Climatic Factors Influencing Parthenocarpy and Normal Fruit-Set in Tomatoes

Abstract

A study has been made of the influence of day and night temps., photo-period, and light intensity upon the effectiveness of 2-naphthoxyacetic acid (2NA) for the setting of parthenocarpic fruit in the tomato, Lycopersicum esculentum var. Essex Wonder. Results include a quantitative comparison of % set, yield and avg. wt. and size, for fruits from normally fertilized plants and from those sprayed with the growth substance. In general, the conditions under which 2NA was most effective paralleled those under which the highest yields of normally fertilized fruits were obtained. At very high day or night temps. especially when light intensity was low 2NA was either poorly effective, or failed completely to induce ovary development, even though small sets of fruits arose by natural fertilization. Under lower temps. % setting was generally somewhat higher in 2NA-treated blossoms, while at very low temps. there was an indication that 2NA may induce a higher set than would occur naturally. Apparently 2NA was ineffective in inducing ovary development in the sterile, malformed blossoms differentiated under unfavorable conditions. Under all conditions 2NA prevented the abscission of sprayed blossoms, even when fruit formation did not occur. The avg. wt. of the spray-induced and normal fruits were not appreciably different. Spray-induced fruits, however, were generally larger at maturity and showed a tendency to hollowness, particularly when grown in low light intensity or short photoperiod. A study of the conditions necessary for induction of natural parthenocarpy in unsprayed emasculated blossoms indicated that low temps. and high light intensity are determining factors.