Abstract
After drought, a major challenge to smallholder farmers in sub-Saharan Africa is low-fertility soils with poor nitrogen (N)-supplying capacity. Many challenges in this region need to be overcome to create a viable fertilizer market. An intermediate solution is the development of maize varieties with an enhanced ability to take up or utilize N in severely depleted soils, and to more efficiently use the small amounts of N that farmers can supply to their crops. Over 400 elite inbred lines from seven maize breeding programs were screened to identify new sources of tolerance to low-N stress and maize lethal necrosis (MLN) for introgression into Africa-adapted elite germplasm. Lines with high levels of tolerance to both stresses were identified. Lines previously considered to be tolerant to low-N stress ranked in the bottom 10% under low-N confirming the need to replace these lines with new donors identified in this study. The lines that performed best under low-N yielded about 0. 5 Mg ha−1 (20%) more in testcross combinations than some widely used commercial parent lines such as CML442 and CML395. This is the first large scale study to identify maize inbred lines with tolerance to low-N stress and MLN in eastern and southern Africa.
Highlights
Maize yields in sub-Saharan Africa (SSA) remain the lowest in the world, averaging 2 Mg ha-1, with production increases resulting largely from land expansion rather than higher yields per unit area (Cairns and Prasanna 2018)
Grain yield under low-N stress was over 4 M ha-1 in Cedara (4.43 Mg ha-1) and Embu (4.26 and 4.60 Mg ha-1) and these sites were subsequently removed from further analysis
Plant height was significantly reduced by 20% and 25% under low-N compared to optimal conditions in highland and sub-tropical environments, respectively
Summary
Maize yields in sub-Saharan Africa (SSA) remain the lowest in the world, averaging 2 Mg ha-1, with production increases resulting largely from land expansion rather than higher yields per unit area (Cairns and Prasanna 2018). At the Abuja Declaration on Fertilizer for the African Green Revolution in 2006 African Union Member States resolved to increase the level of fertilizer use to at least 50 kg ha-1 by 2015 (African Development Bank 2006). This deadline has passed and fertilizer use remains between 5 and 10 kg ha-1, far below the Euphytica (2019) 215:80. For smallholder farmers in many parts of SSA low-N stress refers to maize grown with no fertilizer on severely N depleted soils resulting in yields between 1 and 2 Mg ha-1. Screening for low-N stress tolerance requires the development and maintenance of long-term sites depleted of N over several seasons to achieve target yield levels of 40% that of well-fertilised trials. In 2010, a large expansion of the CIMMYT-coordinated network of N-depleted yield testing sites was initiated in ESA in collaboration with national agricultural research systems (NARS) and private seed companies, in recognition of the importance of N-depleted environments in African maize production
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