Construction of a linkage map and genetic analysis for resistance to cotton aphid and powdery mildew in melon

A genetic linkage map of melon was constructed based on 74 RAPDs, 21 AFLP markers, and cotton aphid resistance gene are mapped using 100 F-2 plants derived from the cross between a highly resistant cultivar 'PMAR No.5' (resistant to both cotton aphid and powdery mildew), and a susceptible cultivar 'Harukei 3'. The map identified 19 linkage groups spanning 1,097 cM of the genome. The linkage groups ranged from 7.7 to 140.7 cM in length and included 2 to 14 markers, respectively. The AFLP marker hD108 was found to be linked to the cotton aphid resistance gene at a distance of 19.6 cM. For QTL analysis of powdery mildew resistance, the lesion area was scored (Disease Index, DI), and the rate of susceptible plants was calculated (Disease Percentage, DP) using leaf discs of F-3 seedlings. DI showed ten QTLs on the linkage groups 4,5,6,10,11,12,15,16 and 17. DP showed eight QTLs on the linkage groups 2,4,6,10,12,15,16 and 17. One of the QTLs on the group 5 was located near the RAPD marker pUBC411, which was supposed to be linked with one of the resistant genes to powdery mildew.