Genetic improvements for high yield and low soil nitrogen tolerance in rice ( Oryza Sativa L.) under a cold environment

Abstract

Eight rice cultivars released in 1905, 1919, 1941, 1954, 1971, 1984, 1987 and 1988 were investigated to identify the traits that contributed to high yield and low soil nitrogen tolerance breeding under cold environment. They were grown in fields at three different nitrogen (N) fertilizer treatments, 0, 6 and 12 g N m −2 (0 N, 6 N and 12 N) in Sapporo, Northern Japan, in 2001 and 2002. All cultivars increased their grain yield (GY) with the increase in soil N availability, and better response to N was observed in modern cultivars released during 1984–1988 compared to old ones (1905–1954). Irrespective of N treatments, the modern cultivars showed better GY than the older ones. Absolute genetic gain was 2.15 or 2.94 g m −2 year −1 at 6 N and 12 N. Under 0 N treatment, although the magnitude of yield increase was small, the genetic gain in GY was still observed at 0.78 g m −2 year −1. The GY increments were achieved mainly through increasing the number of spikelets (SPK) which depends on the number of panicle (PAN) at any level, and the PAN could be increased by enhancing the number of tillers. The extinction coefficient ( k) showed that the older cultivars had a spreading plant type, on the other hand, the modern cultivars had an erect plant type which seemed to be a better plant structure in terms of light distribution. This change on plant structure would allow the modern cultivars to have a larger LAI with improved light capturing resulting in better GY in modern cultivars than the old cultivars having similar LAI with modern cultivars. These breeding strategies could work for the high-yielding rice breeding program under cold environments irrespective of soil nitrogen conditions.