Factors responsible for the sex expression of Japanese cucumber. IV

Abstract

This paper presents further studies of correlations between the auxin content and the growth and sex expression of the cucumber plant. The results obtained in the previous report indicated that the higher auxin content, restricting the vegetative growth, induced the sex reversion. For the purpose of increasing the auxin content the spray of 10 ppm solution of naphtha leneacetic acid was applied in the following two ways. (1) NAA sprays of 10 ppm were repeated at 2-, 4-, 6-, and 8-day intervals during 40 days in the cold bed. With shortening of the interval of the repe-tition, the male flower formation being retarded, the female flower formation was progressively accelerated. Under the short day condition (8 hours) at 2-and 4-day intervals applications, and under the long day condition (15 hours) at 2-day intervals application, no male flower being formed, the first female flower bloomed as the first flower on the fourth node. (2) NAA sprays of 10 ppm were repeated at 4-day intervals between once and ten times in the cold frame. With thrice applications, the female flower formation was noticeably accelerated. The female flower formation progressed according with the repetition times of spray application. At nine times of repeated applications, without forming any male flower, the first female flower bloomed as the first flower on the fourth node. (3) It may be reasonably concluded that auxin level in the cucumber plant is responsible for the sex expression as the physiological ground. The higher auxin level, restricting male flower forma-tion, favors the female flower formation. It is previously shown by the authors that the cucum-ber flower is hermaphroditic in nature. Sex pattern shown in the cucumber development is of the physiological nature progressing in accordance with the plant growth, thoroughly associated with the auxin content.