Studies on the Seedling Emergence in Crops : Seed size and elongation force of soybean seedlings

Abstract

Using an unbonded strain gauge transducer (1 kg) and an automatic balancing null recorder, the vertical elongation force (Ef) exerted by a seedling was measured at 24-26°C in darkness. The materials were thirty-four soybean cultivars (Glycine max (L.) Merr.) and six cultivars of six leguminous species including kidney bean (Phaseolus vulgaris L.), green gram (P. radiatus L. var. typicus Prain), lupin (Lupinus spp.), hyacinth bean (Dolichos lablab L.), asparagus bean (Vigna sequipedalis Wigth) and peanut (Arachis hypogaea L.). One seed was sown in a plastic pot 5 cm in diameter and 10 or 12 cm in depth. The seedbed was made from sandy loam soil which had been sieved through a 2.38-mm screen and which had about 13% moisture by volume. The soil was compacted to about 0.1 kg/cm3. The seeds were covered with 3 to 7 cm of loose, uncompacted soil. The seedlings were then grown in a dark chamber at 24-26°C. When the seedling had grown to 3, 5 or 7 cm in height, just emerging from the soil, the cotyledones of seedlings were attached to the force receptor of the transducer which was adjusted to 0 vertical force. Light effects on seedling growth were minimized byT handling them quickly under dim green light. Hypocotyl diameter was measured for calculation of stem area on seedlings which were grown under the same conditions as those used for the Ef tests. When the seedling had grown to 3 cm in height and was beginning to emerge, the loose surface soil was removed. The diameter at the center portion of the seedling, 1.5 cm above the stemroot junction, was measured to 0.1 mm using a caliper. Five to 16 seedlings of each entry were used for the Ef test, and three seedlings were used in the measurement of the diameter of hypocotyl. The results obtained were as follows. 1. The maximum Ef of 3 cm tall seedling in soybean varied according to seed mass of the same variety. In each material, the maximum Ef increased about 40g in small seed lot and about 10g in large seed lot with increasing 50mg of a seed weight. 2. In 3cm tall soybean seedlings, the mean value for the maximum Ef of a variety was positively correlated with seed mass (h=0.949). The maximum Ef per unit mass of seed was smaller in large-seeded soybean compared to small-seeded soybean. Furthermore, highly positive correlations were found between seed mass and strm area (r=0.952), and stem area and maximum Ef (r=0.934). The results indicate tha the large-seeded soybean produce large stems and therefore a large Ef. 3. In each of 3, 5 and 7cm tall seedlings, when seed mass is the same among soybean variety and another leguminous species which produed a hypocotyl, the mean value for the maximum Ef of a species was almost the same between soybean and green gram or lupin. However, the Ef was less in soybean than in kidney bean, hyacinth bean, asparagus bean and peanut.