无效株是影响群体整齐度的重要因素，主要包括：自交株、空秆、小穗株及病虫害株等。
The main factor that affects population's uniformity is invalid plant including inbred lines, barren stalk rate, diseases and pest insects plant in populations of different yield level.
通过五点取样法，对病虫害进行分级和定点定株调查。
The investigation was made by sampling in five locations for diseases and pests.
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