Mungbean seedling were transferred to thermocol sheet that was placed over a plastic tub with 4.2 l of basal nutrient solution. Two P level created by adding KH2PO4 : Sufficient (250 ?M) and low P (3 ?M). Drought stress was imposed after 1 week of transplanting by removing the thermocol sheet from the nutrient solution. Initially, seedling roots were exposed to air for 1 hr for acclimatization. Further, exposing time to air were increased for 3 hrs for a period of 5 days. Exposure time to air was 10.
00 h to 13.00 in drought treatments. Composition of basal nutrient solution was same as mentioned in the basic experiment. Three replications with three seedlings each were maintained for all treatment combinations. After 2 weeks post- transplant, The intensity of drought was assessed by visual scoring on a (1-5) scale; 1= healthy plants without drought symptoms, 2 = green plants with slight wilting or leaf rolling, 3 = leaves turning yellowish green with moderate wilting, 4 = leaves yellowbrown with severe wilting or drying along the tips and edges of the unifoliolate leaves, 5 = Fully dried shoot of the plants.
3.4. Plant Growth conditions
3.4.1. Experiments I (Field study)
A field study with 1250 mungbean accessions was conducted at Issapur farm, ICAR-NBPGR, New Delhi. Recommended crop cultivation practices were adopted for this experiment. (Plate)
3.4.2. Experiment II (Hydroponic culture under controlled environment)
Mungbean seedling raised as described in basic experiment and transferred to thermocol sheet placed over a round tub containing 4.2 l nutrient medium. (Plate). Seedling placed on a thermocol sheet at a spacing 2.5 cm x 2.5 cm. Composition of basal nutrient solution and environment variables were same as mentioned in the above method of stress imposition.
The solution was aerated regularly by aquarium air pump and replaced in every 3 days. Three replications with three plants each were kept for all treatment combinations.
3.4.3. Experiment III and IV (Soil culture under natural environment)
Soybean plants were grown during Kharif season from 27 July to 12 November 2012 to assess the growth and yield parameters under sufficient and low soil P availability (Plate 1C). The weather parameters recorded during the crop season is presented in Appendix 1. Seeds were soaked overnight in deionized water and treated with Bradyrhizobiumjaponicum culture. Sowing was done in earthen pots (30 cm diameter) containing 12 kg sandy loam soil. The pH (soil:water::1:5) and EC of the soil was 8.2 and 0.174 mS m-1 respectively. In the low P soil, available P extracted by Olsen