Genotypic variation in spike fertility traits and ovary size as determinants of floret and grain survival rate in wheat

Spike fertility traits are critical attributes for grain yield in wheat ( Triticum aestivum L.). Here, we examine the geno - typic variation in three important traits: maximum number of floret primordia, number of fertile florets, and number of grains. We determine their relationship in determining spike fertility in 30 genotypes grown under two contrast - ing conditions: field and greenhouse. The maximum number of floret primordia per spikelet (MFS), fertile florets per spikelet (FFS), and number of grains per spikelet (GS) not only exhibited large genotypic variation in both growth conditions and across all spikelet positions studied, but also displayed moderate levels of heritability. FFS was closely associated with floret survival and only weakly related to MFS. We also found that the post-anthesis process of grain set/abortion was important in determining genotypic variation in GS; an increase in GS was mainly associ - ated with improved grain survival. Ovary size at anthesis was associated with both floret survival (pre-anthesis) and grain survival (post-anthesis), and was thus believed to ‘connect’ the two traits. In this work, proximal florets (i.e. the first three florets from the base of a spikelet: F1, F2, and F3) produced fertile florets and set grains in most cases. The ovary size of more distal florets (F4 and beyond) seemed to act as a decisive factor for grain setting and effec - tively reflected pre-anthesis floret development. In both growth conditions, GS positively correlated with ovary size of florets in the distal position (F4), suggesting that assimilates allocated to distal florets may play a critical role in regulating grain set.We thank Guozheng Liu for help with statistical analyses, Ahmad Mohammad Alqudah for critically reading previous versions of the manu - script, Mechthild Pürschel for her excellent technical assistance, and Karin Lipfert and Heike Ernst for help in figure design. This study received finan - cial support from the Chinese Scholarship Council to ZG and from the EU-FP7 KBBE-2011–5 ‘ADAPTAWHEAT’ project number 289842 and the HEISENBERG Program of the German Research Foundation (DFG), grant no. SCHN 768/8-1 to TS