2007 Volume 76 Issue 2 Pages 245-252
The relationship between drought resistance and deep root system was examined using eight Japanese upland rice and one lowland rice variety with medium to late maturing cultivated in the upland field for six cropping seasons. The number and thickness of roots at each depth were observed by eye by the excavation method in 1994 to 1996. The root length and weight at each soil depth were measured by the monolith method in 1996, and by the core sampling method in 1998, 2001 and 2002. A varietal difference was observed in root growth through six cropping seasons. In particular, a marked difference was observed in root density in the soil layer deeper than 30 cm from soil surface. Drought resistant variety, Yumenohatamochi stably showed a high root density in a deeper soil layer. On the other hand, root density of a susceptible variety, Mizuhatamochi, was low. Therefore, it was concluded that root growth in a deeper soil layer had a close relationship with drought resistance. Yumenohatamochi, Rikuto-norin-mochi 26 and Mizuhatamochi were selected as standard varieties of 'deep','slightly deep' and 'shallow' rooting, respectively. The observed root density in the deep soil layer examined by the monolith method and the core sampling method showed a significant positive relationship with that examined by the excavation method. Therefore, the core sampling method was considered to be a practicable and reliable collection method of roots in drought resistance breeding of upland rice.
