Growth Analysis on the Plant Type in Peanut Varieties, Arachis hypogaea L. : V. Air temperature and some internal factors affecting the seasonal change of the growth rate of main stem and its difference between infraspecific two varietal groups

Abstract

To clarify the role of main stem in the establishment of canopy of the individual peanut plant, seasonal change of 2 indices of main stem growth rate (elongation rate, cm/day, abbreviated to SER and leaf emergence rate, 1vs./day, LER) and their difference between infraspecific two varietal groups were studied, using the data dealt in previous paper (MAEDA, 1968). Thirty one, mainly tropical, varieties, of which taxonomic positions were known and divided by the author (MAEDA, 1964), were sown monthly from April to August (table 1 and fig. 1). Results obtained and discussions are as follows : 1. Number of leaves and length of main stem at harvest were larger significantly (p<0.01) in varietal group E (v.g.E) than those of varietal group P (v.g.P) in all of plots (table 2). 2. From the behavior of SER and LER in the 1st growth period (mean air temperature: ca. 19°C) and in the 2nd growth period (ca. 22°C) in April-sow. plot (fig. 2), it was considered that such a range of temperature affected slightly against the leaf emergence and development of epicotyl primordia which hnd differentiated in the dormant embryo, but it was inhibitory against the new differentiation in epicotyl apex which follows the former. Thus, the lag-phase in main stem growth had been observed in April-sow. plot disappeared in later sowing plots, and the number of leaves emerged during the 1st growth period of each of the plots increased with the delay of sowing time (table 3). 3. SER and LER in both varietal groups showed highly positive correlation to the mean air temperature in the 1st growth period of each of plots (during ca. 20 days after germination) respectively (fig.3, A), contrary, the lower correlations were obtained for all of growth periods (v.g. E: 0.564**, v.g. P: 0.325n.s.). 4. And the values of regression coefficients between SER and LER of the 1st growth period differed significantly (p<0.001) with those of later growth periods in each of the plots (fig. 3, B). These facts may suggest that the degree of influence of the air temperature upon the SER and LER differs with growth stages. 5. It was considered that the advantage in the morphological differentiation of the embryo) in dormant seed in v.g. P, compared with v.g. E (MAEDA, 1972) is a reason for the higher SER and LER in the 1st growth period of April∼June-sow. plots in v.g. P than v.g. E (figs. 2 and 3, A). 6. By the difference in the pattern of seasonal change, and lower values and earlier decline of both rates in v.g. P, having much branches' apices than v.g. E, having fewer ones, the action of growth competetion between main stem apex and apices of the branches, as the another internal factor affecting SER and LER, was supposed. That is, it may be said that the severer physiological stress upon the main stem apex in v.g. P caused by such a competetion seemed to be a reason for the earlier decline of growth, and subsequently, of the shortness in length and fewness in the number of leaves of main stem in this varietal group, comparing with the v.g. E, having longer main stem with much leaves, and of which growth continues until later. The fact shown by SOEJIMA et al. (1967) that the main stem of the peanut of a Virginia tybe variety, of which all of branches were excised artificially, continued its elongation until about twice as tall as the control plants, also may support the above-mentioned opinions.