Identification of Growth Stages Sensitive to Waterlogging during Seedling

<ns2:p>Waterlogging often occurs after winter oilseed rape (Brassica napus L.) is sown in Yangtze River basin, China, which leads to poor seedling establishment and seed yield penalties. Identification of the growth stage/s sensitive to waterlogging is critical for developing appropriate management strategies and improving the productivity of direct-sown winter oilseed rape. In this study, the impact of waterlogging on the seedling emergence and establishment of winter oilseed rape over a range of initial growth stages was assessed in replicated pot experiments. Waterlogging was imposed for 1, 3 or 5 days at various phases using a completely randomized design (CRD). The results showed that, pre-emergence waterlogging reduced seedling emergence significantly, whereas post-emergence waterlogging for 5 days did not affect seedlings survival although the seedling dry matter production was reduced in most cases. The seriously reduced seedling emergence, dry matter production and the shorter hypocotyl elongation after waterlogging at the radicle growth indicate that this phase was probably most sensitive to waterlogging. Nearly half of the seedlings failed to emerge after waterlogging at the radicle growth for 1 day, and more than 90% did not emerge after waterlogging for up to 3 days. The hypocotyl became longer after waterlogging at cotyledon emergence and expansion, resulting in taller seedlings with low resistance to stress during winter. Therefore, waterlogging from the radicle growth to cotyledon expansion was critical for seedling emergence and growth. The seedlings had a higher compensatory growth in dry matter accumulation after mild waterlogging at cotyledon emergence. For nutrient uptake, N, P and Na decreased but K increased in plants after waterlogging.</ns2:p>