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Title:Identification of fungi and bacteria associated with internally discolored horseradish roots
Author(s):Yu, Junmyoung
Advisor(s):Babadoost, Mohammad
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Amoracia rusticana
soilborne disease
internal root discoloration
Abstract:This study was conducted to identify fungi and bacteria associated with the internally discolored horseradish roots. During 2008-2009, 75, 306, 115, and 120, horseradish roots from California, Illinois, Ontario (Canada), and Wisconsin, respectively, were collected and tested for the presence of fungi and bacteria. The roots were surface-disinfected and five segments (5 mm thick) were cut from each root and placed onto acidified potato dextrose agar (A-PDA) and nutrient agar (NA) in Petri plates. The plates were incubated at 22-24 C with 12 h light/12 h darkness. Small plaques from the edges of the growing fungal colonies were transferred onto PDA. Morphological characteristics of fungal isolates were examined and compared with the references. Molecular identification of the fungal isolates was accomplished by sequence analysis of the PCR products, resulting from using fungal universal primers (ITS5 and ITS4 for all fungal isolates), mitochondrial DNA primers cox3A-cox3B and nad1A-nad1B for Verticillium isolates, and elongation factor 1 alpha primer EF-1H-EF-2T and mitochondrial small subunit rDNA primers NMS1-NMS2 for Fusarium isolates. A total of 18 fungal genera were identified, which included Alternaria (3.8% roots), Arthopyreniaceae (0.4%), Chaetomium (0.6%), Colletotrichum (2.3%), Cordyceps (2.3%), Cylindrocarpon (0.9%), Fusarium (31.8%), Neonectria (1.3%), Penicillium (4.4%), Phoma (0.1%), Phomopsis (0.4%), Pyrenochaeta (2.7%), Rhizoctonia (0.1%), Rhizopus (1.0%), Rhizopycnis (0.4), Trichurus (0.6%), Ulocladium (0.4%), and Verticillium (38.0%). In greenhouse tests Verticillium dahliae, V. longisporum, Fusarium acuminatum, F. commune, F. oxysporum, and F. solani caused internal root discoloration, and F. commune caused root rot in horseradish plants. Single-cell colonies of isolated bacteria were grown on NA. Characteristics of each purified colony were recorded. Isolated bacteria were identified based on the analysis of sequences of 16S rDNA, resulting from polymerase chain reaction (PCR) - restriction fragment length polymorphism (RFLP) assay. A total of 52 bacterial species in 20 genera were identified, which were classified into five classes, Actinobacteria (50 roots), Alphaproteobacteria (10 roots), Bacilli (234 roots), Betaproteobacteria (4 roots), and Gammaproteobacteria (287 roots). The majority of the isolates were identified as Bacillus and Pseudomonas, which were isolated from 185 and 204 roots, respectively. Results of in vitro tests showed that three Bacillus isolates and two Pseudomonas isolates strongly inhibited the growth of Verticillium and Fusarium species.
Issue Date:2010-08-31
Rights Information:Copyright 2010 Junmyoung Yu
Date Available in IDEALS:2010-08-31
Date Deposited:2010-08

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