Ground Cover Supplement : GC Supplement - Managed environment facilities
14 Early vigour early vigour avoids drought stress new research is investigating whether high early vigour can help dry-sown wheat crops to overcome early season water deficits by dr bob french and dr Jairo palta hIgh-vIgour whEats can maintain good root and shoot growth under early season drought stress and recover more quickly with follow-up rain than low- vigour wheats, according to recent research at the Managed Environment facility (MEf) in Merredin, western australia. using a CsIro-developed wheat population ranging from high to low early vigour, the research indicates that high early vigour can help wheat overcome early season drought stress while also enabling the crop to out-compete weeds. although the research is in its infancy, it could lead to the breeding of higher- vigour wheats to cope with the increasing incidence of early season droughts. the CsIro high-vigour wheats have larger embryos, giving their first few leaves more surface area. this enables the wheats to cover the ground more quickly, increasing the amount of soil water that is converted to leaf and root biomass rather than lost through evaporation. along with the CsIro population, other wheat and barley cultivars and advanced breeding lines are also being screened for their ability to establish rapidly and evenly in drying seedbeds and to survive early water deficit and maintain high productivity. Importantly, the screening is occurring under field conditions and will therefore be directly applicable to the water deficits experienced in commercial fields. two common types of early season drought are being simulated in the trials. Crops are either sown into dry soil with a range of follow-up ‘rain’ (irrigation treatments) ranging from five to 55 millimetres about a week after sowing, or are sown into moist soil followed by rain exclusion using rain shelters for six to eight weeks. Each drought treatment is being compared to irrigated (unstressed) cereals. the impact of the two early season drought types on seedling emergence and survival, early biomass, tiller numbers, and heading and flowering dates are being recorded for each treatment. sEEDlinG EMErGEncE and SurvIval Preliminary results indicate that the type of water deficits commonly experienced in southern australia following establishment are rarely severe enough to cause crop death but the sensitivity of seedling establishment to water deficit varies between genotypes (figure 1). Early vigour could be influencing this sensitivity, but further research is required to confirm this. early vIgour and drought type results from a 2013 trial show that the early vigour trait is more important in environments experiencing early drought stress than in unstressed or late- stressed growing seasons (figure 2). root vIgour the most promising high-vigour lines were investigated further under controlled conditions to monitor their root growth during and after drought stress. four wyalkatchem A - derived lines (two with high early vigour and two with low early vigour) were grown along with wyalkatchem A in specialised rhizo-boxes, carefully filled, layer by layer, to a depth of one metre with soil collected from an area close to the MEf site at Merredin. to simulate field conditions, the lines were sown into dry soil and five days later the equivalent of 20mm of rainfall was supplied to the soil, with no follow-up watering for the next 32 days (the post-sowing ‘drought’ period). after 32 days, water was supplied and the one-metre soil profile maintained close to field capacity. root growth and proliferation were mapped each week, with leaf area and shoot biomass measured at the end of the experiment. the simulated 20mm ‘rainfall’ after sowing penetrated and wet the top 10 to 11 centimetres of the soil profile, generating an initial volumetric soil water content of about 24 per cent. roots of all four lines grew in the wet top layer of the soil profile, but the root growth of one of the high-vigour lines (w090913) was significantly faster than that of the other lines. seventy hours after the simulated 20mm rainfall, the root extension down the soil profile of w090913 was 10 to 11cm, about double that of the wyalkatchem A control at 5.3cm (figure 3). the 32-day ‘drought’ following emergence reduced root growth of the high- vigour line w090913 less (77.4 per cent) than the remaining lines w011206, w110905 and w260310 (83.4 to 86.5 per cent). photo:CSIro 14 The contrast in growth between two wheat lines differing in early vigour: the low early vigour wheat variety Axe A (left) and a high early vigour CSIRO line (right). This photograph was taken about six weeks after water stress was relieved and demonstrates the ability of the high early vigour line (right) to recover from and tolerate early drought stress.
GC Supplement - Grain and Graze
GC Supplement - Root and crown diseases 2014