Cotton is the world's most important fibre crop. It is also the second oil seed crop of the world (Khan et al., 1999). It is a major foreign exchange earner in Pakistan, where it is cultivated mostly in Sindh and Punjab provinces. Cotton is a halophytic crop, which is generally grown in mildly saline soil (Ashraf, 2002). However, its yield and quality is reduced at high salt levels.
Some 6.67 million hectare in Pakistan is seriously affected (Alam et al., 2000). Introduction of salt tolerant cotton varieties will play a key role in increasing the agriculture productivity of cotton under saline condition. The object of this project was the identification of genetic markers associated with the salt tolerance of cotton. 40 genotypes were tested with salt treatments.
Sixteen genotypes were tested with (150 followed by 250 mM) and the response of nutrition; photosynthesis and basic geometry were measured. The plant height, nodes per plants, fresh and dry weight, chlorophyl I content, transpiration rate, stomata! conductance and CO2 uptake of cotton plants were reduced significantly by NaCl. Na+ uptake in all yo ung and old plants parts
were increased significantly by salt (150 fo llowed by 250 mM) treatments as compared to control treatments. K+ and Ca++ uptake in some young and old plants parts were increased signifi cantly and in some of p lant parts decreased by salt (150 followed by 250 mM) treatments as compared to control treatments. Genotypic response was significantly different in most of genotypes by salt. A rudimentary mapping population was developed for breeding
and genetics. But no phenotypic and genenotypic variation were observed between genotypes.
Meanwhile, microsatellite DNA sequences (SSR; potential genetic markers) were sought. Seventeen pairs of primers were used on the tlu·ee selected lines and on 28 different cotton genotypes. The number of alleles per primer with a range of I to 5 with in average of 2.5 SSR fragment per primer were observed. The polymorphism information content (PIC) values with a range of 0.00 to 70. The genetic similarity of SSR between genotypes with a range of 0.72 to
0.95 in G. hirsutum was higher than of G. stocksii, S6 x DNH 40 and G. stocksii x G. hirsutum (0.14).