QUANTITATIVE TRAIT ANALYSIS OF FRUIT-QUALITY IN CUCUMBER - QTL DETECTION, CONFIRMATION, AND COMPARISON WITH MATING-DESIGN VARIATION

A cross within C. sativus var, sativus (GY14 x P1432860) and molecular markers were used to determine the number, magnitudes of effect, and overall variation described for genes conditioning the quantitatively inherited traits of length, diameter, seed-cavity size, color, L/D (le ngth/diameter), and S/D (seed-cavity size/diameter). QTL effects were detected with MAPMAKER/QTL using 100 F-3 lines evaluated in a replicat ed field trial of two harvests over 2 years at one location. Multilocu s models were constructed by fixing significant intervals and re-scann ing using MAPMAKER/QTL. Marker inclusion in multilocus models was comp ared to an ANOVA ''backward elimination'' procedure. Generally the sam e loci were associated with QTLs among the two methods of model constr uction. Heritabilities of individual QTLs were confirmed by analysis o f related backcrosses (67 BC1P1 lines and 68 BC1P2 lines). The majorit y of QTLs were confirmed in at least one backcross population. Pairs o f backcrosses allowed overall additive variances and heritabilities to be calculated using a North Carolina Design III(NCIII design) and est imates were compared to overall variances attributable to markers. Her itability estimates using markers were comparable, but generally lower than additive variances estimated by co-variance relationships in the NCIII design. This suggests that neither the number nor the magnitude of QTL effects were overestimated. The utility of backcrosses to conf irm individual QTLs and the overall variance described by QTLs is reco mmended to avoid false positives and over-estimation of effects. The n umber of QTLs, and/or the proportions of phenotypic variation describe d by markers and the mating design, agreed with previous reports of he ritabilities employing similar germplasm.