Is the source-sink ratio at anthesis a driver to avoid yield reductions caused by late foliar disease in wheat?

Abstract

Late foliar diseases that appear during the grain filling period reduce radiation interception/absorption decreasing assimilation supply, inducing reductions in grain weight and yield. We hypothesize that crops with higher source-sink ratio (established immediately after anthesis) could have more capacity to avoid reductions in terms of yield, at same level of foliar disease. Thus, it is speculated that the yield reduction caused by late foliar diseases is a complex interaction between current photosynthesis availability per grain and the remobilization capacity according to the sink size determined demand. The objective of the present study was to analyze physiological attributes associated with yield reduction caused by late foliar diseases in wheat when source-sink ratio is modified. Experiments were carried out during two consecutive years (2009 and 2010) applying a combination of (i) two disease levels (i.e. healthy and diseased plots), (ii) two different levels of incident radiation applied immediately previous to anthesis, to reduce grain number exclusively (i.e. non-shaded and shaded plots) and (iii) source-sink manipulations during grain filling (i.e. control and trimmed spikes). Shading during pre-anthesis significantly reduced grain number and then, the source-sink ratio was modified between non-shaded and shaded plots, being two fold higher in non-shaded than in shaded plots. In both years and shading treatments, diseases appeared after anthesis, the diseased plots showing higher values of non-green leaf area than healthy plots, in both shaded and non-shaded treatments. Late foliar diseases significantly reduced grain yield in both, 2009 and 2010 mainly due to reductions in grain weight. There was significant interaction in the crop performance to foliar diseases between shading treatments and growing seasons. While the reduction caused by late foliar diseases was similar between shading treatments during 2009, in 2010 significant differences were observed, being reductions lower in shaded than in non-shaded plots. The source-sink manipulation treatment confirmed these responses, as there were no significant differences in grain weight of trimmed spikes between healthy and diseased crops, confirming that the grain weight reduction due to late foliar diseases is driven by the source sink balance.