Two different phenotypes of MDH-1 isozyme were observed in two clonal hybrid cultivars UC157F1' and 'Cito'. Segregation of presence versus absence of the MDH-1 bands fitted with a 3:1 ratio in UC157F1' and 1:1 in 'Cito'. Bulked segregant analysis for detecting RAPD markers linked to the Mdh-1 isozyme and the sex determination loci was performed separately using polymerase chain reaction with 50 different 12-base oligonucleotide primers. Two primers showed polymorphic amplified fragments, CMNA15690 and CMNA21870, between different MDH-1 phenotypes only in "UC157F1'. No polymorphic markers, however, were detected between male and female plants in the two cultivars. These two RAPD markers were examined in individual plants of UC157F1', and confirmed to be linked to both Mdh-1 and sex determination loci. Although the linkage distance between Mdh-1 and these RAPD markers could not be calculated here, the distances between sex determination locus and CMNA15690 and between sex determination locus and CMNA2187o were estimated at 30 and 28 cM, respectively.
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