Document Type
Thesis - University Access Only
Award Date
2004
Degree Name
Master of Science (MS)
Department / School
Plant Science
First Advisor
Thomas E. Chase
Abstract
Isolates of the Diaporthe/Phomopsis (D/P) complex were collected from soybean (Glycine max (L.) Merrill) plants with stem canker symptoms in commercial soybean fields in South Dakota during 1999-2001. RFLP (restriction fragment length polymorphism) analysis of the ITS (internal transcribed spacer) region of nuclear ribosomal DNA, was carried out to identify 276 cultures. Polymerase chain reaction (PCR) amplified DNA fragments (ca. 580-640bp) defined by the primer pair ITS4'ITSs were digested with restriction enzymes Alu /, Hha /, and Rsa /. Analysis of resultant RFLPs enabled classification of isolates into two main groups: 212 (77.1 %) were the northern stem canker pathogen, Diaporthe phaseolorum (Cook & Ellis) Sacc. var. caulivora K. L. Athow & R. M. Caldwell (DPC, anamorph Phomopsis phaseoli (Desmaz.) Sacc), including the two subgroups DPC A (61.1%) and DPC B (16.0%), and 40 (14.5%) were the seed decay pathogen Phomopsis longicolla T. W. Hobbs (PL, teleomorph unknown). Twenty-three isolates (8.4%) could not be identified by ITS-RFLP, but were demonstrated not to be members of the DIP complex by morphological characteristics, pathogenicity, and other molecular methods.
Nineteen DPC isolates (10 DPC A and 9 DPC B), originating from fields in several counties within three years, were assessed for variability by RAPD (random amplified polymorphic DNA) analysis. Seventy-one random primers were screened. Among the 277 fragments amplified, 87 were polymorphic. These were generated by 30 primers. Based on RAPD profiles, a phenetic analysis was conducted with the NTSYS (version 2.1) UPGMA (unweighted pair[1]group method, arithmetic average) program. The calculated dendrogram suggested a high degree of genetic variability among the DPC isolates; DPC A & DPC B were indistinguishable by RAPD. The range of Jaccard's similarity coefficients among isolates was 0.295 to 0.842, while the majority of the isolates shared a similarity coefficient lower than 0.65. Sixteen of these isolates were inoculated on the susceptible soybean variety Mustang 151 RR in the greenhouse to assess pathogenicity. All the isolates showed high virulence and killed plants at a rate no less than 66. 7%; two isolates killed plants up to 100%.
It was noted that DPC A and DPC B isolates never originated from the same plant. This phenomenon might relate to_the seed borne nature of the disease, and prompted studies on vegetative compatibility. Most DPC isolates were examined for VCGs (vegetative compatibility groups) in this study. Isolates collected from the same plant, but different cankers, were often found to be in the same VCG. This finding has implications for understanding the etiology of northern stem canker.
Library of Congress Subject Headings
Soybean -- Diseases and pests.
Diaporthe phaseolorum.
Pathogenic fungi -- Molecular aspects.
Canker (Plant disease) -- Pathogenesis.
Publisher
South Dakota State University
Recommended Citation
Zhang, Dongxiu, "Molecular Identification and Population Variability of Diaporthe Phaseolorum Var. Caulivora From Soybeans in South Dakota" (2004). Electronic Theses and Dissertations. 1103.
https://openprairie.sdstate.edu/etd2/1103
Rights Statement
