In recent years, with the promotion of rain-shelter cultivation and double cropping techniques, grape production in hot zones has achieved off-season and high-efficiency production. However, hot-region grapes face problems such as poor flower bud differentiation, uneven germination, and "flower running", which are the main constraints on stable and high-quality production. This study aims to systematically investigate and evaluate the inflorescence attachment characteristics and development quality of 98 grape germplasms in hot zones Guangxi, clarify the adaptability differences among different germplasms in hot zones, and provide theoretical basis and technical guidance for variety breeding and production management.

This study investigated and evaluated the germination rate, flower bud rate, shoot formation rate, number of inflorescences per shoot, inflorescence attachment node, inflorescence type and quality of 98 grape germplasms in hot zones Guangxi for two consecutive years, covering European, American, and European-American hybrids. It deeply analyzed the quality differences and patterns among different varieties and inflorescence attachment nodes.

Under the treatment of hydrogen cyanamide, all 98 germplasms could germinate and form shoots smoothly, among which 92 varieties could form normal inflorescences. The average germination rate was 90.42%, the shoot formation rate was 92.13%, the flower bud rate was about 61.06%, and the average number of inflorescences per shoot was 1.67. However, abnormal inflorescences were quite prominent, with a total proportion of 40.56%. This study classified abnormal inflorescences into three major types: tendrils type, differentiation cessation type and trophic tissue type. Among them, the tendril type was the most common, further divided into one to five tendril types, and all investigated varieties had two tendrils type inflorescences; the differentiation cessation type included single head type (only scales or death point), tendrils death point type, and branch death point type; the trophic tissue type included branch tendril and leaf tendril types. Shine Muscat showed all abnormal types and were representative materials of high sensitivity. Among the 8 investigated nodes, the inflorescence attachment was most concentrated at the 3rd and 4th nodes, accounting for 27.99% and 27.06% of the total inflorescences, respectively. The abnormal inflorescence rate at the 3rd node was the lowest, only 17.22%. Further population analysis indicated that V. vinifera L.×V. labrusca L. had higher flower bud rates (68.60%), more inflorescences per shoot (about 1.8), and higher normal inflorescence rates than V. vinifera (flower bud rate 46.59%). Moreover, varieties with high germination rates, flower bud rates, and shoot formation rates had more inflorescences per shoot and significantly lower abnormal inflorescence rates.

The attachment node of inflorescences significantly affects their quality performance. Among them, the middle nodes, especially the 3rd node, had the lowest abnormal inflorescence rate. Therefore, in production, for varieties prone to abnormal inflorescences, it is recommended to prioritize the retention of inflorescences at the 3rd node. Varieties with high germination rates, flower bud rates, and shoot formation rates and more inflorescences per shoot are more likely to obtain normal and high-quality inflorescences. Different grape populations show significant differences in inflorescence development and abnormal occurrence. V. vinifera L.×V. labrusca L. perform better in hot zones, with higher flower bud rates and normal inflorescence proportions. They are recommended as the preferred germplasm resources for cultivation in hot zones.

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.

3-year-old Shine Muscat grape under two-crop-a-year cultivation was used as the material to investigate the differences of physical and chemical indexes of basic quality, flavonoid components and contents between summer grape and winter grape, which would provide the theoretical basis for the quality control of Shine Muscat grape under two-crop-a-year cultivation.

The climatic data, such as the sunshine duration, light intensity, temperature and rainfall during the whole growth period of Shine Muscat grape, were recorded. The physical and chemical indexes of basic quality in berries of summer and winter grapes of Shine Muscat were determined at the young fruit stage, expansion stage, softening stage, beginning maturity stage, and maturity stage, respectively. Meanwhile, the components and contents of flavonols and flavanols in the peel of summer and winter grapes of Shine Muscat grape were detected by LC-MS/MS.

In terms of the climate factors, the summer grape of Shine Muscat displayed weak illumination and low temperature at early growth stage but strong illumination and high temperature at late growth stage of the whole developing period, while the winter grape was opposite. The average sunshine duration, average temperature and effective accumulated temperature in the growth period of summer grape were higher than those of winter grape, but the rainfall was lower than that of winter grape. The hydrothermal coefficient of summer grape was higher than that of winter grape from the beginning of maturity stage to maturity stage. In terms of the basic quality, the content of soluble solid of summer grape was significantly higher than that of winter grape at maturity stage, and the peel thickness of summer grape was significantly lower than that of winter grape. There was no significant difference in the single berry weight, fruit equatorial and longitudinal diameter and titratable acid content between summer and winter grape. In terms of the components and contents of flavonols, the content of total flavonols in peels of summer and winter grape showed a downward trend during the fruit developing stage. The content of total flavonols in different periods of summer grape was significantly higher than that of winter grape. The main flavonol in summer grape was quercetin-3-O-glucoside, while the main flavonol in winter grape was kaempferol-3-O-galactoside. In terms of the components and contents of flavanols, the content of total flavanols in summer and winter grape also showed a downward trend. The eight identical flavanols were detected in the peels of both summer and winter grape, and the main flavanols were catechin, epicatechin and procyanidin B₁. The contents of total flavanols, catechin, epicatechin and procyanidin B₁ in summer grape were significantly lower than those in winter grape during fruit development. The contents of gallic catechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, and procyanidin B₂ at fruit maturation stage of summer grape were significantly higher than those of winter grape. The principal component analysis showed that there were differences in flavonols between summer and winter fruits. The regression analysis showed that catechin, quercetin-3-O-Glucoside and procyanidin B₁ were the main components for distinguishing the flavonoids from summer and winter grapes.

In the study conducting year, the quality of summer grape of Shine Muscat was better than that of winter grape. During the whole grape developing stage, the content of total flavonols in summer grape was significantly higher than that in winter grape, while the content of total flavanols in summer grape was significantly lower than that in winter grape. The main components of flavonols were different between summer and winter grape of Shine Muscat, while the main components of flavanols were the same, namely catechin, epicatechin and procyanidin B₁. The content of the main components of flavanols in winter grapes was significantly higher than that in summer grape, which might probably explained why the astringency taste of winter grape was stronger than that of summer grape. The differences in light and temperature during the growth period may be an important factor that caused the difference in the components and contents of summer and winter grapes of Shine Muscat.