Biyomühendislik

Cotton Leaf Curl Virus (CLCuV) is a major threat in enhancing cotton production in Pakistan. Economic loss due to this disease during last decade is estimated about 75 million rupees. This disease spread in epidemic from 1992-1995. The first CLCuV resistant variety was evolved in 1996. Resurgence of this disease occurred in 2001 (Burewala) breaking resistance of all exiting available germplasm of cotton. Interspecific hybridization for leaf curl virus resistance is the only economical and long term approach to tackle this hazardous problem. A total of 3338 genotypes were screened at Cotton Research station Vehari during 2003 - 2004 but none of these genotypes showed resistance to this disease. Two cultivated diploid species viz G. herbaceum A1,              G. arboreum A2, G. anomalum B1, G. capitisviridis B4, G. gossypoides D6,                  G. laxum D8, G. stocksii E1, G. somalense E2, G. areysianum E3 and G. longicalyx F1 did not showed the symptoms of this disease through petiole grafting. Gossypium arboreum is immune to CLCuV, two artificial allotetraploids of 2(G. hirsutum L x        G. anomalum).x 3G.hirs. and 2(G. arboreum L x G. anomalum). x 2G.hirs. were manually hybridized under field conditions. These two hybrids were also crossed for gene pyramiding [{.2 (hirs. x G. anom.) x 3G. hirs.} x {2G. hirs. x 2 (G. arbo. x G. anom) x          2G. hirs }] x 2G. hirs. Exogenous hormones containing 50 mg/l Gibberellic Acid and 100mg/l Naphthalene Acetic Acid was applied to control boll shedding. 3:1 ratio was not observed in above said combinations. Some plants were found resistant against CLCuV by using petiole grafting technique. But no resistance was observed. Maximum tolerance was found in this combination i.e [{.2 (hirs. x G. anom.) x 3G. hirs.} x {2G. hirs. x 2 (G. arbo. x G. anom) x 2G. hirs }] x 2G. hirs. By using this material CIM-608 has been evolved which is having high tolerance to CLCuV; this will increase cotton production and will be a source of food security.
Key words: Cotton, Introgression, CLCuV, Tolerant

Cotton leaf curl virus poses a major threat to cotton productivity in Pakistan. Screening
of germplasm to explore resistant source is a basic step towards the solution of this
hazardous problem. With this objective genetic material comprising 11060 genotypes of
cotton of different research centers was tested at Cotton Research Station, Vehari during
2002 to 2007.  During 2002-03, 3694 genotypes were tested on the basis of cotton leaf curl
virus disease incidence and 30 (Code No./varieties 124, 141, 170, 185, 218, 244, 252, 338,
FVH-153, VH-176, 609, 721, 723, 724, 752, 834, 891, 918, 1018, 106, 111, 114, 115,
141, 156, 160, 175, 178, 183, 253) lines showed no symptoms of this disease. Out of 2792
genotypes screened during 2003-04, 7 (Code No./varieties 124, 170, 244, 252, VH-176,
VH-209, 609) were found virus free.  During next three years i.e., 2004 to 2006, all the
genotypes (4364) showed susceptibility to cotton leaf curl virus disease. Two genotypes
(China-1 and China-2) out of 210 tested during 2007 exhibited resistance to cotton leaf curl
virus (CLCuV). 119 genotypes were screened on the basis of cotton leaf curl virus intensity
during 2002-07, out of which 37 (Code No./varieties 654, 1050, 1411, 1448, 124, 141,
170, 185, 218, 244, 252, 338; 609, 721, 723, 724, 752, 834, 891, 918, 1018; NIBGE-106,
NIBGE 111, NIBGE 114, NIBGE- 115, NIBGE 141, NIBGE156, NIBGE160, NIBGE
175, NIBGE 178, NIBGE 183, NIBGE 253, FVH-153, VH-176, VH-209, China-1,
China-2) lines were found virus free. Twenty four lines were tested against Cotton Leaf
Curl Virus on the basis of sick plot technique during 2002-07. Among these lines 609 from
Cotton Research Station Multan, 3232 from Central Cotton Research Institute Multan, VH156
from
Cotton
Research
Station
Vehari,
China-14
from
Nanjing Agri.University
China


showed
minimum
disease
incidence
0.8%,
7.6%,
14.75%
and 23.5%,
respectively. The

results of recent research demonstrated that it is possible to explore resistant material from
germplasm through screening on the basis of incidence and intensity. The same can be
utilized in the breeding programme for evolving CLCuV tolerant/resistance verities of
cotton.