University of Western Ontario

Stamens and lodicules of male sterile-silky (ms-si or si1) tassel spikelets are lemma-like structures --D.W. Dales, R.I. Greyson and D.B. Walden As reported in MNL 63:88, the male sterility of male sterile-silky (ms-si) results from failure in development of functional stamen locules. The extent of stamen and anther development varies and ranges from no development to structurally normal but non-functional. We report here further details on the extent of development of floral organs from mature tassel spikelets.

For each of the genotypes 1) homozygous recessive ms-si; 2) heterozygous ms-si (wild type, WT); and 3) Oh43, greater than three hundred spikelets from thirty or more nursery plants were analyzed at maturity. The following observations were made on the flowers at maturity:

1) Glumes, lemmas, paleas and gynoecium of the three genotypes were essentially normal.

2) Lodicules of Oh43 and wild type (WT) were similar, but those of ms-si resembled additional lemmas. This close resemblance made it difficult to distinguish (other than by position) the lemma-like lodicules from the true lemmas.

3) The six stamens (three in each spikelet's upper and lower florets) of the WT and Oh43 were similar and normal.

4) More than sixty percent of the ms-si spikelets examined possessed stamens with a planar dimension rather than the normal radial, and development to the mid-portion of the range mentioned previously.

5) Only the stamens of the upper ms-si floret developed to an abnormal state while those of the lower floret became aborted at an early stage. The abnormal stamens varied in appearance but in general resembled lemmas. Either the complete stamen or each locule (four in total for each stamen) had been modified to mimic a lemma. There were instances where any number (zero to four) of the locules were lemma-like while the others looked normal.

6) For those stamens from ms-si flowers in which the anther locules were modified, the connective tissue was intact and similar to those from Oh43 and WT flowers except that the connective tissue at the tip of ms-si stamens continued, in some instances, to expand or grow to various lengths (zero to five centimetres from the tip of the locules) to develop what we have termed the silk-like structure (SLS).

In summary, the lodicules and stamens of ms-si tassel spikelets resemble lemma-like structures. This recalls other species, i.e. barley and tomato, reports of staminal transformation into other floral parts (M. L. H. Kaul, Male sterility in higher plants, Springer-Verlag, 1988) and (V. G. Meyer, Bot. Rev. 32:165-218, 1966). Terms such as phylody, petaloidy and pistiloidy are used to describe these variations. For the ms-si phenotype, we have used "lemma-like" to describe these modifications.

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