aco rn fruit shapes were the most resistant. The straightneck, crookneck and or namental gourd groups showed medium levels of field resistance. The zucchin i, cocozelle, pumpkin and vegetable marrow groups of morphotypes were the m ost susceptible. Isozyme spectra of peroxidases for II selected C. pepo cul tivars representing different groups of morphotypes with various levels of field resistance were analysed as well. They could be ranged into three bas ic groups which correspond with the cultivar's level of field resistance. T his phenomenon is discussed as a potential biochemical marker in C. pepo se lection. (C) 1999 Elsevier Science B.V. All rights reserved.