QTL for stay-green traits in wheat in well-watered and water-limited environments

"Stay-green" plants retain green leaf area longer after flowering than senescent types. This can prolong carbon assimilation during grain filling, increasing yield, particularly under terminal drought stress. A population of doubled haploid wheats (Triticum aestivum L.) derived from a cross between stay-green SeriM82 and senescent Hartog was grown in eight environments with varying degrees of water limitation. The dynamics of normalised difference vegetative index (NDVI) was followed post-flowering to evaluate change in leaf greenness. Quantitative trait loci (QTL) were identified for components of stay-green including i) maximum NDVI (Nmax), ii) an indicator of the maximum rate of senescence (SR), iii) thermal time from flowering to commencement of senescence (OnS), iv) thermal time from flowering to mid-senescence (MidS), and v) the integral of NDVI from flowering to 1500 degrees Cd after flowering (SGint). Genetic regions associated with QTL for stay-green traits were identified (i) in both wet and dry environments on chromosomes 4A, 4B, 4D (constitutive stay-green); (ii) primarily in wetter environments on 2A and (iii) primarily in dryer environments on 5B. Other regions associated with QTL for stay-green were identified on 3B and 7B in a mixture of environment types. In some environments, stay-green QTL co-located with QTL for seminal root angle, seedling root number and/or for yield. Other stay green QTL were co-located with yield but not seminal root angle and seedling root number. This suggests genetic regions associated with seminal root angle and seedling root number are not solely responsible for the high yielding, stay-green phenotype. Selection for stay-green traits will increase the rate of genetic progress for adaptation of wheat to both well-watered and water-limited environments.