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Alan Bowring - Post-anthesis contribution of leaves and stem to wheat yield in the northern cropping region of New South Wales
In Australia, the current industry used contribution values for various plant components such as leaves, stems and heads to grain yield in wheat have been based on estimates which originate from north-western Europe. These contribution values often form the basis of foliar disease management strategies. A number of studies have been conducted assessing these relative values using a variety of methods but limited studies have been conducted of a field based nature in the northern cropping region of NSW.
In the 2008 and 2009, three trials investigated the contribution of the flag leaf, penultimate leaf and stem for contribution to grain yield in the period from anthesis to maturity. Methods of assessment included defoliation of leaves and desiccation of leaf tissue with a solution of potassium iodide. Assessment of the remobilisation of stem assimilate in the form water soluble carbohydrate (WSC) was also conducted. Defoliation methods were considered to alter the radiation interception properties of the canopy, potentially leading to compensatory adjustment of other components. Grain yield differed significantly between treatments for both years. The average contribution of the flag leaf to grain yield was found to be 23%, while the penultimate leaf was not assessed due to treatment structure. Although WSC was not significantly affected by treatment, it was found to contribute between 16-21% of the final grain yield. Grain number differed significantly across all trials.
Due to the early anthesis treatment timing, reduction in grain yield was thought to be a response to reduction in the source capacity of the plant (leaf loss), leading to a corresponding reduction in sink size (grain number) through floret loss at fertilisation or cell division. Contribution values widely differed from the current values commonly used by industry. This was not surprising given the vastly different environment and varieties utilised in northern NSW compared to north-western Europe. This study forms a preliminary basis for investigation of component contribution values for wheat yield in the northern grains region of Australia.