Date of Award

Summer 8-20-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Ek Han Tan

Second Committee Member

Jianjun Hao

Third Committee Member

Gregory Porter

Abstract

Solanum tuberosum L. is the world's most important non-cereal food crop, capable of producing more food per land unit on less water than any other crop. Only rice, wheat, and maize are produced in larger quantities than potato. The potato tuber, a modified stem turned storage organ is nutrient dense and a staple in diets across the world. The potato crop is expected to grow and contribute significantly to the global food supply. However, potato production has increasingly been threatened by unfavorable environmental conditions, and susceptibility to pest and disease. Perhaps the most famous of all the Irish Potato Famine caused by the oomycete Phytophthora infestans. Constraints on potato production through abiotic and biotic factors have been tackled through crop improvement or breeding programs. As a tetraploid crop, the potato breeding cycle can take many years from conception to variety release. This process takes on average,10 years to complete. This lengthy breeding cycle does not mean that traditional potato breeding is unsuccessful, simply resource intensive. Due to the demands on available resources caused by potato breeding cycles, some pest and pathogen resistances may not be incorporated into commercial germplasm, which is further influenced by the amount of pressure the pathogen exerts annually on the potato crop. The tetraploid nature of the crop and the ease of which tubers can be obtained and shipped has led to a vegetative propagation system for seed tubers. Although regulated through certification programs, diseases are still able to penetrate these proactive cultural practices as was the case in, 2015 when there was an outbreak of Dickeya dianthicola struck the Northeast potato growing regions in the U.S. and quickly spread throughout the country because of limited control measures. A recently released variety from the University of Maine Breeding Program, Caribou Russet, was shown to have tolerance to potato blackleg and soft rot (PBSR) caused by Dickeya dianthicola strain ME30. In this work, an effective Dickeya dianthicola isolate ME30 culturing method and inoculation workflow is established to repeatedly and reliably phenotype for the potato blackleg soft rot resistance phenotype. Using this workflow and a population of primary dihaploid Caribou Russet, the underlying genetic source of tolerance observed at the tetraploid state is sought. This work provides a workflow to enable reliable means of phenotyping PBSR resistance in Caribou Russet, as well as incorporating and identifying PBSR resistance into future germplasm for potato breeding. Potato haploid induction holds promise in revitalizing the industry through implementation of a true potato seed system via a diploid potato breeding system. Potato haploid induction also allows researchers to investigate the genetics of agronomically important traits in a setting with less complex epistatic effects, and simpler segregation ratios. By leveraging haploid induction crosses in the cultivated potato, the underlying genetic sources of tolerance to PBSR infection can be mined from the potato genome. Dickeya dianthicola isolate ME30 characterization resulted in the creation of a linear regression model which describes the relationship of optical density at 600nm to the estimated colony forming units per milliliter of culture, as well as the identification of an optimal inoculum concentration at which to vacuum infiltrate tubers for disease phenotyping. Subsequent validation of this workflow occurred during the disease phenotyping experiment on a population of primary dihaploid Caribou Russet. These data were then used for QTL mapping. QTL mapping revealed no significant QTL. Nonetheless, a peak was detected along chromosome 6 aligning with previous published literature on PBSR resistance. Thus, suggesting that there is an underlying genetic source of resistance within the primary dihaploid Caribou Russet gene pool.

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