Abstract
Varietal differences harvest index (HI) and yield (Y) were examined using 60 Japanese varieties (J group) and 20 high-yielding varieties bred in Asian countries (H group). HI varied from 36.8% to 53.4%. Mean values of HI were 43.5% in the J group and 48.8% in the H group. Y ranged form 22.6g/plant to 40.0g/plant. The mean value of Y in the J group was 27.8g/plant, and that in the H grouo was 34.1g/plant. A significant positive correlation was found between HI and Y in the H group, but the correlation was not significant in the J group. There was a significant negative correlation between HI and total dry weight at the maturing time (W2) in the J group, but the correlation was not significant in the H group. The relationship between HI and dry matter production was examined by dividing HI into the following three components, based on the number of spikelets (N) and total dry weight at the heading time (W1), and W2. HI=Y/W2=[W1/W2]×[N/W1]×[Y/N] HI showed a negative correlation with W1/W2 in both groups. HI also had a positive correlation with N/W1 in the J group and with Y/N in the H group. W1/W2, N/W1 and Y/N are presumed to be indicators of the balance of dry matter production around heading time, the efficiency of spikelet production and the ripening ability, respectively. Therefore, these results suggest that varieties with relatively higher dry matter productivity after heading have higher HI in rice. Furthermore, HI was assumed to be affected by the efficiency of spikelet production in the J group and by the ripening ability in the H group.
