Research and Practice on High Photosynthetic Efficiency Breeding of Grapes in Hot Climate Regions

Grapes (Vitis vinifera) hold significant economic importance in hot climate regions. However, high temperatures pose severe challenges to their photosynthetic efficiency, as well as to fruit yield and quality. At the same time, these extreme conditions provide unique natural selection pressures conducive to breeding grape varieties with both high photosynthetic efficiency and heat tolerance. This study aimed to elucidate the impact of high temperatures in hot regions on grape photosynthetic efficiency, assess the feasibility of breeding for high photosynthetic efficiency under such conditions, and employ photosynthetic parameters for the early selection of hybrid progenies exhibiting high efficiency, heat tolerance, and superior fruit quality. The findings are intended to offer scientific foundations and practical support for high-efficiency grape breeding in hot climates.

A total of 187 germplasm resources, including Shine Muscat, and 683 progenies from five hybrid crosses were used as experimental materials. We measured the net photosynthetic rate (P_n), stomatal conductance (G_s), heat tolerance indicators (F_v/F_m, PI_abs, ET_o/CS_m and W_K), and soluble solid content (Brix) of the fruits. These data were analyzed to determine the distribution characteristics of photosynthetic efficiency and to evaluate the heat tolerance of the hybrid progenies. Based on these evaluations, we identified elite lines with both high photosynthetic efficiency and heat tolerance.

High temperatures significantly inhibited grape photosynthetic efficiency, with the net photosynthetic rate decreasing by up to 30.28% at 40 ℃. However, compared to the first crops of summer fruit leaves formed in a milder environment, the second crops of winter fruit leaves, developed under high-temperature conditions, exhibited higher photosynthetic efficiency and stability, indicating that high-temperature climates in hot regions provide a unique environment for uncovering high-efficiency potential. The net photosynthetic rate and other photosynthetic efficiency indicators in the hybrid progeny population followed a normal distribution, suggesting that photosynthetic efficiency in grapes can be enhanced through generational selection in high-efficiency breeding. Five excellent hybrid lines with high photosynthetic efficiency were selected, among which the line 21A-7-297 had a net photosynthetic rate of 24.88 μmol·m^-2·s^-1, 26.42% higher than the parent Shine Muscat and a fruit Brix of 22.03, 15.34% higher. Heat tolerance analysis showed that 21A-7-297 and 21A-7-145 maintained maximum photochemical efficiency (F_v/F_m) values of 0.61 and 0.62 under 47 ℃ heat stress, significantly higher than the parent Ruiduhongyu (0.44), demonstrating better heat adaptation.

This study revealed the impact of high temperatures in hot regions on grape photosynthetic efficiency and used photosynthetic and heat tolerance parameters for early screening. Hybrid lines with high photosynthetic efficiency, heat tolerance, and good fruit quality were rapidly obtained from the hybrid progeny populations, demonstrating the feasibility and effectiveness of high-efficiency breeding for grapes in hot regions. Future work can further optimize high-efficiency breeding strategies based on an in-depth understanding of the underlying mechanisms of high photosynthetic efficiency.