The influence of season and land use on the occurrence of Metarhizium spp. in the Cape Peninsula region, South Africa

Abstract

To investigate the environmental relationships between the occurrence of Metarhizium spp., season and land use in the Cape Peninsula region, soil samples were collected from randomly selected sampling sites within nature reserves and agricultural farms. Soil samples from the same sites were collected in different seasons (winter and summer), and Metarhizium spp. were isolated from the soil samples by insect baiting and plating soil, and identified. Soil pH, texture, and nutrient contents of air-dried composite soil samples were analysed, and the seasonal rainfall data were recorded. The associations between the number of Metarhizium isolates with soil nutrient contents and seasonal rainfall were assessed. Farm sites had a significantly higher number of Metarhizium isolates (36 of 40 isolates collected) and higher concentrations of soil macronutrients, P, Ca and N (NO3), than in soil samples from the reserves, while higher average monthly rainfall in winter correlated with higher occurrences of Metarhizium isolates. In conclusion, wet, cold winters and vegetable farming favoured the higher occurrence of Metarhizium spp. in the Cape Peninsula region.