Abstract
Pearl millet (Pennisetum spicatum (L.) Korn.) and maize (Zea mays L.) are C-4 grass species grown for feeding humans and animals in Almadinah Almunawwarah, which is in the western part of Saudi Arabia. During the winter, the mean temperature, which drops to 14 degrees C, represents a major problem for the growth of these species in this region. Therefore, the objectives of this research were to investigate the growth response and the photo-synthetic performance of P. spicatum and Z. mays under a low temperature stress. The treatments involved day -time and nighttime temperatures of 14/12 degrees C (low temperature) and 24/22 degrees C (optimum temperature). The results indicated that low temperature significantly reduced all growth and physiological parameters, including seed ger-mination, leaf expansion, leaf area, shoot length and root length of the two species compared to those of the con-trol. Additionally, the low temperature significantly decreased the light-saturated assimilation rate (A(sat)), quantum yield (phi), saturated rate of carbon dioxide uptake (A(max)) and efficiency of carboxylation on both species compared to those of the control. Moreover, the values of Fv/Fm and the chlorophyll contents of both species were significantly reduced by low temperature compared to those of the control. It can be concluded that both species had little tolerance to low temperatures.