The effect of source-sink ratio (i.e., the ability of the leaves to produce photosynthate versus the capacity of the grain to accommodate the assimilates) on dry matter accumulation and leaf senescence during the grain filling period of two short-season maize (Zea mays L.) hybrids was investigated in 1979 and 1980. Source-sink ratio of the maize hybrids was altered by ear removal at midsilking and at 3 wk after midsilking; by partial fertilization of the topmost ear so that treatment ears contained approximately 50% of kernel number of the control; and by removal of all leaf blades but that of the ear leaf at 2 wk after midsilking. Crop growth rate during the period from 3–5 wk after midsilking was reduced by 30% for the partly fertilized treatment and by 60% for both ear removal treatments. During the period from 5 to 7 wk after midsilking, the treatment-by-hybrid interaction for crop growth rate reflected different patterns of leaf senescence. In one hybrid, treatments which caused reductions in sink size delayed leaf senescence and increased the crop growth during the 5 to 7-wk postsilking interval, relative to the control. The reverse was evident for the other hybrid. Partial defoliation tended to cause the remaining ear leaf to senescence slightly earlier than in the control. Apparently two types of leaf senescence occurred: senescence due to assimilate starvation, and senescence due to excessive assimilate accumulation. The former caused by excessively low source-sink ratio and the latter caused by excessively high source-sink ratio. These results indicate that a delicate balance exists between sink and source during the grain-filling period of maize, and that disturbance of this balance can cause substantial yield reductions, plus an acceleration of leaf senescence and maturation processes.
Effects of pollination-prevention on leaf senescence and post-silking nitrogen accumulation and remobilization in maize hybrids released in the past four decades in China
