Document Type

Thesis - Open Access

Award Date

2025

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Madalyn Shires

Abstract

Soybean cyst nematode (SCN), Heterodera glycines (HG) Ichinohe, is an endoparasitic nematode and one of the major yield-limiting pathogens of soybean (Glycine max L.) in the United States. Soybean cyst nematode alone accounts for more than $1.5 billion economic loss annually in North America. First reported in the U.S.A. in 1954 in New Hanover County, North Carolina and later in 1995 in Union County, South Dakota. Prior to this study, SCN has spread in 34 counties in the state. As a soil pathogen, which can adapt to most soil conditions under soybean production and beside soybean, it is hosted on a wide range of crops and weeds belonging to plant families including Asteraceae, Brassicaceae, and Fabaceae. The nematode can often go undetected in the absence of visually obvious symptoms and can cause yield loss of 30% in heavily infested fields. Several soybean plant introductions (PI) are used as resistance sources for breeding resistant cultivars against SCN. However, PI 88788, is the single major source of resistance accounting for approximately 90% of resistant cultivars. This study was conducted to examine the distribution of SCN populations and assess its virulence phenotypes in South Dakota. A total of 362 soil samples from 49 counties across South Dakota were processed and 60% of the tested samples were positive with SCN population density ranging from 50-62,000 per 100 cm3 of soil. A total of 51 SCN field populations representing 39 counties were subjected to HG Type test using three resistance sources PI 548402 ‘Peking’, PI 88788, and PI 437654 for characterizing their virulence phenotypes. Five different HG Types were identified in South Dakota and HG Type 1.2- was the predominant one followed by HG Type 2-. The result of this study suggests that SCN field populations are overcoming the major resistance genes found in ‘Peking’ and PI 88788. The study also indicates the necessity to follow long rotation cycles utilizing both resistant sources and non-host crops. The second study focused on designing and validating molecular diagnostic tools, Quantitative Polymerase Chain Reaction (qPCR) and Recombinase Polymerase Amplification (RPA) for rapid screening of SCN populations and assessing presence in the fields. Initially, a qPCR assay was developed and optimized; the assay highly specific detecting SCN population exclusively and did not cross react with other plant-parasitic nematodes. A real-time RPA assay was developed and optimized for the same target region for detection of SCN under isothermal conditions. Amplification was observed for H. glycines only and no amplification was observed for non-target nematodes, making the assay very specific. This assay also amplified soil DNA extracts of all H. glycines making it suitable for infield diagnostics. The third study focused on identification and evaluation of alternative hosts of SCN. Greenhouse study was conducted for a total of 10 diverse crops and four weeds for their suitability to host two SCN populations, HG Type 0 and 1.2- and female index (FI) were determined. HG Type 0 showed dry beans have statistically significant higher FI (10.93) and for HG Type 1.2- field pennycress had statistically higher FI (22.79), followed by dry beans (FI, 17.09). Dry beans and field pennycress were found to be good hosts of SCN whereas other plant species were poor hosts of SCN in South Dakota.

Library of Congress Subject Headings

Soybean cyst nematode -- South Dakota. 
Soybean -- Diseases and pests -- South Dakota. 
Plant diseases -- Diagnosis. 
Soybean cyst nematode -- Pathogenesis.      

Publisher

South Dakota State University

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Rights Statement

In Copyright