Source-sink relationships in maize grown in a cool-temperate area

Abstract

The objectives of this work were to: a), establish whether maize yield in Balcarce (Argentina 3745'LS; 5818'LO) is limited by the source of assimilates or by the number and size of the reproductive sinks; b), establish whether hybrids that differ in length of the growing cycle present differences in their source-sink relationships; c), de- termine to what extent the evolution of carbohydrate (CH) reserves in the plant is modified by different source-sink re- lationships. The experiment was conducted at Balcarce over a 2-year period with 2 hybrids (short season: SPS 240, long season: D2F11). The treatments consisted of 2 levels of source reduction (45 and 55% shading during the grain filling period, GFS), 2 levels of reproductive sink reduction (45 and 55% shading aroung flowering, FS) and an un- shaded control. The different shading treatments had a constant reduction of radiation with variable shading duration (30-38 days). The results indicate the existence of a colimitation by source of assimilates and reproductive sinks be- cause grain yield dropped similarly in response to shading during the flowering and the grain filling periods. FS re- duced grain number/unit area and slightly increased 1 000 kernel weight. GFS reduced 1 000 kernel weight, and to a lesser extent grain number/unit area. The study of dry matter and CH accumulation or remobilization in response to shading at the R3-R5 period, relative to those of the control treatment, was useful to indicate trends toward sink or source limitations. Relative to the control, shading at any period produced a decrease in stem CH content during the treatment period. During the post-shading period, the FS treatments presented a greater CH accumulation in stems than the control. This is explained by the decrease in reproductive sink number that produced a drop in their demand of CH and by the increased importance of the stem as an alternative sink for assimilates. GFS treatments produced a strong increase in CH remobilization rate from stem during the treatment period. The 2 hybrids did not show statisti- cally significant differences in their source-sink relationship. Nevertheless, a tendency toward a source limitation was evident in the long season hybrid.