Negative Effects of Late Sowing on Wheat Production in Middle and Lower Reaches of Yangtze River Valley and Breeding Strategies
The wheat sowing date is delayed largely because of planting late mature japonica rice varieties in large area and replacing artificial transplanting by machine transplanting and seed planting.Furthermore,the farmers harvest rice later until rice grain drier as it matures completely.That may bring the consequences of shortening the growth period,decreasing accumulated temperature and length of radiation for wheat production,thus leading deficiency on the nutrition growth of wheat.It also makes wheat more susceptible to scab and powdery mildew,increases the risk to encounter high temperature during grain-filling stage and pre-harvest sprouting before harvest.So late sowing has been the main hinder to get high yield for wheat.Although the adverse effects of late sowing could be compensated by cultivation measures,the basic and efficient measure is to breed cultivars suitable for late sowing.The strategies to breed wheat varieties with high-yielding in late sowing condition are proposed as screening on the following characteristics:(1) varieties with early and fast growth in seedling,rooting,growing and tillering,with relatively high growth and tillers occurrence while in wintering period; (2) varieties with strong resistance to diseases,especially to scab,waterlogging and resistance to pre-harvest sprouting; (3) varieties with high grain-filling speed and heat tolerance,therefore compensation the adverse effect of shortening grain-filling time by grain-filling speed.
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