Berry set and development in Vitis vinifera L.

Abstract

The formation and growth of grape berries was studied in Canterbury, New Zealand on Chardonnay, Pinot noir, Cabernet Sauvignon, and Merlot. Experimentation was set up to examine: changes in yield components, the development of individual flowers, and the growth and cellular makeup of seeded, seedless, and shot berries. Vine yield components were manipulated by altering vine phenology using delayed winter spur pruning and alginate gel encapsulation. Flower development was studied by tagging flowers at capfall and describing the resulting berries at véraison .The set and development of the tagged flowers was altered with girdling and leaf area removal treatments to change carbohydrate availability. Finally the growth curves and cellular makeup of the different types of berries were described from a separate sample of berries.

The timing of phenological growth stages may have an important role in determining components of yield. Bunch weight increased (38%) with delayed winter spur pruning, due to a larger average berry weight. The increase in average berry weight resulted from changes in the berry population, with the proportion of large seeded berries increasing within bunches, associated with a possible reduction in the proportion of smaller seedless berries. Treatments that delayed bud break also delayed flowering date, perhaps to a time when weather conditions were more favourable for berry development. A weak relationship between the warmth of the bud break period and yield, as well as bunch weight, was found; this may be an indirect relationship.

Studying individual flowers showed that berry set and development could be altered by manipulating carbohydrate availability. Girdling changed the development of some flowers. The proportion of seeded berries that formed was unaffected by girdling, while the proportion of seedless berries increased. The response of shot berries and flowers that abscised differed between 1999 and 2000. In 1999 the proportion of shot berries decreased, while in 2000 it was the proportion of abscised flowers that decreased after girdling. Leaf area reduction on girdled shoots had an opposite effect to girdling, with extreme levels of leaf removal (75%) reducing the proportion of shot and seeded berries that formed. The percentage of abscised flowers increases dramatically with leaf area removal, while the proportion of seedless berries was unaffected. However, a weak positive relationship between total shoot leaf area and seedless berry development exists. The data from yield components and of individual flowers suggest that the population of berries are fluid in nature. Shot berries and flowers that abscise appear to be a pool from which seedless berries can form, when carbohydrate availability allows. The antibiotic spectinomycin was applied to alter fruit set and seed development of berries, though no effect was identified. The lack of a spectinomycin effect may have been the result of incorrect timing of treatment application.

The mean overall fruit set differed between the 1999 (41 %) and 2000 (71 %) seasons. The greater fruit set and different behaviour of abscised flowers (c.f. shot berries in 1999) in 2000 might be a reflection of the warmer than average flowering period compared to the cooler flowering period of 1999: This suggests that environmental conditions at flowering may influence fruit set.

Flowers were found to vary in size at capfall, but neither flower size (ovary diameter) nor the time of capfall of individual flowers had any influence on berry set and development. Flower size and environmental conditions affected the progression of capfall. Smaller flowers tend to undergo capfall after larger flowers, and the progression of flowering is disrupted when rainfall and associated low temperatures occur. Temperatures above 15°C were found to advance capfall in the 1999 and 2001 seasons. With flowers undergoing capfall over an extended period of time (about 20 days), individual flowers will experience quite different environmental conditions. However, no strong relationships between daily assessments of temperature at capfall and berry set or berry development were found. The strong effect of carbohydrate availability on berry development (as found with girdling and leaf area removal) suggests that light intensity (due to its impact on current photoassimilate supply) may be more valid an environmental index than temperature.

The extent of berry growth is determined by the seed. A strong relationship between berry size and seed content was found. A minimum level of seed development (>0.5mg fresh weight at harvest) is required for double sigmoid berry growth, which occurs as a consequence of cell division and expansion. Both seeded and seedless berries exhibit double sigmoid growth curves, however when seedless berries have less than 0.5mg seed content they show a single sigmoid growth curve. Seedless berries grow only as a result of cell expansion. Failure of the ovules to develop mean that shot berries only show a small amount of growth immediately post-capfall then halt all growth.

A model of berry formation has been proposed, where flower abscission and fruit set are considered as contrasting processes and the formation of shot and seedless berries occurs when the normal process of seeded berry development fails. Once abscission has been prevented (i.e. the flower is set), the extent to which the flower develops is determined by what stage during pollination (shot berry) and fertilisation (seedless berry) that seed formation fails.