Source and Sink Limitations on Grain Yield in Modern Corn Hybrids.
Mark E. Westgate and Lucas Borras. Iowa State University, 1577 Agronomy Hall, Ames, IA 50011-1010
A dramatic decrease in leaf area associated with defoliation injury alters the balance between source capacity and sink strength. Grain yield responses to such changes in assimilate availability imposed during different phenological stages have provided clear evidence that crops experience periods during the growing cycle when yield is mainly limited by source capacity, sink strength, or co-limited by both. The so called ‘critical period’ when yield is strongly source limited, has been reasonably well established for most major crops. In maize, this period is known to coincide with flowering, when the number of kernels is being set. As such, yield variation in maize is more often related to the number of seeds formed per unit area. And genotypic sensitivity to unfavorable environmental conditions has been ascribed to reductions in source capacity and biomass partitioning around flowering. Likewise, decreases in assimilate availability per growing kernel during grain-filling period promote large reductions final kernel weight. Yet similar increases in assimilate supply during this stage of development have little impact on final kernel weight; a clear indication of a limitation in sink capacity. We have shown that kernel water relations can be used to predict kernel sink capacity and assess the potential for continued grain filling after maximum water content has been achieved. We will show how this new water relations model can be used to normalize grain development across environments, genotypes, and even species. Its application for assessing source/sink limitations for grain filling under stressful conditions, such as defoliation, will be presented.