Abstract
Rain-fed upland rice (Oryza sativa L.) is one of the important crops in Sub-Saharan Africa (SSA) accounting for over 40% of the area under rice cultivation. In SSA, upland rice is primarily established by dry direct seeding (DS), which saves time and labour, although DS is associated with poor seedling emergence and establishment. It is thought that coleoptile and mesocotyl elongation in rice seedlings enhance emergence in deep sowing. A screen house study was conducted from May to December 2011 at Tokyo University of Agriculture in Japan to determine the effect of coleoptile and or mesocotyl elongation on seedling emergence in deep sowing. Six upland rice genotypes which vary in coleoptile + mesocotyl lengths, and another ten genotypes varying only in mesocotyl lengths were selected and evaluated for seedling emergence at 2, 4, 6 and 8 cm sowing depths. The experiment was laid out in a split-plot design based on randomised complete blocks. Seedling emergence was significantly reduced by sowing depth. Across the genotypes, seedling emergence was not associated with coleoptile + mesocotyl length. And although coleoptile and mesocotyl lengths both increased with sowing depth, seedling emergence in deep sowing was affected largely by mesocotyl elongation rather than coleoptile elongation. We found that only those genotypes that significantly elongated their mesocotyls like Nutsurikui and Plu-go were able to emerge from deep sowing. Our results therefore suggest that seedling emergence in dry direct seeded upland rice can be improved by planting genotypes with long mesocotyls. Key words: Coleoptile, dry direct seeding, mesocotyl, upland rice.
Highlights
Rain-fed upland rice (Oryza sativa L.) is one of the important crops in Sub-Saharan Africa (SSA) where it accounts for over 40% of the land under rice cultivation (WARDA, 2002)
In Experiment 1, we found that selection for long coleoptile or mesocotyl length based on seedling emergence under submergence had little effect on seedling emergence in dry direct seeding
This paper has shown that it is possible to improve seedling emergence in dry direct seeded upland rice by planting genotypes with long mesocotyls
Summary
Rain-fed upland rice (Oryza sativa L.) is one of the important crops in Sub-Saharan Africa (SSA) where it accounts for over 40% of the land under rice cultivation (WARDA, 2002). It has increasingly become popular amongst first time rice growers in non traditional rice producing regions of SSA like Uganda because; (1) the yields are stable even in adverse environments (Bouman, 2001), (2) initial cost of establishment is lower because the cost of paddy field development has been deducted (3) it is easy to convert to non rice upland crops and vice versa, and most importantly, (4) it is easy to plant through direct seeding by broadcasting, drilling or dibbling seeds in prepared dry to moist soil.
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