Prediction of berry cracking in Thompson Seedless grape

Abstract

To evolve a prediction model of berry cracking in grapes based on its relationship with environmental factors,
the percentage of berry cracking was recorded in 25 vineyards of Thompson Seedless in India. Data on growing
degree days from fruit pruning, average relative humidity, cumulative rainfall, average soil moisture tension,
average maximum temperature, and average wind speed, all during the preceding three days of cracking were
recorded from the automatic weather station and the soil moisture sensors installed in the affected 25 as well
as an equal number of unaffected vineyards. Growing degree days, average relative humidity, and cumulative
rainfall had a positive relationship with cracking while the soil moisture tension, maximum temperature, and
wind speed had the negative. The maximum threshold level for degree days was 1415, while the minimum for soil moisture tension was 31.2 kPa. Relative humidity of 74.1 per cent and cumulative rainfall of 20.5 mm accounted respectively for 41 and 67.5 per cent berry cracking. Maximum temperature of 26.6°C and wind speed of 9.8 km/hr accounted respectively for 41.4 and 45.4 per cent variation in berry cracking. The multiple regression function Y = -104.55 + 0.1723X1 + 0.0826X2 + 4.1161X3 + 0.4813X4 - 4.5706X5 - 8.0401 X 6 was found to determine berry cracking by 92.4 percent. A non-significant difference of 2.2 per cent was observed between the observed and predicted cracking in the validation of the model in the 2024 fruiting season. Observed and predicted per cent berry cracking in individual vineyards are presented graphically.