الفهرس 
المقدمةOnly 14 pages are availabe for public view
 |  | from | 144 |  |  |
| | | from | 144 | | |
Abstract
An important renewable resource, cotton (Gossypium spp.) is the world’s leading natural fiber and the second largest oilseed crop global production. It is a source of fiber, cattle feed and edible oil. In Egypt cotton fibers are important for both export and local textile industry.
Genetic variability is the driving force behind all breeding efforts. It is impossible to make any genetic progress through selection unless there are genetic differences among plants in a breeding population. The greater the genetic variation in the gene pool, the more rapid progress can be made.
Unless methods are improved to transfer useful allelic variation from diverse to adapted germplasm without negative agronomic effects, cotton germplasm resources will remain largely underused and the trend towards increased uniformity will probably continue (Van Esbroeck et.al., 1997).
In Egypt, cotton-breeding program is based upon the hybridization-selection method that resulted in several commercial varieties; most of these varieties were isolated throughout individual plant selection following hybridization.
Also, area of planting cotton is confronted with competition with winter crops, mostly with wheat and partially with sugar beets and other minor crops. Late planting of cotton after harvest of the aforementioned crops is encouraged by the growers to get better income. Therefore, improvements of cotton cultivars able to tolerant late planting become a must.
In vitro techniques can provide means for obtaining somaclonals and induced variants that can serve as important genes for tolerance to environmental stresses e.g. late planting as well as resistance against biotic stresses; disease and insect resistance. Also, through genetic engineering (Zhang and Zhao, 1997). However, the successful application of in vitro methods is greatly dependent on a reliable regeneration system. Although somatic embryogenesis and regenerated plants have been obtained from various explants of some cotton species in numerous labs, and regenerated procedures have been used to obtain genetically modified plants after Agrobacterium-mediated transformation (Umbeck et al., 1987 and Rajasekraran et al., 1996) or after DNA-coated particle bombardment McCabe and Martinell, 1993.
The production of genetically modified cotton has been one of plant biotechnology’s greatest success stories. Genetically modified cotton, one of the first transgenic crops in commercial production on a large scale, now accounts for the vast majority of cotton acreage in the U.S. and increasingly so in cotton- producing countries around the world. The recovery of transgenic plantlets requires approximately 8 to 10 months and occurs in three discrete stages; 1) Callus Induction, 2) Somatic Embryogenesis, and 3) Germination of Somatic Embryos.
Cotton (Gossypium) traditional breeding programmes have produced steady improvement in agronomic traits, but the lack of useful economic characters in commercial cotton cultivars still remains a major challenge (Sawahel, 1997a). Recently, however, cotton has entered the biotechnology arena, which, by advances in genetic transformation technology, promises to meet this challenge by incorporating foreign genes for the desired agronomic traits (Sawahel, 1997b; Sawahel and Cove, 1992). Although interspecific hybridization has been difficult in cotton (Pudir, 1972), advances have been made using biotechnological techniques such as ovule culture (Thengane et al., 1986), protoplast culture (Peeters et al., 1994), somatic embryogenesis (Finer, 1988), and genetic transformation (Firoozabady et al., 1987; Umbeck et al., 1987; McCabe and Martinell, 1993) using Agrobacterium (Perlak et al., 1993) and particle bombardment (Finer and McMullen, 1990). However, most of the reports on in vitro regeneration and genetic transformation of cotton are restricted to either wild spp. or Coker varieties of G. hirsutum, which are not widely cultivated. Thus, time-consuming backcrossing is required to introduce novel characteristics into other cotton varieties. The success of any cotton (G. barbadense L.) improvement programme by biotechnological approaches depends on the availability of plant regeneration and genetic transformation systems. However, there is a need to develop a new cotton transformation system that is rapid, simple, and relatively efficient.