Abstract
Maize is a food security crop cultivated in the African savannas that are vulnerable to the occurrence of drought stress and Striga hermonthica infestation. The co-occurrence of these stresses can severely damage crop growth and productivity of maize. Until recently, maize breeding in International Institute of Tropical Agriculture (IITA) has focused on the development of either drought tolerant or S. hermonthica resistant germplasm using independent screening protocols. The present study was therefore conducted to examine the extent to which maize hybrids simultaneously expressing resistance to S. hermonthica and tolerance to drought (DTSTR) could be developed through sequential selection of parental lines using the two screening protocols. Regional trials involving 77 DTSTR and 22 commercial benchmark hybrids (STR and non-DTSTR) were then conducted under Striga-infested and non-infested conditions, managed drought stress and fully irrigated conditions as well as in multiple rainfed environments for 5 years. The observed yield reductions of 61% under managed drought stress and 23% under Striga-infestation created desirable stress levels leading to the detection of significant differences in grain yield among hybrids at individual stress and non-stress conditions. On average, the DTSTR hybrids out-yielded the STR and non-DTSTR commercial hybrids by 13–19% under managed drought stress and fully irrigated conditions and by −4 to 70% under Striga-infested and non-infested conditions. Among the DTSTR hybrids included in the regional trials, 33 were high yielders with better adaptability across environments under all stressful and non-stressful testing conditions. Twenty-four of the 33 DTSTR hybrids also yielded well across diverse rainfed environments. The genetic correlations of grain yield under managed drought stress with yield under Striga-infestation and multiple rainfed environments were 0.51 and 0.57, respectively. Also, a genetic correlation between yields under Striga-infestation with that recorded in multiple rainfed environments was 0.58. These results suggest that the sequential selection scheme offers an opportunity to accumulate desirable stress-related traits in parents contributing to superior agronomic performance in hybrids across stressful and diverse rainfed field environments that are commonly encountered in the tropical savannas of Africa.
Highlights
Maize is a dominant staple food crop with 70% of its grain used directly for human consumption in sub-Saharan Africa (Vogel et al, 2019)
The rainfall recorded during the period in which the regional trials were evaluated at Ikenne was very low, except for 2012/ 2013 that received an appreciable rainfall in November and February (Supplementary Figure S1)
Relative to fully irrigated condition, the drought stress attained in this study reduced average hybrid yield by 66% in 2012, 18% in 2013, 62% in 2014, 72% in 2015, and 79% in 2016
Summary
Maize is a dominant staple food crop with 70% of its grain used directly for human consumption in sub-Saharan Africa (Vogel et al, 2019). Its low average grain yields that are pervasive in farmers' fields pose a serious threat to food security and livelihoods of millions of farmers in Africa. Farmers face many challenges that affect yields, among which drought and a parasitic weed known as Striga hermonthica (Del.) Benth have been recognized as the most widespread stresses limiting the productivity of maize in Africa (Ejeta, 2007; Edmeades, 2013). Maize plants with attached Striga plants to their roots exhibit stunted growth resulting from the withdrawal of water, nutrients and assimilate from the host by the parasite (Gurney et al, 1999) causing yield loss of up to 100% in severely infested fields in Africa (Kim et al, 2002; Ejeta, 2007). The projected rising temperatures and uncertainties in rainfall patterns associated with climate change will further accentuate the intensity and frequency of drought in many parts of Africa (Masih et al, 2014; Shiferaw et al, 2014) and create ideal conditions for S. hermonthica to thrive and expand its distribution into suitable new habitats (Mohamed et al, 2007)
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