**3. Materials and method**

proline, malondialdehyde, acid phosphatase, peroxidase and superoxide dismutase (SOD), but the significant reduction of P uptake and soluble protein content. The results based on the correlation analysis showed that the economic yield of wheat landraces had relationships

Effect of drought on the growth and yield of wheat were investigated. Drought during grain filling further decreased yields. Plots with a lower plant density demonstrated a smaller decrease in yield due to drought. There was a significant positive linear relationship between the number of shoots per plant and nodal root axes per plant. There appeared to be a difference between cultivars in root system architecture, and in their response to drought, but these differences were not reflected in grain yield [28]. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant growth substances such as salicylic acid, auxins, gibberellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit [29]. The possibility of reducing the proliferation of roots to increase yields at higher seeding rates and conserving the soil water at different growing stages in water-limited environments was studied. In the severe drought towards the end of the growing season, grain yield decreased as the seeding rate increased, but under the more favorable conditions the reverse was true. Averaged over the seeding rates, grain yield was significantly increased; grain yield and yield components were higher and root pruning at spring-growth stage recorded the highest water use efficiency [30]. The leaf net photosynthetic rate and stomatal conductance were significantly decreased under drought. The leaf transpiration rate was decreased by drought. The intercellular CO<sup>2</sup> concentration was increased under drought, while it was decreased most of the time from mid-

with their morphological and physiological characteristics under P-deficiency [27].

day to the afternoon. The leaf stomatal limitation was increased under drought [31].

growth of leaves, roots, photosynthesis and dry mater accumulation [33].

**2.3. Phosphorus × drought and root signaling**

Root length, root dry weight and seedling dry weight are the major traits to select for studying tolerant genotypes under water stress conditions [32]. It is reported that drought affect the plant water status during ear formation and flowering stage. Water availability mostly affects

Phosphorous availability is correlated with moisture conditions of the soil, because higher water content in soil due to frequent irrigation generally leads to a better mobility and

**2.2. Drought and root signaling**

4 Global Wheat Production

Two experiments were carried out to study root signaling in response to different water regimes and level of phosphorus. First one was about screening of wheat genotypes for drought tolerance conducted in the laboratory. The sowing apparatus used was Petri dishes (9 cm diameter) in which 9 different varieties of wheat were sown under different level of PEG (polyethylene glycol) to induce stress. From these 9 varieties two varieties which gave better results under drought conditions were selected. These two varieties were further sown in the second experiment which was conducted in a polythene bags (2.5 feet long, 10 cm diameter). In the second experiment eight treatments were applied which were replicated thrice. The detail of both the experiments is given as under.
