Identification of donors for low-nitrogen stress with maize lethal necrosis (MLN) tolerance for maize breeding in sub-Saharan Africa

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

Gains in Maize Genetic Improvement in Eastern and Southern Africa: I. CIMMYT Hybrid Breeding Pipeline

“…More accurate selection through increased repeatability increases selection response for the trait of interest. Recent combined analysis of the southern Africa regional trials of CIMMYT and partners and managed drought and low‐N stress trials in ESA showed that the repeatability ( H ) of the managed stress trials in this study was lower than that of nonstress trials and that plot residual variance under abiotic stress was high (Weber et al, 2012; Cairns et al, 2013b; Das et al, 2016). In this study, the combined H was above 0.5 for all stress treatments; however, several trials had to be removed due to low H .…”

“…Prior to 2009, the lowest phenotyping capacity in the CIMMYT ESA breeding pipeline was for low‐N stress, with less than 10 ha of N‐depleted land available for screening in ESA (Magorokosho et al, 2010). The low‐N phenotyping capacity has recently been expanded, with sites in 10 countries on 48 ha of N‐depleted land (Das et al, 2016). Drought phenotyping capacity has increased since 2006, with managed drought screening capacity increasing from 6 to 35 ha (Magorokosho et al, 2010; Makumbi, 2011; Cairns et al, 2013a).…”

“…The multilocation testcross characterization of large sets of inbreds from tropical maize programs worldwide allowed the systematic identification of the best drought and low‐N donors (Cairns et al, 2013b; Das et al, 2016). The top 10 testcrosses yielded at least 0.65 Mg ha −1 more under drought stress than the current key line used in drought breeding (CML444) crossed to the broadly adapted tester CML539 (Cairns et al, 2013b).…”

“…The top 10 testcrosses yielded at least 0.65 Mg ha −1 more under drought stress than the current key line used in drought breeding (CML444) crossed to the broadly adapted tester CML539 (Cairns et al, 2013b). Under low N stress, the top 10 testcrosses (crossed to the broadly adapted tester CML539) yielded at least 1 Mg ha −1 more than lines previously considered to be low‐N tolerant (including CML504 and CZL02012) under severe low‐N stress (Das et al, 2016). Donors for both drought and low‐N stress have been incorporated into the CIMMYT ESA maize stress breeding pipeline.…”

Assessing the Potential of Extra-Early Maturing Landraces for Improving Tolerance to Drought, Heat, and Both Combined Stresses in Maize

“…This is particularly true for tropical maize in which little additional gain in maximum drought-tolerance has been achieved in the last decade [29]. Addressing this issue and hence, ensuring progress in genetic improvement of maize under abiotic stress conditions requires identification of donor lines with beneficial traits that will bring new genetic variation [29,44]. Landrace gene pools of maize from areas that frequently experience DS at elevated temperatures may provide a useful source of novel alleles for abiotic stress tolerance [27,45].…”