Do wheat breeders have suitable genetic variation to overcome short coleoptiles and poor establishment in the warmer soils of future climates?

Increases in air and soil temperatures will impact cereal growth and reduce crop yields. Little is known about how increasing temperatures will impact seedling growth and crop establishment. Climate forecast models predict that by 2060, mean and maximum air temperatures in the Australian wheatbelt will increase by 2-4°C during the March-June sowing period, and particularly at lower latitudes. Concomitant increases in soil temperature will shorten coleoptile length to reduce crop establishment, particularly where deep sowing to access sub-surface moisture. Mean coleoptile length was reduced in commercial wheat (Triticum aestivum L.) germplasm with increasing soil temperature (106mm and 51mm at 15°C and 31°C, respectively). Coleoptile lengths of modern semidwarf varieties were significantly (P<0.01) shorter than those of older tall wheats at 15°C (95mm and 135mm) and 31°C (46mm and 70mm). A 12-parent diallel indicated large additive and small non-maternal genetic effects for coleoptile length at 15°C and 27°C. Large genotype rank changes for coleoptile length across temperatures (rs=0.37, P<0.05) contributed to smaller entry-mean heritabilities (0.41-0.67) to reduce confidence in selection for long-coleoptile genotypes across contrasting temperatures. General combining ability effects were strongly correlated across temperatures (rp=0.81, P < 0.01), indicating the potential of some donors in identification of progeny with consistently longer coleoptiles. Warmer soils in future will contribute to poor establishment and crop failure, particularly with deep-sown semidwarf wheat. Breeding long-coleoptile genotypes with improved performance will require targeted selection at warmer temperatures in populations incorporating novel sources of reduced height and greater coleoptile length.