Degree Type

Thesis

Date of Award

2016

Degree Name

Master of Science

Department

Plant Pathology and Microbiology

Major

Plant Pathology

First Advisor

Daren Mueller

Second Advisor

Steven Whitham

Abstract

Soybean vein necrosis virus (SVNV) rapidly became a widespread soybean (Glycine max) virus within a few years of its initial confirmation in 2008. The economic impact of soybean vein necrosis (SVN) disease remains unknown. Soybean is a crop of global importance with nearly 4 billion bushels of soybeans produced in the United States in 2014. This study was designed to pursue two main questions; is there any yield loss or change in seed quality associated with SVN and are there horticultural or cover crop species that could be serving as sources of SVNV inoculum?

In order to determine if there was any yield loss or change in seed quality associated with SVN, field studies were conducted in six states in 2013, 2014, and 2015. Quantitative parameters, including seeds per pod, pods per plant, yield, and 100-count seed weight, as well as qualitative parameters, including protein and oil concentration, were assessed from plants or seeds collected from research and commercial production fields. Results of this study did not find any impact on yield by SVN. However, seed quality was affected. In Iowa, oil concentration decreased by 0.11% as disease incidence increased by 1% (P=0.04). Changes in fatty acid profiles of seed were also observed; linolenic, linoleic and stearic acids decreased between 0.5 and 0.15% in 2 of 6 locations that were tested. These results suggest that infection by SVNV negatively affects soybean seed quality, which may affect the marketability of soybeans for premium markets.

Some tospoviruses, such as Tomato spotted wilt virus, are globally important pathogens with extensive host ranges. Because SVNV is a Tospovirus and questions have been raised about soybean being the primary plant host, this study investigated the ability of specialty and cover crops that were commonly present in Iowa to serve as alternative hosts for SVNV. Additionally, insect vector feeding preference was examined on the cover crop species. Eighteen cover crop and seven specialty crops were tested using mechanical and direct thrips inoculations. Presence of SVNV was determined with ELISA. Systemic infection of buckwheat and local infections of melon and winter pea were found. Symptoms were observed on buckwheat and melon. Soybean thrips were found to prefer alfalfa, buckwheat, and crimson clover, and red clover; although they were able to feed on all plant species tested if no other food was presented.

The results from this study indicate changes in fatty acids, oil content, and seed size in soybean seed from SVN symptomatic plants, but no yield loss was seen. Timing of infection may play a role in the extent of damage from SVNV infection. Management of SVNV, as with many viral diseases, may include reduction of inoculum sources and monitoring of insect vectors. This study tested 25 plant species to determine if they could serve as sources of primary inoculum each growing season. Buckwheat, melon, and pea were all found to be susceptible to SVNV infection when direct thrips inoculated. None of these plants are perennials or found in large areas near soybean in the Midwest and thus are not considered to be of concern to soybean farmers.

Copyright Owner

Melissa Irizarry

Language

en

File Format

application/pdf

File Size

113 pages

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