QTL Mapping of Flowering and Branching Traits in Petunia

The flowering intensity of individual plants is determined by the number of flower buds per branch along with the number of branches. Understanding the genetic control of traits contributing to overall flowering intensity could aid in breeding more floriferous cultivars. The objective of the study was to perform quantitative trait locus (QTL) mapping analysis with multi-year phenotypic data from an interspecific Petunia axillaris × P. exserta F₇ recombinant inbred line (RIL) population. Total flower bud number, flower buds on the primary stem, total branch number and number of branches with flowers were evaluated for two seasons on 171 RILs and the parental species at 14, 17 and 20°C under a 16-hour photoperiod. A high-density single nucleotide polymorphism-based genetic linkage map for this population was generated using genotyping-by-sequencing. From 7 linkage groups, 6,291 SNP markers were combined into 363 bins. The bins were used to build a bin-based linkage map spanning a total of 377 cM with an average bin distance of 1.04 cM. Results from the analysis of the first season’s data identified 12 QTL at 14°C, 12 QTL at 17°C, and 13 QTL at 20°C for the four flowering and branching traits. Two QTL explained 26.4% and 34.2% of the phenotypic variation for total flower bud number and total branch number in linkage group 2 and 3 respectively at 14°C. Five QTL on linkage group 4 explained 25.7-36.5% of the variance for total flower bud number, flower buds on the primary stem, and total branch number at 20°C. These results will be validated using the second season’s data. Results from both analyses will be used for identifying candidate genes associated with traits contributing to flowering intensity.