TEMPERATURE RESPONSES OF TROPICAL MAIZE CULTIVARS SELECTED FOR BROAD ADAPTATION

Maize cultivars with broad thermal adaptation may be useful in areas w here the crop experiences large fluctuations in temperature, or when a cultivar is targeted for several areas with contrasting temperature r egimes. This study evaluated the effects of temperature on development and yield of maize cultivars differing in both adaptation and selecti on history. Experiments were sown in seven tropical environments where the mean temperature during the growing season varied from 13 degrees C to 28 degrees C. Cultivars adapted to tropical highland, tropical m idaltitude, tropical lowland and temperate environments were included. Among these were comparisons of cycles 0 and 6 (C-0, C-6) of three po pulations, which had been improved through international progeny trial s grown at several sites within specific adaptation zones. An addition al cultivar, CIMMYT's Large del Dia, was represented as 100 full-sib p rogenies, and grown in an adjacent trial in each environment. This cul tivar was formed by selecting within a broadly-based composite for yie ld across adaptation zones, and for photoperiod insensitivity. Measure s of development included rates of emergence and leaf appearance, and times to anthesis and silking. Final leaf number, grain yield, and yie ld components were also measured. In two of the three comparisons, C-6 selections significantly outyielded their C-0 equivalents across envi ronments. No differences between C-0 and C-6 were observed in yield st ability, as measured by standard deviation of yield across environment s, or in developmental patterns. Principal components and cluster anal yses revealed that Large del Dia differed from other cultivars in emer gence rate, leaf appearance rate, and anthesis date. Across environmen ts 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 Large del Dia was similar to that observed among cultivars of different adaptation groups. Selection wit hin a broad-based population for adaptation to diverse environments re sulted in a cultivar with a unique response of development to temperat ure, more stable grain yield over a wide range of temperatures, but wi th less specific adaptation to any single environment. While the tempe rate maize cultivar also exhibited stable yields across environments, tropical cultivars were more specific in their adaptation. Results ind icate that it may not be possible to select a cultivar with high and s table grain yield across temperatures ranging from 13 degrees C to 28 degrees C, because cool- and warm-temperature adaptation may be mutual ly exclusive traits. Broad adaptation is possible across a more modera te range of temperatures, however and can be improved by selection. (C ) Elsevier Science B.V.