Genetic segregation of chlorophyll content and light compensation point in a hybrid grapevine population

【Objective】The growth and development of grapes are closely linked to light intensity. The efficiency of photosynthesis and nutrient accumulation directly affects grape yield and quality. In greenhouse or protected cultivation environments, grape growth is often significantly impacted by reduced light levels. During early-season cultivation in northern China, light conditions are inadequate, with daily sunlight hours only around 65% of those in open-field cultivation. In addition, factors such as shading from the greenhouse structure, film aging, and dust accumulation further reduce solar radiation and ultraviolet radiation intensities, making them substantially lower than in open- field cultivation. These factors contribute to a decrease in the photosynthetic capacity of grapes, which in turn affects flower bud differentiation, fruit development, yield, and fruit quality. Moreover, inappropriate variety selection in protected environments can result in lower photosynthetic efficiency, poor flower bud differentiation, reduced flowering, and a significant yield loss. Chlorophyll content and the light compensation point are the key traits closely associated with leaf photosynthetic capacity, and play a crucial role in grapevine tolerance to low light.【Methods】To explore the genetic patterns of chlorophyll content and light compensation point in grapes, this study used a hybrid grape population derived from crossing a lowlight-tolerant female parent, ZhuoSeXiang, with a low light-sensitive male parent, HeiCuiWuHu. Over two years, the chlorophyll content and light compensation point were measured continuously in both parents and their offspring. Chlorophyll content was determined using the colorimetric method, and the light response curves were measured using a Li6400 photosynthesis system. Healthy functional leaves were selected for the measurements, with the criteria being dark green, thick, and free from disease, pests, or mechanical damage.【Results】The results showed that, for chlorophyll a, chlorophyll b, and total chlorophyll contents, the maternal parent had significantly higher levels than the paternal parent. The offspring exhibited a broad range of segregation, with most of the offspring’s chlorophyll content falling between the levels of the two parents. However, some individual plants had a chlorophyll content higher than the maternal parent or lower than the paternal parent. The distribution of chlorophyll content in the offspring approximated a normal distribution. The coefficients of variation (CV) for chlorophyll a, chlorophyll b, and total chlorophyll contents in 2023 were 12.38%, 17.15%, and 13.05%, respectively, and increased to 18.70%, 22.11%, and 19.24%, respectively, in 2024, showing a slight annual variation. In contrast to the chlorophyll content, the light compensation point of the maternal parent was significantly lower than that of the paternal parent. The offspring displayed a broad range of segregation, with the light compensation point of most offspring plants falling between those of the parents. However, some individual plants had values higher than the maternal parent or lower than the paternal parent. The distribution of light compensation point values also approximated a normal distribution. The CV for the light compensation point in 2023 and 2024 were 38.11% and 46.64% , respectively, showing a slight annual variation. Based on Spearman’s rank correlation analysis, a significant correlation was found in chlorophyll a content, chlorophyll b content, and total chlorophyll content between years, with p-values less than 0.05 and Spearman’s correlation coefficients around 0.20. However, the p-value for the light compensation point between years was 0.200, indicating no significant correlation. Spearman’s rank correlation was also used to analyze the correlation between the two rounds of chlorophyll content measurements in 2024. The p-values for chlorophyll a content, chlorophyll b content, and total chlorophyll content were all much less than 0.01, indicating highly significant correlations. The Spearman correlation coefficients were around 0.3, confirming that the variation in chlorophyll content in the hybrid offspring was stable. Spearman’s rank correlation was also used to analyze the relationship between the light compensation point and chlorophyll content in 2023 and 2024. The p-values for the correlation between the light compensation point and chlorophyll a content, chlorophyll b content, and total chlorophyll content were all greater than 0.05, with Spearman correlation coefficients close to 0, indicating no significant correlation. The phenotypic variance in the offspring was significantly higher than that of the parents, suggesting extensive genetic segregation. The heritability of chlorophyll content was generally higher than that of the light compensation point, with some differences observed between years. Among the chlorophyll traits, the heritability of total chlorophyll content was the highest, followed by chlorophyll a content, while the heritability of chlorophyll b content was the lowest.【Conclusion】In conclusion, this study reveals the genetic characteristics of grape chlorophyll content and light compensation point. The findings provide valuable data for further research on the genetic mechanisms underlying grape tolerance to low-light environments. By understanding these genetic patterns, it may be possible to develop grape varieties better suited for cultivation under low-light conditions, thereby improving yield and fruit quality in protected cultivation systems.