Determination of the frost sensitivity of avocado cultivars
1994
Koussevitzky, S.
Frost during winter limits the distribution of crops of tropical and subtropical origin to frost free regions. There are three races of avocado (Persea americana Mill.) according to their regions of development: West Indian, Guatemalan and Mexican. There is a pronounced difference between the races in their frost sensitivity, the West Indian being the most sensitive, the Guatemalan intermediate, and the Mexican the most hardy race. There are also differences between varieties in each race. The frost sensitivity of commercially grown varieties is known from many years of field observations. In recent years, efforts are made to find varieties with higher yield and bigger fruits than the existing ones. Their frost sensitivity is not known. This work comes to establish a method for defining frost sensitivity of cultivars, in order to fit them to potential growing region. The same method could serve as a tool to determine frost sensitivity as one of the criteria in breeding. Frost sensitivity was determined by DTA (Differential Thermal Analysis), a method which measures the freezing elnostratures of leaves. The freezing point of a leaf was determined by identifying the temperture at which heat of fusion, created by freezing water is emitted. Three commercial varieties with known frost sensitivity : Ettinger-frost hardy, Fuerte-interme-diate and Hass-frost sensitive, served to check the reliability and resolution of the method, and as standards for determining frost sensitivity of new varieties. By using the DTA method we were able to show, that three of the new cultivars-T142, Tx531 and Ardith-are frost sensitive like Hass, and one-Green Gold-was more frost hardy than Fuerte. We were also able to point that the sensitivity to frost is influenced by the yield load of the tree, by the developmental stage of the leaves and by hardening
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