Effect of calcium peroxide coating, soil source, and genotype on rice (Oryza sativa L.) seedling establishment under hypoxic conditions

Unstable seedling establishment is still noticed when calcium peroxide-coat ed seeds are used for uniform seedling establishment in direct-seeded lowla nd rice culture. To observe the genotype response of calcium peroxide-coate d seeds, Oryza sativa L. var. Haenuki and Sasanishiki, were grown in test t ubes and in plastic pots containing soils from: Oami hill (Oami B) and Akit a Prefecture (Akita calcareous) (Experiments 1 and 2). The soils collected from upland and lowland areas from the Shonai Agricultural Experiment Stati on (Shonai alluvium), Yamagata University farm (University alluvium), and S hinjo Agricultural Experiment Station (Shinjo volcanic), Yamagata Prefectur e, Japan were used to observe the response of soil types and soil sources i n Haenuki in the case of calcium peroxide-coated seeds (Experiment 3). The seedlings were grown under hypoxic conditions at 30 degreesC. The growth du ration 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-coat ed seeds were sown. Seedling establishment of Haenuki was slightly affected regardless of whether coated or non-coated seeds were used in the Oami B a nd 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 coat ed 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 coa ted and non-coated seeds in the Shonai alluvium upland and lowland, Univers ity alluvium upland, and Shinjo volcanic lowland soils. However, in the cas e of the calcium peroxide-coated seeds, plant height was adversely affected in the Shonai and University alluvium upland soils. In the University allu vium lowland soil, seedling establishment was markedly reduced when coated seeds were used. As the degree of reduction in this soil was not conspicuou s, the worst performance of Haenuki might be attributed to factors other th an anaerobic toxins like volatile fatty acids or hydrogen sulfide (Experime nt 3). This study revealed that the efficacy of calcium peroxide coating of seeds varied with the genotypes, soil types, and soil sources.