The use of rootstocks is gaining importance in Indian viticulture due to problems associated with abiotic stresses, such as drought and salinity, and also to improve scion characteristics. Thompson Seedless is the only commercial cultivar grown for both fresh consumption and raisin making. Dog Ridge was the only popular rootstock used by grape growers prior to late 1990s. But this rootstock was known to induce more vigour in scions, resulting in reduced bud fruitfulness and thereby fruit yield. To identify alternate rootstocks suitable for Thompson Seedless, a study was initiated in the National Research Centre for Grapes, Pune, India during the year 2001. Five rootstocks with own rooted vines were evaluated in this study. During the initial years, Thompson Seedless grafted on Dog Ridge produced the highest yield, with good quality fruit. Over the years we could observe uneven bud sprouting, gaps on the cordon due to dead wood formation, and reduced yield in vines grafted on Dog Ridge rootstocks. In contrast, Thompson Seedless grafted on 110R performed well in terms of moderate vigour, increased fruitfulness and consistently higher yield. Dog Ridge and St. George produced a lower yield, owing to increased vigour measured in terms of pruning weight, total shoot length and cane diameter. Rootstocks 110R, 1103P and 99R are also known to increase water-use efficiency during critical growth stages of fruit bud differentiation and full bloom. No significant influence of rootstocks was observed for most of the fruit composition parameters. Larger and bolder berries were produced on Dog ridge and 110R rootstock, while they were the smallest on own rooted vines.
Ten grape rootstocks were subjected to moisture and salinity stress in two separate experiments. The influence of these stresses on gas exchange, water relation, and biochemical parameters was monitored at various stages of stress cycle. Both stresses indicated significant changes in the physiological and biochemical parameters studied. Some biochemical constituents increased by several folds in few rootstock cultivars which also recorded increased osmotic potential suggesting their role in osmotic adjustment. Some of the rootstock cultivars such as 110R, 1103P, 99R, Dogridge, and B2/56 recorded increased phenolic compounds under stressed conditions. The same rootstock also recorded increased water use efficiency. The increased accumulation of phenolic compounds in these cultivars may indicate the possible role of phenolic compounds as antioxidants for scavenging the reactive oxygen species generated during abiotic stresses thus maintaining normal physiological and biochemical process in leaves of resistant cultivars.
The influence of cluster exposure to sunlight on fruit composition of 'Norton' grapes was studied. Three exposure levels, such as fully exposed, partly exposed, and fully shaded, were established by canopy management practices, such as shoot positioning, shoot thinning, and leaf removal. Row orientation significantly impacted fruit composition with east west orientation and resulted in high total soluble solids, anthocyanin, and tannin content. Titratable acidity, total phenol, and juice potassium was highest in vines planted in north south row orientation. Fully shaded clusters had the lowest total soluble solids, lower glucose and fructose content, and highest juice potassium and malic acid content. Fully exposed clusters displayed lowest titratable acidity. Fully exposed clusters on the west and south side of the canopy received photosynthetically active radiation of more than 1,100 µ mole m -2 sec -1 , while partly exposed and fully shaded clusters received less than 10% of total photosynthetically active radiation at solar noon. Berries on fully exposed clusters exhibited a temperature that was about 10-15 • F higher than air temperature, while fully shaded clusters were about 1-2 • F higher than air temperature.
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