The superiority of the lines, detected by the yield tests in M₄, was accomplished by different means. The high yield of the line No. 144, for example, was achieved by a drastic increase of its 1000-grain weight, while in line No.2553 a significantly higher density (number of ears per m²⁾ was established. Not one of the lines in Group I showed a significant increase in the number of spikelets per ear, although the primary character in M₂ used to select this group was based on the ear length. This again indicates that the selection was not made for this characteristic but for its variance. Some high yielding lines were also isolated in the untreated control population. But their improvement was based on an equal increase in all of the three components (see Table 2). The shift of the yield structure in most of the superior lines of the Group I and II indicates the mutative nature of the changes; it also offers new opportunities for a combination breeding by crossing.

Literature

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(Received October 2, 1968)