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A high yielding Sultana clone, H5, infected with yellow speckle and leafroll diseases was compared over 5 harvests with 6 heat-treated H5 clones, 3 of which still contained both diseases and 3 from which leafroll had been eliminated, and also with a Thompson Seedless clone from California.
There were no differences between the untreated H5 clone and the ThompsonSeedless clone which was infected with only yellow speckle for any of the measured variables in any season.
The mean yield of heat-treated H5 clones was reduced by 6 % in those which still contained both diseases and was not affected in those from which leafroll had been eliminated. The mean weight of annual shoot growth, berry weight, calculated bunch weight, sugar concentration and pH and titratable acidity of juice, did not differ between the 4 groups.
Long periods of heat treatment produced no clones with yields or annual shoot growth superior to the untreated source clone. Except for expression of leaf symptoms associated with leafroll, all 6 heat-treated H5 clones showed no obvious morphological differences from their original source clone, nor did the heat-treated Thompson Seedless clone.
Effects of Thermotherapy and Virus Status on Yield, Annual Growth and Grape Composition of Sultana
1984, Vitis, vol 23, pages 268-273
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