Genetic analysis of productive tiller number and green leaf duration under late-seasoned heat and drought stress environment in spring wheat
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Climate change is affecting the growing environment for spring wheat (Triticum aestivum L. em. Thell) in the northern Great Plains, challenging breeders to identify traits and genes that will allow reliable grain yield under drought and heat stress conditions. The first objective of this study was to evaluate the genetic basis of productive tiller number (PTN) and its relationship to economic traits under a wide range of environments. Correlation of PTN with economic traits was determined using three recombinant inbred line populations. Quantitative trait loci (QTL) analysis was conducted with a mapping population generated from a cross between Reeder and Conan. Our results showed a consistent positive correlation between PTN and grain yield under drought and heat stress conditions as well as well-watered conditions across three spring wheat populations. The major stable QTL, QTn.mst-6B, was consistent across environments and populations, and the positive allele from Reeder increased grain yield. The second objective of this study was to evaluate the genetic basis of green leaf duration (GLDAH) which has been reported as a drought and heat stress resistant trait in several crops. Additionally, the relationship of GLDAH to agronomic traits and a root trait was assessed using the Reeder/Conan population. Correlation analysis showed a positive relationship between GLDAH and test weight, seed weight, seed diameter under heat and drought stress conditions but not cool, well-watered conditions. In contrast, GLDAH had a neutral relationship with grain yield under the stress conditions, but showed negative correlation under well-watered conditions. Major QTL QGfd.mst-4A had a consistent effect under hot, dry conditions for the populations. The Reeder allele of QGfd.mst-4A resulted in longer GLDAH and also increased the amount of xylem exudate, indicating higher root mass and/or activity. These results suggested that i) QTn.mst-6B may be useful for improvement of spring wheat production under a wide range of environment and ii) QGfd.mst-4A may contribute to heat and drought stress resistance potentially through root function, but may negatively affect grain yield under well-watered conditions in the northern Great Plains of North America and similar environments.