Evaluation of Rhizobium spp. as effective biocontrol agents for Aphanomyces root rot in field pea (Pisum sativum L.)
Date
2023-11-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-9256-5137
Type
Thesis
Degree Level
Masters
Abstract
Aphanomyces root rot (ARR), caused by the soil-dwelling oomycete Aphanomyces euteiches, poses a significant threat to global pulse crop production, causing severe root damage and yield reductions in field pea and other legume crops. Given the limited effectiveness of traditional disease management methods, this study explored the biocontrol potential of Rhizobium spp., dinitrogen (N2) fixing bacteria known for their symbiotic relationship with legume roots and use as N fertilizer replacements.
Obtained in this study from the nodules of Pisum sativum L. trap plants, a total of 70 bacterial isolates were screened for antagonistic activity towards A. euteiches in dual plate bioassays. An additional 24 isolates from existing culture collections and field collected legume nodules were also subjected to these assays. Most isolates, which were identified as rhizobia, were non-antagonistic. In comparison, three non-rhizobial nodule endophytes (NREs) isolated from the nodules of P. sativum trap plants— Burkholderia strain SU2B2, Kosakonia cowanii LL3B1, and Pseudomonas chlororaphis subsp. aurantiaca LL3B2 — exhibited antagonistic activity towards A. euteiches in vitro. Notably, K. cowanii LL3B1 was capable of completely halting A. euteiches colony growth for over 30 days.
In three sets of completely randomized sterile growth pouch assays, NREs K. cowanii LL3B1 and P. chlororaphis subsp. aurantiaca LL3B2, when applied as liquid seed inoculants, demonstrated the potential to enhance P. sativum nodulation by Rhizobium strains and reduce disease severity without affecting initial leaf development. Additionally, they increased N2-fixation in P. sativum compared with uninoculated controls.
This study also revealed the diversity of Rhizobium associated with P. sativum nodules, by isolating and identifying seven distinct species within the Rhizobiaceae family from P. sativum nodules. While none showed independent antagonism towards A. euteiches, the presence of certain Rhizobiaceae species alongside K. cowanii LL3B1 and P. chlororaphis subsp. aurantiaca LL3B2 showed potential to synergistically enhance antagonistic activity towards A. euteiches in vitro when evaluated in dual plate bioassays. Additional research is recommended to assess their impact on plant health and potential synergistic effects when applied as seed inoculants along with rhizobia.
These findings indicate that NREs, particularly K. cowanii and P. chlororaphis subsp. aurantiaca, hold potential as biocontrol agents against ARR. Consequently, further investigation of the biocontrol capabilities of bacteria associated with legume nodules may improve the efficacy of current disease mitigation strategies.
Description
Keywords
Aphanomyces, root rot, pea root rot complex, oomycete, field pea, Pisum sativum, Rhizobium, rhizobia, rhizobial, biocontrol, biological control, nodules, dual plate, NREs, non-rhizobial nodule endophytes, kosakonia, pseudomonas, kosakonia cowanii, pseudomonas chlororaphis, pseudomonas aurantiaca, rhizobiaceae, rhizobia ecology, soil microbial interactions, legume biocontrol, aphanomyces euteiches, crop disease mitigation, biocontrol bacteria agriculture, growth pouch
Citation
Degree
Master of Science (M.Sc.)
Department
Soil Science
Program
Soil Science