Genotypic differences in the agronomic performance of ratoon rice in a cool-temperate environment in central Japan

Context

The major challenge for the rice–ratoon-rice system in cool-temperate environments is to ensure high ratooning ability from stubbles after harvesting of main rice crops. The choice of locally adapted cultivars with high ratooning ability is crucial for this system.

Objective

We aimed at identifying modern ultrashort-duration cultivars with high ratoon rice yield in central Japan (35°N to 36°N), which represents the northern limit for growing a ratoon crop, and to elucidate the associated growth characteristics.

Methods

We evaluated 15 ultrashort-duration cultivars (13 japonica and 2 indica) in 2019, 8 (7 japonica and 1 indica) in 2020, and 3 (all japonica) in 2021 in the rice–ratoon-rice system in Tokyo, Japan.

Results

Ratoon rice yield was not negatively correlated with the main rice yield in any year. However, the tiller regeneration rate (the ratio of tiller number in the ratoon rice season to the panicle number in the main rice season) was strongly and significantly positively correlated with ratoon rice yield. The indica cultivars (‘TNAU6484’ and ‘ADT30’) had lower tiller regeneration rates and lower ratoon rice yield than the japonica cultivars. Two japonica cultivars (‘Akitakomachi’ and ‘Ichibanboshi’) had the highest tiller regeneration rate and the highest ratoon rice yield. The stem nonstructural carbohydrate concentration was positively correlated with ratoon bud length at the harvest of the main rice crop.

Conclusions

We found significant differences among cultivars in their ratooning ability. The nonstructural carbohydrates accumulated in stems at the harvest of the main rice crop might contribute to quicker and greater growth of ratoon rice crops in central Japan. Despite competition between stems and grains for photosynthate, this growth characteristic does not necessarily lower the yield of the main rice crop in ultrashort-duration japonica cultivars.

Implications

Two japonica cultivars were identified for the rice–ratoon-rice system in cool-temperate environments of mid-latitudes. Improvement of ratooning ability of japonica rice should be targeted by thorough evaluation of germplasms to increase ratoon rice yield in cool-temperate environments.