Poor fruit set of sultanas in the Murray Valley is sometimes attributed to excessively high temperatures around flowering time. Experiments with small fruiting sultana vines in pots suggest that water stress is the more important factor.
Fruit set was significantly less when a 3-day period of water stress was imposed at flowering or 1, 2, or 4 weeks after flowering, but not when it was imposed 6 weeks after flowering. Three days with maximum temperatures above 45oC at or 1 week after flowering did not reduce fruit set when ample water was supplied.
When controlled environments combining day temperatures between 21 and 30oC with night temperatures between 19 and 25o were used, no significant differences in fruit set were found, although shoot growth increased with increasing night temperature.
Shoot elongation slowed down during periods of applied water stress but recovered, when the stress was ended, to a rate greater than that of plants which had not been stressed.
The Effect of High Temperature Regimes or Short Periods of Water Stress on Development of Small Fruiting Sultana Vines
Australian Journal of Agricultural Research, 1965, vol 16, pages 817 – 823