Studies on Aspergillus flavus on Tiger Nut (Cyperus esculentus) Incubated at Different Regimes of Light and Two Temperatures

Abstract

An experiment was carried out to ascertain the effect of light regimes (continuous day light, continuous darkness and alternating day light and darkness) on the growth of A. flavus on tiger nut at temperature of 28oC and 30oC. The experiment was a 2 x 3 factorial laid out in a completely randomized design (CRD) replicated 10 times. A. flavus was isolated from naturally infected tiger nuts obtained from different sellers at Delta Park, Abuja Park and Choba campus, University of Port Harcourt, Rivers State, Nigeria. The isolation and sub-culturing were done using Malt Extract Agar (MEA). A tiger nut-based-medium (15ml/Plate) was centrally inoculated with 6-day-old inoculums of A. flavus and incubated appropriately. Assessment of fungal growth was done daily for 10 days and mycelia diameter and mycelia growth rate obtained from the data. Result from the statistical analysis showed that the effect of light regime and temperature on the mycelia diameter of A. flavus was highly significant (P<0.001) and the interaction between light regime and temperature was also significant (P<0.0.01). Growth rate also showed significant (P<0.001) main effect of temperature and light regime and the light regimes x temperature was also significant (P=0.03). The highest mycelia growth rate and mycelia diameter occurred in continuous day light, followed by continuous darkness and finally alternating day light and darkness, with all higher at 30oC. Thus, storage of tiger nut under continuous day light and/or at temperature 28oC and above should be discouraged, in order to reduce microbial spoilage caused by Aspergillus flavus.