The Impact of Push-pull Technology on Incidence and Severity of Maize ear rots and Mycotoxins in Western Kenya

Soil is the primary reservoir for fungi of which Aspergillus and Fusarium species are the main causal agents of maize ear rot and mycotoxin production. Season and cropping systems are known to influence soil fungal community structure. 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. The current study was carried out to investigate the distribution of Aspergillus and Fusarium fungi causing ear rots and producing mycotoxins from soil collected from maize fields under push-pull and maize monocrop systems in three sub-counties (districts) (Vihiga, Kisumu and Siaya) in western Kenya. Out of 60 fields (20 per district and 10 per cropping system), 120 soil samples were collected at silking stage of maize during the short rain (March to May) season of 2014 and long rain seasons in 2015. 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 long (68.4%) than the short rainy seasons (31.6%). In cropping systems, the frequency of occurrence of A. flavus was high in maize monocrop systems (60.2%) than in push-pull system (39.8%). However, A. parasiticus was more frequent in push-pull (71.4%) than maize monocrop systems (28.6%); and during the short (78.6%) than the long rainy seasons (21.4%). Majority (81.3%) of A. flavus and A. parasiticus were toxigenic. There was low recovery of Fusarium spps 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 suggested external inoculum source for fusarium ear rot infections common in most maize fields in western Kenya