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Larry J. Bettiga

Vine growth and yield variables were measured for grape (Vitis vinifera) planted as green-growing and dormant ‘Chardonnay’ benchgrafts during the first 8 years after vineyard establishment. Benchgrafts of ‘Freedom’ and ‘Kober 5BB’ rootstock were evaluated. Vines planted as green-growing benchgrafts had smaller trunk and cordon diameters and lower pruning weights. Growth variables measured were higher for ‘Freedom’ benchgrafts than ‘Kober 5BB’. Yields were higher for vines planted as dormant benchgrafts in three of the first six production years when compared with vines established with green-growing plants. Productivity was higher for vines planted with dormant benchgrafts or grafted on ‘Freedom’ rootstock because the permanent framework of vines in these treatments was fully developed earlier in the training process, which allowed for earlier crop production.

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S. Kaan Kurtural, Andrew E. Beebe, Johann Martínez-Lüscher, Shijian Zhuang, Karl T. Lund, Glenn McGourty and Larry J. Bettiga

A field study was conducted for three consecutive seasons in the hot climate of central California to assess the performance of ‘Merlot’ grapevine (Vitis vinifera) grafted onto ‘Freedom’ [Fresno 1613-59 × Dog Ridge 5 (27% V. vinifera hybrid)] during training system conversion to facilitate mechanization. The traditional head-trained and cane-pruned (CP) system was either retained or converted either to a bilateral cordon-trained, spur-pruned California sprawl training system (HP), or to a bilateral cordon-trained, mechanically box-pruned single high-wire sprawling system (SHMP). After the conversion, SHMP sustained greater yield with more clusters per vine and smaller berries without affecting the canopy microclimate. This was due to a higher number of nodes retained after dormant pruning. The SHMP canopies, compared with CP and HP; filled allotted canopy space earlier based on photosynthetically active radiation (PAR) transmitted through the canopies, populating the space allotted per vine, favoring higher production efficiency. There were no adverse effects of training systems on berry composition or flavonoid concentration, during or after conversion to mechanical management. However, experimental year effect was obvious on anthocyanin composition of ‘Merlot’ berries, increasing trihydroxylated (i.e., delphinidin-based) anthocyanins in the latter years of the experiment. Our results also provided evidence that earlier canopy growth coupled with sufficient reproductive compensating responses allowed for increased yields while reaching commercial maturity without a decline in anthocyanin content with the SHMP. Converting CP to SHMP reduced labor operations costs by 90%. Furthermore, the SHMP had greater gross revenue and resulted in greater net income per acre even when the conversion year was taken into account. Therefore, SHMP is recommended for growers within the hot climate of the central San Joaquin Valley as a means to maintain productivity of vineyards while not sacrificing berry composition at the farm gate.