Document Type

Dissertation - Open Access

Award Date

2019

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Febina Mathew

Keywords

Fusarium, Heterodera glycines, Interaction, Pathogenicity, Root rot, Soybean

Abstract

In South Dakota, Fusarium-associated diseases (e.g. seedling diseases, root rot and sudden death syndrome) are emerging threats to soybean production. Several species of Fusarium have been reported to cause these diseases in the soybean producing regions of the United States and in the world. However, little information is available on the species of Fusarium causing soybean root rot in South Dakota and their pathogenicity. Therefore, the objectives of this study were to (1) characterize the species of Fusarium causing soybean root rot in South Dakota; (2) evaluate the cross-pathogenicity of species of Fusarium causing root rot of soybean and corn; (3) screen soybean germplasm for resistance to F.graminearum under the greenhouse conditions; (4) determine the interaction of F.graminearum and F.proliferatum with Heterodera glycines (soybean cyst nematode, SCN) on soybean roots in the greenhouse; and (5) determine the effect of soil nutrients on the association of F.virguliforme and F.proliferatum with H.glycines under both greenhouse and field conditions. In 2014, a survey of 200 commercial soybean fields across 22 counties in South Dakota was conducted during the reproductive growth stages of the soybean development. From the roots of the diseased plants sampled, 11 species of Fusarium were identified using morphology and molecular techniques. Among the 11 species of Fusarium, F.graminearum (51%) followed by F.acuminatum (30%) were the most frequently recovered, while F.virguliforme, F.solani, F.equiseti-incarnatum complex, F.commune, and F.subglutinans were among the least frequently recovered (< 2%). Fifty-seven isolates were arbitrarily selected from a total of 1130 isolates that represented the 11 species of Fusarium to test for their pathogenicity on soybean. It was determined that isolates of F.oxysporum, F.armeniacum, and F.commune caused the greatest root rot severity on soybean plants in the greenhouse. In addition, there were significant differences in root rot severity caused among the 57 isolates on soybean when compared to the non-inoculated control plants and among the isolates within F.acuminatum, F.oxysporum, F.proliferatum, and F.solani. Results of the cross-pathogenicity among Fusarium isolates causing root rot of soybean and corn in South Dakota showed that there were significant differences among individual isolates and the non-inoculated control on both crops. Two F.proliferatum isolates and one F.graminearum isolate from corn caused significantly greater root rot severity compared to the others and the non-inoculated on soybean and corn. Soybean germplasm screening for resistance to F.graminearum, revealed eight accessions that were significantly less susceptible to the fungus, and may be used as potential sources of resistance in breeding programs to develop soybean cultivars with resistance to root rot caused by F.graminearum. A greenhouse experiment on the association of F.graminearum and F.proliferatum with H.glycines detected no synergic interaction between the fungus and the nematode. The root rot severity caused by the F.graminearum and F.proliferatum isolates did not significantly increase in the presence of H.glycines. The presence of F.graminearum did not affect the nematode egg counts when compared to H.glycines only treatment. However, the presence of F.proliferatum reduced the reproduction of H.glycines on soybean roots though not statistically significant. To study the effect of soil nutrients on the association of F.proliferatum and F.virguliforme with H.glycines in the field, two rates of N-P-K fertilizers (15:15:15 and 50:80:110) were used on SCN susceptible and SCN resistant soybean varieties. The root rot severity caused by the isolates of F.virguliforme and F.proliferatum did not increase with either N-P-K rates application. At harvest, the number of SCN egg count per 100 cc of soil was higher (>9000 per 100 cc of soil) in SCN susceptible plots compared with SCN resistant variety irrespective of the N-P-K fertilizer rate application. The highest soybean yields were obtained from plots with SCN resistant soybean variety with application of starter N-P-K fertilizer rate. Overall, the collective findings from this study indicate that the isolates representing the 11 species of Fusarium were pathogenic on soybean in South Dakota. In fields with a history of Fusarium root rot, soybean growers are recommended to adopt proactive management strategies to minimize the impact of the disease, which includes use of fungicide seed treatments, well-drained planting beds, tillage practices, and resistant cultivars (if available).

Library of Congress Subject Headings

Soybean -- Diseases and pests -- South Dakota.
Fusarium diseases of plants -- South Dakota.
Root rots -- South Dakota.
Soybean cyst nematode.

Format

application/pdf

Number of Pages

200

Publisher

South Dakota State University

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Rights Statement

In Copyright