Effect of Plant Density and Temperature Variation Arising From Planting Date on corn seed sizing (Zea mays L. cv. SC 704)

To investigate the effect of competition and thermal condition in key stages of corn growth and development on relative composition of seed size and shape, parental inbred lines of single cross 704 were planted in accordance with its seed production guideline in five sowing date and five plant density. Seed yield, seed yield components and weight ratio of four major seed shape and size were analyzed in regard to mean daily temperature and daily growth degree day (based on CERES function) of different phenological stages including, seedling emergence to tassel emergence, fertilization and pollination to physiological maturity. Results showed that the average of maximum temperature higher than 34°C during fertilization lead to increase in weight ratio of Large-round seeds in favor of Large-broad ones. For each degree Celsius increase or decrease in maximum temperature during fertilization from 34°C, the proportion of broad seeds decreased or increased, respectively, about %38±0.3.When daily growth degree days during seed filling dropped lower than 13°C, the relative composition of Large-round size decreased. The higher inter plant competition changed the relative weight of Large-round seeds in favorite to Large-broad seeds, in the way that the highest proportion of broad seeds and lowest proportion of off-size seeds produced from 60000 and 70000 plant per hectare.