Robert Wieners and Shui-zhang Fei
Introduction
Kentucky bluegrass (Poa pratensis) is an important turf species with a rather unique reproductive process. The ability of certain plants of Kentucky bluegrass to reproduce via seed asexually is called apomixes. Highly apomictic cultivars are very desirable to reduce plant-to-plant variation within a turf stand. Therefore, the ability to identify apomictic plants for breeding purposes is important. In this study, we chose a USDA core collection, which contains germplasm from many locations that have been shown to be genetically diverse. These collections could prove to be a useful source of genetic diversity for desired traits in breeding programs.
Materials and Methods
A USDA core collection with 38 accessions from 14 different countries was selected for analysis. The procedure for analysis comes from Matzk et.al. (2000.) A flow cytometer was used to determine DNA content in picograms for somatic tissue (leaf tissue). Reproductive mode was determined by analysis of mature seed. By comparing the relative positions and amplitude of the means of the nuclei peaks from the flow cytometry data, a model can be constructed based on known reproductive processes within Kentucky bluegrass. These models appear in Table 1. The data from the flow cytometry measurements appear in Table 2. After analysis, plants were planted during October 2002 at the ISU Horticulture Research Farm for further evaluation of breeding potential.
Table 1. Pathways of recombination that could be constructed from the C values of embryo and endosperm nuclei of Kentucky bluegrass.
| Female gametes | Embryo | Endosperm | Male gametes | ||||||
|---|---|---|---|---|---|---|---|---|---|
| C values in histogram1 | Reduced | Unreduced | Zygotic | Parthenogenic | Fertilized | Autonomous | Reduced | Unreduced | Seed formation |
| 2C + (3C) | X | X | X | X | Sexual, reduced sperms | ||||
| 2C + (5C) | X | X | X | X | Pseudogamous, reduced sperms | ||||
| 1C + (3C) | X | X | X | X | Reduced, Parthenogenic | ||||
1 Endosperm values in parentheses.
From Matzk et. al. (2000)
Results
Several reproductive modes are present within the 38 accessions tested. The majority of accessions possess both sexual and apomictic seed. Sexual reproduction and Pseudogamous seed formation were the most prevalent, however, some accessions did exhibit parthenogenic seed formation. The mean DNA content of the accessions also confirms that the collection is relatively genetically diverse.
Works cited
Matzk, F. Meister, A. Schubert, I. An efficient screen for reproductive pathways using mature seeds of monocots and dicots. The Plant Journal, 2000. 21 (1), 97-108.
1 DNA content of majority (minority) of plants sampled.
2 Observed peaks from flow cytometry histogram embryo (endosperm).
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ISU Turfgrass:2003 Turfgrass Report | College of Agriculture |
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