The Use of Growth-regulating Chemicals to Induce Parthenocarpic Fruit in the Calimyrna Fig.

Certain varieties of many species of plants develop their fruits parthenocarpically or without fertilization. The apple and pear occasionally produce parthenocarpic fruits but generally under special nutritive conditions (10). In some varieties of grapes, figs, bananas, and oranges, parthenocarpy is of great economic importance (4, 14). Because of this naturally occurring phenomenon, attention has been directed toward inducing parthenocarpy in other fruits and vegetables by the application of hormones of various synthetic growth-regulating substances. Early investigations by GUSTAFSON (9) on chemically-induced parthenocarpy stimulated research in this field and, at the present time, it is possible to produce parthenocarpically several different vegetables, as well as fruits of some ornamental plants. Similar attempts to increase fruit set or to induce seedlessness in some of our more important tree crops, such as the apple, orange, and grapefruit (1, 8, 11, 15) have failed entirely. A review of literature has revealed that all attempts to promote parthenocarpic fruit development in a temperate zone commercial tree fruit, where it did not already occur naturally, have been unsuccessful. This paper presents the results of preliminary experiments that were successful in chemically inducing parthenocarpic development of fruit of the Calimyrna fig. Of the four most important fig varieties produced in California, the Mission, Adriatic, and Kadota, which are considered to be of the common type, are characterized by being completely parthenocarpic. On the other hand, the Calimyrna, the leading drying variety in the state, is of the Smyrna type, and exhibits the typical characteristics for this group by being almost completely non-parthenocarpic. The syconia of the Smyrna type mature only after the flowers have been pollinated and the ovules fertilized. Pollination of the Calimyrna variety is accomplished by the fig-wasp, Blastophaga psenes L., which carries pollen from the male or caprifig to the stigmas of the Calimyrna, a process termed caprification. Thus in the produietion of Calimyrna figs the use of caprifigs and fig-wasps is indispensible. However, accompanying commercial caprification are several problems of vital concern to the grower. He must either maintain caprifig