IMPROVEMENT IN GRAIN YIELD AND LOW-NITROGEN TOLERANCE IN MAIZE CULTIVARS OF THREE ERAS

SUMMARY Maize ( Zea mays L.) is the most important staple crop in West and Central Africa (WCA), but its production is severely constrained by low soil nitrogen (low N). Fifty-six extra-early open-pollinated maize cultivars developed during three breeding eras, 1995–2000, 2001–2006 and 2007–2012, were evaluated under low N and high soil nitrogen (high N) at two locations in Nigeria in 2013 and 2014, to investigate the genetic gains in grain yield and identify outstanding cultivars. During the first breeding era, the emphasis of the programme was on breeding for resistance to the maize streak virus (MSV) and high yield potential, while the major breeding emphasis during the second era was on recurrent selection for improved grain yield and Striga resistance in two extra-early-maturing source populations, TZEE-W Pop STR (white) and TZEE-Y Pop STR (yellow). Starting from the third era, the source populations were subjected to improvement for tolerance to drought, low N and resistance to Striga . A randomized incomplete block design with two replications was used for the field evaluations. Results revealed genetic gains in grain yield of 0.314 Mg ha −1 (13.29%) and 0.493 Mg ha −1 (16.84%) per era under low N and high N, respectively. The annual genetic gains in grain yield was 0.054 Mg ha –1 (2.14%) under low N and 0.081 Mg ha –1 (2.56%) under high N environments. The cultivar 2009 TZEE-OR 2 STR of era 3 was the most stable, with competitive yield across environments, while 2004 TZEE-W Pop STR C 4 from era 2, and TZEE-W STR 104, TZEE-W STR 108 and 2012 TZEE-W DT STR C 5 from era 3 were high yielding but less stable. These cultivars should be further tested on-farm and commercialized in WCA. Substantial progress has been made in breeding for high grain yield and low-N tolerance in the sub-region.