|Keywords (Extracted from title, table of contents and abstract of thesis)
wheat (triticum aestivum l.), genotypes, drought tolerance, situ techniques, crop improvement, in vitro techniques, somaclones, calli, relative water content, early maturing, high maturing, high yielding
Wheat (triticum aestivum L.) the major staple food in Pakistan, is grown both on imaged and rainfed areas. Its per acre production in rainfed area is extremely low due to drought and several other reasons. Keeping in view the importance of wheat in the country and its lower production in rainfes area, a research project was conducted at Institute of Biotechnology and genetic Engineering, NWFP Agricultural University, Peshawar, Pakistan, during 1998-2002. In situ experiments were conducted to investigate the responses of wheat to water stress whereas; In vitro studies were conducted in induce somaclonal variations for drought tolerance. In in situ experiments, ten wheat genotypes were grown hydroponically in ½ strength Hoagland solution. Water stress was induced using 00, 10, 20, 30 and 40% polyethylene glycol (PEG-6000). Data were recorded and analyzed for various morphological and physiological characteristics. All the genotypes responded differently to PEG-induced stress. PEG-stress had a significantly negative (P 0.01%) effects on survival number of tillers and leaves, leaf area, shoot length, root length, root shoot ratio and relative water content (RWC) whereas, it had significantly positive (P 0.01%) effects on praline and absicisic acid (ABC) accumulation. The results of these experiments suggested that these techniques could be used for screening a large number of genetic materials for various stresses and praline and ABA could be used as indices for screening drought tolerance. In in vitro experiments, first cultural conditions were standardized for the wheat genotypes. In this experiment, MS medium supplemented with 2 mg 1-1 2,4-D was foud superior (P 0.01%) for callusing and a combination of 0.1 mg 1-1 IAA and 1.0mg-1 BAP was found better for regeneration. In the second experiment, embryogenesis Calli of these genotypes were exposed to various concentrations of PEG. Calli of only five wheat genotypes survived PEG-induced stress, from which only twelve somaclones were developed. These somaclones were grown in glass house with their respective parents for comparison. In comparison to their respective parents, somaclones SC-GHZ1, SC-TAT7 and SC-ICP8 flowered and matured one week earlier, SC-TAT7 and SC-!CP8 produced additional tillers, SC-ICP8 produced additional leaves, SC-ICP9 accumulated increased RWC. Seven somaclones were taller, SC-F/S3, SC-TAT7, SC-ICP-8 and SC-KW12 produced larger spikes and increased number of spikelets spike-1 SC_TAT7, SC-ICP8 and SC-KW12 produced increased number of grains spike, grain weight spike-1 and grain weight plant-1 SC-ICP8 produced heavier 100-grain weight. All the somaclones developed in this study accumulated enhanced amount of praline and ABA in comparison to their respective parental praline and ABA. From breeding point of view, these somaclones could be an asset, especially the early maturity and high yields of SC-YAT7, SC-ICP8 and SCKW12, could be a breakthrough and may be used for the production of new early maturing, high maturing, high yielding and drought tolerant varieties.