Exploratory quantitative trait locus analysis for fruit-related traits in kiwifruit (Actinidia chinensis Planch.)

Fruit quality is a key criterion used to select new cultivars in kiwifruit breeding programs. The aim of this research was to identify quantitative trait loci (QTLs) that control traits related to fruit quality in an F₁ population derived from the cross of ‘C8’ (female) and ‘A54.19’ (male) diploid kiwifruit. A small female progeny was evaluated over 3 years for several traits: fruit weight, absorbance of chlorophyll (I_AD) values of the skin and flesh, flesh firmness, soluble solids content (SSC), titratable acidity (TA), pH, dry matter (DM) content and ripening time (RT). Single or multiple QTL mapping models were applied separately for each year and all years combined. As a result, a total of 24 QTLs were detected on 12 different linkage groups (LGs). Some QTLs, such as flesh firmness, skin and flesh chlorophyll absorbance, are reported for the first time in kiwifruit. However, QTLs were not consistent among years, and were rarely identified in both parents in corresponding LGs. These results were expected, because of the limited size of the progeny. This work was the first attempt to identify genomic regions that control fruit-quality traits in the mapping cross population. Extension of the cross population to about 400 female individuals has been undertaken, and this will guarantee a more reliable and robust identification of QTLs related to fruit quality in future analyses.