Management of Mycotoxigenic Fungi and Associated Mycotoxins in Maize by Use of Hermetic Storage

Abstract

Maize is a staple food crop in Kenya with about 90% of the rural households depending on it. However, the grain is vulnerable to degradation by mycotoxin producing fungi in the field and during storage. Mycotoxins produced by these fungi cause significant economic losses and deleterious health effects to humans and animals. Strategies such as storage of maize in hermetic bags have been developed to reduce post-harvest grain losses due to pest attack, fungal growth and mycotoxin contamination. The objective of this study was to determine the effect of hermetic storage on the population of fungal species and levels of aflatoxin and fumonisin in maize. A survey was carried out in October, 2015 to obtain information on maize production practices in Kilala and Mukuyuni Locations of Kaiti District, Makueni County, Kenya. Soil samples were collected at planting and analysed for the population and incidence of mycotoxin producing fungi. Maize grains were sampled at harvest and three months after storage in polypropylene and hermetic bags. Mycotoxin producing fungi in soil and ground maize were isolated and identified based on cultural and morphological characteristics and DNA analysis using ITS1F and ITS4R primers. Aflatoxin and fumonisin in maize grains sampled at harvest and after three months of storage were determined using VICAM method. Over 50% of the farmers in Kaiti District were smallholder who practiced mixed cropping, used simple land preparation methods, applied soil amendments and did not practice crop rotation. Fifty seven percent of farmers stored their maize in modern stores while 43.4% stored maize inside family living houses. Maize was mostly stored in polypropylene bags and the most common storage problem reported by farmers was infestation by insect pests mainly weevils. Eighty seven percent of the farmers had prior knowledge of mycotoxins and considered it a major challenge in maize production. Aspergillus spp., Fusarium spp. and Penicillium spp. were commonly isolated from soil and maize grain samples. Penicillium spp. was the most prevalent fungal species in soil and maize grains with a mean population of 9.0 x 103 CFU/g soil and 7.0 x103 CFU/g maize. The population of mycotoxin producing fungi in maize sampled three months after storage was 39.7% higher than at harvest. The type of storage bag had a significant influence (p ≤ 0.05) on the overall population and diversity of fungal species isolated from maize grains. The population of mycotoxin producing fungi was 78% higher in maize stored in polypropylene bags compared to hermetic bags. The fungal DNA obtained from maize sampled at harvest was positive for 300-bp and 500-bp amplification product while maize sampled three months after storage in the two types of bags generated amplicons of 500-bp amplification product. Total aflatoxin in maize sampled at harvest and after three months storage ranged from <5 to 42.7 ppb with 55% lower aflatoxin content in PICS bags than in PP bags. Fumonisin levels in maize grains sampled at harvest and after three months storage in the two bag types ranged from < 2 to 6.0 ppm. Storage of maize grains in hermetic bags for three months reduced fumonisin levels by 57% compared to polypropylene bags. The hermetic bags effectively reduced fungal population and levels of aflatoxin and fumonisin in maize grains. Therefore, storage of maize in hermetic bags offers an effective and chemical free-method that will enable farmers preserve high quality grains.