Application of SPAD number in measuring photosynthesis pigments of barley (Hordeum vulgare L.) leaves under water deficit

Water is one of the most important limited factors affecting crop productions including barley (Hordeum vulgare) in the world and Iran. Due to vital role of photosynthesis on growth and development of plants، the chlorophyll amount of leaves always has been known as a prominent physiological parameter among plant physiologists. Since chemical measuring of leaves chlorophylls is an expensive and time consuming procedure، using of SPAD instrument as an alternative method is cheap and simple، so scientists should pay more attention it than before. However، first of all they should consider the relationship between SPAD number and chlorophyll amount of leaves. In order to study the correlation coefficient between these two parameters in barley (CB 7402 cultivar) under different irrigations، an experiment as a completely randomized design in four replications under greenhouse conditions (25oc and 35% relative humidity) was conducted. Different water potential levels (0، -5، -7 and -12 bar) were induced by weight method on the basis of the amount of water lost each day. For this purpose، at the first، water potential of the soil sample was measured by pressure plate method، and then on the basis of weight of soil in each pot and the studied water potential، amount of water needed for each treatment was calculated. In order to keep the water potential constant، daily application of water was made on the basis of weight of each pot during the experiment (two months). The barley seeds were sown in pots، every day pots conditions were monitored and after appearing the main leaves، every week the SPAD numbers were recorded. After two months، we harvested the leaves which their SPAD numbers were recorded، and the chlorophyll amount of them was measured through chemical procedure (Arnon method). The data were statistically analyzed by SPSS software. The analyzed results revealed that there was an strong relationship between SPAD number and chlorophyll amount of barley leaves especially under field capacity condition (r = 0. 84); the correlation، however، significantly decreased under lower water potential.