Phylogeny, Molecular Detection, and Genetic Variation of Fusarium oxysporum, Vascular Wilt Pathogen of Lettuce

Persistent Link:
http://hdl.handle.net/10150/194000
Title:
Phylogeny, Molecular Detection, and Genetic Variation of Fusarium oxysporum, Vascular Wilt Pathogen of Lettuce
Author:
Mbofung, Gladys Chia
Issue Date:
2006
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This work encompasses studies on the phylogeny of F. oxysporum f. sp. lactucae, the development of a PCR-based seed assay for the detection of this fungus in seed, the potential of seed transmission of the fungus that may result in seed dissemination, and the genetic variation existing within pathogen populations. In phylogenetic analysis, the mtSSU and EF-1α sequences provided limited phylogenetic resolution and did not differentiate the lactucae isolates from other F. oxysporum isolates, while the IGS region resolved lactucae race 1 isolates as a monophyletic group with three other f. spp. of F. oxysporum. In all analyses, lactucae race 2 isolates comprised a separate lineage that was phylogenetically distinct. Based the IGS, PCR primers were designed for detection of the fungus, and a PCR-based seed assay was developed for detection of the fungus in seed. This assay allowed for detection of the pathogen from artificially infested seed lots with infestation rates as low as 0.5%. To investigate seedborne transmission, the moderately resistant cultivars Sharpshooter, Vulcan, and King Henry were inoculated and grown to maturity in the greenhouse. The pathogen was recovered from sections of surface disinfested inflorescence stalks at rates of 14.3 - 62.7% but not from the floral parts. The incidence of recovery from nondisinfested seeds was between 0.02% and 0.08%. The pathogen was not isolated from surface disinfested seeds suggesting that it was externally seedborne. The pathogen was recovered from pathogen-free seeds mixed with infested debris suggesting infested seed may contribute to recently documented dissemination of this pathogen worldwide. Isolates of Fusarium oxsyporum f. sp. lactucae were analyzed for genetic diversity using inter-simple sequence repeat molecular markers. Results revealed 2 main groups within the Arizona isolates corresponding to eight haplotypes in 2005, which evolved from 2 haplotypes in 2001. Haplotype 1-05 was widespread, occurring in two of the four countries where F. o. f. sp. lactucae has been reported. 23 haplotypes were identified among the California isolates that clustered into two subgroups. The clustering of isolates from Arizona suggests that there has been more than one introduction of the pathogen into Arizona.
Type:
text; Electronic Dissertation
Keywords:
Phylogeny; Fusarium; oxysporum; genetic; detection; seedborne
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Plant Pathology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Pryor, Barry M.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titlePhylogeny, Molecular Detection, and Genetic Variation of Fusarium oxysporum, Vascular Wilt Pathogen of Lettuceen_US
dc.creatorMbofung, Gladys Chiaen_US
dc.contributor.authorMbofung, Gladys Chiaen_US
dc.date.issued2006en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis work encompasses studies on the phylogeny of F. oxysporum f. sp. lactucae, the development of a PCR-based seed assay for the detection of this fungus in seed, the potential of seed transmission of the fungus that may result in seed dissemination, and the genetic variation existing within pathogen populations. In phylogenetic analysis, the mtSSU and EF-1α sequences provided limited phylogenetic resolution and did not differentiate the lactucae isolates from other F. oxysporum isolates, while the IGS region resolved lactucae race 1 isolates as a monophyletic group with three other f. spp. of F. oxysporum. In all analyses, lactucae race 2 isolates comprised a separate lineage that was phylogenetically distinct. Based the IGS, PCR primers were designed for detection of the fungus, and a PCR-based seed assay was developed for detection of the fungus in seed. This assay allowed for detection of the pathogen from artificially infested seed lots with infestation rates as low as 0.5%. To investigate seedborne transmission, the moderately resistant cultivars Sharpshooter, Vulcan, and King Henry were inoculated and grown to maturity in the greenhouse. The pathogen was recovered from sections of surface disinfested inflorescence stalks at rates of 14.3 - 62.7% but not from the floral parts. The incidence of recovery from nondisinfested seeds was between 0.02% and 0.08%. The pathogen was not isolated from surface disinfested seeds suggesting that it was externally seedborne. The pathogen was recovered from pathogen-free seeds mixed with infested debris suggesting infested seed may contribute to recently documented dissemination of this pathogen worldwide. Isolates of Fusarium oxsyporum f. sp. lactucae were analyzed for genetic diversity using inter-simple sequence repeat molecular markers. Results revealed 2 main groups within the Arizona isolates corresponding to eight haplotypes in 2005, which evolved from 2 haplotypes in 2001. Haplotype 1-05 was widespread, occurring in two of the four countries where F. o. f. sp. lactucae has been reported. 23 haplotypes were identified among the California isolates that clustered into two subgroups. The clustering of isolates from Arizona suggests that there has been more than one introduction of the pathogen into Arizona.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectPhylogenyen_US
dc.subjectFusariumen_US
dc.subjectoxysporumen_US
dc.subjectgeneticen_US
dc.subjectdetectionen_US
dc.subjectseedborneen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePlant Pathologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairPryor, Barry M.en_US
dc.contributor.committeememberBirky, Jr., C. Williamen_US
dc.contributor.committeememberVanEtten, Hans D.en_US
dc.contributor.committeememberMatheron, Michael E.en_US
dc.contributor.committeememberGordon, Thomas R.en_US
dc.identifier.proquest1975en_US
dc.identifier.oclc659746550en_US
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