Crop-Scientific Studies on the Yield-Forecast of Lowland Rice. : (XXX) Tracing up developmental processes of young panicles on all individual tillers. (4)

Abstract

1) The authors divided the whole period from differention of flag leaf primordia to heading into 21 stages, as seen in the previous paper. (Vol. 23;24, 1955) 2) It has been made clear, that the first bract primordia can always be found as a vestige on the neck-node of an adult panicle, the second bract on the base of the second branch, and the third on that of the third branch in first order. Sometimes the first bract changes into a flag leaf, and one can easily recognize such a case by observing an imperfect neck-node and a well developed or a degenerated first branch inside the sheath of the flag leaf on an adult plant. 3) All vestiges on adult panicles can be classified into four kinds-bracts, spikelets, branches in first and second order. But the vestige on the base of the top branch which can be seen on every panicle has been proved to be a compound vestige of a bract and a growing point. 4) Investigating successive cross-sections of young panicles, the authors have found the large bundles in the axes of panicles were divided into each branch one by one. 5) The lowest branch on the axis always differentiates first, but it starts last to grow, that is to say, the order of differentiation among branches is quite contrary to that of growth among them. The same is true with secondary branches, while the order in differentiation of spikelets is in accordance with that of their growth. 6) Duration of each differentiation stage on an individual stem has been made clear, as seen in Table 1. (The weather in 1953 was rather bad, and that in '54 was nearly normal.) 7) By tracing up the developmental process on all culms of three hills every other day, the authors have succeded, for the first time, in ascertaning on a whole field, when the beginning, the middle and the late periods of every developmental stage occur respectively, and how long the duration of each stage is. An instance of it can be seen in Fig. 1. 8) After examining the methods of identifying each stage without microscopical investigations, the authors have found the following methods to be recommendable: (a) Age-index of the plant, which is represented by the perce ntage of the number of leaves which emerged on a main stem by a given time to the finally attainable number of leaves of the stem, showed good fits for identifying the stage. (The finally atainable number of leaves on the main stem of a definite variety keeps constant every year under a definite culture condition.) And the relation between the-indexes and the developmental stages is given in the Table 1. (b) Length of the young panicle can be utilized to a considerable extent in knowing each stage : stage VII.... 0, 4∼0, 5 cm., VIII.... 0, 5∼0, 9 mm., IX∼X.... 0, 8∼1, 3 mm., XI.... 1, 5∼3, 0 mm., XII.... 3, 5∼15, 0 mm., XIII.... 1, 5∼5, 0 cm., XV-XVI.... 10∼17 cm., XVIII.... nearly full length, XIX.... full length. (c) Distance between the blade-ear of the flag leaf and that of the second leaf can be utilized conveniently to identify the stage of the reduction division of pollen-mother-cells which is the most critical period for rice plants in growth. The prosperous period of the reduction division occurs generally at a time when the blade-ear of the flag leaf begins to appear out of the second leaf-sheath. (d) The length of the spikelet increases with the developmental stage of the panicle, attaining the full length at the end of extine-formation stage (XIX). The first or the second meiotic division can generany be seen in spikelets grown half as large as full length. (e) The numbere of days prior to heading which has hitherto been employed can also be used only under normal weather.