Heterotic affinity and combining ability of exotic maize inbred lines for resistance to aflatoxin accumulation

Robert L. Brown,Abebe Menkir,Marilyn L. Warburton,Alejandro Ortega-Beltran,Joao Augusto,Ranajit Bandyopadhyay,W. Paul Williams,Silvestro Meseka

doi:10.1007/s10681-018-2254-8

Abstract

Aflatoxin accumulation in maize (Zea mays L.) kernels is a serious economic and health problem that reduces grain quality and nutritional values and causes death to livestock and humans. Understanding the genetic parameters and heterotic responses of exotic maize inbred lines can facilitate their use for developing aflatoxin resistant parents of hybrids in Africa. This study was designed to (1) determine the heterotic affinities of aflatoxin resistant exotic lines, (2) identify exotic inbreds with good combining ability, and (3) determine the mode of inheritance of resistance to aflatoxin contamination in these lines. A line × tester mating design was used to determine combining ability of 12 yellow and 13 white inbreds and classify them into heterotic groups. The inbreds were crossed to two adapted testers representing two African heterotic groups and the resulting testcrosses along with hybrid checks were evaluated in separate trials at two locations for 2 years in Nigeria. General combining ability (GCA) effects were more important than specific combining ability effects for aflatoxin and grain yield. Among 15 exotic inbred lines having negative GCA effects for aflatoxin and 13 with positive GCA effects for grain yield, six combined the two desired traits. Five white and six yellow endosperm testcrosses were found to be good specific combiners for the two desired traits. The exotic lines with negative GCA effects for aflatoxin accumulation will be used as donor parents to develop backcross populations for generating new inbred lines with much higher levels of resistance to aflatoxin accumulation.

Highlights

Aflatoxins are a group of naturally occurring, highly toxic and carcinogenic secondary metabolites produced by certain Aspergillus species when infecting184 Page 2 of 15 several agricultural crops including maize, groundnut, and cottonseed
The ratio of General combining ability (GCA) sum of squares was greater than scores. Line tester interaction (SCA) sum of squares for aflatoxin accumulation, grain yield, and most of the measured traits
Mean squares for line 9 environment interaction were significant for aflatoxin accumulation, days to silking, and maize streak virus (MSV), whereas the

Summary

Introduction

Aflatoxins are a group of naturally occurring, highly toxic and carcinogenic secondary metabolites produced by certain Aspergillus species when infecting184 Page 2 of 15 several agricultural crops including maize, groundnut, and cottonseed. Amongst the various aflatoxin-producing species, A. flavus and A. parasiticus are the most common causal agents of contamination in animal feed, human food, and exportable grain (Brown et al 1999). Aflatoxin contamination of maize (Zea mays L.) is a serious pre- and post-harvest problem because aflatoxin-producing fungi may infect the crop prior to harvest and remain with it and produce aflatoxins throughout harvest and storage (Brown et al 1995, 1999; Williams et al 2008). Aflatoxin-producing fungi are widespread in tropical and sub-tropical maize growing regions where environmental conditions are highly conducive (Hennigen and Dick 1995) for both fungal growth and subsequent aflatoxin formation. The health effects of maize contaminated with aflatoxin can be more serious in developing countries because a large proportion of the grain is used for human consumption and there is limited capacity to monitor the level of aflatoxin contamination in the grain (Widstrom 1996; Menkir et al 2006). In June 2016, 14 people died in the Dodoma region of Tanzania after consumption of maize contaminated with high aflatoxins levels (http://allafrica.com/stories/201607290685. html)

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