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Date Permissions Signed

11-20-2020

Date of Award

Fall 2020

Document Type

Masters Thesis

Department or Program Affiliation

Department of Environmental Sciences

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Bunn, Rebecca

Second Advisor

DeVetter, L. W. (Lisa Wasko)

Third Advisor

Bauman, Jenise

Abstract

Chemical controls for agricultural pests and diseases can have detrimental effects on human health and the environment. One alternative is to introduce soil microbes, such as arbuscular mycorrhizal fungi (AMF), that can improve crop resilience to pests and pathogens. While many plants form symbioses with AMF, not all crops benefit from inoculation. We conducted three studies that questioned the effect of AMF from various sources on R. idaeus growth and resilience to pests/pathogens. First, in a small observational study, we investigated whether AMF colonization of raspberry roots covaried with stand vigor. In two subsequent greenhouse experiments, we asked (1) if AMF inoculation could increase the growth of Rubus idaeus cv. Meeker (red raspberry), (2) if AMF inoculation would improve plant resistance to the pathogen Phytophthora rubi and parasitic nematode Pratylenchus penetrans, and (3) if the source of AMF mattered.

In each greenhouse study, we grew R. idaeus with differing AMF inoculum prior to exposing them to pest/pathogens. Plants in the first greenhouse study were inoculated with no AMF, a constructed AMF community, or whole-soil inoculum from the root zone of wild Rubus parviflorus or farmed R. idaeus. All plants received small microbes (๐œ‡m) from mixed inocula. After 10 weeks, those plants were challenged with neither, either, or both P. rubi and P. penetrans. We measured plant biomass and height, shoot nutrients, AMF colonization of roots, and nematode densities. The second greenhouse study was conducted earlier in the spring and with younger plants. Plants first received AMF from the root zone of farmed R. idaeus, commercial AMF inoculum, or no AMF. After 5 weeks, half the plants were challenged with P. rubi. Plant height, biomass, and survivorship was assessed.

In contrast with our expectations, we found R. idaeus farm soil harbored AMF propagules at a similar density and infectivity as wild soil โ€“ both colonized 91% of roots despite high soil phosphorous. A lack of biomass or nutrient differences in plants receiving P. rubi and P. penetrans in the first experiment indicates we did not achieve pest/pathogen densities that impact plant growth. In contrast, conditions more favorable to P. rubi in the second experiment led to high rates of pathogen infection. In this experiment, whole-soil inoculum from the commercial farm increased the survival rate of young R. idaeus challenged with P. rubi by 300%, while commercial inoculum offered no benefit. We found no evidence that mycorrhizal inoculum altered nematode densities in roots or soil. Plants receiving P. penetrans had 315-680 nematodes/g root, with 55% lower densities in plants that also received P. rubi, suggesting an interaction between these organisms.

We conclude that the soil microbial communities on mature R. idaeus farms contain beneficial AMF, and that these biotas increase plant resilience to the pathogen P. rubi, at least under greenhouse conditions. These results are a promising step in the development of strategies to promote crop resilience and long-term sustainability of raspberry production.

Type

Text

Keywords

mycorrhizal fungi, AMF, soil ecology, crop science, pathology, nematode

Publisher

Western Washington University

OCLC Number

1226323288

Subject โ€“ LCSH

Vesicular-arbuscular mycorrhizas; Red raspberry--Diseases and pests--Biological control; Nematodes--Biological control; Soilborne plant pathogens--Biological control

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the authorโ€™s written permission.

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