Date of Award

5-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Advisor

Reighard, Gregory

Abstract

Peach Tree Short Life (PTSL) is a complicated disease syndrome involving nematodes, temperature, soil conditions, pruning and secondary pathogens. The disease occurs commonly in the southeastern U.S., and possibly in other areas of the U.S., Europe, South America and South Africa as the related Bacterial Canker Complex. PTSL causes premature tree death during the 3rd or 4th year after planting, resulting in large economic losses for growers. Recently, Guardian® &lsquo BY520-9&rsquo rootstock was selected for its tolerance to PTSL; however, the genetic basis for this tolerance remains unknown.
Nemaguard, a PTSL susceptible rootstock, and Guardian® selection 3-17-7 were crossed. Each 1 plant was selfed to create segregating 2 populations. One hundred and seventy Simple Sequence Repeat (SSR) markers, each uniquely mapped to chromosomal locations on the Prunus reference genome, were used to screen the parents and F1-11. Forty-seven SSR markers showed polymorphism among the parents, and were heterozygous in F1-11. Segregation data obtained from the F2-11 population for SSR marker inheritance and PTSL-response were compiled to identify nuclear genomic regions associated with the response to PTSL disease syndrome.
Of the 47 polymorphic SSRs, nine (distributed on 4 linkage groups) were genetically linked with the response to PTSL. Identified SSR markers would be useful in crop improvement and facilitating tolerance rootstock selection. A QTL was associated with the response to PTSL as well. The upper terminus of linkage group 2 appears to be important because both the individual SSR analysis and the QTL analysis linked this region with the response to PTSL. The genes controlling the tolerance or susceptibility of PTSL may reside in this region. In the future, developing more SSR or other high-resolution markers to saturate this region will further define the specific region, and ultimately lead to identification of the candidate genes.
The second project described in this dissertation is the genotyping peach rootstock seedlings using DNA-fingerprinting with microsatellite/SSR markers. Peach seedling rootstocks are usually drived from open pollination. Seedlings are difficult to distinguish morphologically, and once grafted, typically no above-ground material is available for visual identification. To avoid misidentification and to protect plant varieties and patents, DNA fingerprinting was investigated as a robust rootstock identification tool. The objective of this study was to distinguish among progeny from eight peach seedling rootstocks: Bailey, Halford, Lovell, Nemaguard, Nemared, Guardian® (selection 3-17-7), S-37 and Kakamas.
Each rootstock could be discriminated by at least one SSR marker. No single perfect marker was found to identify all rootstocks. Rootstock seedling identification was conducted by screening open-pollinated seedlings. It is more difficult than parent genotype identification, because heterozygous patterns obtained in a rootstock clone segregate in its seedlings. However, unique segregation patterns were found in the rootstock seedlings. Single SSR markers could identify seedlings of rootstocks Nemared, Bailey, Kakamas and Nemaguard. Seedlings of 3-17-7 and S-37 could be identified by marker combinations. Seedlings of Lovell and Halford can be identified from the other rootstocks. However, there were no SSRs or marker combinations to uniquely differentiate Lovell from Halford seedlings. The SSR markers presented in this study could be used as a practical fingerprinting system for rootstock seedling identification. This technology is useful to test rootstocks for trueness to type for nursery operators and growers, and also will be helpful in protecting seed propagated proprietary rights (i.e., PVP) for breeders.

Included in

Genetics Commons

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