EFFECTS OF SOIL-TEMPERATURE ON ROOT AND SHOOT GROWTH TRAITS AND IRON-DEFICIENCY CHLOROSIS IN SORGHUM GENOTYPES GROWN ON A LOW IRON CALCAREOUS SOIL

Iron deficiency chlorosis (FeDC) is a common disorder for sorghum [Sorghum bicolor (L.) Moench] grown on alkaline calcareous soils. Four sorghum genotypes were grown in growth chambers on a low Fe (1.3-mu-g/g DTPA-extractable), alkaline (pH 8.0), calcareous (3.87% CaCO3 equivalent) Aridic Haplustoll to determine effects of different soil temperatures (12, 17, 22 and 27-degrees-C at a constant 27-degrees-C air temperature) on various root and shoot growth traits and development of FeDC. As soil temperature increased, leaf chlorosis became more severe, and shoot and root dry weights, root lengths, and leaf areas increased markedly. Shoot/root ratios, shoot weight/root length, leaf area/shoot weight and leaf area/root weight and root length also increased while root length/root weight decreased as soil temperature increased. Severe FeDC developed in all genotypes even though genotypes had previously shown different degrees of resistance to FeDC. Genotypes differed in most growth traits, especially dry matter yields, root lengths, and leaf areas, but most traits did not appear to be related to genotype resistance to FeDC. The most FeDC resistant genotype had the slowest growth rate and this may be a mechanism for its greater resistance to FeDC.