The Effect of Irrigation Regime and Green Pruning on Some Qualitative, Physiological Traits and Yield of Yaghooti Grape

Yaghooti grape (Vitis vinifera L.) is an important variety in Iran and also it is the most important horticultural product of Sistan region. This variety is of interest for economical aspect. Because continuous drought in Sistan region has been a serious threat to the grape production, local farmers have to manage the problem by reducing the volume and irrigation intervals. The canopy plays a key role in radiation energy capture via photosynthesis apparatus, water use as regulated by transpiration, and microclimate of ripening grapes and also grape yield, quality, vigor, and the prevention of grape diseases. Since vines has high vegetative growth makes them compete with the reproductive growth, therefore vines be pruned every year.

In order to evaluate the effects of irrigation regime and green pruning on some physiological traits and fruit yield of Yaghooti grape, the present research was conducted in the research and extensional garden of Zahak city during 2017-2018. An experiment was carried out in the form of a split plot based on randomized complete block design with three replications. Three irrigation regimes of 100, 75 and 50 percent of the grape water requirement based on the potential evapotranspiration of grape and green pruning with three levels including the control plot or the local practice of not green pruning (P1), pruning the green branches starting from the sixth leaf above the last grape bunch (P2) and pruning the green branches starting from the sixth leaf above the last grape bunch along with green pruning of the green branches without fruit and pruning the unproductive brunches (P3) were allocated to main and sub-plots, respectively. ‘Yaghooti vines were 8 years old and trained as a traditional system. The vines were spaced 3 × 3 m. Water requirement of grape was determined according to the FAO method using data from a Class A evaporation pan. The analysis of variance for each variable was performed with the PROC GLM procedure in SAS 9.4. Multiple linear regression was used to determine the relationships of leaf relative water content, proline, soluble sugars, relative membrane permeability, chlorophyll index, and leaf area to fruit yield.

By reducing water consumption from 100 to 75% of grape water requirement, leaf relative water content, fruit juice acidity, chlorophyll index, leaf area and fruit yield decreased 10.1, 6.5, 8.6, 11 and 18.8%, respectively and also proline, soluble sugars and relative membrane permeability increased 67.3, 8.75 and 44.84%, respectively. The P3 treatment compared to control induced an increase in relative leaf water content, chlorophyll index, and fruit yield by 14.7, 12.2 and 25%, respectively as well as a reduction in proline, soluble sugars, relative membrane permeability, fruit juice acidity and leaf area index by 18.34%, 12.1%, 6.8%, 8.3% and 21.3%, respectively. Also the results indicated that providing the 100% of the water requirement combined with pruning the green branches starting from the sixth leaf above the last grape bunch in combination with green pruning of the green branches without fruit and pruning the unproductive brunches (P3) caused the highest grape fruit yield (7797 kg ha-1). Also the interaction effect of meeting 75% of the water requirement and the green pruning had the same result as that of meeting 100%of water requirement under no green pruning conditions. In other words, the green pruning could result in saving 25% of water used by the grape cv. Yaghooti without reducing fruit yield. The multiple linear regression analysis indicated that proline and leaf area were the most important traits impacting fruit yield in Yaghooti cultivar.

Reducing the water potential of vine causes different responses. The most important are a decrease in number cells of fruit, vegetative growth, leaf area, relative leaf water content, chlorophyll content, fruit yield, and increase in the compatible osmolytes. The growing shoots are a strong sink for the consumption of photosynthetic materials. The above mentioned effect causes an increase in the branch overgrowth and its overshadowing. All this factors compete with vine fruit production. So, green pruning and removal of apical dominance eliminates a strong place of nutrient absorption. In other words, green pruning results in a greater accumulation being used by flowers and fruits, causing sufficient light penetration into the crown and reducing evapotranspiration, leading to an increased water consumption and fruit yield.