Identification of QTLs Controlling Resistance/Tolerance to Striga hermonthica in an Extra-Early Maturing Yellow Maize Population

Baffour Badu-Apraku,Samuel Adewale,Agre Paterne,Robert Asiedu,Melaku Gedil

doi:10.3390/agronomy10081168

Abstract

Striga hermonthica parasitism is a major constraint to maize production in sub-Saharan Africa with yield losses reaching 100% under severe infestation. The application of marker-assisted selection is highly promising for accelerating breeding for Striga resistance/tolerance in maize but requires the identification of quantitative trait loci (QTLs) linked to Striga resistance/tolerance traits. In the present study, 194 F2:3 families of TZEEI 79 × TZdEEI 11 were screened at two Striga-endemic locations in Nigeria, to identify QTLs associated with S. hermonthica resistance/tolerance and underlying putative candidate genes. A genetic map was constructed using 1139 filtered DArTseq markers distributed across the 10 maize chromosomes, covering 2016 cM, with mean genetic distance of 1.70 cM. Twelve minor and major QTLs were identified for four Striga resistance/tolerance adaptive traits, explaining 19.4%, 34.9%, 14.2% and 3.2% of observed phenotypic variation for grain yield, ears per plant, Striga damage and emerged Striga plants, respectively. The QTLs were found to be linked to candidate genes which may be associated with plant defense mechanisms in S. hermonthica infested environments. The results of this study provide insights into the genetic architecture of S. hermonthica resistance/tolerance indicator traits which could be employed for marker-assisted selection to accelerate efficient transfer host plant resistance genes to susceptible genotypes.

Highlights

Maize (Zea mays L.) is the most widely grown staple food crop in sub-Saharan Africa (SSA), and accounts for a large proportion of carbohydrates, proteins, lipids and vitamins for millions of people in the sub-region [1,2]
Transgressive segregation was observed for all traits in that some of the F2:3 families showed higher and lower levels of grain yield, Striga damage, number of emerged Striga plants and ears per plant compared to the parental lines (Table 1)
Correlation analysis revealed significant and positive correlations between number of ears per plant and grain yield whereas negative and significant correlations were observed between the ears per plant and Striga damage as well as between Striga damage and grain yield (Figure 2)

Summary

Introduction

Maize (Zea mays L.) is the most widely grown staple food crop in sub-Saharan Africa (SSA), and accounts for a large proportion of carbohydrates, proteins, lipids and vitamins for millions of people in the sub-region [1,2]. The root hemi-parasitic plant Striga hermonthica is an important biotic constraint limiting maize production in SSA. The S. hermonthica problem in SSA is the result of the shift from traditional cereal based farming system which facilitated longer fallow periods which ensured that the soil Striga seed bank was maintained at levels that plants could tolerate [1]. The pressure on agricultural land has necessitated land use intensification, cereal mono-cropping and reduced fallow periods resulting in increased Striga seed bank and infestation levels that threaten the livelihood of millions of farmers [3,4]. De Groote et al [5] reported that over six million hectares of agricultural land in Western, Eastern and Southern Africa are seriously affected by Striga.

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