Study of yield loss and its mechanisms caused by grain shattering habit of crops.

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Grain shattering habit is one of elemental traits on plants because of the importance on wild plants for the seed dispersal, but on grain crops it causes the yield loss before harvest. Recently, the cultivation area of soybean and buckwheat is increasing in the upland filed converted from paddy in Japan, but these crops are suggested to show severe yield loss caused by the grain shattering habit at the harvesting stage. Thus, current study demonstrated the yield loss at the grower's field, and the mechanisms of the yield loss were investigated on the variation of cultivars, and the growing conditions.In this study, the amount of yield loss caused by the shattering habit was various among cultivars, years and locations, and severe damage on yield was observed by several reasons. For example, 20 to 30% of grain yield was dropped in soybean field because growers lose the adequate harvesting time due to the competition with the harvest process of other crop such as rice, and more than 50% … More of grain yield of buckwheat was blown off by typhoon. The grains shed by typhoon before harvesting was available as the seed for the next cultivation under weed control by plowing. The grain shattering habit of buckwheat was caused from thin pedicels, and the diameter of pedicel was genetically correlated with the size of seed grain, thus the cultivars of heavy grain type showed resistance on the shattering compared to the cultivars of small grain type. To prevent from severe loss by shattering, the early harvesting on buckwheat was suggested to change the grain quality, because the grain quality was drastically changed at the grain ripening period. On soybean, the clear relationship between the grain shattering habit and other morphological traits was not observed. However, growers suggested that the difference of the growth stage in a field embarrassed them to decide the harvesting time, and the misjudgment of harvesting time caused the decrease of the yield and the grain quality. The difference of the growth stage in a filed was caused by several reasons such as the variation of soil conditions, and the illumination of streetlight. The spatial analysis on the difference of the growth stage in a filed demonstrated the difference of growth stage occurred randomly in the field and became small gradually as soybean maturated. The light quality of a streetlight influenced the plant growth of soybean due to the short day plant, but blue-green light and halogen lump showed smaller effect on the delay of plant growth. Less