Efficacy of selected plant extracts in the control of fungal dry rot of white yam (Dioscorea rotundata) tubers in Kogi State.
The word 'yam' refers to the tuber of the botanical genus Dioscorea in the family Dioscoreaceae (Degras, 1998). In Nigeria, Adamawa, Taraba, Benue, Nassarawa, Kogi, Edo and Kaduna states are the major yam producing states.
Edible species of yam include D. rotundata Pour, D. cayenensis Lam; D. inspida Dennst; D. bulbifera L; D. opposita Thumb; and D. trifida Lare (Onwueme, 1978). Nigeria cultivates six species, namely: D. rotundata Pour (white yam), D. cayenensis Lam (yellow yam) D. alata L (water yam), D. esculenta (Lour) Burk (Chinese yam), D. bulbifera L. (Aerial yam), and D. dumenterum pax (Cluster yam) (Adeniji, 1970).
Many fungi have been identified by various workers as causal organisms of various yam diseases. (Taiga 2003, 2005, Taiga and Olufolaji, 2008).
Chemical control measures have been tested and found effective in the control of yam rots (Nwankiti, et al, 1990), but he remarked that those chemicals were expensive and not usually easily affordable by most farmers in Nigeria.
Recently, Sawdust extract from Camwood was used to control yam tuber rot caused by fungi (Anon, 1991, Ejechi and Ilondu, 1999, Ojo and Olufolaji, 2005, Taiga and Olufolaji, 2008).
This research is aimed at isolating and identifies fungal pathogens associated with dry rot of yam tubers in storage and to test the efficacy of plant extracts in preventing rot depth caused by fungal pathogens in vivo.
Materials and methods
Rotted Dioscorea rotundata (Ekpe line) tubers were collected from farmers in Ibaji yam farming area in Kogi State, Nigeria; healthy yam tubers were also bought from the same source. The rotted tubers were washed with tap water and later distilled water before they were surface sterilized with 2% sodium hypochlorite and left to dry for 30 minutes, in order to avoid contamination by microorganisms.
The media used for fungi isolation was Yam Dextrose Agar (YDA). This was prepared by modifying the methods of Ejechi and Ilondu (1999). From the rotted yam samples, 0.5-1 cm pieces were cut at the periphery of the rotted tissues with a sterile scalpel, surface sterilized in 2.0% Sodium hypochlorite for 30 second and then rinsed in three changes of sterile distilled water and two pieces incubated on YDA per Petri-dish at room temperature (25[+ or -]3[degrees]C) for 5 days before observing for fungal colonies. Pure cultures of each fungal isolate were maintained by aseptic transfer to a freshly prepared medium. Pathogenicity test was carried out on the isolated fungi according to Koch's postulate.
Three different plant leaves (A. indica, A. barbadensis and N. tabacum) that have been found to posses fungicidal properties in vitro (Taiga, et al, 2008) were tested for efficacy in vivo. Each plant leaf samples was washed thoroughly in cold running tap water, air-dried and separately micronized with a hammer mill into a fine powder. The succulent leaves of Aloe barbadensis were used directly after washing in cold running tap water and air-dried. Cold water extraction was obtained by adding 10, 20, 30 and 40g of the powder of each plant leaf to 100 ml of distilled water separately in 250 ml beaker. This was left for 24 hours and subsequently filtered through four fold of sterile cheese cloth. These preparations gave 10, 20, 30 and 40% crude aqueous extract. Similarly, some quantity of Aleo leaves were blended with 100 ml of sterile distilled water, using a warring blender and left for 24 hours before filtration. Hot water extraction was obtained by infusing the same quantity of plant materials in 100 ml of sterile distilled water, using a 250 ml Erlenmeyer's flask in a water bath set at 100[degrees]C for 30 minutes. This was allowed to cool and the crude extract was obtained from the infusion by filtration through four folds of sterile Cheese cloth, to give concentrations of 10, 20, 30 and 40% respectively. Each of the extract concentration was kept aseptically in 150 ml conical flasks where they were exposed to UV light for further sterilization.
The effect of both their cold and hot aqueous extract concentrations, on prevention of rot depth was tested by using a sterile cork borer to create a hole of 5.0 mm diameter on each yam tuber. A disc of each fungus culture (4.0 mm diameter) was soaked for 30 seconds in 1ml of plant extract in sterile Petri-dish; and immediately introduced into the hole, using sterile mounting needle and forceps; the tissue previously removed from the hole was replaced after about 2.0 mm had been cut off to compensate for the thickness of the inoculants. The point of inoculation was sealed with Vaseline and the inoculated tubers were incubated on clean laboratory table for 5 days at room temperature (25[+ or -]3[degrees]C).
