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Abstract
Unstable seedling establishment is still noticed when calcium peroxide-coated seeds are used for uniform seedling establishment in direct-seeded lowland rice culture. To observe the genotype response of calcium peroxide-coated seeds, Oryza sativa L. var. Haenuki and Sasanishiki, were grown in test tubes and in plastic pots containing soils from: Oami hill (Oami B) and Akita Prefecture (Akita calcareous) (Experiments 1 and 2). The soils collected from upland and lowland areas from the Shonai Agricultural Experiment Station (Shonai alluvium), Yamagata University farm (University alluvium), and Shinjo Agricultural Experiment Station (Shinjo volcanic), Yamagata Prefecture, Japan were used to observe the response of soil types and soil sources in Haenuki in the case of calcium peroxide-coated seeds (Experiment 3). The seedlings were grown under hypoxic conditions at 30°C. The growth duration for in vitro culture was 7 d in the dark and 10 d for pot culture in the phytotron under natural day and night conditions. The Akita calcareous soil failed to accumulate dissolved oxygen even when calcium peroxide-coated seeds were sown. Seedling establishment of Haenuki was slightly affected regardless of whether coated or non-coated seeds were used in the Oami B and Akita calcareous soils. The coating of seeds of Sasanishiki, led to poor seedling establishment in these soils, whereas in the case of Sasanishiki, seedling establishment was as good as that of Haenuki when the seeds were not coated in the Oami B soil. In Haenuki, plant height increased when coated seeds were used in in vitro culture but in pot culture, plant height was similar between the coated and non-coated seeds in both soils (Experiments 1 and 2). Haenuki also showed a similar seedling establishment between coated and non-coated seeds in the Shonai alluvium upland and lowland, University alluvium upland, and Shinjo volcanic lowland soils. However, in the case of the calcium peroxide-coated seeds, plant height was adversely affected in the Shonai and University alluvium upland soils. In the University alluvium lowland soil, seedling establishment was markedly reduced when coated seeds were used. As the degree of reduction in this soil was not conspicuous, the worst performance of Haenuki might be attributed to factors other than anaerobic toxins like volatile fatty acids or hydrogen sulfide (Experiment 3). This study revealed that the efficacy of calcium peroxide coating of seeds varied with the genotypes, soil types, and soil sources.