Genomic Analysis of Life History Traits, Disease Resistance, and Evolutionary Origins of the Greens-type Poa annua L.

Open Access
- Author:
- La Mantia, Jonathan
- Graduate Program:
- Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2008
- Committee Members:
- David Robert Huff, Dissertation Advisor/Co-Advisor
David Robert Huff, Committee Chair/Co-Chair
Surinder Chopra, Committee Member
Majid R Foolad, Committee Member
Dawn S Luthe, Committee Member
Scott Warnke, Committee Member - Keywords:
- phenotypic instability
Auxin F-Box
greens-type
Poa annua - Abstract:
- Poa annua L., commonly known as annual bluegrass or meadow grass, is a species of turfgrass that has been distributed from Europe to every continent including regions of Antarctica. It has flourished as a winter annual, germinating at the end of summer, maintaining a tall, coarse vegetative growth during the fall and winter, and ending its life cycle in the spring with a prodigious seed set. It lacks the characteristics of a sustainable turf such as heat and drought tolerance and disease resistance. However, fairly recently on an evolutionary time scale, a new biotype of Poa annua has evolved. The “greens-type” has transformed its life history traits to a perennial type grass exhibiting prolific tiller density, with a dwarfed stature and fine leaf texture. The additionally traits; tolerance to heat and drought, and resistance to anthracnose, pink snow mold, and dollar spot also vary among greens-types. This biotype of P. annua can be found on older elite golf course putting greens, flourishing under mowing heights of a 1/10th of an inch and thus produces an extremely fast, uniform playing surface. In 1927, Piper and Oakley described the perennial, greens-type’s utility in a letter from the USGA; “The perennial type provides a dense uniform playing surface ideal for putting greens.” In the past 80 years there have been three attempts to breed and release an elite commercial cultivar of a “greens-type” perennial P. annua; the University of California (1950s), the University of Rhode Island (1970s), and the University of Minnesota (1980s-1990s). Nevertheless, all three attempts have failed. The limiting factor that has impeded the release of a commercial cultivar has been the stability of the greens-type’s morphology. During the breeding process, the greens-type is left unmowed to increase seed production. Over the course of several generations without mowing the greens-type biotype is lost and population reverts back to a large, coarse textured annual-type that is functionally and visually unacceptable to the golf course industry. Presented here is an examination of the greens-type phenotype, its inheritance, instability, and regulation, and breeding for disease resistance in stable greens-types. The F2 progeny from a Lemon House (annual-type) x PSU 98-2-26 (greens-type) cross were measured for inflorescence branching, culm length, tiller length, leaf length, panicle length, and spikelet number. Preliminary data indicated that the greens-type phenotype linked single branching inflorescences with dwarfed culms, tillers, leaves, panicles, and number of spikelets. The data also suggested that a single recessive gene regulated the greens-type phenotype. Yet, advanced generation progeny from the Lemon House x PSU 98-2-26 and two greens-type x greens-type populations did not confirm the single gene hypothesis. The inheritance patterns from these populations also failed to conform to tetrasomic or disomic models as well as gene complementation and three and four gene quantitative trait loci models. Finally, the observation of somatic reversions of greens-types sporting annual-type reproductive tillers indicated that the greens-type phenotype is unstable and regulated by a non-mendelian mechanism. The unstable nature of the greens-type complicated the process of defining an efficient approach to elucidating the mechanism for this phenotype. In the end, a candidate gene approach was taken. While many plant pathways can confer dwarfism through genetic mutation, the greens-type’s response to gibberellic acid narrowed the potential candidates. The GA biosynthetic genes were cloned and used for expression analysis. In the greens-type PSU 98-2-26, GA20oxidase was over-expressed in comparison to the annual-type. These results suggested that greens-type might be deficient in GA biosynthesis; however the greens-types resistance to the synthetic auxin NAA eliminated that possibility. Auxin signaling genes were then cloned and used for expression analysis. The Auxin F-Box gene was down regulated in PSU 98-2-26 and F3 greens-type progeny in comparison with the Lemon House and F3 annual-type progeny. In addition, this gene was suppressed in PSU 98-3-30 and related F5 greens-type progeny. The creation of recombinant inbred lines to map dollar spot resistance in greens-type P. annua was severely inhibited by the unstable nature of the greens-type phenotype. A small number of F5 and F7 progeny from the cross of two greens-type parents; PSU 98-3-30 (susceptible), PSU 98-6-27 (resistant) maintained the greens-type phenotype. In the field trial, PSU 98-6-27 was confirmed as being more resistant to dollar spot than PSU 98-3-30. Several progeny were as resistant as PSU 98-6-27 and were significantly more resistant than PSU 98-3-30. On the other end of the spectrum, progeny were found to be significantly more susceptible than PSU 98-3-30. The field results indicated that there may be a resistance QTL within PSU 98-3-30 and therefore may be at least two genes that confer resistance. This also indicates that breeding for dollar spot resistance greater than that of PSU 98-6-27 may be possible. Despite the unstable nature of the greens-type phenotype, it is possible to create transfer traits from one greens-type to another. In addition, preliminary evidence suggests that mowing may enable the greens-type phenotype to be inherited to the next generation. Therefore, the breeding and release of the first elite, stable greens-type seeded cultivar may be possible.