Abstract

A genetic linkage map for papaya was constructed using 513 AFLP markers, an isozyme marker, and a morphological marker. The map, consisted of 15 linkage groups that covered 2066 cM of the papaya genome. Two hundred and eighty one plants from a F₂ population derived from Kapoho X Saipan Red were used to create the map. Two qualitative traits (PGM and fruit-flesh color) as well as three quantitative traits (node number at floral conversion, carpellody, and fruit weight) were analyzed. The fruit-flesh color locus was located on LG-14 with a linked marker at 4.1 cM distance. Two noteworthy features (blocks of consecutive markers with dominant alleles arising from a single parent and unidirectional segregation distortion) were noticed in the mixed-phase linkage map. To create a reliable marker order for QTL analysis, two coupling-phase maps, one for each parent, were created. A single QTL explaining 64.3% of the trait, node number at floral conversion, was identified on LG-4 by the interval mapping method. The AFLP markers identified for flesh color (M1527AKF) and node number at floral conversion (M2104EK5 and M0832AK2) can be used in marker assisted selection and map based cloning. More than 50% of the markers that showed significant association with carpellody in the nonparametric Kruskal-Wallis test were located on four linkage groups (LG-2, LG-3, LG-4 and LG-7). A block of markers on LG-7 showed significant association with carpellody in each of the two seasons studied. Although the broad sense heritability was high (74.0%) for mean fruit weight, only five markers were identified as having significant association with the trait by single marker analysis, and no QTL peak was identified by interval mapping. In another study, an AFLP marker that consistently co-segregates in coupling phase with the normal phenotype at the diminutive mutation locus in papaya var. Sun Up, was detected using bulked segregant analysis. Lastly; a 281-bp fragment of lycopene β-cyclase (LCY-B) gene was isolated from papaya (Accession No. AY753202), which can be used as a probe in investigating the possibility of polymorphism in LCY-B gene as the molecular basis for fruit-flesh color difference in papaya.