Amylolytic And Beta-Glucanase Activities of Yam Rot Fungi.
ABSTRACT
Yam is in the class of roots and tubers that is a staple of the Nigerian and West African diet but fungi organisms can degrade it causing yam rot by producing amylolytic and beta-glucanase enzymes which breakdown starch and cellulose, respectively into sugars.
They were produced using yam rot fungi isolated on SDA medium. The isolates obtained were all Aspergillus sp, they were identified using their morphological characteristics, lactophenol cotton blue stain and slide culture test.
Pathogenicity test was carried out to check if the isolates could cause rot. Agar plate screening was carried out to check for the enzyme activites of the isolates, this was done on starch agar and carboxymethyl cellulose agar.
It was detected by the disappearance of the blue colour and red colour, respectively around the colony producing a clear zone. The Aspergillus isolates were used to produce amylase and β-glucanase enzyme in spectrophotometric enzyme assay in which the enzyme activity was determined at OD540nm.
Amylase and beta-glucanase production was carried out using the 4 isolates in solid state fermentation. The amount of beta-glucanase produced was 0.0097U/ml for Aspergillus spC followed by Aspergillus spD which gave 0.0020U/ml, Aspergillus spA gave 0.0015U/ml and Aspergillus spB being the least producer measuring 0.0005U/ml.
All isolates showed good results for the production of amylase, in other words, they are all good producers of amylase with Aspergillus spB being the least producer with 0.0335U/ml, Aspergillus spA is the best producer with 0.0800U/ml, followed by Aspergillus spC (0.0601U/ml) and Aspergillus spD (0.0500U/ml).
INTRODUCTION
Yam popularly called “Ji” in Igbo Language is a tropical crop belonging to the Family Dioscoreaceae in the genus Dioscorea. It has as many as 600 species out of which six are economically important staple species.
These are: Dioscorea rotundata (white guinea yam), Dioscorea alata (water yam), Dioscorea bulbifera (aerial yam), Dioscorea esculant (Chinese yam) and Dioscorea dumetorum (trifoliate yam).
Out of these, Dioscorea rotundata (white yam) and Dioscorea alata (water yam) are the most common species in Nigeria (Izekor and Olumese, 2010).
Yams are grown in the coastal region in rain forests, wood savanna and southern savanna habitats. Yams are perennial herbaceous vines cultivated for the consumption of their starchy tuber in Asia, Africa, Central and South America, and Oceania.
Nigeria is by far the world’s largest producer of yams, accounting for over 70–76 percent of the world production.
According to the Food and Agricultural Organization report, in 1985, Nigeria produced 18.3 million tones of yam from 1.5 million hectares, representing 73.8 percent of total yam production in Africa.
The tubers themselves are also called “yams”. There are many different cultivars of yams example: Dioscorea rotundata, Dioscorea bulbifera, Dioscorea esculenta etc.
Yam is in the class of roots and tubers that is a staple of the Nigerian and West African diet, which provides some 200 calories of energy per capita daily.
In Nigeria, in many yam-producing areas, it is said that “yam is food and food is yam”. Yam is one of the major sources of carbohydrate, minerals, vitamins B6 and C and also dietary fibre.
However, the production of yam in Nigeria is substantially short and cannot meet the growing demand at its present level of use.
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