Characterization, development of a field inoculation method, and fungicide sensitivity screening of the Pythium blight pathogen of snap bean (Phaseolus vulgaris L.)

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dc.contributor.authorHarrison, Leigh Annen
dc.contributor.committeechairRideout, Steven L.en
dc.contributor.committeememberFreeman, Joshua H.en
dc.contributor.committeememberBush, Elizabeth A.en
dc.contributor.committeememberStromberg, Erik L.en
dc.contributor.committeememberLangston, David B.en
dc.contributor.committeememberHong, Chuanxueen
dc.contributor.departmentPlant Pathology, Physiology, and Weed Scienceen
dc.date.accessioned2017-04-06T15:44:53Zen
dc.date.adate2011-05-05en
dc.date.available2017-04-06T15:44:53Zen
dc.date.issued2011-03-08en
dc.date.rdate2016-09-30en
dc.date.sdate2011-03-22en
dc.description.abstractNew Jersey, Georgia, and the Eastern Shore of Virginia (ESV) are important snap bean (Phaseolus vulgaris L.) growing regions, but profitability is threatened by Pythium blight. Causal agents of Pythium blight on snap bean were identified using morphological characterization and sequence analysis of the rDNA-internal transcribed spacer (ITS) regions of 100 isolates. Most isolates were Pythium aphanidermatum (Edson) Fitzp. (53%), and also included Pythium deliense Meurs (31%; all from Georgia), Pythium ultimum Trow (12%), Pythium myriotylum Drechsler (2%), Pythium catenulatum Matthews (1%), and unknown Pythium sp. (1%). To our knowledge, this is the first report of P. deliense in Georgia and on common bean and squash (Cucurbita pepo L.); as well as the first report of P. catenulatum on lima bean (Phaseolus lunatus L.) and in New Jersey. Fungicide labeling and cultivar selection for Pythium blight management is hindered by difficulties associated with conducting successful trials, because the disease occurs sporadically and clustered in the field. Three P. aphanidermatum-infested inoculum substrates were evaluated at three concentrations. The vermiculite/V8 juice (5:3 weight to volume) inoculum (10,000 ppg/0.3 m) consistently caused at least 50% disease in 3 field trials. Sensitivity of the Pythium blight pathogens was determined in vitro against five fungicides. Twenty-two Pythium isolates representing P. aphanidermatum, P. deliense, P. ultimum, and P. myriotylum were inoculated to media amended with each active ingredient at 0, 100μg/ml, the concentration equivalent to the field labeled rate if applied on succulent beans at 187 L/ha, and the equivalent if applied at 374 L/ha. All isolates were completely sensitive (100% growth reduction, or GR) to all active ingredients at the labeled rates, except azoxystrobin. At 100μg/ml azoxystrobin, one P. deliense isolate had 8.9% GR. All isolates had 100% GR to copper hydroxide at 100μg/ml, and the lowest GR on mefenoxam-amended medium was 91.9%. At 100μg/ml cyazofamid, all P. deliense isolates were completely sensitive and variation was observed in P. aphanidermatum isolates. At 100μg/ml potassium phosphite, significant GR similarities were recorded within isolates of the same species, and less than 50% GR was observed in all P. deliense isolates.en
dc.description.degreePh. D.en
dc.identifier.otheretd-03222011-000425en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-03222011-000425/en
dc.identifier.urihttp://hdl.handle.net/10919/77324en
dc.language.isoen_USen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectfield evaluation proceduresen
dc.subjectazoxystrobinen
dc.subjectcyazofamiden
dc.subjectPythium aphanidermatumen
dc.subjectPythium ultimumen
dc.subjectPythium delienseen
dc.subjectPythium myriotylumen
dc.subjectPythium catenulatumen
dc.subjectITS regionen
dc.subjectmorphological characterizationen
dc.subjectmefenoxamen
dc.subjectpotassium phosphiteen
dc.subjectcopper hydroxideen
dc.titleCharacterization, development of a field inoculation method, and fungicide sensitivity screening of the Pythium blight pathogen of snap bean (Phaseolus vulgaris L.)en
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplinePlant Pathology, Physiology, and Weed Scienceen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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