EFFECTS OF BACTERIAL INOCULATION ON OSMOLYTE PRODUCTION, SALINITY TOLERANCE, AND TRANSCRIPTION IN RECURRENTLY-SELECTED SALINE-TOLERANT ALFALFA BREEDING LINES
Date
2024-01-25
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-1476-4445
Type
Thesis
Degree Level
Masters
Abstract
Previous studies have highlighted the effectiveness of both plant breeding and soil inoculation in the mediation of salinity stress in alfalfa (Medicago sativa L.), however few have examined the effects of utilizing both of these techniques in tandem. The objectives of this study were to: 1) assess the effectiveness of Ensifer meliloti and Halomonas maura as inoculants to improve salinity tolerance in alfalfa, 2) assess the effectiveness of recurrent selection in improving fitness of alfalfa in saline conditions, and 3) assess whether inocula would confer additional benefits to salt-adapted alfalfa populations as indicated by both phenotypic and RNA sequencing data. To achieve these aims this study grew three alfalfa generations sequentially selected for salinity tolerance in association with inocula E. meliloti and H. maura alone and in tandem and compared against plants given a 60 kg/ha nitrogen amendment under 0, 8, or 16 dS/m of salinity. Results showed that while biomass was only increased in saline conditions through the nitrogen amendment, E. meliloti did confer increased salinity tolerance through increases of the osmoprotectant proline. Recurrent selection for salt tolerance in alfalfa increased chlorophyll content, stem count, and plant height, however generation G2 displayed equal or superior performance compared to generation G3, suggesting the onset of an inbreeding depression. The RNA-seq study found that generation G2 plants displayed an upregulated component of the TOR signalling pathway which modulates growth under stressful conditions, and that E. meliloti modulated genes responsible for metabolism of the osmoprotectants proline and glycine betaine as well as sulfur uptake in salt stressed plants. In summary, despite strong inhibition of mutualism by 8 dS/m salinity rhizobium confer beneficial effects on alfalfa include significantly higher proline production and improved sulfur uptake; recurrent selection increased chlorophyll content, stem count, and height, however a potential inbreeding depression caused by high selection pressure may have prevented gains in biomass from becoming significant in later generations.
Description
Keywords
Alfalfa, Rhizobium, Salinity-Tolerance, Western Canada
Citation
Degree
Master of Science (M.Sc.)
Department
Plant Sciences
Program
Plant Sciences