Effect of Pruning Severity and Bud Number Per Cane on Yield and Quality of Grape (Vitis vinifera L.) cv. Rotabi

 The Rotabi grape cultivar holds significant importance in the Bavanat region of Fars province. There are two distinct methods of pruning employed for this cultivar: Cane pruning and Spur pruning. These methods vary primarily in the length of one-year-old wood that is preserved after pruning. Cane pruning involves retaining long fruiting canes, typically those with more than 3 buds per cane. Conversely, Spur pruning utilizes shorter canes, usually those with 1-2 buds. The common method of training Rotabi vines in Shiraz vineyards is in the form of bush training. This method of vine training is compatible with spur pruning, in which the canes are usually pruned into 2 to 3 buds. For this reason, there is not enough information about the response of this cultivar to cane pruning. This study was conducted in order to determine the correct method of pruning Rotabi vines based on scientific principles appropriate to its genetic characteristics.
 
 This study was performed on 17-year-old vines of Rotabi cultivar in one of the vineyards of Shiraz of Fars province (Iran). In this study, the response of this cultivar to two levels of pruning severity (light pruning with formula 40 + 20 and severe with formula 20 + 20) and three levels of the number of the buds per cane (3, 6, and 9 buds) during three years in Shiraz region of Fars province (Iran) was evaluated. A factorial experiment based on randomized complete block design was used with three blocks. Quantitative and qualitative characteristics such as yield, average weight of cluster, average number of clusters/vine, titratable acidity (TA), pH of fruit juice, TSS%, bud fruitfulness, the average weight and the number of berries/bunch was recorded.
 
 Results showed that effects of pruning severity on yield, the number of bunch/vine, bunch weight, pH, bud fruitfulness and berry weight was significant (p≤0.01). Effect of cane length on yield, the number of bunch/vine, bunch weight, bud fruitfulness and the number of berry/bunch was significant (p≤0.01). but on berry weight, TA, pH and TSS% of fruit juice was not significant. Interactions between pruning severity with buds per bearing unit on yield, the number of bunch/vine, berry weight and the number of berry/bunch (p≤0.01) and on TA (p≤0.05) was significant. The highest fruit production per hectare (yield) and the number of bunches per vine were obtained in vines subjected to light pruning. However, in vines that underwent severe pruning, bud fruitfulness and berry weight were greater than in lightly pruned vines. The most substantial yield was achieved with 6-bud and 9-bud canes. Yet, the highest number of bunches was observed in vines with 3-bud and 6-bud canes. Bud fruitfulness reached its peak in the 6-bud cane category, while it was at its lowest in the 3-bud cane group. The number of berries was the same in the 3-bud and 9-bud cane treatments, and it exceeded the number of berries in the 6-bud cane group. Notably, due to the interaction between pruning severity levels and the number of buds per cane, the highest yield was recorded in light pruned vines that underwent cane pruning, specifically in the groups of light pruning with 6-bud canes and light pruning with 9-bud canes. The highest number of berries was observed in light pruning with 9 buds. As a result of this study, it was found that by increasing the number of buds/cane or in other words by increasing the cane length to 6 and 9 buds in this cultivar, the fruit yield/vine increased, and but fruitfullness decreased. Increased yield in light pruning can be due to the increase in the number of bunches/vine due to the increase in the number of buds in this type of pruning. Therefore, to increase the yield of this cultivar, cane pruning + 9 buds/cane should be applied. This type of pruning is not compatible with conventional pruning methods (spur pruning) in the cultivation area of this cultivar. Therefore, it is necessary to develop training systems compatible with cane pruning (such as four-arm kniffin system) in these areas.
 
While severe pruning led to higher bud fruitfulness, it resulted in lower fruit production per vine (yield) compared to lightly pruned vines. One possible explanation for this difference is that light pruning retained more buds compared to severe pruning. As a consequence, light pruning produced more bunches, ultimately yielding a greater quantity of fruit compared to the severe pruning method. The highest yield (31.3 t/ha) and the highest number of bunches/vine (103) was observed in light pruned vines. Also, the highest yield was obtained in 6-bud and 9-bud canes (31.4 and 31.3 t/ha) respectively. Yield increased with increasing cane length to 6 or 9 buds. Therefore, in order to achieve more yields in this cultivar, cane pruning of at least 6 buds should be applied. But in the end, for better management of vines and the possibility of using standard vine training systems compatible with cane pruning, preferably cane pruning with 9-bud/vine is recommended.