Characterisation and pathogenicity of Phytophthora colocasiae on taro

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dc.contributor.advisor MacDiarmid, R en
dc.contributor.advisor Tyson, J en
dc.contributor.advisor Bowen, J en Maslen-Miller, Amy en 2017-03-09T02:33:26Z en 2016 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract In 1993, taro leaf blight (TLB) disease decimated Samoa’s entire taro (Colocasia esculenta) crop within 6 months, halting all international export. TLB disease is caused by the fungus-like oomycete Phytophthora colocasiae. This oomycete is commonly spread in windy and wet conditions and causes necrotic lesions on taro leaves and causes corm rot post-harvest. Using 40 P. colocasiae isolates this project aimed to 1) establish the genetic differences between P. colocasiae isolates and their phylogenetic relationships, 2) determine the differences in pathogenicity between P. colocasiae isolates on taro leaves and corms, and 3) determine whether corms of tolerant taro varieties will become infected by P. colocasiae. P. colocasiae were characterised using elongation factor 1-alpha (EF1a) sequencing in the ambition to determine their intraspecific genetic variability; EF1a from only one isolate (Pc 50) was achieved and this showed remarkable variability indicative of either an impure isolate or a heterokaryon. An existing in vitro leaf disc assay was used to test the pathogenicity of the different isolates of P. colocasiae on three cultivars of taro whereby their growth rates were measured compared based on the diameter of the necrotic lesion. A range of pathogenicity was observed in the lesion diameter for the 27 P. colocasiae isolates. An inoculation assay was developed to infect corms in vitro with P. colocasiae isolates. This new assay was then used to test the pathogenicity of the P. colocasiae isolates on three taro cultivars (Fijian white, Fijian pink and Samoan pink). Infection of corms was assessed by destructive examination and re-isolation to determine the presence of infectious P. colocasiae and to prove Koch’s postulates. This novel assay demonstrated the infection variability from 16 P. colocasiae isolates on three taro cultivars. A weak correlation exists between the pathogenicity of P. colocasiae isolates on leaves and corms of Samoan cultivars. Further research that addressed a variety of taro cultivars may strengthened this correlation. The overarching aim, to address the relationship between genotype and pathogenicity of P. colocasiae isolates, was not resolved. Further investigation using pure isolates derived from hyphal tip or single spore isolation will provide more robust information about this relationship. In addition, the new in vitro corm assay may provide a basis for investigating tolerance of new varieties and the biosecurity risks of exported taro crops. Keywords: Phytophthora colocasiae, Colocasia esculenta, Taro Leaf Blight (TLB), elongation factor 1-alpha (EF1a) en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264906311702091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.title Characterisation and pathogenicity of Phytophthora colocasiae on taro en
dc.type Thesis en Biological Science en The University of Auckland en Masters en
dc.rights.holder Copyright: The author en
pubs.elements-id 616529 en
pubs.record-created-at-source-date 2017-03-09 en

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