Adaptive strategies identified among tropical maize landraces for nitrogen-limited environments

Landraces of maize (Zea mays L.) may serve as components of source populations for traits with adaptive value for nitrogen-deficit environments because traditionally they have been managed at more restricted levels of soil fertility than those used during the development of improved cultivars. Grain yields, N uptake, and N partitioning patterns of 38 landrace accessions from CIMMYT's germplasm bank and 26 improved tropical cultivars were compared under adequate and limited levels of soil N in the winter season at Poza Rica, Mexico. The improved cultivars generally outyielded the landraces at both N levels by an average of 56%. Improved cultivars were not consistently superior, however, in total N recovery, in aboveground biomass or in the fraction of N partitioned to the grain under limited N. The landraces had greater grain N concentrations at both N levels. It is concluded that landraces can contribute useful traits for stable production in N-limited environments, but that selection on the basis of grain yield alone may be insufficient. As a part of routine screening activity, a further 171 accessions were evaluated at the same two N levels, 112 in the summer, and 59 in the winter season. A preliminary principal components analysis was used with landrace data from each season to identify key traits related to N uptake and allocation patterns. Based on these traits, cluster analysis identified six groups within each cropping season. Each cluster was divided into early and late-flowering groups, and principal components analysis was repeated within each subgroup on these variables. Some clusters performed well under adequate N but not under limited N, while others showed the opposite response. This indicated specific adaptation to N environments, in which total N accumulation, N partitioned to the grain, and grain N concentration varied independently. In some cases, the clusters revealed an association with geographical areas where accessions were collected, but no relationship was observed between precipitation at the collection sites for a cluster and crop performance. When breeding maize for large and stable grain yield under N-limited conditions a reasonable strategy would be to develop early and late-maturing source populations from landraces that exhibit large N uptake, partition a large proportion of dry matter and N to the grain, and maintain a large grain N concentration under limited N supply. (C) Elsevier Science B.V.