Fusarium in subsistence agro-environments, African dark green leafy vegetables (morogo) and consumer health : an ecological approach

Abstract

Traditionally, the African diet consists of grain-based staples supplemented with a variety of pulses, tubers and green leafy vegetables. In the northern parts of South Africa, the term morogo is used with reference to a collection of dark green leafy vegetables either grown for subsistence, or gathered from the field. Derived from wild African varieties, morogo crops are well adapted to local growing conditions and require low water and agrochemical inputs. Some morogo plants appear spontaneously in soil disturbed by ploughing, while others are grown as soil cover in maize lands.The accessibility of morogo vegetables, whether by means of simple cultivation or collection, is a unique advantage to resource-limited rural and peri-urban households depending on home-grown food for sufficient nutrition. Though make is less drought resistant than the traditional African grains (i.e. millet varieties, sorghum, signal and bushman grasses), it gained preference as subsistence crop because of larger yields produced under favourable conditions. However, Fusarium infestation of maize and contamination of human food with their toxins have globally become a major health and economic concern. Fumonisins, a group of potent structurally-related secondary metabolites produced by various Fusarium species, have also been reported in home-grown maize in South Africa. Dietary fumonisins have diverse biological effects that have been linked with organ toxicity, carcinogenesis and immune suppression. A number of fumonogenic Fusarium species have furthermore been identified as causative agents of opportunistic infections in immune compromised individuals. In South African, an estimated 10.9% of the population was HIV-positive in 2006. The rural sector is disproportionately affected by the pandemic. The presence of Fusarium in subsistence agro-environments thus has aggravating health implications for rural families who in many instances are food-insecure and in addition affected by chronic diseases HIV infection and AIDS. The present study investigated the incidence of toxigenic Fusarium in rural subsistence agro-environments and food gardens of peri-urban households. The most prolific fumonisin-producers, F. proliferatum and F. verticillioides, were predominantly isolated from various components of the environment. Other fumonigenic species included F. oxysporum and F. subglutinans. Fusarium was isolated in significantly higher numbers from environmental samples of localities where maize was also growing. The genetic predisposition of isolates for fumonisin production was demonstrated. Moreover, fumonisin Bi was detected in samples of household morogo.