Abstract
A stay-green phenotype enables crops to retain green leaves longer after anthesis compared with senescent types, potentially improving yield. Measuring the normalized difference vegetative index (NDVI) during the whole senescence period allows quantification of component stay-green traits contributing to a stay-green phenotype. These objective and standardized traits can be compared across genotypes and environments. Traits examined include maximum NDVI near anthesis (Nmax), senescence rate (SR), a trait integrating senescence (SGint), plus time from anthesis to onset (OnS), mid-point (MidS), and near completion (EndS) of senescence. The correlation between stay-green traits and yield was studied in eight contrasting environments ranging from well watered to severely water limited. Environments were each classified into one of the four major drought environment types (ETs) previously identified for the Australian wheat cropping system. SGint, OnS, and MidS tended to have higher values in higher yielding environments for a given genotype, as well as for higher yielding genotypes within a given environment. Correlation between specific stay-green traits and yield varied with ET. In the studied population, SGint, OnS, and MidS strongly correlated with yield in three of the four ETs which included well-watered environments (0.43-0.86), but less so in environments with only moderate water-stress after anthesis (-0.03 to 0.31). In contrast, Nmax was most highly correlated with yield under moderate post-anthesis water stress (0.31-0.43). Selection for particular stay-green traits, combinations of traits, and/or molecular markers associated with the traits could enhance genetic progress toward stay-green wheats with higher, more stable yield in both well-watered and water-limited conditions.
Highlights
Developing cultivars with superior adaptation to water- to changes in the yield rankings of genotypes in different limited environments has been impeded by complex inter- water-limited environments (Cooper et al, 2001; Richards actions between genotype and environment (G×E), leading et al, 2002)
For crops at GAT11rf and KTP11rf, water deficit built up to reach a maximum near or following anthesis, but this stress was relieved by rainfall soon thereafter, allowing grain filling to finish with little water-stress, corresponding to ET2 (Fig. 1)
We found little correlation between yield and leaf greenness (NDVI) near the completion of senescence in most environments (Christopher et al, 2014), since in the north eastern Australian target population of environments (TPE), the leaf canopy of wheat is usually fully senesced at the time of spike maturity (Christopher et al, 2008)
Summary
Developing cultivars with superior adaptation to water- to changes in the yield rankings of genotypes in different limited environments has been impeded by complex inter- water-limited environments (Cooper et al, 2001; Richards actions between genotype and environment (G×E), leading et al, 2002). The stay-green phenotype has been linked to improved yield stability in a number of cereal crop species including wheat and sorghum, under terminal drought stress (recently reviewed in Gregersen et al, 2013). Selection for stay-green has been targeted to improve crop adaptation to water-stressed environments in a number of crops including sorghum and wheat (Christopher et al, 2008, 2014; Borrell et al, 2012, 2014a, b; Jordan et al, 2012; Lopes and Reynolds, 2012; Gregersen et al, 2013)
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