Physiological and Cytological Analyses of the Thousand-Grain Weight in ‘Zhongyan96-3’ Wheat

Wheat-yield improvement is pivotal for meeting the food demands of an increasing global population. Thousand-grain weight (TGW) is a main component of wheat grain yield, and the grain-filling rate (GFR) is a crucial trait that determines the grain weight. Here, we aimed to clarify the natural development of the excellent characteristics of faster GFR and greater TGW in ‘Zhongyan96-3’ (ZY96-3) wheat by observing grain-filling parameters, identifying grain histological features, and analyzing related gene expression levels. ZY96-3 has the strong advantages of early maturity, a fast GFR and high TGW than its parents ‘Guinong 19’ (GN19) and ‘Chinese Spring Wheat’ (CSW). Here, we found that ZY96-3 possessed a greater TGW than GN19 and CSW after 10 days post-anthesis during different grain developmental periods. The TGW was positively correlated with GFR (including the mean and maximum values) and the secondary grain-filling parameters of GFR, including the rapid and slight increase stages. Interestingly, the seed coat cells formed a compact layer in ZY96-3 later than in GN19 and CSW. Additionally, ZY96-3 possessed larger A-granules than GN19 and CSW by 16.27% and 38.83%, respectively. In particular, dynamic changes in starch-, grain size-, and protein-related gene expression levels were consistent with the dynamic TGW changes during grain developmental periods. Thus, our findings indicated that ZY96-3 possessed a greater TGW owing to larger GFR parameters and higher starch and protein biosynthesis capacities than GN19 and CSW; therefore ZY96-3 may be an important germplasm resource for wheat-yield improvement.