The results obtained were subjected to statistical analyses using one-way ANOVA at 5% level of significance.
Results and Discussions
Various workers have identified many fungi as causal organisms of various yam diseases (Anon, 1991; Ejechi and Ilondu, 1999, Amadioha and Obilor, 2002, Taiga and Olufolaji, 2008). Four pathogenic fungi (Fusarium oxysporium, Rhizopus stolonifer, Penicilium oxalicum and Aspergillus niger) were isolated from the rotted D. rotundata (Bannett and Hunter, 1972).
Several studies have been carried out and reported on the use of higher plant extracts in the control of fungal and other related diseases (Olufolaji, 1999; Amadioha and Obilor, 2003; Ojo and Olufolaji, 2005, Taiga and Olufolaji, 2008). The results from this study showed that 30 and 40% concentrations of cold and hot extracts of N. tabacum, completely prevented rot-depth caused by the four isolated pathogens (F. oxysporium, R. stolonifer, P. oxalicum and A. niger) in the yam tubers tested; thus, recording zero mean rot lesions, hence the test of homogeneity of variance could not be performed for F. oxysporium, A. niger, P. oxalicum, and R. stolonifer; an indication that hot extract of N. tabacum was highly efficacious in controlling the four fungal pathogens associated with rot of yam tubers, Fig 1c.
The hot extract of A. barbadensis at 20, 30 and 40% concentrations completely prevented F. oxysporium, R. stolonifer and P. oxalicum from causing rot depth lesion, while only its 40% concentration of the cold extract had similar effect on the three pathogens like the hot extract, Fig. 1a.
On the other hand, results of A. indica showed that 30 and 40% concentrations of its hot aqueous extract completely prevented F. oxysporium, R. stolonifer and P. oxalicum from causing rot depth lesion, while only the 40% concentration of the cold extract had similar effect on the three pathogens like the hot extract, Fig. 1b.
Although the cold and hot extracts of A. barbadensis and A. indica, as well as, the cold extract of N. tabacum at 40% concentration also completely prevented yam tuber rots caused by F. oxysporium, P. oxalicum and R. stolonifer; non of the extracts could completely prevent rot lesion caused by A. niger.
Differences in the toxicity of the different extracts might be due to the presence of inhibitors to the fungitoxic principles (Qasem and Ab-Blan, 1996; Amadioha, 2002); coupled with the observations of Uzuegbu and Okoro (1999), Amadioha and Uchendu (2003) Figures 1a-1c.
[FIGURE 1 OMITTED]
[FIGURE 1b OMITTED]
[FIGURE 1c OMITTED]
Generally, the findings of this research showed that N. tabacum, A. barbadensis and A. indica extracts possess fungicidal properties at different concentration levels. However, only cold and hot extracts of N. tabacum at 30 and 40% concentrations were able to prevent fungal rot caused by all four isolated pathogens in yam tubers treated. The susceptibility of the isolated pathogens to the tested plant extracts varied with extraction method used in preparing the plant extracts (weather cold or hot extract), as well as the concentrations of the extracts. The work showed that F. oxysporium, R. stolonifer and P. oxalicum were more susceptible to all the three plants extracts, while A. niger was less susceptible to all the plant extracts. The hot extract of N. tabacum was most fungitoxic, followed by hot extracts of A. barbadensis and A. indica.
This study showed that the 30 and 40% concentrations of either hot or cold extracts of N. tabacum plant extracts are more efficacious in the control of fungal dry rot disease of yam tubers (D. rotundata, Ekpe line) in storage.
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Taiga, A. and D.B. Olufolaji, 2008. In vitro screening of selected plant extracts for Fungicidal properties against Dry rot fungi of yam tubers (Dioscorea rotundata) in Kogi State, Nigeria. International Society Biotechnology Conference (ISTB-2008), Majitar, India, pp: 309-311.
Department of Biological Sciences, Kogi State University, Anyigba, Nigeria
Corresponding Author: Taiga, A., Department of Biological Sciences, Kogi State University, Anyigba, Nigeria
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|Title Annotation:||Original Article|
|Publication:||American-Eurasian Journal of Sustainable Agriculture|
|Date:||Sep 1, 2009|
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