Evaluation and Optimization of Agro-industrial Wastes for Conidial Production of Metarhizium anisopliae isolates under Solid State Fermentation

Abstract

Metarhizium anisopliae is known to cause high level of epizootics for more than 200 insect species in versatile agro-ecologies. Concerns on environmental pollution and resistance development to chemical insecticides need environmentally safe and economically viable approaches. Therefore, here we investigate a cheap and large scale industrial production of virulent enthomopathogenes on agricultural wastes. Three Metarhizium anisopliae isolates were grown on agricultural wastes to evaluate their conidia production potential under Solid state fermentation (SSF) technique. Coffee husk, tea waste, wheat bran and vegetable wastes were used as substrates to determine their capability for maximum conidiation of the isolates. Among these, vegetable wastes were the best media to yield 5.80 ±0.72 (107), 4.44±0.55 (107) and 5.58±0.66 (107) conidia/gram of substrate under quantitative assessment for isolate AUMI1, AUMI2 and AUMI3 respectively, at 60% moisture content.  Statistically on two sample t-test vegetable wastes shows significant difference in conidia production when compared to 2 mm and 4 mm sized coffee husk used as substrates. The optimization for temperature indicated that all substrates supported their maximum conidia yield within 27 – 300C range of temperature. The 3.5 pH value used in the present study for optimization was best favored only for coffee husk as substrate. The high conidia yielding substrates were best productive at pH 6.29, 6.63 and 5.4 for vegetable wastes, wheat bran and tea waste, respectively. All isolates incubated on wheat bran was highly productive under sufficient exposure to light. AUMI1 produced high conidia under exposure to light while the higher yield of AUMI2 and AUMI3 was produced under dark condition on vegetable wastes. Therefore, as successful microbial control of insect pests depends on large scale and cheap industrial productivity, cultivation on vegetable wastes and wheat bran under SSF can be a plausible solution.