Growth Analysis on the Plant Type in Peanut Varieties, Arachis hypogaea L. : IV. Relationship between the varietal difference of the progress of leaf emergence on the main stem during pre-flowering period and the degree of morphological differentiation of leaf primordia in the embryo

Abstract

Following 2 experiments were undertaken to re-investigate in detail the varietal difference of the number of main stem leaves on the day of first flowering (MAEDA, 1968), using 6 varieties (see, note of fig. 1) differing the plant type, of which seeds have been storaged under low moisture in room temperature during 10 months after harvest. Experiment I. Varietal difference of the leaf emergence on the main stem during the pre-flowering period (48 days after seeding) under controlled condition (day : 14 hours, 27°C, 18∼20 klx; night: 10 hours, 22°C). Leaf emergence (full expansion of 4 leaflets) of 10 plants from 50 plants (10pl. × 5 replications) per a variety, in density of 6 × 7.5 cm per a plant, were observed every day. Experiment II. Morphological differentiation of the leaf primordia in the matured embryo of the selected newly shelled seeds of the same materials in Exp. I. The 1st and 2nd leaf primordia (plumule) were observed with dormant seeds, and the primordia of upper order of leaves were observed with 20- and 40-hours-incubated seeds placed on the moistend vermiculite at 30°C in dark, to avoid breakage of primordia of cured seeds which are too fragile to dissect under microscope. The embryos of incubated materials were cut-off and at once fixed in 80% alcohol solution. Results obtained and considerations are as follows : 1. A clear turning point of leaf emergence rate on the main stem was observed about 2 weeks after seeding in each of all varieties, and the number of leaves at the turning point was about 4 in large-seeded varieties (SP1, SP2, and P 1) and a small-seeded variety E 1, and about 3 in the other small-seeded varieties (E2 and P2) (fig. 1). Accordingly, varietal difference in the number of main stem leaves on the characteristics in leaf emergence of 2 varieties, P 2 and E 2. 2. Higher rate of leaf emergence (LER) shown by the regression coefficient until turning point after the 1st and 2nd leaf had unfolded, declined after turning point in every varieties. Thus, a difference in the behavior of LER before and after turning point between the peanut and the soybean which shows acceleration of LER after turning point (5th or 6th foliage leaf emergence period, OIZUMI, 1962), was noted. In the peanut which shows weak or no apical dominance, this fact may be explainable by the presence of competitive inhibition upon the leaf emergence on the main stem by vigourous growth of the primordia of cotyledonary laterals had developed in the embryo and would follow after the main stem's growth when seed germination occurred. 3. Close relationship between the occurrence of turning point of leaf emergence rate and the number or degree of morphological differentiation of embryonic leaves was suggested. Then, from the anatomical and microscopic observations of plumules and upper order-leaves' primordia, it was clarlified that 5 primordia (the 1st∼5th leaf primordia) with the developed leaflets and the lowery developed 6th primordium were observed in large-seeded varieties, SP1, SP2, and P1. However, 4 well developed and 1 or 2 lowery developed ones were observed in 2 small-seeded varieties, E 2 and P 2. And variety E 1 showed the intermediate tendency in the degree of development of leaf primordia (fig. 2, A∼D and table 1). The gap of the degree of differentiation of leaf primordia recognizable between the 4th and 5th primordia (or between 3rd and 4th) in each variety differing the seed size, appeared to be a reason of occurrence of the turning point of leaf emergence rate and, at the same time, of the varietal difference of the progress of leaf emergence on the main stem in the peanut. 4. And also it may be said that the verietal difference of LER during the pre-flowering period obtained in this experiment is a reason of the varietal difference in the number of main stem leaves on the day of first flowering reported by the author. [the rest omitted]