Oospore populations of Peronospora viciae : quantification, germinability and survival

D.J. van der Gaag

Research output: Thesisinternal PhD, WU

Abstract

<p>Peronospora viciae causes downy mildew on pea, field and broad bean. Two pathogens can be distinguished, P. viciae f.sp. pisi on pea (Pisum sativum) and P. viciae f. sp. fabae on field and broad bean (Vicia faba). These pathogens form resting spores, called oospores, in their host plant tissue. The oospores infest the soil after decomposition of the surrounding plant tissue and are the means by which the pathogens survive in the absence of host plants. In the present thesis aspects of the population biology of the oospores were investigated. Numbers of oospores were determined by extraction from plant tissue or soil. A vital stain test and a germination assay were used to assess viability and germinability of oospore populations. Monoconidial isolates of the two pathogens were able to produce oospores in monoculture and thus both pathogens are homothallic. P. viciae f.sp. pisi had a minimum temperature of about 10°C for oospore production and P. viciae f.sp. fabae below 5°C Dry-stored oospores of P. viciae f.sp. pisi germinated in water and appeared independent of an exogenous chemical stimulus for germination. Germinability of these oospores increased with oospore age up to a certain point and was related to their infectivity in a bioassay. Dry-stored oospores of P. viciae f.sp. fabae did neither germinate in water nor did they infect seedlings in a bioassay. After incorporation in field soil, oospore populations of both pathogens declined rapidly, and small, probably non-random, proportions of the original oospore populations survived for more than a year. The ability of oospores of P. viciae f.sp. pisi to germinate in water declined rapidly after incorporation in soil. Low percentages of oospores extracted from soil germinated in water, but relatively high disease incidences were obtained after inoculation of pea seeds with these oospores which suggested that soilexposed oospores become dependent on a chemical stimulus for germination. Oospores of P. viciae f.sp. fabae were infective after incubation in field soil for two years.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Zadoks, J.C., Promotor
  • Frinking, H.D., Promotor, External person
Award date24 Mar 1997
Place of PublicationS.l.
Publisher
Print ISBNs9789054856641
Publication statusPublished - 1997

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Keywords

  • plant pathogenic fungi
  • erysiphales
  • mildews
  • microorganisms
  • cell differentiation
  • spores
  • plant pests
  • plant diseases
  • epidemiology
  • distribution
  • germination
  • seed germination
  • seed dormancy

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