Validation of a Model for the Growth and Development of the Thompson Seedless Grapevine. I. Vegetative Growth and Fruit Yield

Abstract

This validation study compares the simulations of a growth model for the grapevine cultivar Thompson Seedless that is driven by weather (temperature and solar radiation) with vine growth patterns observed in the field. The growth of vegetative (leaf and stem) dry matter was estimated, and harvest fruit yields were measured in six vineyards over a 300 km latitudinal range in the San Joaquin Valley in California in 1983. In general, vegetative dry matter increased linearly when plotted on degree days (°D) above 10°C until véraison, after which time it leveled off. Crop yield was highly variable both within and between the study vineyards. The model simulated leaf and stem growth accurately at two vineyards. At one vineyard, the simulation was consistently higher than the observations after bloom, while at the remaining three, simulations were lower through about mid-season. The model simulated fruit yield accurately at four sites, and underestimated yield at the remaining two, where leaf and stem simulations were also below those observed. The roles of trellis type and of water stress in producing the discrepancies between the model and the observations are discussed. Some problems of using plant models for prediction are briefly discussed.