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Open‐pollinated varieties (OPVs) still represent a significant proportion of the maize (Zea mays L.) seed system in many countries of sub‐Saharan Africa. The International Maize and Wheat Improvement Centre (CIMMYT) has been breeding improved maize varieties for the stress‐prone environments experienced by most smallholder farmers in eastern and southern Africa for over 30 yr. Hybrid breeding is now the major focus of the CIMMYT breeding pipeline. However, OPVs are generated within the hybrid pipeline. This is the first study to document genetic gain for maize grain yield under both optimal and stress (random and managed drought, low nitrogen [N], and maize streak virus [MSV]) conditions within the CIMMYT eastern and southern African OPV breeding pipeline. Genetic gain was estimated using the slope of the regression on the year of OPV release in regional trials over a 12‐yr period (1999–2011). Open‐pollinated varieties were separated into two maturity groups, early (<70 d to anthesis) and intermediate‐late (>70 d to anthesis). Genetic gain in the early maturity group under optimal conditions, random drought, low N, and MSV was 109.9, 29.2, 84.8, and 192.9 kg ha−1 yr−1. In the intermediate‐late maturity group, genetic gain under optimal conditions, random drought, low N, and MSV was 79.1, 42.3, 53.0 and 108.7 kg ha−1 yr−1. No significant yield gains were made under managed drought stress for both maturity groups. Our results show continued improvement in OPVs for both yield potential and stress tolerance.

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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. Electronic supplementary material The online version of this article (10.1007/s10681-019-2406-5) contains supplementary material, which is available to authorized users.