Armillaria root rot of tea in Kenya : characterization of the pathogen and approaches to disease management

W. Otieno

Research output: Thesisinternal PhD, WU

Abstract

The rare occurrence of basidiomata and rhizomorphs constrains diagnosis of Armillaria root rot and identification of <em>Armillaria</em> species in Africa. This has had a negative impact on taxonomic research on the genus <em>Armillaria</em> in the continent, where the existence of various genetic groups of the fungus is more easily demonstrated by techniques that do not depend on the presence of basidiomata. DNA analysis by RAPD, ISSR, and RFLP of the IGS and ITS regions showed that <em>Armillaria</em> pathogenic on tea in Kenya consists mainly of two groups. Neither of these is identical to <em>A. mellea</em> , the species to which the disease has been largely attributed in the past. Based on morphological characteristics we conclude that the more predominant of the two groups is probably <em>A. heimii</em> and that the other group may represent a hitherto undescribed species.</p><p>Infected root residues in the soil comprise the major sources of <em>Armillaria</em> inoculum from which primary infection of tea starts. From these the fungus spreads rapidly within a plantation. Due to the scarcity of rhizomorphs it is assumed that the principal mode of spread of the fungus is through mycelial transfer at points of root-to-root contact. The available control measure against Armillaria root rot is the eradication of the fungus from infested sites through mechanical removal of the inoculum sources and infected plants. However, removal of inoculum is cumbersome and difficult to carry out manually. An isolate of <em>Trichoderma harzianum</em> was selected that readily colonized wood and strongly reduced viability of <em>Armillaria</em> inoculum. <em></em> Use of this isolate to control <em>Armillaria</em> would work better when applied in combination with soil disinfestation by solarization. By increasing soil temperatures, solarization for 10 wk completely inactivated woody <em>Armillaria</em> inocula, which could be reduced to a solarization period of 5 wk if it was followed with application of <em>T. harzianum</em> . Soil amendment with coffee pulp, earlier reported to enhance development of <em>T. harzianum</em> , did not increase colonisation of <em>Armillaria</em> inoculum sources by the antagonist but did cause a slight reduction in inoculum viability. It is concluded that a combination of solarization with subsequent introduction of <em>T. harzianum</em> has good prospects for managing Armillaria root rot.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Jeger, M.J., Promotor
  • Termorshuizen, A.J., Promotor, External person
Award date11 Feb 2002
Place of PublicationS.l.
Print ISBNs9789058085818
Publication statusPublished - 2002

Keywords

  • tea
  • camellia sinensis
  • plant pathogenic fungi
  • armillaria mellea
  • armillaria
  • identification
  • genetic analysis
  • disease control
  • biological control
  • kenya

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