The effect of source-sink restriction and plant density changes on the role of assimilate remobilization in corn grain yield.

In order to study the effect of source-sink restriction and various plant density on the remobilization of assimilates stored in vegetative parts to the ear corn hybrid single cross 704, a split-block experiment as randomized complete block design with three replications was carried out in Ahvaz in summer 2011. In this research the source restriction was imposed through defoliation of the leaves and the sink restriction was imposed by cutting theear at the end of pollination stage as the main factor including the defoliation of the upper leaves of the corn, defoliation of lower leaves, removal of 50% of the ear, and no defoliation and no ear removal (control) in main plots and the plant density as the sub factor including 60000 plants per hectare, 75000 plants per hectare (control) and 90000 plants per hectare in sub plots. Results indicated that source-sink restriction and plant density had significant effect on the rate, contribution, and efficiency of photosynthesis and assimilates remobilization. The highest grain yield by 868.67 g/m 2 belonged to the control treatment (no defoliation or ear removal)due to producing more grains and the heavier weight of 1000-grain and the lowest grain yield by 646.33 g/m 2 belonged to the treatment with the removal of 50% of ear due to significant decrease of grains in the corn and the number of grains per square meter in spite of the increase of the weight of 1000-grain. The treatment with 50% removal of ear had the lowest rate and contribution of remobilization (9.9%) because of the sink restriction, but the treatment with the defoliation of the upper leaves of the ear had the highest rate and contribution of remobilization (39.31%) due to significant decrease of rate and contribution of photosynthesis (60.69%).In this experiment, the increase of plant density increased the grain yield significantly because of the increase of the grains per square meter and the weight of 1000-grain despite the decrease of grains per ear so that the density of 90000 plants per hectare had the highest grain yield by 886.33 g/m 2 . This treatment devoted the least contribution of photosynthesis (71.74%) and the most contribution of remobilization (28.26%) in the production of grain yield to itself due to close competition among the plants especially further shadowing of the leaves. The interactive effect of the factors showed that the treatment with the defoliation of upper leaves of the ear and with density of 90000 plants per hectare had the highest contribution of remobilization (43.37%) and the lowest contribution of photosynthesis (56.63%) in grain weight which indicated that the decreasing effect of removal of the upper leaves of the ear and the increase of plant density on photosynthesis through the decrease of leaf area and the increase of leaves shadowing.