Microbial Approaches to Support Andean Quinoa Production
Open Access
- Author:
- Testen, Anna Louise
- Graduate Program:
- Plant Pathology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 09, 2012
- Committee Members:
- Paul Anthony Backman, Thesis Advisor/Co-Advisor
- Keywords:
- quinoa
international agriculture
seedborne diseases
downy mildew
phosphate solubilizing bacteria
Ecuador
Bolivia
PGPR - Abstract:
- Quinoa, Chenopodium quinoa, is an Amaranthaceous seed crop, grown as a staple food and high-value export of the Andean region of South America. Research into quinoa production has increased due to the crop’s ability to produce a highly nutritious seed under adverse environmental conditions. Quinoa production has increased greatly in South America in order to meet North American and European consumer demand. Increased production has led to the conversion of marginal land into quinoa fields and a subsequent decrease in sustainable production practices. Therefore, it is necessary to research sustainable methods of quinoa production. There has been substantial research into certain production methods, such as irrigation and improved quinoa lines, but there is little research into the use of microbes to enhance quinoa production. Plant growth promoting Bacillus species were examined for their ability to colonize quinoa and to promote quinoa growth, but neither Bolivian isolates nor commercially available isolates were shown to enhance quinoa growth. Root colonization by Bacillus strains could only be reliably measured through the use of spontaneously generated rifampicin resistant mutants. A subset of plant growth promoting bacteria, the phosphate solubilizing bacteria, were examined to determine if the tricalcium phosphate solubilizing phenotype was specific to certain Bacillus species. Bacillus populations isolated from Pennsylvanian Chenopodium album, Ecuadorean C. quinoa, and Bolivian C. quinoa were screened for the ability to solubilize tricalcium phosphate and this phenotype was paired with 16S sequence data to determine if there were species based patterns of tricalcium phosphate solubilization. Nearly all isolates of B. megaterium (100% of isolates) and B. subtilis (99%) groups were capable of tricalcium phosphate solubilization, whereas members of the B. simplex (51%) and B. cereus (39%) groups varied greatly in their ability to solubilize tricalcium phosphate. This indicates the tricalcium phosphate solubilizing phenotype is ubiquitous in certain Bacillus species and these species could be targeted in screens for plant growth promoting bacteria. However, in assays in which the effects of a phosphate solubilizing B. megaterium were compared to a non-solubilizing B. simplex isolate, no differences were observed in plant growth or plant phosphorus content, so the role of the tricalcium phosphate solubilizing phenotype is still unclear. The key disease of quinoa is downy mildew caused by Peronospora variabilis (formerly Peronospora farinosa f. sp. chenopodii). Seed-based detection methods using sequencing and PCR with specific primers were developed to detect seedborne oospores of P. variabilis. Thirty-two lots of imported, consumable quinoa seeds were screened using these methods and the pathogen was detected in 25 lots using the sequencing based method and 23 lots using the PCR with specific primers method. Therefore, seedborne oospores likely play a significant role in the spread of quinoa downy mildew and it is critical to develop management methods for seedborne oospores. Seedborne oospores are the likely source of initial inoculum for the introduction of P. variabilis to Pennsylvania. Phylogenetic analyses of the quinoa downy mildew pathogen from Ecuadorean and Bolivian quinoa samples showed that the pathogen that infects weedy Chenopodium species in Ecuador is P. variabilis (based on ITS sequences). Therefore, weedy Chenopodium species could harbor P. variabilis and further studies are required to determine if weedy Chenopodium can act as green bridges for P. variabilis between and during quinoa growing seasons. To combine Bacillus and P. variabilis research together, biological control assays were performed to determine if Bacillus could reduce the severity of quinoa downy mildew infections. Both Bacillus mycoides BmJ and Bacillus pumilus GB34 appeared to reduce sporulation of P. variabilis compared to an uninoculated control in two studies, but these results were non-significant. Results of all these studies, along with protocols, were prepared for Ecuadorean and Bolivian collaborators, so that this research can be applied in key quinoa producing areas of South America. By identifying which Bacillus species groups solubilize tricalcium phosphate, collaborators can focus research efforts on these species groups in quinoa growth assays for plant growth promotion. Protocols for isolating and screening Bacillus isolates for plant growth promoting phenotypes, such as IAA and chitinase production, were developed to allow for consistent results amongst collaborators in the United States, Ecuador and Bolivia. Three new diseases of quinoa were reported in the United States, and through this research, simple, reliable methods for working with each pathogen were developed and shared with collaborators. Molecular methods to detect P. variabilis in quinoa seeds and plant tissue highlighted how quinoa seeds could potentially serve as sources of inoculum for P. variabilis. Finally, an extension program for rural Andean farmers in Tiraque Province, Bolivia was developed to teach farmers about integrated pest management of quinoa downy mildew. Quinoa production could benefit greatly from research into how to manage both beneficial and pathogenic microbes. Incorporating beneficial microbes could help promote plant growth and reduce disease. Identifying sources of inoculum for P. variabilis and being able to rapidly detect P. variabilis in seeds and plant tissues will aid in development of integrated strategies to manage quinoa downy mildew. These microbial approaches could help support Andean quinoa production in years to come.