Study the effect of drought stress on yield and some physiological characteristics of indigo (Indigofera tinctoria)

Drought stress in arid and semi-arid regions of the world, including Iran, more than any other factors decline the plant growth and production. So selection the drought tolerant and resistant plants for arid and semi-arid areas is the major importance. Indigo (Indigofera tinctoria L.) is one of the resistant plants to drought which is suitable for sowing in dry and hot areas of the country . Therefore, considering the above mentioned, this study was carried out in order to effect of drought stress on yield and some physiological characteristics of Indigo in Jiroft area.The 27 experiment was planned in a randomized complete block design with four treatments (1 - irrigation at field capacity (FC) as a control , 2 - Irrigation at the 75% field capacity (mild stress), 3 - Irrigation at the 50% field capacity (moderate stress ) and 4 - Irrigation at the 25% water at field capacity (severe drought) with four replications in Jiroft and Kahouj Agricultural Research Center during 2005-2006. During the different growth stages, yield (total leaf dry weight), stem dry weight, plant height, branch numbers per plant, proline content in leaf and root, total soluble carbohydrates in leaves, the amount of photosynthetic pigments and the rate of uptake of potassium, zinc and calcium in leaf were measured and recorded. The results showed that the effect of different levels of drought stress on dry weight of leaves and stems, leaf and root proline, total soluble carbohydrates in leaves, the amount of chlorophyll a, chlorophyll b and total chlorophyll, potassium and zinc absorption rate on the leaves was significant . The chlorophyll a/ b ratio and uptake of calcium ion were not affected by different levels of drought stress. Mild drought stress has not significant affect on leaf dry weight (total yield) but the total yield decreased with increasing severity of drought stress. The highest total yield, was observed in control and mild drought stress by 3548 and 3420 kg/ ha, respectively. Drought stress causes the accumulation of compatible osmolytes in indigo plants such as proline and soluble carbohydrates. Stress intensity increases the soluble carbohydrates content in the leaves, but the difference was not significant between moderate and high stress levels. With increasing drought stress, the leaf and root proline accumulation increased, and the highest value was observed in the severe stress. Also the results revealed that the amount of chlorophyll a, b and total chlorophyll up to mild stress level was constant and there was no significant difference with control. Afterward with increasing intensity drought stress, photosynthetic pigments were significantly reduced. Potassium ion absorption increased with increasing intensity of drought up to moderate stress level and afterward has dropped. Zinc ion absorption was affected by drought and the highest value was obtained in the severe stress treatment. The absorption of calcium ions was not affected by drought stress.