Genetic architecture of stay-green in maize

Delayed senescence in plants is often described as stay-green. Stay-green has been identified in several grain crops including maize, and has been associated with abiotic stress tolerance in some of these crops. In this study, several populations of maize were analyzed to find evidence of functional stay-green and define the genetic mechanisms causing this phenomenon. Functional stay-green was found within a set of temperate maize germplasm. The maize inbred lines Mo20W, LH123HT, and PHG35 exhibited different types of increased functional stay-green. Hybrids created from Mo20W also exhibited the functional stay-green phenotype. Two separate advanced backcross recombinant inbred line mapping populations were created with Mo20W as one parent and B73 and Mo17 as the recurrent parents. These populations were tested in three environments under drought and high temperature stress. The ratio vegetative index and photosystem II operating efficiency of the leaf above the earleaf was measured in both populations. Several quantitative trait loci for the ratio vegetative index and photosystem II operating efficiency were discovered on chromosomes one, two, three, four, six, and nine. Select lines from the mapping populations were used in a North Carolina II experiment with the B73 backross lines used as females and the Mo17 backcross lines used as males. Backcross lines were selected based on close phenotypic resemblance to the recurrent parents and elevated levels of late-season ratio vegetative index. Hybrids synthesized from the backross lines exhibited higher ratio vegetative index values during the grain fill period than hybrids synthesized from Mo17 and B73. Photosystem II operating efficiency was positively correlated with grain yield across environments. A subset of the maize nested association mapping population that was crossed to PHZ51 was also analyzed for stay-green in four environments in 2010. Joint linkage mapping discovered four quantitative trait loci across the 23 recombinant inbred families for the stay-green trait. The quantitative trait loci were discovered in families with parents from both temperate and tropical germplasm pools of maize. The timing of senescence and the cause of stay-green in maize is still unclear. The maize mutant pre1 exhibits a premature senescent phenotype and could be important for understanding the senescence process. A bulk segregant analysis strategy was combined with array based genotyping and deep sequencing platforms to locate the loci responsible for the phenotype of pre1. Several candidate genes are hypothesized. The results of these studies suggest that genetic diversity for functional stay-green in maize exists in both the temperate and tropical germplasm pools. The diversity for this trait could be exploited for increasing abiotic stress tolerance in maize