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Evaluation of a new method for testing the pathogenicity of molds to yam tubers
Frank Chukwunwike Ogbo1, Kingsley Chukwuebuka Agu2
1PhD, Ogbo Frank C- Professor, Applied Microbiology and Brewing Department, Nnamdi Azikiwe University, PMB 5025, Awka, Anambra State, Nigeria.
2MSc, Agu, Kingsley C- Lecturer II, Applied Microbiology and Brewing Department, Nnamdi Azikiwe University, PMB 5025, Awka, Anambra State, Nigeria.

Article ID: 100002M08FO2015
doi:10.5348/M08-2015-2-OA-2

Address correspondence to:
Frank Chukwunwike Ogbo Awka
Anambra
Nigeria, 234
Phone: +234-8035642014

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How to cite this article
Ogbo FC, Agu KC. Evaluation of a new method for testing the pathogenicity of molds to yam tubers. Edorium J Microbiol 2015;1:9–17.


Abstract
Aims: The Objective of this study was to compare methods involving cutting of yam, with a method developed in our lab, which exposes the yams to the pathogens but without cutting the protective skin as well as to estimate the weight loss and percentage severity of rots caused by rot-causing molds of yam tubers.
Methods: A total of thirteen test molds viz., Aspergillus sp., Aspergillus tamarii, Aspergillus niger, Aspergillus flavus, Fusarium solani, Lasiodiplodia theobromae, Mucor circinelloides, Paecilomyces sp., Fonsecaea sp., Phialophora sp., Graphium sp., Saccharomyces sp. and Exophiala sp., as identified using the partial ITS rDNA sequencing analysis and a BLAST search using the GenBank sequence database, isolated from previous works from five yam varieties namely: Dioscorea dumetorum, two varieties each of D. alata and D. rotundata, were used for this study. Comparative pathogenicity tests were carried out with fresh, healthy yam tubers by the methods described by Okigbo and Nmeka, (2005) and a method developed in our laboratory. The percentage weight loss over a period of four weeks, symptoms observed and percentage severity of rots produced by the pathogenic molds were all studied.
Results: The ability of both tests to detect severity of spoilage were studied and recorded as + (symptoms noticed), – (No symptom noticed) and +/C (symptoms noticed and consistent). Only seven isolates were pathogenic by the method of Ogbo and Agu, whereas all thirteen isolates were pathogenic by the method of Okigbo and Nmeka (2005). There was no significant difference p>0.05 between the weight losses and percentage severity of rots amongst the test molds with both methods except in the case of D. alata var. abana mmee tested with Fusarium solani which displayed high percentage rot severity of 450.00 by the method of Ogbo and Agu as against 153.85 displayed by the method of Okigbo and Nmeka (2005). Results obtained helped to ascertain the state of the molds (opportunistic pathogens or pathogens).
Conclusion: Only molds capable of breaching the protective cover of yam tubers and eliciting original symptoms consistent with those seen in previous studies and reported in other literatures were actual yam pathogens.

Keywords: Fungal rots, Fungal spoilage, Pathogenicity tests, Yam varieties

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Author Contributions:
Frank Chukwunwike Ogbo – Substantial contributions to conception and design, Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Kingsley Chukwuebuka Agu – Analysis and interpretation of data, Revising it critically for important intellectual content, Final approval of the version to be published
Guarantor of submission
The corresponding author is the guarantor of submission.
Source of support
None
Conflict of interest
Authors declare no conflict of interest.
Copyright
© 2015 Frank Chukwunwike Ogbo et al. This article is distributed under the terms of Creative Commons Attribution License which permits unrestricted use, distribution and reproduction in any medium provided the original author(s) and original publisher are properly credited. Please see the copyright policy on the journal website for more information.