Comparative Studies on Dry Matter Production, Plant Type and Productivity in Soybean, Azuki Bean and Kidney Bean : VI. Differences in the early vegetative growth in relation to seed weight and character of cotyledon

Abstract

In this study, differences in the early vegetative growth for the three crops were analyzed in relation to their seed size (weight). Seeds of five varieties (strains) with different seed weight for each crop (Table 1) were sown under field conditions (40×20 cm, singling), and dry matter decreases in seeds (cotyledon) and increases of dry weight and leaf area in seedlings were measured during the month after emergence. The results obtained were summarized as follows: 1. Although kidney bean and azuki bean consumed reserve food about 95% on the average within 10 days after emergence, soybean consumed it only about 70% and dry weight of the cotyledons changed little during thc 10-20 days after emergence (Fig. 1 and Table 2). 2. The efficiency of conversion of reserve food to active plant body (economic ratio) was 1.5, 1.4 and 0.9 on the average in kidney bean, soybean and azuki bean, respectively. In soybean it was lower in varieties with larger seed (Table 2). 3. Dry weight and leaf area in seedling at each sampling date showed highly positive correlations with the initial seed dry weight. However, the r values with consumed dry weight were higher than those with the initial seed dry weight. A highly positive correlation coefficient was also obtained between dry weight and leaf area in seedling over crop, variety and sampling date (Fig. 4). 4. Growth rate was related with mean leaf area, but not with net assimilation rate during the month after emergence (Fig. 3). 5. Relative growth rate and relative leaf growth rate differed little among varieties and crops. These parameters including net assimilation rate, specific leaf area and distribution ratio of dry matter to leaf were not correlated with the initial seed dry weight (Table 3). 6. In soybean, the cotyledons of two varieties with smaller seed were maintained for longer period and their dry weight increased slightly during the 10-30 days after emergence (Fig. 1). In addition, specific cotyledon area (cm2/g) and net assimilation rate were higher in these varieties than in other larger seed ones (Table 4). 7. The compound interest law existed in the seed-seedling weight relationship during the month after emergence (Fig. 2). However, the differences in the early vegetative growth for each crop were, partially, due to the differences in consuming and economic ratio of reserve food.