Environmental and Genetic Modification of Leaf Number in Maize, Sorghum, and Hungarian Millet1

Abstract

In Zea mays L., Sorghum vulgare Pers., and Setaria italica (L.) Beauv, leaf number, an attribute differing with genolype and modified by temperature and photoperiod, is correlated with plant weight and height, photosynthetic area, time of flowering, and length of life cycle. Eighteen lnaize hybrids representing a wide range of genotypes, two maize races, three sgrghum varieties, and Hungarian millet were grown variously in CERES, the Canberra phytotron, under intense sunlight radiation and a variety of daylength and temperature regimes. In maize, the average change in leaf number per degree increased from 0.17 to 0.33 over the day/night temperature range 15/10, 21/16, 30/25, and 36/31 C under 16‐hour daylengths, with about the same average increase under 10.hour days. Under short days, at 30 and 21 C, leaf numbers were reduced 2.6 and 1.8 below long‐day values. With 30 C day temperature and 16‐hour daylength, the earliest hybrid developed 15 leaves, the latest 22.3. Leaf numbers per plant were greatest at the higher temperatures, least at the lower, the average difference being almost six leaves per plant. For plants grown at high temperatures, cold treatments up to emergence of the 7th leaf decreased leaf number only in the earlier hybrids. Changes in nutrient level did not alter leaf numbers in the one hybrid studied. Within temperature regimes, leaf number was correlated with dry weight, leaf area, and height per plant at tasseling and with days to tassel emergence. Leaf numbers in sorghum and Hungarian millet responded to environmental changes in abaut the sanle manner as in maize.