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Title:Characterization of arbuscular mycorrhial fungi on Glycine max and its influence on plant disease severity
Author(s):Pawlowski, Michelle Lynn
Director of Research:Hartman, Glen L.
Doctoral Committee Chair(s):Hartman, Glen L.
Doctoral Committee Member(s):Heath, Katy D.; Lambert, Kris N.; Miller, Andrew N.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Arbuscular mycorrhizal fungi
biological control
Glycine max
soybean cyst nematode
sudden death syndrome
Abstract:With an ever-growing human population and apparent environmental impacts due to climate change, producers and researchers need to investigate more ecologically conscious alternatives to increase agricultural production. One method to consider is using a group of beneficial microbes called arbuscular mycorrhizal fungi (AMF) that form associations with over 80% of all terrestrial plant species and assist plants by increasing nutrient uptake, drought tolerance, and resilience against pathogens and pests. However, the level of benefit may be variable and be host-genotype dependent. Genotype variation to AMF colonization and degree of benefit has been identified in crops, including soybean; however, very few soybean genotypes have been evaluated and no information is known about the genetics controlling AMF colonization in soybean. The overall goal of this project was to evaluate larger panels of soybean genotypes to gain a better understanding how host genotype influences AMF colonization and how AMF may affect above-ground biomass and plant protection. The goal of the second chapter was to to identify genomic regions associated with mycorrhizal colonization in soybean. A genome-wide association analysis was deployed using a diverse panel of 350 exotic soybean accessions inoculated with Rhizophagus intraradices. Roots of all accessions were microscopically evaluated for colonization by R. intraradices using a modified gridline intersect method. Root colonization differed significantly (P < 0.001) among genotypes ranging from 11-70%. A whole-genome resequencing-derived SNP dataset identified six quantitative trait loci (QTL) significantly associated with R. intraradices colonization that explained 24% of the phenotypic variance. Candidate genes identified in these QTL regions included homologs to known nodulin protein families and other symbiosis-specific genes. The third chapter focused on if soybean genotypes differ in AMF-mediated growth and if breeding impacted this relationship. A panel of 49 soybean genotypes were grown in a greenhouse for six weeks with or without R. intraradices. Mycorrhizal responsiveness was measured by taking the percent difference in above ground dry weights of plants inoculated with R. intraradices compared to non-inoculated control plants. There was a significant genotype effect on mycorrhizal responsiveness ranging from -7% to 115% increase in above ground dry weights compared to the non-inoculated control. The level of AMF-mediated above ground dry weights was significantly correlated (r = 0.45; P < 0.0001) with release year of the soybean cultivar. The results of this study indicate breeding may have indirectly selected for increased mycorrhizal responsiveness and shows the large effect soybean genotype has on AMF-mediated growth stimulation. The fourth chapter focused on the interaction between soybean genotype, R. intraradices, and Fusarium virguliforme, a necrotrophic soilborne pathogen that causes sudden death syndrome of soybean. Six soybean genotypes were inoculated with F. virguliforme and with or without R. intraradices in a greenhouse experiment. There was a significant (P < 0.05) reduction of 45% and 28% in area under the disease progress curve values and in relative F. virguliforme quantities, respectively, in soybean roots of R. intraradices-colonized plants compared to plants not colonized by R. intraradices averaged over the six soybean genotypes. Root weight of R. intraradices-colonized plants increased (P < 0.05) by 58% compared to plants not colonized by R. intraradices. A nutrient analysis of root tissues showed increases (P < 0.05) in nutrient concentrations in plants colonized by R. intraradices for phosphorus, potassium sulfur, boron, and sodium compared to roots not colonized by R. intraradices. This study showed that R. intraradices considerably reduced SDS severity and F. virguliforme colonization while simultaneously increasing growth and nutrient uptake. The fifth chapter focused on different AMF species and their ability to suppress soybean cyst nematode (SCN; Heterodera glycines). SCN is a widely occurring pathogen and the leading cause of soybean yield losses in the USA. There is a need to find additional SCN management strategies as sources of SCN resistance have become less effective in keeping SCN populations in check. In one experiment, all five AMF species tested (Claroideoglomus claroideum, Diversispora eburnean, Dentiscutata heterogama, Funneliformis mosseae, and R. intraradices) reduced (P < 0.05) the number of cysts on soybean roots by 59% to 81% compared to soybean roots without AMF. In two other experiments, F. mosseae reduced the counts of SCN juveniles (J2-J3 stages) in soybean roots by 60% and was able to suppress egg hatching by as much as 30%. These experiments showed that AMF were able to suppress SCN cyst counts and at least with F. mosseae, reduce SCN juveniles in roots and suppress egg-hatching. The results of this project provide substantial insights into the relationship between soybean, AMF, and pathogen. I found a considerable amount of genetic variation in level of AMF colonization and mycorrhizal responsiveness. This shows a major component of the success of AMF inoculants may be attributed to host genotypes. More research should be done to gain a better understanding of the genetics behind mycorrhizal responsiveness. This information could be applied to breeding programs to create more responsive cultivars to alleviate the need for fertilizers. I also found a significant reduction in disease severity for both SDS and SCN. The mechanisms behind AMF-mediated plant protection against SDS and SCN seems to be multi-faceted, however a direct suppression of SCN was found. Further research is needed to exploit the potential usefulness of these AMF in field conditions and to determine the usefulness of AMF as a viable management tool to help alleviate yield loss due to disease as well as the need for pesticides.
Issue Date:2019-09-20
Type:Text
URI:http://hdl.handle.net/2142/106156
Rights Information:Copyright 2019 Michelle Pawlowski
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12


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