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1.Studies on Breeding of Rice for Adaptability to Nature Farming

Hirokazu Nakai(Institute for Agro-Microbiology)

Present studies were started in 1991, aiming at the development of rice varieties adaptable to Nature Farming (NF) without using any agrochemicals and chemical fertilizers. The studies were focused on the evaluation of rice varieties for adaptability to NF, until 2004. Since then, the practical breeding has been performed in order to complete the breeding purpose. About 120 varieties of rice, which include both native and improved modern varieties of japonica and indica types, were grown in the rice fields of a farmer in Nagano-prefecture. All the varieties used were evaluated for main agronomic traits and some quality of rice, e.g. grain yield, eating quality, nutritious value and so forth. Temperature of the soil and the plant body of rice was measured in both farming systems. In addition, physical and chemical analyses were made on the soil. In 2005, the crossings among some varieties were made to start the breeding in bulk and/or pedigree methods in farmer's rice fields in 16 different areas across Japan.
The experimental results obtained are as follows: (1) Responses of varieties for each trait were specific to both farming systems. Some varieties were found to be higher for grain yield in NF than in conventional farming (CF), though the yield was lower in NF on average. (2) The average yield in NF was decreased by 30 % and 20 % for the modern and native varieties, respectively. The result suggested that the panicle weight type of native varieties might be more adaptable to NF. (3) Eating quality of the varieties measured by a relevant analyzer, which was developed by NIREKO Company, was significantly higher in NF on average. (4) The content of minerals, Mg, K, Mn and Cu, measured by the radioactivation analysis, was found to be higher in NF only for Mg and Cu. The content of minerals was correlated with chemical characteristics of the soil. (5) The temperature of both soil and plant body of rice was found to be significantly higher in NF. The result suggests that the higher temperature of both the soil and plants might be an important factor for NF to be highly tolerant to cold damage. (6) A number of F6 lines were selected for higher yield and better eating quality in NF in the process of the breeding.
It is concluded from the present studies that variety is one of the most important factors for increasing rice yield in NF and that the development of varieties adaptable to NF or low input sustainable agriculture would be promising.