The relationship between grain and ovary size in wheat: An analysis of contrasting grain weight cultivars under different growing conditions

Abstract Grain size correlates with ovary size at anthesis, across cultivars, spike position, temperature changes, and source-sink manipulations, and it has been suggested that this correlation may be a functional (i.e. causal) one. To investigate possible causality, this relationship was studied across different agronomical/environmental conditions, such as nitrogen fertilization levels, plant densities, and growing seasons (i.e. 2014 and 2015), in two wheat cultivars with different grain size. Grain volume correlated with ovary volume within cultivars, across the whole dataset. However, ovary volume varied more than 10-fold, while grain volume varied only about 0.5-fold. In 2014, grains were only slightly smaller or, in the most fertilized treatments, not statistically different than in 2015, despite 3–4-fold smaller ovaries. Even within 2015 data, the various treatments resulted in large variations in ovary volume, but grain volume was unaffected. The results indicated that ovary size varies significantly with agronomical/environmental conditions (i.e., nitrogen and density treatments, and season), while grain size is more conservative within cultivars. The cultivar's typical grain size can be achieved, if resources are not limiting, independent of large variations in ovary size.