Abstract
We investigated seedling establishment, germination at 15ºC and early growth of seedlings in 15ºC water in 52 varieties. Field experiments were conducted in May and July. Seeds were sown 5 mm in depth in plastic nursery boxes and the boxes were placed in a submerged paddy field. The plants were continuously irrigated with 14ºC water for 9 days after the appearance of the first leaf in the July trial. Highly significant varietal differences in the percentage of seedling establishment (%ES) were observed in both trials. Several foreign cultivars showed higher %ES than “Iburiwase” that showed the highest %ES among Hokkaido varieties. The %ES was divided into three components: percentage of seedling emergence (EM), percentage of first leaf elongation in the emerged seedlings (FLE/EM) and percentage of establishment of the first leaf elongated seedlings (ES/FLE). The contribution rate of each component was evaluated by multiple regression analysis. The contribution of EM was the highest in the May trial, while that of ES/FLE was also high in the July trial. Significant positive correlations were observed between the %ES and the early growth characters of seedlings, such as second leaf length, shoot length and maximum root length, while the correlation between germination coefficient and %ES was low. The present results indicate that several foreign cultivars with high %ES are useful as breeding materials for direct-seeding and also we need to pay more attention to the early growth of seedlings rather than germination.
