Ground Cover Supplement : GC Supplement - Managed environment facilities
6 Water productivity traits FIGURE 1 Visual difference in leaf area and size between high-vigour (left) and low-vigour (right) YitpiA lines typical of those in the MEFs. FIGURE 2 Change in leaf size with successive recurrent selections for early vigour: (left) low-vigour commercial variety AnnuelloA; (centre) more vigorous cycle 1 selection; and very vigorous cycle 4 selection (right). cv. AnnuelloA Cycle 1 vigour selection Cycle 4 vigour selection photos: Dr GurjEEt Gill, univErsity oF ADElAiDE, AnD MichAEl ZErnEr, sArDi table 2 impact of the early vigour trait on leaf area (50 days after sowing) and final biomass and grain yield at two sites in Western Australia. LAI@50DAS final biomass (g/m2) Grain yields (g/m2) Harvest index Wongan Hills 1999 (453mm) High vigour 0.37 678 337 0.49 Low vigour 0.32 573 293 0.49 ** ** ** ns Merredin 1999 (274mm) High vigour 0.39 634 266 0.41 Low vigour 0.30 574 247 0.43 ** ** ** ns ** = significantly different ns = not significant LAI @ 50 DAS = Leaf area index at 50 days after sowing many environmental factors can affect trait measurement so it is critical that assessment and validation of traits is done as close as possible to the realities of a grower’s paddock. FroM pAGE 4 eArly vigOur The inspiration to pursue the early vigour trait in wheat came from barley – the most vigorous winter cereal. To determine wheat’s capacity for greater vigour, CSIRO screened 5000 wheats collected from all over the world by measuring the size of the first two leaves (a ‘phenotype’ that can predict much of the variation in early vigour in winter cereals). Twenty-eight lines with high vigour emerged from the 5000 wheats, which were then crossed through a method known as ‘recurrent selection’ to bring together all the different vigour genes into a concentrated set of lines. These highly vigorous lines produce large, thick stems and wide leaves all the way up the stem and are about 10 centimetres taller than typical dwarf varieties (Figures 1 and 2). Developing the high-vigour lines took almost 20 years – highlighting that new traits can take a long time to develop before they are ready for assessment and use in breeding. Early vigour improves wheat’s ability to establish and grow more vigorously early in the season. The trait improves the ability of wheat roots to scavenge for water and nutrients while the shoots are more efficient at shading the ground, helping to conserve soil moisture and providing the crop with better competition against weeds. These characteristics are proving especially suited to southern and western growing regions, where as much as 70 per cent of rainfall is not available to the crop because it is lost through evaporation from the soil surface. Early vigour enables wheat to grow faster early in the season when the air is cooler and moist and when photosynthesis is more water-efficient. In this way, the plants convert more carbon dioxide to biomass while losing less water through the leaves (Table 2). During field trials it became apparent that the ‘Green Revolution’ genes used to reduce wheat’s stature (Rht1 and Rht2 genes) were antagonising the early vigour selection, acting like a handbrake on seedling vigour and leaf growth. As a result, CSIRO launched a search for alternative dwarfing genes that reduce stature without stunting early growth. It was one such gene that was used in CSIRO’s ‘vigorous wheats’. The researchers found that in addition to above-ground shoot vigour, the selection process also improved root vigour and the capacity for increased nutrient uptake (see page 14).
GC Supplement - Grain and Graze
GC Supplement - Root and crown diseases 2014