Post - emergence changes of cotyledonary area and physiological indices in various soybean cultivars.

In this study, the grafting method was used to create composite plants material with the same scion but different cotyledons and the parts below cotyledons. The cut - in grafting method was used to study the changes of cotyledon area from cotyledon stage ( V_c ) to second - node ( V₂ ) stage. The widely - planting soybean varieties over the years in Huanghuaihai Plains of China were used as stock genotypes, and Zhonghuang 39 was as scion. 3 soybean varieties with diiferent 100 - seed weight were selected as test materials, and the post - emergence changes of cotyledons area and physiological indices and their effects on seedling growth and development in soybean by setting the shading and normal sunshine treatments were studied. The results showed that cotyledon area increased during the seedling period from V_C to V₂ among all the tested varieties, with the increment range from 65.61% to 209.29%. The increment of cotyledon area from V₂ to V_C was negatively correlated with the cotyledon area at V_C stage. The cotyledon area increment from V_C to V₂ decreased with the releasing years of the varieties. Beginning from Day 9 after emergence, the cotyledon area constantly declined in all varieties, and the contents of chlorophyll a, total chlorophylls and the dry weight of cotyledons decreased along with the seedling growth, the chlorophyll b content increased first and then decreased. Cotyledon soluble sugar content decreased for some days and then increased gradually, and finally decreased with aging cotyledons. After the shading, the changes of cotyledon area, dry weight, chlorophyll a, b and soluble sugar contents became more prominent than those in normal sunshine treatment, indicating that limiting the cotyledon "source" functions could affect the synthesis, degradation and transport of chlorophylls and soluble sugars in cotyledons, and the changes of cotyledon area and their dry weight. Removing cotyledons had impacts on seedling growth and development, with shorter seedling height, slower development process, and lower seedling dry weight. It was concluded that cotyledon is one of the important vegetative organs of soybean at seedling stage. Cotyledons should be protected and effectively utilized in soybean management. [ABSTRACT FROM AUTHOR]