Spatiotemporal population dynamics of aflatoxigenic Aspergillus species and their ecological requirements across groundnut-growing areas of Ethiopia

The worldwide economic crop groundnut is infected by aflatoxigenic Aspergillus species (AAS), for which the soil is the main inoculum reservoir. Thus, to assess the spatiotemporal dynamics and association of AAS populations with biophysical factors, a total of 300 soil samples were collected (pre-planting, flowering, and physiological maturity) from five groundnut-growing districts in three zones of Ethiopia in 2019. AAS were isolated by dilution plating and their aflatoxin-producing potential determined using special media and UV light. Logistic regression models were used to analyze the effect of biophysical factors on AAS population dynamics. AAS populations varied across groundnut-growing districts and over time. In the Fedis district, the highest relative density of A. flavus non-sclerotia producer (NSP) strain (30.1%) and small sclerotia (S-strain) producers (26.1%) were recorded at pre-planting and maturity, whereas large sclerotia (L-strain) producers (4.1%) and A. parasiticus (11.6%) were recovered from the Kucha district at flowering and maturity, respectively. From Humbo and Kucha districts, the highest populations of A. flavus (10.3 × 10 4 cfu/g soil) and A. parasiticus (5.5 × 10 4 cfu/g soil), respectively, were recorded at maturity. The smallest population of AAS had a strong association with altitudes > 1640 m a.s.l., higher pH (> 7), low organic matter (0.572–1.378), and sand-sandy loam soil, factors which can be considered as management options. A. flavus S-strain prevalence had a positive relationship with increased soil temperature > 30 °C, which highlights the need for mitigation strategies as the climate warms.