Dual-purpose crops for grazing and grain production can be highly profitable, provided grazing does not cause significant loss of grain yield. In many plants, defoliation causes a transient reduction in the allocation of resources to stem and root growth and remobilisation of soluble resources to re-establish leaf area rapidly. In Australia, the usual autumn and winter period of defoliation for grazed crops, May–July, coincides with a phase of near-linear root depth penetration in ungrazed crops, and the crop recovery period after grazing occurs during stem elongation, when grain number and yield potential are determined. However, few studies have investigated the potential impact of crop defoliation through grazing on root growth of wheat in the field. We investigated the effect of defoliation by grazing or shoot removal on the root growth of wheat crops in four field experiments in south-eastern Australia in which the timing, frequency and intensity of defoliation varied. Despite significant impacts of defoliation on aboveground biomass (50–90% reduction) and grain yield (10–43% reduction) in all experiments, we found little evidence of effects on the rate of root penetration or final rooting depth. A notable exception was observed in one experiment when defoliation commenced very early (four-leaf stage, Zadoks growth stage Z14) in a repeatedly defoliated crop, reducing rooting depth from 1.65 to 1.35 m. The only other measured impact on roots was in an early-sown winter wheat crop grazed by sheep for 3 months (6 June–3 September), in which root length density was reduced by ~50% in surface layers above 1.0 m depth, but there was no impact on maximum root depth or root length density at 1.0–2.0 m depth. Our results suggest that grazing has little impact on the rooting depth of wheat unless it occurs very early and repeatedly, when plants are allocating significant resources to establish the primary roots. However, there may be some reduction in the density of roots in surface layers during recovery after long-term grazing, presumably associated with reduced proliferation of the nodal root system. We conclude that most significant yield penalties due to grazing relate to impacts on the assimilation of aboveground resources, rather than to reduced water or nutrient acquisition by roots.

Deeper plant root systems are desired for improved water and nitrogen uptake in leaching environments. However, phenotyping for deep roots requires methods that enable plants to develop deep roots under realistic conditions. Winter cereals raise further complications as early growth occurs under low light and temperature during autumn and winterconditions not met in standard glasshouse facilities. This study used tube rhizotrons of 2 m length, positioned outdoor under a rainout shelter to screen for depth penetration rates (DPR) of roots. Rooting depths of 1 to 1.5 m were achieved with 23 widely grown North European winter wheat cultivars in two autumn/winter and two summer experiments and nine of the cultivars were represented in two or more experiments. Heritability of DPR of roots was only consistent in autumn/winter experiments (27 %) signifying the importance of phenotyping in relevant seasons and environments. Depth penetration rate of roots varied significantly within the tested cultivars, from 1.39 (±0.35) mm°C-1 day-1 for cv. Tuareg to 2.07 (±0.34) mm°C-1 day-1, for cv. Mercedes. This study documented consistent differences of DPR among North-European winter wheat cultivars in long tube rhizotrons under semi-natural conditions, which may form part of future phenotyping facilities for deep rooting traits.

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The MS imaging system is a rapid method for the separation of live and dead cocoons of B. curculionis. This study shows the potential of developing an MS imaging system to facilitate sorting of live and dead cocoons and optimize augmentative control of Hypera weevil pests. © 2018 Society of Chemical Industry.

Back to Main Page 1. Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 2 Given name: [Nanna Karkov] Last name [Ytting]. Also, kindly confirm the details in the metadata are correct.