Distribution of Aspergillus and Fusarium ear rot causative fungi in soils under push-pull and maize monocropping system in Western Kenya

Abstract

It is imperative to establish the distribution and density of soil fungal communities as a requisite for formulating strategies for management of ear rot infections and mycotoxin contamination. In a two seasons study, short (SR) and long rainy (LR) seasons, we investigated the distribution of Aspergillus and Fusarium fungi causing ear rots and producing mycotoxins from 120 soil samples collected from maize fields under push-pull (PP) and maize monocrop (MM) systems in Western Kenya. Cultural methods were used for identification of Aspergillus and Fusarium species, while molecular techniques were used for confirmation of Fusarium section Liseola. Detection of total aflatoxins in cultures of section Flavi isolates was carried out by enzyme-linked immunosorbent assay (ELISA). A total of 338 fungi were isolated; 80% were identified as Aspergillus and 4.4% Fusarium. The distribution of fungi was significant with season but not cropping systems. The frequency of occurrence was higher during the LR (68.4%) than the SR (31.6%). In cropping systems, the frequency of occurrence of Aspergillus flavus was higher in MM (60.2%) than PP (39.8%). However, Aspergillus parasiticus was more frequent in PP (71.4%) than MM (28.6%); and during the SR (78.6%) than the LR (21.4%). Majority (81.3%) of A. flavus and A. parasiticus were toxigenic. There was low recovery of Fusarium species in soil samples. These findings show that soils from both cropping systems are potential for Aspergillus infection and aflatoxins contamination; however, low Fusarium distribution in soil suggest external inoculum source for Fusarium ear rot infections common in most maize fields in Western Kenya.

A comparative study on the impact of fiveDesmodiumspecies on soil microbiome reveals enrichment of selected bacterial and fungal taxa

“…Indeed, reports of lower mycotoxin producing fungi in push-pull plots where Desmodium spp. are used as intercrops (Maxwell et al, 2017; Owuor et al, 2018; Njeru et al, 2020) as well as associational resistance in maize grown on soil from long term push-pull fields (Mutyambai et al, 2019) may be the first clue about the important role of Desmodium spp. in shaping soil microbial communities leading to diverse ecological benefits related to food production and safety.…”

“…were found in high abundance in soils of maize monoculture compared to long-term push-pull farms that employed Desmodium intercrops (Mwakilili et al, 2021). Similarly, (Maxwell et al, 2017) reported lower frequency of Aspergillus flavus in maize cobs from monoculture plots than in Desmodium intercropping push-pull systems, but an opposite trend for A. parasiticus. It is possible that the soils of the area are rich in these fungal taxa and the time under Desmodium spp.…”

“…For example, a study by Njeru et al (2020) revealed that maize coming from push-pull plots had lower levels of mycotoxins and mycotoxin-producing fungi compared to that from monoculture. In a separate study, the frequency of occurrence of a mycotoxin-producing fungus Aspergillus flavus was lower in push-pull than maize monoculture plots (Maxwell et al, 2017). These findings are in line with our previous study where we show that push-pull farming and Desmodium intercropping in cereal farming impact diversity of fungal communities more than bacteria (Mwakilili et al, 2021), manipulation of fungal communities in the soil to promote competitive beneficial filamentous fungi has been established as a method to manage mycotoxins in cereals (Sarrocco et al, 2019).…”

Mycotoxin Contamination Risks Due to Handling Practices of Indigenous Chicken Feeds in Kenya

“…This is because the soil is an essential habitat for mycotoxigenic fungi species such as Aspergillus and Fusarium spp. [21]. A similar study [20] reported that 37.6% and 39.1% of the farmers in Nandi and Makueni counties, respectively, were not drying maize on a canvas instead they were drying their unshelled maize directly on the ground.…”