**Abstract**

Aflatoxins are carcinogenic secondary metabolites produced predominantly by the fungi *Aspergillus flavus* and *parasiticus.* The toxin contaminate maize grains and threatens human food safety. Survey in Ghana revealed aflatoxin contamination of maize in excess of 941 ppb which is way beyond WHO and USA approved limits of 15 ppb and 20 ppb respectively. Host plant resistance is considered as the best strategy for reducing aflatoxins. This study was designed to (1) identify and select suitable maize lines that combine aflatoxin accumulation resistance and good agronomic traits under tropical conditions and (2) assess the genetic diversity among the exotic and locally adapted maize genotypes using significant morphological traits. Thirty-six maize genotypes, 19 from Mississippi State University, USA and 17 locally adapted genotypes in Ghana were evaluated for aflatoxin accumulation resistance and good agronomic characteristics across six contrasting environments using a 6x6 lattice design with three replicates. Five plants each per genotype were inoculated with a local strain of *Aspergillus flavus* inoculum at a concentration of 9 x 107 /3.4 ml, two weeks after 50% mid silking. Total aflatoxin in the kernels were determined at harvest using HPLC method. Statistical analysis for agronomic traits and aflatoxin levels were performed using PROC GLM procedure implemented in SAS. The result indicated that genotype by environment interaction was significant (p < 0.05) for aflatoxin accumulation resistance and many other agronomic traits. Five genotypes (MP715, NC298, MP705, MP719, CML287 and TZEEI- 24) consistently displayed stable resistance across the environments and may serve as suitable candidates for developing aflatoxin resistant hybrids. Cluster analysis showed two distinct groups (locally adapted and exotic genotypes), an indication of re-cycled alleles per region. Broad sense heritability estimates for grain yield and aflatoxin accumulation resistance were moderately high, which could permit transfer of traits during hybrid development.

**Keywords:** Maize, *Aspergillus*, Aflatoxin Accumulation, Genetic Variation

## **1. Introduction**

Adaptability and productivity of maize across a wide range of agro- ecologies makes it a suitable food security crop for most parts of the world [1]. However, a

major limitation to the contribution of maize towards food supply is the contamination of grains by aflatoxins. Aflatoxins are carcinogenic secondary metabolites produced mainly by *Aspergillus sp.* which contaminates maize grains during preand post- harvest seasons and renders the grains unwholesome for consumption by both humans and livestock [2]. In addition to the health risks, aflatoxin contamination is a serious challenge because the pathogen is globally widespread and causes considerable economic losses by down-grading grain quality, nutritional value and taste [3]. Due to the danger it poses to human health, several countries have set for limits to regulate aflatoxin contamination in many agricultural products including maize. Allowable limits set by Japan is 0 ppb, while the European Union and United States of America have limits of 2–4 ppb and 20 ppb respectively [4].

Approaches for the control and reduction of aflatoxin have relied on good agronomic practices, application of biocontrol preparations of atoxigenic strains of *A. flavus* (including aflasafe and aflaguard), and the use of resistant host plant germplasm [5] as well as BT varieties. Host plant resistance is seen as the method of choice since it exploits the accumulation of resistance alleles into single hybrid varieties [6] and is simple for the farmer to use.

Considerable efforts over the years have led to the development and identification of aflatoxin resistant breeding lines. However, some of these lines lack good agronomic characteristics in temperate environments [6] and may additionally lack other disease or insect resistance in tropical environments. They are useful in crosses involving elite or acceptable lines for the incorporation of novel alleles which confers aflatoxin accumulation resistance into hybrid varieties.

Studies on germplasm diversity and characterization have utilized morphological and/or molecular data for grouping of entries and breeding lines into various heterotic groups. These heterotic groupings can be used to rule out many unproductive hybrid crosses and reduce the total number of testcrosses that should be generated to ultimately find the highest yielding hybrids.

In this way, phenotypic evaluation and groupings of inbred lines could be useful in the identification of suitable inbred lines for the development of superior hybrids with high yields and aflatoxin resistance. Assessing the genetic diversity among the exotic and locally adapted maize genotypes would be useful in selecting potential parents with diverse genetic backgrounds that could be utilized in a breeding program for hybrid development.

The objectives of this study were to: (1) identify and select suitable lines that combine aflatoxin accumulation resistance and good agronomic traits under tropical environmental conditions. (2) assess the genetic diversity between exotic and local maize genotypes using significant morphological traits.
