Rahman, Mehboob-ur-1; Ali, Ahmed1; Qaiser khan, Ali1; Abbas, Ammad1; Rahmat, Zainab1; Sarfraz, Zareen1; Khalid, Anum1; Gul, Maryam1; Munir, Atif1; Atifiqbal, Muhammad1; Scheffler, Jodi2; Scheffler, Brain2;
1National Institute for Biotechnology & Genetic Engineering (NIBGE) Faisalabad, Pakistan. 2Jamie Whitten Delta States Research Center, Stoneville, Mississippi, USA
Cotton leaf curl, a disease of viral origin, is transmitted by a whitefly (Bemisiatabaci), was first reported in 1912 in Nigeria, and later spread to Egypt, Sudan, India and Pakistan, and recently in China. The disease has significantly challenged the sustainability of cotton production in Pakistan with annual yield penalty of two million bales. Efforts were made in developing resistant cotton varieties, which upheld the resistance for couple of years but overcame by the evolution of new strain of the virus (now called as cotton leaf curl Burewala virus). For protecting the most important natural fiber producing crop, a mega project aiming at the improvement of genetics of the cotton plant for combating the disease, was initiated in 2011 under Pak-US (managed through ICARDA, Pakistan) joint venture program. Till now, more than 3500 cotton accessions have been screened; and 33 accessions were found asymptomatic while G. hirsutum 2472-3 and G. hirsutum 3661 showed high tolerance to the disease. Among the asymptomatic, G. hirsutum Mac-07 (photoperiod insensitive) is being used extensively by multiple cotton research institutes for developing resistant cotton cultivars. A number of mapping populations by involving tolerant and resistant cotton genotypes with the mostsusceptible cotton species were developed. For example, mapping populations were developed by crossingG. hirsutum 2472-3 (tolerant), G. hirsutum Mac-07 (resistant) and highly sensitive genotypes G. barbadense PGMB-66, G. barbadense PIMA S7, respectively. A total of 1200 SSRs were surveyed on parent genotypes of G. hirsutum 2472-3 and G. barbadense PGMB-66 (Cross-I). Out of these, 113 were found polymorphic. These were surveyed on F2population. In second population (derived from a cross G. hir 2472-3/G. bar PIMA S-7, Cross-II), we surveyed 170 SSRs. Out of these, 24 polymorphic were surveyed on F2population. Similarly, we too surveyed 435 SSRs on the parent genotypes of third mapping population (Mac-7/PIMA S-7, Cross-III). A total of 18 polymorphic primers were surveyed on F2 population. Based on our limited studies, we were able to identify two QTLs i.e. QCLCuD25 and QCLCuD26 from Cross-I population study, six QTLs i.e. QCLCuD3, QCLCuD4, QCLCuD7, QCLCuD8, QCLCuD9, QCLCuD14 from Cross-II population study, and three QTLs from cross-III population. These studies will pave the way for not only initiating marker-assisted breeding for the development of resistant cotton cultivars in Pakistan but will also provide a comprehensive information to the international cotton community for combating the disease.