Why Corn Seed Purity Declines and How to Improve It
The level of corn yield is also closely related to the purity of the variety. For the same variety, planting high-purity seed yields more than planting low-purity seed, and as purity declines, yield also decreases. So what causes the decline in corn seed purity? How can it be improved? Let us take a look together.
1. What causes the decline in corn seed purity?
1. Biological contamination. The conditions of the isolation zone and the removal of off-types and inferior plants failed to meet the standards required by the state, and pollination by other varieties caused biological contamination.
2. Detasseling during seed production was not timely. The tassels of some parental inbred lines shed pollen while still inside the husk leaves, and detasseling was not carried out in time, resulting in self-pollination.
3. Seed harvesting, threshing and storage were not strictly controlled, and off-type ears were not removed strictly according to quality standards; threshers, cleaning machines and other equipment were not thoroughly cleaned, causing mechanical contamination. Every important step in corn seed production can lead to a reduction in the seed germination rate. In seed production fields, the parents may stay green and mature late, the grain filling may be incomplete, and the moisture content may be high. If the seed encounters low temperatures, cold damage or frost during the milk-ripening stage and is forced to be harvested, or if the ears suffer freeze damage on the drying yard after harvest, the seed germination capacity can be reduced. After the seed is put into storage in dark, damp or poorly sealed warehouses, and so on. All of these factors can lead to a reduced seed germination rate.
2. How can the decline in corn seed purity be improved?
1. Select and maintain pure inbred lines
First, select inbred lines whose various traits are completely stable; second, strictly set up isolation zones during propagation; third, reduce the number of propagation generations and assign dedicated personnel to bag and purify them year by year.
2. Set up isolation zones according to standards
First, spatial isolation: the spatial isolation between different varieties must be no less than 200 m. Second, natural barrier isolation: on the premise that the spatial isolation is no less than 100 m, use villages, roads, forest belts, high walls and other natural barriers for isolation, and plant 2-5 m of paternal rows, sorghum, tall flax and other crops at the edge of the seed production field for protection.
3. Strictly remove off-types
Removing off-types at the seedling stage: remove off-types at the seedling stage when there are 4-5 leaves. For plots with many variant plants and severe differences between large and small seedlings, postpone the removal time and choose to carry it out at the 6-7 leaf stage, and adhere to the principle of “remove the large and the small, keep the middle.”
Removing off-types before detasseling: remove off-types before detasseling in late June. According to the physiological characteristics of the parents, such as plant height, stalk thickness, leaf color, leaf width, and the angle between the leaf and the stalk, carefully identify each plant, remove off-type and inferior plants as well as abnormal plants, and strictly carry out the removal of off-types from the male parent with the attitude of “rather kill by mistake than leave one out.”
4. Accurately judge the flowering period and detassel in time
Timely, clean and thorough detasseling is the key to ensuring corn purity. In the Hexi irrigation district, corn detasseling is mainly concentrated from late June to mid-July. The flowering period should be judged accurately, labor should be organized in advance, and the detasseling time should be reasonably arranged. Achieve 95% of tassels removed in the first detasseling pass, the remaining 5% of tassels removed in the second pass, and in the third pass search for missed plants in the middle of the field and around the field ridges. Throughout the entire detasseling process, strictly ensure that it is done regardless of wind or rain and without stopping for irrigation.
5. Cut down the male parent at the right time
After pollination is completed, when 80% of the female parent silks have wilted, the male parent can be cut down. Depending on the maturity of the variety, this is generally carried out from late July to early August. This work should be done early rather than late, and no plants should be missed or left behind.
6. Carefully select ears in the later stage
Ear selection after harvest and before processing is the guarantee for improving seed purity. Around the time of seed harvest in late September, strict ear selection must be carried out. When the ears enter the processing plant, use conditions such as drying and transport on the processing line to conduct a final ear inspection, removing off-type ears, inferior ears and diseased ears. At the same time, in links such as transport, drying and threshing, avoid mechanical contamination between varieties.