Date of Award

Summer 2019

Project Type

Thesis

Program or Major

Genetics

Degree Name

Master of Science

First Advisor

Anissa M Poleatewich

Second Advisor

Anissa M Poleatewich

Third Advisor

Thomas M Davis

Abstract

Quinoa (Chenopodium quinoa Willd.) is a potential new crop for New England because of its high nutritional qualities and environmental adaptability; however, its susceptibility to disease such as downy mildew, caused by Peronospora variabilis Gaum is a significant obstacle. Downy mildew is a key disease of quinoa causing yield reductions up to 33% in tolerant varieties and 99% yield loss in susceptible varieties. Warm temperatures and high humidity in New England provide optimum conditions for pathogen infection and spread, negatively impacting quinoa growth and yield. This pathogen is able to persist in the seed coat of quinoa and overwinter in soils, making it difficult to manage in a farm setting. These characteristics, as well as reports of fungicide resistance in other downy mildew systems, make genetic resistance the most effective strategy to combat this pathogen. P. variabilis has been reported in North America, specifically in Alberta, Canada and Pennsylvania however it is not known to occur in New England. This research serves as preliminary work for future studies to identify genes contributing to disease resistance in New England native Chenopodium species for future use in breeding programs. The specific objectives of this research were to (1) optimize molecular protocols to detect P. variabilis and confirm the presence of the pathogen in New Hampshire, (2) evaluate differential resistance to downy mildew among Chenopodium accessions, (3) identify other potential pathogens of Chenopodium spp. in New England, and (4) investigate molecular relationships among New England P. variabilis isolates. A molecular pipeline involving touchdown PCR was developed and used to confirm the presence of P. variabilis on Chenopodium species in New Hampshire. Field trials conducted at the UNH Woodman Research Farm evaluated downy mildew disease severity on ten Chenopodium accessions representing four species. Disease severity for each treatment was compared and significant differences were observed among treatments. C. berlandieri var. macrocalycium ecotypes collected from Rye Beach, NH and Appledore Island, ME exhibited the lowest mean disease severity over the season. P. variabilis was isolated from each of the 10 accessions and COX2 sequences were compared; phylogenetic analyses suggest no effect of host species; however, New Hampshire isolates formed a clear cluster when compared with Pennsylvania and South American isolates, suggesting the presence of distinct populations based on geographic location. A second disease causing stem lesion symptoms was observed in the 2018 field trial. Stem lesion incidence was significantly different among Chenopodium accessions, with certain quinoa accessions (37P, QQ065, cultivar Faro) exhibiting low incidence; however, definitive conclusions were not reached in regard to the identity of the stem lesion causal agent. Overall, results from this study provide the first step in identification of potential New England native sources of resistance to downy mildew within the genus, confirmation that downy mildew is present and may be problematic for New England quinoa growers, and documentation of another unknown quinoa pathogen that will need to be managed. These results also provide preliminary information needed to further investigate resistance at the genomic level in Chenopodium spp. and pathogenicity factors in P. variabilis.

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