The incidence of mycotic and mycotoxigenic Fusarium in a peri-urban food-garden environment
The present study was conducted in Phokeng, a peri-urban residential area outside Rustenburg in the North-West Province. To supplement their restricted diet, households of low socio-economic status often maintain food gardens where traditional African green leafy vegetables (morogo) are grown with maize as the traditional staple. Some of morogo plants are collected from the field where they grow spontaneously as natural flora. Questionnaires were used to obtain information regarding the composition and socio-economic status of households, the utilisation of morogo vegetables and methods of morogo preservation. Herbarium samples of 10 morogo plants were prepared for botanical species identification. The study investigated the occurrence of Fusarium species in the environment of peri-urban home gardens. Environmental components sampled for mycological analysis included maize, soil, air and the two most commonly-consumed morogo vegetables, namely thepe (Amaranthus sp.) and lerotho (Cleome gynandrd). Three home gardens in Phokeng where maize and morogo vegetables were growing together in a mixed system, were selected for sampling. Samples were also taken from the food garden of a family living on the nearby Zuurplaat farm and four sampling localities where morogo was growing some distance from maize. The presence of eleven Fusarium species was of interest to this study, not only for the mycotoxigenic risks to the consumer, but also for their potential to cause opportunistic infections in immune-suppressed and immuno-compromised individuals. Standard methods were employed for Fusarium isolation and morphologically-based species identification of isolates. The following Fusarium species were isolated from the different environmental components: F. avenaceum, F. chlamydosporum, F. dimerum, F. equiseti, F. oxysporum, F. poae, F. proliferatum, F. semitectum, F. solani, F. subglutinans and F. verticillioides. Results indicated fumonisin-producing F. proliferatum and F. verticillioides as well as F. solani were predominantly isolated from localities close to, as well as away from maize. Though F. subglutinans and F. oxysporum are not considered major producers of fumonisins in maize, these two species were also isolated in higher numbers from sites where maize was growing. HPLC analysis detected fumonisin Bi in some of the household morogo samples. Molecular techniques were applied to indicate the correct species identification of a selected number of isolates. Primers for PCR amplification of 6-tubulin and translation elongation factor 1-α (TEFl-α) gene fragments, and subsequently sequencing of the amplified DNA, verified the correct identification of F. proliferation, F. subglutinans, F. solani and F. oxysporum from morogo vegetables. The PCR amplified product of a FUM1 primer confirmed the presence of fumonisin-encoding genes in these isolates, thus demonstrating their potential to produce fumonisins. Statistical processing of results indicated Fusarium was isolated in significantly higher numbers from the air, and in notably higher numbers from soil, of localities near maize than away from maize. The same species were predominantly recovered from air, and isolated in higher numbers from both lerotho and thepe. Species isolated in highest numbers from lerotho included F. oxysporum, F. proliferatum, F. solani and F. verticillioides. However, the number of Fusarium isolates recovered from thepe was significantly lower than from lerotho. These results suggest that maize play an important role in maintaining fumonigenic Fusarium in the environment of peri-urban food gardens. Leaf surface characteristics of lerotho probably was a factor in trapping air-borne Fusarium spores more effectively compared to thepe. Apart from toxigenic risks to consumers, the eleven Fusarium species represented by isolates in the present study, have all been reported as etiological agents in cases of human fusariosis. In most cases, opportunistic fusarial infections in immuno-compromised patients were fatal. The presence in a peri-urban environment of Fusarium human pathogens, particularly in the air, enhances the risk of life-threatening opportunistic infections in HIV-positive individuals. Inhalation and skin contact are reportedly the two most common ways by which Fusarium pathogens gain entry to human hosts. High levels of Fusarium in the air thus increases the possibility of infection, particularly in an environment where humans have a larger population density. The present study demonstrated the presence of eleven mycotoxigenic and mycotic Fusarium species in household food gardens and indicated a major role for home-grown maize in maintaining these harmful fungi in the peri-urban environment.