| چکیده انگلیسی مقاله |
Introduction
Yaghooti grape is the oldest grape variety in Iran and is the most important horticultural product in the Sistan region, which is cultivated in more than 90% of the vineyards of this region. The issue of water scarcity in Sistan has become a serious threat to grape production in recent years, forcing local grape growers to manage this problem by reducing the volume and frequency of irrigation. Proper irrigation management, which involves determining the optimal timing and the required amount of irrigation for grapevines, is of particular importance. Therefore, the purpose of this research is to investigate the physiological response of Yaghooti grapes to lack of water in different stages of growth in order to achieve the highest yield and also increase the production and income of gardeners in Sistan region.
Materials and Methods
This experiment was conducted as strip-split plot design based on randomized complete block design with three replications at the Zahak Research Station from 2019 to 2023. The experimental treatments included an irrigation regime of control (full irrigation), irrigation after 35% soil moisture deficiency, and irrigation after 70% soil moisture deficiency. These treatments were applied to horizontal plots and while the irrigation stages including from bud burst to flowering, from flowering to fruit color change, from berry color variation to harvest, and from harvest to leaf fall, were assigned to vertical plots. The traits including the relative leaf water content, leaf area, proline, soluble sugars, relative permeability of leaf cell membrane, canopy temperature and chlorophyll index were measured one week before flowering, cluster color change, fruit harvest and leaf color change. The row spacing was three meters, and the vine spacing within rows was two meters. Irrigation scheduling was determined based on the treatments using a TDR moisture meter. After full maturity (uniform ruby color of the cluster with a Brix above 17), the trait of cluster length was measured using a ruler and the cluster width and berry diameter were measured using a caliper. The traits of cluster number and number of berries per cluster were counted and cluster axis weight (average weight of three cluster axes per plant), fresh berry weight (average weight of 10 berries per cluster), cluster weight (average weight of four clusters per plant) and yield (average yield of three plants per plot) were measured using an OHAUS digital scale with an accuracy of 0.01 g (Gatti et al., 2012). For statistical analysis, after ensuring the normality of the data, analysis of variance was performed using SAS software version 9.4 and using the GLM procedure. Composite variance analysis related to the three years was performed when the Bartlett test confirmed the homogeneity of variances.
Results and Discussion
Deficit irrigation resulted in a reduction in cluster rachis weight, cluster length, cluster width, number of berries per cluster, berry diameter, berry weight, cluster weight, number of clusters per vine, and fruit yield, along with an increased rate of yield reduction. Reducing the water availability for grapevines led to a decrease in the traits affecting fruit yield. This reduction varied for each trait depending on the specific stage of deficit irrigation. For all traits, deficit irrigation applied during the flowering to veraison stage was the most sensitive to irrigation reduction. The highest (6500 kg) and lowest (1111 kg) fruit yields were obtained under full irrigation and irrigation after 70% depletion of available water during the flowering to veraison stage, respectively. The highest fruit yield under deficit irrigation was observed during the fruit harvest to leaf fall stage. Across all deficit irrigation regimes, the lowest fruit yield was associated with the flowering to veraison stage. Irrigation after 35% depletion of available water during the stages of bud break to flowering, flowering to veraison, veraison to fruit harvest, and fruit harvest to leaf fall resulted in yield reductions of 32.8%, 43.2%, 8.8%, and 5.6%, respectively, compared to full irrigation at the corresponding stages. Irrigation after 70% depletion of available water during the same stages caused yield reductions of 73.7%, 82.8%, 36%, and 24.5%, respectively, compared to full irrigation (Table 3). Although the effect of year on fruit yield was not significant, there was a reduction of 7.3% and 12% in the second and third years compared to the first year, respectively (Table 4). A multiple linear regression analysis was performed for the fruit yield of Yaghooti grape. The traits influencing the predictive equation for yield (Yield) included cluster length (CL), cluster width (CWi), cluster weight (CWe), and the number of clusters per vine (C/V), as shown in Model 1.
Model 1) Yield = 3481 + 126 CL – 68 CWi + 14 CWe + 185 C/V
The highest (82.7%) and lowest (4.8%) fruit yield reduction rates were observed under irrigation after 35% depletion of available water during the flowering to veraison stage and irrigation after 70% depletion of available water during the fruit harvest to leaf fall stage, respectively. The highest rate of fruit yield reduction occurred when deficit irrigation was applied during the flowering to veraison stage. Conversely, the lowest rate of fruit yield reduction was observed when deficit irrigation was applied during the fruit harvest to leaf fall stage.
Discussion
The results showed that fruit yield responded differently to deficit irrigation. Deficit irrigation during the bud break to flowering and flowering to veraison stages had the greatest impact on reducing fruit yield, with the effect being more pronounced during the flowering to veraison stage. However, the impact of deficit irrigation during the veraison to fruit harvest and fruit harvest to leaf fall stages on yield was less compared to the bud break to flowering and flowering to veraison stages. The lowest fruit yield and the highest rate of yield reduction were observed under irrigation after 70% depletion of available water during the flowering to veraison stage, amounting to 1111 kg.ha-1 and a yield reduction rate of 82.7%, respectively. The results showed that irrigation after 35% soil moisture deficiency during the stages of bud burst to flowering, from flowering to fruit color change, from berry color variation to harvest and from harvest to leaf fall reduced fruit yield by 27.9, 38, 7.1, and 4.1 percent compared to full irrigation in the corresponding stages, respectively. In general, by reducing the irrigation rate in the stages from berry color variation to harvest by 35% soil moisture deficiency, water consumption can be saved and yield is not significantly reduced. |