Effect of source restriction on yield and physiological indexes of corn (Zea mays L.) hybrid KSC704 in water deficit stress

The effect of source restriction on yield and physiological indexes of corn was studied in Varamin، Iran، during 2007-2008 and 2008-2009 growing seasons. The experiment was carried out in a complete randomized block design with split plot arrangement. The irrigation regimes were allotted to main plots. The intensity and time of defoliation combination were allotted to sub plots. In moderate irrigation plots، the irrigation was done when the soil water content reached to 75% of available water content. In under stress plots، two short periods of water-holding were applied at V8 and tasseling growth stages. Defoliation treatments were consisted of: Control، cutting 1:3 of leaves at V8، cutting of 2:3 of leaves at V8، Cutting 1:3 of leaves at tasseling and cutting 2:3 of leaves at tasseling. This result showed that remobilization efficiency of stem reserves for grain yield is mostly related to sink capacity than source strength. Under moderate irrigation، later or more intensity defoliation decreased the RGR. While under drought stress، cutting the 2/3 of leaves did not decrease the relative growth rate. The improved NAR due to defoliation caused to compensate the decreased leaf area. So، late and more intensity defoliation could not decrease the CGR. The grain yield of 8. 9 t ha-1 was attained by moderate irrigation which was a results of 16. 4% and 27. 3% greater biomass and harvest index compared to the water stress conditions. This indicates that pot-anthesis water deficiency decreased the sink capacity more than source strength. The results showed that under water deficiency and source strength restriction، the stem reserves play an important role in grains filling process. But under high soil water supply، these reserves will be needed when the source strength is limited after flowering stage. Under moderate irrigation، there were not significant differences among defoliation treatment for remobilization efficiency of reserves from stem to grains.