MAPPING AND QTL ANALYSIS OF HORTICULTURAL TRAITS IN A NARROW CROSS INCUCUMBER (CUCUMIS-SATIVUS L) USING RANDOM-AMPLIFIED POLYMORPHIC DNA MARKERS

An XO-point genetic map [77 random-amplified polymorphic DNAs (RAPD), F (female sex expression), de (determinate), and ll (little leaf)] was constructed from a narrow cross in cucumber using the determinate, gy noecious, standard-sized leaf line G421 and the indeterminate, monoeci ous, little leaf line H-19. The map defined nine linkage groups and sp anned ca. 600 cM with an average distance between markers of 8.4 +/- 9 .4 cM. The RAPD loci BC-551 and BC-592 were found to flank ll at 3.4 a nd 12.2 cM, respectively. The locus OP-L18-2 was linked (16 cM) to de, and the F locus was flanked by markers at 44 and 31 cM. One-hundred F -3 families were used to identify quantitative trait loci (QTL) for se x expression, main stem length, number of lateral branches, days to an thesis, fruit number and weight, fruit length and diameter, and fruit length: diameter ratio in two replicated test locations (Wisconsin and Georgia). QTL on linkage group B explained major portions (R-2 = ca. 2 to 74%) of the variation observed for sex expression, main stem leng th, lateral branch number, and fruit diameter (LOD = 2.1 to 29.8). Alt hough ca. 62 to 74% of the variation for sex expression was associated with a putative QTL spanning the F locus (OP-AJ-2 to F and F to de), other regions (three) of the genome were important for the determinati on of sex in the F3 families examined depending upon environment. The number of genomic regions affecting main stem length (five) and number of lateral branches (three) coincided with expectations as determined by calculations of minimum number of genes in previous studies. Evalu ation of QTL associated with several fruit number determinants of earl y, first-harvest yield demonstrating additive genetic variance (i.e., sex expression, main stem length, and number of laterals) suggests tha t marker-assisted selection may have utility for the development of de terminate, multiple lateral branching germplasm suited for once-over m echanical harvesting in this population.