The effect of tiller removal on the growth and development of the main shoot of spring wheat was investigated in plants grown in a glasshouse or growth cabinets. The removal of tillers at different stages from just prior to flag leaf appearance to 10 days after anthesis greatly increased the grain and straw yield of the main shoot. The earlier the tillers were removed the greater was the increase in yield. The increase in grain production was due to an increase in the number of grains per spikelet particularly in the mid and lower regions of the ear. The nitrogen content of the grain was also increased following tiller removal. Additional mineral nutrients supplied either early or late were accumulated by the grain but did not influence the response to tiller removal and it was concluded that neither the number of grains set nor grain growth were limited by the supply of major nutrients. Additional nutrients however greatly increased the yield of tillers and this was associated with a large increase in the grain N, P and K percentages.In a separate experiment tillers were removed just before ear emergence and the plants were transferred to growth cabinets with either a low or high light regime. Although grain yield was greatly reduced in the lower light regime tiller removal significantly increased the number of grains per ear but to a lesser degree than in the higher light regime. It was concluded that the supply of carbon assimilate was more important than the supply of mineral nutrients in influencing grain set.The overall response to tiller removal suggests that tillers compete with the main shoot for assimilate and as a result the potential growth and yield of the latter is greatly restricted.

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