Incidence, Morphological and Molecular Characterization of Fusarium Species and Levels of Fumonisins in Selected Maize Genotypes in Nakuru County, Kenya

Abstract

Maize (Zea mays L.) is one of the staple food crop for people in Kenya. This crop usually get contaminated by Fusarium spp. that produces mycotoxins, Fumonisins (FBs). This group of fungal toxins occur in maize when infected by Fusarium verticillioides. Most common toxin is Fumonisin FB1, whose intake above 2.0 mg/kg body weight/day have been found to play a role in neural tube defect in humans and causes Oesophangeal cancer in rats. Data on incidence of different Fusarium species and FB1 levels in various maize genotypes grown in Kenya is not available. Objectives of this study were to; determine incidence of Fusarium spp. that infect maize genotypes, carryout morphological and genetic diversity of Fusarium species infecting maize genotypes and establish levels of FB1 and FB2 in maize genotypes grown in Nakuru County-Kenya. By use of purposive sampling, maize kernels showing no symptoms of Fusarium ear rot infection were collected from 277 farmers’ stores in Molo and Njoro sub-Counties. Percentage incidence of Fusarium in each maize genotype was established after isolation on Pentachloronitrobenzene (PCNB) Agar and identification first carried out using morphological characteristics (colour) produced on the media followed by spore morphology on potato dextrose Agar (PDA). Eight Fusarium species were identified from the samples. Further identification using DNA sequencing of the Translation elongation factor 1-alpha (TEF-1α) gene, the isolates were confirmed as F. temperatum, F. verticillioides and F. boothi. Levels of Fumonisin (FBs) in maize were determined using Liquid Chromatography- Mass spectrometry (LC-MS). The research findings revealed that all maize hybrids grown were infected by Fusarium ear rot and the highest % incidences were found in H629 (95.83 %). Lowest % incidence was recorded in P30G19 maize (43.33 %). Molecular DNA sequences analysis revealed that, maize genotypes in Nakuru County were infected by F. temperatum, F. boothii and F. verticillioides. Levels of Fumonisin B1 was highest in H629 (4437.53 μg/kg) and much lower in H614 (1315.7 μg/kg). Using correlation analysis, a relationship between FB1 levels and % incidence of Fusarium spp. was found to be significant (r = 0.699, P = 0.05). It was established that molecular technique, using DNA sequencing is a more accurate method in identification of this fungi on maize kernels. Findings from present study showed that Fusarium spp. infects all maize genotypes grown in Nakuru County, Kenya. The finding therefore reveals that maize kernels may be asymptomatic but they are infected by Fusarium ear rot. It further highlights the levels of FBs in specific maize genotypes. The study will enlighten the public, farmers and agricultural officers on safer maize genotypes and levels of Fumonisins (FBs) in each. Farmers in Nakuru County, therefore, should consider growing H614, H6218 and H6210 which had lower levels of fumonisins (FBs).