Abstract
Recurrent drought and Striga hermonthica (Del.) Benth parasitism constrains maize production in sub-Saharan Africa (SSA). Transfer of resistance genes from wild relatives can improve resistance to drought and Striga in tropical maize. The objectives of this study were to (i) determine the combining ability of 12 extra-early yellow maize inbreds derived from Zea diploperennis and tropical maize germplasm; (ii) classify the inbreds into heterotic groups using heterotic grouping based on the general combining ability (GCA) of multiple traits (HGCAMT) method; (iii) examine hybrid performance under contrasting environments; and (iv) examine the stability of hybrid combinations involving the inbreds. Sixty-six diallel crosses involving the inbreds plus four checks were evaluated for two years under drought, Striga-infested and rainfed environments in Nigeria. Significant differences (p < 0.05) were observed for the effects of genotype, environment, genotype × environment, GCA and specific combining ability (SCA) on grain yield and other measured traits. Inbred lines such as TZdEEI 7 × TZEEI 63 derived from Z. diploperennis and tropical germplasm exceeded the checks by a range of 28 to 41%. Across environments, the hybrid TZdEEI 1 × TZdEEI 7, which was derived from Z. diploperennis, was the highest-yielding with a grain yield of 4302 kg ha−1. The results revealed the predominance of GCA over SCA effects for most measured traits, suggesting that additive gene action governed the inheritance of Striga resistance and drought tolerance related traits in the inbreds. The 12 inbreds were classified into three heterotic groups, while TZEEI 79 and TZdEEI 7 were identified as inbred testers and TZdEEI 7 × TZEEI 12 as a single-cross tester across environments. Hybrid TZdEEI 9 × TZEEI 79 was the highest-yielding and most stable. Other promising hybrids were TZdEEI 7 × TZEEI 79, TZdEEI 1 × TZdEEI 7 and TZdEEI 12 × TZEEI 95. These hybrids should be extensively tested on-farm for potential commercialization in SSA. Overall, our results highlighted the importance of harnessing beneficial alleles from wild relatives of maize for improvement of resistance to Striga and tolerance to drought in adapted maize germplasm.
Highlights
Significant effects of genotype and general combining ability (GCA) was observed for all measured traits under drought condition except for anthesis-silking interval, ear height and ear aspect
GCA was the main component accounting for the differences among the maize hybrids, and the selection of promising hybrids for Striga and drought resistance is possible based solely on the prediction from GCA effects
The single cross hybrids that have high specific combining ability (SCA) effects for grain yield and other traits under the stress conditions can be recommended for extensive evaluation to confirm the consistency of performance of the hybrids in contrasting environments
Summary
Maize (Zea mays L.) is a widely adapted major staple food crop, providing calories for over 300 million people in sub-Saharan Africa (SSA). There is a rapid increase in the importance of the crop due to its wide adaptation to varying agroecologies, relative ease of production, processing, storage, and transportation [1]. Striga hermonthica (Del) Benth parasitism and recurrent drought are fighting against its increased production and productivity, in the savannas. Resistance to Striga describes the ability of the host plant to stimulate the germination of Striga seeds but prevent the attachment of the parasites to its roots or kill the attached parasites. Under Striga infestation, resistant cultivars support significantly fewer Striga plants and produce greater yield than susceptible cultivars [4,5,6]
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