Yield impact of source-sink-regulated senescence in hybrid maize and genetic architecture in exPVP inbreds

Prior genetic studies on source-sink-regulated senescence in maize have characterized some genes associated with the trait, but the impact on yield is unknown and the molecular understanding of this trait is still in its infancy. We phenotyped source-sink-regulated senescence in a commercial maize exPVP inbred population and assessed its correlation with yield and other commercially relevant agronomic traits in testcrosses under field conditions. Genome-wide association studies were conducted in both inbred and F1 hybrid populations. The effect of most significant alleles for senescence regulation in inbred germplasm was compared with their effect on yield in the F1 hybrids to investigate genetic co-regulation. Source-sink-regulated senescence of inbred parents was correlated with the yield of intra-family hybrids but was not generally correlated with the yield of hybrids made from crosses between two heterotic groups. Stronger senescence response was positively correlated with increased kernel numbers. Several genetic loci were identified as highly significant, including loci on chromosomes 1 and 4, which overlap kernel trait hotspots from previous studies. Single factor testing of DELLA mutants supports the conclusion that the GA-DELLA signaling pathway attenuates the senescence response to sink disruption in maize. The genetic basis of source-sink-regulated senescence may have contributed to evolutionary fitness in inbred lines through increased kernel numbers but are not strong drivers of yield in the modern F1 hybrids. This could permit selection of loci regulating senescence for inbred improvement without affecting yield in commercial hybrid breeding.