Evaluation of Indirect Ploidy Indicators in Dactylis L. subspecies1
- Edzard van Santen and
- M. D. Casler2
The importance of maximizing heterozygosity in tetrasomic tetraploids, such as orchardgrass (Dactylis glomerata L. ssp. glomerata Hayek), has been demonstrated. Germplasm transfer from 2x Dactylis ssp. utilizing diploid clones that produce 2n gametes (meiotic mutants), enhances heterozygosity. Because most meiotic mutants produce n as well as 2n gametes, depending on environmental conditions, the ploidy level of progeny from interploidy crosses will not be uniform. Ploidy determinations are therefore necessary. Several indirect ploidy indicators (yield, vigor, leaf blade dimensions, leaf blade area, and stomatal guard cell length) were evaluated for their usefulness in identifying tetraploid hybrid progeny reliably and with minimal effort. Cultivated 4r clones, 1x germplasm, and their selfed and hybrid progeny were utilized in this study. Dry matter and vigor data were obtained during four successive growth periods in the greenhouse. The remaining traits were evaluated once at the beginning of the first growth period (10 Jan. 1984) and a second time immediately before the last harvest (1 May 1984). Dry matter yield was shown to be unsuitable as an indirect ploidy indicator because of a large overlap in clonal mean ranges from different ploidy levels. Stomatal guard cell length can be a reliable ploidy indicator only if tetraploid inbred clones and triploid hybrid clones are not expected among the progeny, as may be the case in 2x–4x crosses. Visual vigor rating was effective but required extensive experimental replication to achieve the necessary precision. Among the leaf blade dimensions, area gave the most dependable separation of tetraploid hybrids. Nongenetic causes were found to contribute less than 20% to the total observed variance for leaf blade area. Because aneuploidy influences fertility in Dactylis, final ploidy determination should always be made cytologically.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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