Identifying factors that determine kernel number in wheat

Understanding Variation in kernel number per unit area (KNO) is of major importance in understanding yield and in identifying opportunities to increase yield potential. Factors that determine KNO should therefore be identified considering wide ranges in both crop and environmental conditions. Several field experiments with various spring wheat cultivars were conducted over three years in Mexico. Wide ranges in crop and environmental conditions were obtained by varying N application rates and timing and by different planting dates and locations. Crop development from emergence (DC10) to physiological maturity (DC90) was divided in three phases, with the intermediate phase II ranging approximately from early booting (DC40) to final anthesis (DC70). A photothermal quotient (PTQ) during phase II failed to explain the variation in KNO. Biomass at anthesis explained 72% of the variance, but could not explain some deviant situations and the relation was strongly cultivar specific. Biomass accumulation during phase II more accurately (80%) explained the deviant situations, except one particular location, and cultivar differences became even more pronounced. At this location KNO was also well explained by non-grain spike weight at a week from anthesis, with a constant number of kernels per unit spike dry matter, while differences among cultivars tended to disappear. Factors that are identified to determine KNO are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.