Construction of the first high-density genetic map and QTL mapping for photosynthetic traits in Lycium barbarum L.

Photosynthesis is essential for plant development as well as crop yield. QTL mapping was conducted for photosynthetic traits such as net photosynthetic rate (P), stomatal conductance (Cond), inner-cellular carbon dioxide (Ci), transpiration rate (Trmmol), limiting value of the stoma (Ls), and water use efficiency (WUE). A high-density genetic map covering 964.03 cM was developed based on a hybrid population of the Goji (Lycium barbarum L.). The genetic map consisted of 23,967 markers with an average distance of 0.040 cM between two adjacent markers. Twenty-nine and three quantitative trait loci (QTLs) for photosynthetic traits and trunk diameter (TD), respectively, were detected, of which 8 QTLs, including 3 for P, 2 for Cond, 1 for Trmmol, 1 for Ci, and 1 for Ls, can be detected in at least 2-year measurements (from 2017 and 2018, as well as the averaged data from 2017 and 2018, which was regarded as a 3rd year, named 1718). Among these measurements, qP1 was detected in all 3 years and considered a stable QTL whereas qLs1 and qLs2 with the highest phenotypic variance explained (PVE%) 32.012 and 17.965 were detected as major QTLs. P, Cond, Ci, Trmmol, Ls, and WUE showed significant correlations with each other except for Cond and WUE whereas P and Cond were significantly correlated with TD (P < 0.05). These findings indicate that P and Cond are critical factors for the growth of plants and QTLs contribute to P, Cond, and TD, which could provide an improved way to enhance the breeding of the Goji in relation to its growth rate.