Temperature responses of tropical maize cultivars selected for broad adaptation

Abstract

Maize cultivars with broad thermal adaptation may be useful in areas where the crop experiences large fluctuations in temperature, or when a cultivar is targeted for several areas with contrasting temperature regimes. This study evaluated the effects of temperature on development and yield of maize cultivars differing in both adaptation and selection history. Experiments were sown in seven tropical environments where the mean temperature during the growing season varied from 13°C to 28°C. Cultivars adapted to tropical highland, tropical midaltitude, tropical lowland and temperate environments were included. Among these were comparisons of cycles 0 and 6 (C 0, C 6) of three populations, which had been improved through international progeny trials grown at several sites within specific adaptation zones. An additional cultivar, CIMMYT's Largo del Dia, was represented as 100 full-sib progenies, and grown in an adjacent trial in each environment. This cultivar was formed by selecting within a broadly-based composite for yield across adaptation zones, and for photoperiod insensitivity. Measures of development included rates of emergence and leaf appearance, and times to anthesis and silking. Final leaf number, grain yield, and yield components were also measured. In two of the three comparisons, C 6 selections significantly outyielded their C 0 equivalents across environments. No differences between C 0 and C 6 were observed in yield stability, as measured by standard deviation of yield across environments, or in developmental patterns. Principal components and cluster analyses revealed that Largo del Día differed from other cultivars in emergence rate, leaf appearance rate, and anthesis date. Across environments its mean grain yield was generally similar to that of the temperate cultivar, and had the smallest standard deviation. The range of grain yields among full-sib progenies of Largo del Día was similar to that observed among cultivars of different adaptation groups. Selection within a broad-based population for adaptation to diverse environments resulted in a cultivar with a unique response of development to temperature, more stable grain yield over a wide range of temperatures, but with less specific adaptation to any single environment. While the temperate maize cultivar also exhibited stable yields across environments, tropical cultivars were more specific in their adaptation. Results indicate that it may not be possible to select a cultivar with high and stable grain yield across temperatures ranging from 13°C to 28°C, because cool- and warm-temperature adaptation may be mutually exclusive traits. Broad adaptation is possible across a more moderate range of temperatures, however and can be improved by selection.