INHERITANCE AND GENETIC-LINKAGE OF FUSARIUM-WILT (FUSARIUM-OXYSPORUM F SP CUCUMERINUM RACE-1) AND SCAB (CLADOSPORIUM-CUCUMERINUM) RESISTANCE GENES IN CUCUMBER (CUCUMIS-SATIVUS)

The inheritance of resistance of the cucumber cv. SMR 18 to the race 1 of Fusarium oxysporum f.sp. cucumerinum, the linkage relationship bet ween resistance to race 1 of F. oxysporum f.sp. cucumerinum, resistanc e to Cladosporium cucumerinum and fruit spine colour, and the reaction s of several cucumber cultivars to inoculations with race 1 of F. oxys porum f.sp. cucumerinum and C. cucumerinum were examined. The inbred l ine Straight 8 (P-1), which has white fruit spines and is susceptible to both fusarium wilt and scab was crossed with the inbred line SMR 18 (P-2), which has black fruit spines and resistance to both diseases. When F-1, F-2, F-3, BC1P1, BC1P2 and BC1P1 selfed progenies were inocu lated at the cotyledon stage with a suspension of spores of race 1 of F. oxysporum f.sp. cucumerinum, the ratios of resistant to susceptible plants indicated that resistance was conferred by a single dominant g ene, designated Fcu-1. When 171 BC1P1 plants were selfed and from each resulting F-2 family different groups of 15-25 seedlings each were te sted for resistance to either disease, segregation data indicated that the Fcu-1 locus and the Ccu locus for C. cucumerinum resistance were completely linked. No evidence for linkage was found between the Fcu-1 (Ccu) locus and the B locus for fruit spine colour. Among the 59 cult ivars tested at the seedling stage, 15 were susceptible, while the rem ainder were highly resistant to inoculations with both pathogens.