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Abstract
An agrometeorological model was developed for assessing the effect of heat stress during flowering and early fruit set on avocado (Persea americana Mill) yields. This model accounted for heat stress only and was considered to occur when the daily maximum temperature was ≥33°C. In addition to the daily maximum temperature, the model considered the duration of such temperatures in days, as well as the timing of the occurrences of such temperatures in relation to the flowering and early fruit set of ‘Fuerte’ avocado. The specifications of the climatic data inputs are based on experimental results in the temperature range of 33° to 43°C extrapolated linearly. A series of weighting factors were used for the duration of heat spells in days. In the temperature range of 33° to 35° the weighting was n − 1; for the 36° to 38° range, 1.4n; and for the 39° to 43°C range, 2.0n. Weighting factors for the timing of the occurrence of heat spells follow closely the near-normal percentage distribution curve of open flowers. At bud burst in March, the weighting is 0.4, increasing to 1.3 at early fruit set by mid-May and decreasing rapidly to 0.3 by the end of June. The functional relationship between the model heat stress output and the yield of avocado for an irrigated, high-yielding plantation shows fairly good correlation, r 2 = 0.42 to 0.51, depending on the statistical method used. The agreement between the heat stress index and the yield of avocados is closely related only during those years when the plantation is subject to heat stress indexes greater than 10. Testing the model on independent data commenced in 1985 and includes a yield memory term.
Abstract
The relations between peel thickness and fruit shape of ‘Marsh Seedless’ grapefruit and various climatic factors were studied at 8 locations in Israel. Peel thickness was affected greatest by winter temp. Low winter temp resulted in fruits with thick peel in the following year. Fruit shape was affected to a similar degree by low winter temp, summer air humidity, and rate of evaporation. Summer temp and the differences between maximum and minimum temp in the spring and fall, had little effect on fruit shape and peel thickness.