Difference of flowering and seed setting among the flower clusters at differents positions in a buckwheat plant (Fagopyrum esculentum Moench)

The experiment was conducted in Meijo University, Nagoya, Japan, to evaluate the difference of flowering and seed setting among the flower clusters at different positions in a buckwheat plant (Fagopyrum esculentum Moench). The seeds of the summer ecotype buckwheat cultivar, Shinanonatsusoba, were sown in 1/5000 a pots fertilized by 5 g of the compound fertilizer (N, P2O5 and K2O content were 15%, 15% and 10% each) on 18 May in 2002. The number of cymes, flowers and seeds on every flower-cluster of the main stem and every branch were counted at harvest. On the main stem, the lowest 4 clusters had the maximum number of flowers, and the upper cluster had a smaller number of flowers. On the lateral branches, 4th cluster at acropetal position had the maximum number of flowers and the upper and the lower clusters from that had a smaller number of flowers. The maximum number of flowers per cluster on the main stem and the primary branches was 45 to 50, that on the secondary branches was 31, that on the tertiary branches was 13, decreasing with the elevation of the order of the branches. The difference of the number of cymes in the flower clusters at different positions on the main stem and the lateral branches showed the same tendency as that of the number of flowers. Calculating with the number of flowers and cymes per cluster, the number of flowers per cyme was 3 to 4 in the clusters on the main stem and the primary branches, 2 to 3 on the secondary branches, and 1 to 2 on the tertiary branches. The number of seeds per cluster showed the maximum in the 3rd to 6th clusters on the main stem, in the 2nd to 6th clusters on the primary branches, in the 2nd to 3rd clusters on the secondary branches, and the upper and the lower clusters from them had a smaller number of seeds. The number of seeds was below one in the clusters on the tertiary branches. The maximum number of seeds per cluster was 6.6 in the clusters on the main stem, 5.9 on the primary branches, and 4.3 on the secondary branches, decreasing with the elevation of the order of the branches. As the decrease in the number of seeds with the elevation of the order of branches and increasing distance of the cluster positions which showed the maximum number on a stem was greater than in the decrease in the number of flowers, the seed-set ratio decreased with them. The seed set ratio was greater, which was 12% to 15%, at 3rd to 11th clusters on the main stem, at 2nd to 6th clusters on the primary branches, at 2nd to 3rd clusters on the secondary branches than the other clusters. In the clusters except the 1st and 2nd clusters on the main stem, the number of flowers have positive correlation with the number of seeds (R**2 = 0.9099), although the 1st and 2nd clusters showed extremely low number of seeds. The regression line between the number of flowers (x) and seeds (y) was y = 0.1623x - 1.6311. As the intersection with x-axis was 10.01, it was shown also from the equation that the seed-set ratio per cluster was not constant, changed with the position of the clusters in a plant, and decreased with decreasing number of flowers per cluster.