**5. Conclusion**

spike with the reduction in quantity of P applied. Similar results were reported by Poulsen et al. [55] who suggested that P fertilization maximizes number of grains per spike in wheat crop.

Spike weight of the both wheat genotypes differed considerably due to their genetic characteristics (**Table 17**). The results depicted that the higher spike weight was recorded for the NARC-2009 (0.52 g) against Sehar-06 (0.46 g). The difference between both genotypes was 11%. Similarly, all the treatments differed potentially for spike weight. Maximum spike weight was recorded for T7 (0.55 g) followed by T8 (0.53 g), while the minimum spike weight was noticed under T1 (0.43). There was 21% difference among highest and lowest treatments. Similarly, the interactive effect was significant for spike weight. Highest spike weight was recorded for NARC-2009 under T7 (0.57 g) while lowest spike weight was observed for Sehar-06 under T1 (0.41 g). There was 28% variation for spike weight among highest and lowest interactions. Increased spike weight might be due to the adequate accessibility and uptake of P by crop plants. In stressed environment phosphorus played role to enhance root signaling. Due to uptake of P in adequate amount maximum numbers of fertile tillers were produced and the spike length, number of spikelet per spike and grains per spike also increased due to photosynthesis, energy storage, transfer, cell division as well as cell elongation so ultimately it results in increase in grain yield. The findings of current study corroborate the conclusions of Al-Karaki and Al-Omoush, [56], and Mehdi et al. [57] who reported that application of P increases spike weight which ultimately enhanced grain yield. Our results were not in accordance with Somayeh and Bahram [58], who reported enhanced spike weight by addition of phosphorus.

Wheat genotypes due to their genetic behavior differed considerably for hundred grain weight at (**Table 18**). Highest hundred grain weight (4.18 g) calculated for genotype NARC-2009 whereas, lowest hundred grain weight (3.71 g) calculated for genotype Sehar-06. Both the genotypes differed 11% for hundred grain weight. All the treatments varied significantly for hundred grain weight. Highest hundred grain weight (4.38 g) recorded for treatment T7

**Treatments/genotypes Sehar-06 NARC-2009 Mean** T1 0.41i 0.47e–h 0.43E T2 0.43hi 0.49d–f 0.45DE T3 0.44g–i 0.49de 0.46DE T4 0.45f–i 0.51cd 0.48CD T5 0.47e–g 0.53b–d 0.49BC T6 0.49de 0.56a–c 0.52AB T7 0.52b–d 0.57a 0.55A T8 0.50de 0.56ab 0.53A

Mean 0.46B 0.528A

LSD for G 0.0149 LSD for T 0.0298 LSD for G × T 0.0421

**Table 17.** Spike weight for both genotypes at maturity.

*4.2.9. Spike weight*

22 Global Wheat Production

*4.2.10. Hundred grain weight*

Root architecture is a highly plastic and environmentally responsive trait that enables plants to counteract nutrient scarcities with different forging strategies. Root-specific traits such as root system architecture, sensing of edaphic stress and root-shoot communication can be exploited to improve resource capture (water and nutrients) and plant development under resource-limited conditions. The ability of plants to respond appropriately to nutrient availability is of fundamental importance for their adaptation to the environment. These signals trigger molecular mechanisms that modify cell division and cell differentiation processes within the root and have a profound impact on root system architecture. Important developmental processes, such as root-hair formation, primary root growth and lateral root formation, are particularly sensitive to changes in the internal and external concentration of nutrients. Phosphorus (P) is one of the most vital nutrients needed for wheat production. Phosphorus plays an important role in root growth and builds resistance against abiotic stresses. It functions as one of the major players in process of photosynthesis, nutrient transport, and energy transfer. Drought stress reduces leaf size, stem elongation, root proliferation, as well as, disturbs plant water relations and reduces water use efficiency in plants. The present study conducted in laboratory as well as in polythene bags. In first experiment (screening test), nine wheat genotypes sown in petri dishes using four treatments (control, PEG−0.50, PEG−1.48 and PEG−2.95) as a medium of growth. The data regarding germination percentage, root fresh weight, root dry weight, root length, shoot fresh weight, shoot dry weight and root shoot ratio recorded from experiment one and analyzed statistically. On the basis of stress tolerance two wheat genotypes were selected for next experiment. Genotypes NARC-2009 and Sehar-06 accumulated maximum germination percentage, root length, shoot length, root fresh weight, shoot fresh weight, shoot dry weight and root shoot ratio. So these two genotypes were selected for further experimentation. In experiment # 2 the effect of different treatments of phosphorus and water stress on root signaling checked. The treatments were 5 different levels of P including (P30 = 0.26 g/bag, P60 = 0.4 g/bag, P80 = 0.53 g/ bag, P100 = 0.66 g/bag and P120 = 0.8 g/bag) and three different water levels designated as WFC, W10% < FC and W20% < FC. The data regarding root length, root weight, root-shoot ratio, root length, root fresh weight, root dry weight, root fresh weight: root dry weight, root hair density, root depth and yield and yield parameters collected and analyzed. Among both the genotypes, NARC-2009 performed well compared to Sehar-06. While discussing treatments higher dry matter and yield and yield parameters were recorded under T7 (P100). With the increasing rate phosphorus root and shoot length was increasing linearly up-to P100 then it was declining. So under pot conditions where nutrients are limiting factor higher rate of phosphorus is essential to boost the productivity of the crop through better action of root signaling. Root signaling played important role in the growth and development of wheat crop. Under stressed conditions plant height, root and shoot length, root and shoot fresh and dry weight, yield and yield parameters decreased but in the presence of phosphorus all these parameters increased.

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