STUDIES ON HEADING CHARACTERISTICS OF PRI MARY AND SECONDARY TILLERS IN RICE (ORYZA-SATIVA L) .1. INFLUENCE OF LEAF-CUTTING ON HEADING CHARACTERISTICS OF PRIMARY AND SECONDARY TILLERS

The purpose of this experiment was to identify the cause of the differ ences in the heading date and the time of panicle differentiation amon g individual tillers in a plant. Three varieties, Norin 1, Nipponbare and Norin 8, were grown in a/2000 Wagner's pots containing paddy field soil. Eleventh to fourteenth leafblades of individual tillers of thre e varieties which correspond to leaf number index (LNI) from 70 to 90 were cut off when they reached their full length. The heading date of each tiller was considered to be the date on which a tip of panicle ap peared more than 5 mm from the leaf sheath of its flag leaf. The young panicle length of individual tillers was also investigated at LNI 90. Heading of primary tillers was delayed by leaf cutting treatment, whe reas no significant changes were observed in the flag leaf position on each stem. Delayed heading was observed on tillers which leaves were cut but scarcely recognized on intact ones even in a same plant. Moreo ver, the heading date of the early variety was delayed remarkably comp ared with the late one. In the case of secondary tillers, their headin g date was delayed compared with their maternal primary tillers. The i nfluence of these leaf cutting treatments on the heading date was limi ted to the tillers that had received the cutting treatment. As the ste ms that had developed longer young panicles headed earlier in the case of both primary and secondary tillers, the authors assumed that the d ays to heading of tillers may have reflected the time of panicle initi ation.