Effects of Several Plant Growth-Regulators on Fruit Set, Yield, and Blossom-End Rot of Six Tomato Varieties Grown Under High Temperatures

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Abstract
Under conditions of high night temp. many tomato flowers normally failed to set fruit. When flowers were sprayed with certain growth-regulators[long dash]p-chlorophe-noxyacetic acid, beta napthoxyacetic acid, 2,4-dTchlorophe-noxyacetic acid (2,4-D), and (orthochlorophenoxy) propionic acid[long dash]a higher total yield and larger fruit size were obtained than were produced by controls. Results in certain cases were striking. There was great varietal variation in response to the treatments with respect to fruit size, total yield, and incidence of blossom-end rot. In general, the indeterminate tomato vars. seemed to be more responsive to the treatments than the determinate, both with respect to increases in fruit size as well as in total yields. Considering all vars. together, no consistant correlation was found between application of growth-regulators and incidence of blossom-end rot. Considering individual vars., however, there was a marked correlation, enough to suggest the possibility that hormonal mechanisms may be involved with this phenomenon. Growth-regulators affected the incidence of blossom-end rot both positively and negatively, depending on the tomato var. and the chemical used. p-Chlorophenoxyacetic acid brought about, in general, the best fruit set and subsequent fruit development, with B-naphthoxyacetic acid second. With several vars., however, the latter was the more effective. The third most effective was 2,4-D, this being better than alpha (orthochlorophenoxy) propionic acid; the plants treated with the latter compound yielded slightly more than the controls. Of the tomato vars. studied, whether the plants were treated or not, the determinate type was superior to the indeterminate for fruit production during the tropical hot season.