Abstract
Using the bread wheat cultivar ‘Minaminokaori’ from Northern Kyushu, we examined the effect of climatic conditions as well as yield and yield component, on the grain protein content. We found that the protein content was negatively correlated with yield and 1000-kernel weight and positively correlated with the duration of sunshine during the ripening period. In the partial correlation analysis of grain protein content wtih 1000-kernel weight, yield and the duration of sunshine, significant correlation was observed only with 1000-kernel weight. These results suggest that the protein content was strongly affected by 1000-kernel weight and that the main factor of fluctuation in the protein content was a change in 1000-kernel weight, which was dependent on the duration of sunshine. Multiple regression analysis demonstrated that the duration of sunshine during the ripening period of wheat (x1) and the amount of nitrogen topdressing at anthesis (x2) were independent variables that were significantly correlated with grain protein content (y), as follows: y=12.40+0.433x1−0.00726x2 (n=18, R2=0.563 and p \<0.01).
