Emergence and biochemical response of contrasting rice genotypes, weedy rice and Echinochloa spp to early flooding

Weeds are a major constraint to direct-seeded rice systems. Emergence and biochemical response of three rice cultivars: two flood-tolerant, Khao Halan On (KHO) and Marzhan Red and one flood-intolerant cultivar, IR64, weedy rice, Oryza sativa f. spontanea; and two weed species, Echinochloa colona and Echinochloa crus-galli to early flooding were evaluated. Dry seeds were sown at 1-cm soil depth and flooded at four depths (0, 1, 5 and 10 cm) depths. Seedling emergence was assessed 21 days after seeding. Lipid peroxidation and total phenolic content were assessed at 4 days after seeding. Flooded to 5 and 10 cm reduce the emergence of IR64 by 55% and 64% than the flooded tolerant rice genotypes. Flooding to 5 and 10 cm decreased completely inhibited emergence of Echinochloa colona than the Echinochloa crus-galli, when flooded to 5 and 10 cm decreased the emergence of weedy rice by 84 and 94%, respectively. Malondialdehyde (MDA) content in IR64 rice genotype and Echinochloa colona increased with greater flood depths. MDA content negatively correlated with seedling emergence (r=-0.36*) of rice genotypes, weedy rice, and Echnochloa spp. Total phenolic content in KHO and weedy rice were higher than the IR64 rice genotype. Total phenolic content negatively correlated (r=-0.43**) with MDA content in rice genotypes, weedy rice, and Echinochloa spp. Echinochloa colona was more susceptible to early flooding indicating higher level of MDA content and lower level of total phenolic content. Weedy rice remain lower emergence and growth, but keeping higher level of phenolic content and lower MDA content. Therefore, understanding of mechanism associated with tolerance to early flooding is relevant to the development of integrated approach for management of Echinochloa spp and weedy rice in wet-seeded areas where flood-tolerant rice varieties are used.