Identification of QTLs for red fruit firmness using the wild tomato species Solanum pennellii LA716 introgression lines

The introgression lines (ILs) of the wild tomato species Solanum pennellii have been widely used to identify genes related to yield, texture, disease resistance and stress tolerance. In addition to flavour, fruit firmness is an important evaluation index and essential trait indicating tomato fruit quality. Quantitative trait loci (QTL) for fruit firmness have been identified through hand squeezing and pericarp puncturing. However, these techniques hardly reveal the force value of the whole fruit suffering from rupture or deformation. In this study, S.pennellii ILs were used to identify QTLs related to fruit firmness through flat-plate compression. Nine QTLs for enhancing and sixteen QTLs for decreasing fruit firmness were successfully identified. Compared with that of M82', the amount of QTLs that enhance fruit firmness increased by 8.76% to 21.00%, and the amount of QTLs that reduce fruit firmness decreased by -8.27% to -30.80%. The QTL Crf12a and Crf-R-7b is the strongest and weakest QTL, respectively, while they are very stable in all independent biological trials. Six QTLs should be further confirmed through open-field trials.