Selection for Seed Growth Characteristics: Effect on Leaf Senescence in Maize

Abstract

Increasing the time that a crop canopy maintains an active photosynthetic apparatus could potentially increase economic yield. The objective of this study was to determine the effect of phenotypic recurrent selection for seed dry matter accumulation rate (DMAR) and seed effective filling period (EFP) on leaf senescence in selections of a maize (Zea mays L.) synthetic population, KyWVS. Selection groups included factorial combinations of high, same (same as Cycle 0), and low DMAR; and long, same, and short EFP. Cycles 3 and 5 were evaluated in the field in 1985 and 1986, respectively. Due to minimal interaction between DMAR and EFP with regard to senescence traits, each DMAR group was averaged across EFP levels and vice versa. Both DMAR and EFP were altered by selection, but the date of pollination remained relatively constant. As indicated by changes in chlorophyll, carbon dioxide exchange rate (CER), and photosynthetic enzyme activities during the grain filling period, selection for DMAR did not affect leaf senescence for either cycle. For both cycles, selection for short EFP led to earlier leaf senescence. For Cycle 5, long EFP genotypes maintained higher CER and higher levels of photosynthetic components at later sampling dates compared with the same EFP genotypes. In all cases differences in senescence were due to the time of completion, and not the time of initiation, of senescence. The results indicated that large genetic changes in DMAR can occur without any influence on leaf senescence. For this maize population, however, changes in EFP were closely associated with changes in leaf senescence characteristics.