Carpel weight, grain length and stabilized grain water content are physiological drivers of grain weight determination of wheat

Among the yield components, grain weight is considered a conservative trait whose determination is still beyond our complete understanding. Crop physiology uses a whole approach to study this complex trait, which can provide helpful information to plant breeders and molecular biologists. This study emphasizes the understanding of pre- and post-anthesis determinants of final grain weight. A field experiment was carried out in two growing seasons evaluating two wheat cultivars contrasting in grain weight potential. Carpel weight at pollination, grain dimensions, grain water, dry matter and volume dynamics were assessed. Among grain dimensions, grain length was the trait, which explained final grain weight (r2 = 0.78; P < 0.01 and r2 = 0.94; P < 0.001 for the 1st and 2nd season, respectively) and it was the first trait to stabilize after anthesis. Water content of grains stabilized little later and also showed a strong association with final grain weight (r2 = 0.93; P < 0.01 and r2 = 0.98; P < 0.01 for the 1st and 2nd season respectively). Most importantly, carpel weight at pollination showed a positive and linear association with final grain weight (r2 = 0.79, P < 0.01 and r2 = 0.86 P < 0.01 for the 1st and 2nd season, respectively) irrespective of the cultivar and grain position. In addition, positive associations were also found between grain volume, water content, grain length, and carpel weight at pollination. Therefore, the associations between pre- and post-anthesis traits found in this study support the hypothesis that grain weight is determined before anthesis and fruit tissues (i.e., pericarp in cereals and sunflower) set an upper limit to grain weight.

► Pre- and post-anthesis traits are physiological drivers of grain weight of wheat.
► Growth of maternal tissues (pericarp) is key in grain weight determination.
► Length is the main post-anthesis trait involved in final grain weight determination.