Andean maize in Argentina: physiological effects related with altitude, genetic variation, management practices and possible avenues to improve yield

In the Argentinean Andean region, maize is a main staple being cropped up to 3,900 m above sea level (masl). Yields are limited by the sharp decrease in temperature associated with altitude but also by a lack of management and breeding technologies to underpin traditional practices. In this review we discuss: (i) the main physiological changes of increasing altitude using experimental reports up to 2,650 m above sea level plus own experiments up to 3,300 masl; (ii) available genetic diversity within local races; (iii) maize cropping systems based on literature and own data from 23 surveys; and (iv) possible avenues for improving yield. Among physiological traits, major penalties are associated with delayed phenology reducing light capture, and low temperatures inhibiting photosynthesis and kernel growth rate. As a result, yields can be reduced up to 85% at 3,300 masl compared with 2,300 masl in contrast to increases at lower latitudes. Local races are characterized by a high genetic diversity that is aiming to be preserved by both in situ and ex situ conservation initiatives. However, little is known about phenotypic variation, impairing the exploitation of these genetic resources in breeding programs. Breeding strategies could consider tillering ability (to buffer stand heterogeneity) and photosynthetic recovery rates from chilling as important target traits, whereas plant density management could overcome penalties related with delayed plantings and phenology. Water availability is currently insufficient, especially at higher altitudes where most farmers rely on water from thaw, and climate change projections suggest this will worsen; thus improving water use efficiency also deserves further work.