STATUS OF WHEAT BREEDING AT GLOBAL LEVEL FOR COMBATING Ug99 – A REVIEW

Abstract

Stem rust in wheat remained under control for several decades all over the earth by the mid-1990's resulting in less emphasis on breeding for resistance to this disease and had not been priority in research for considerable era. The manifestation and expansion of races of Puccinia graminis f. sp. tritici commonly known as Ug99 with virulence for the Sr31 resistance gene in 1998 in Uganda  renewed interest in breeding for  resistance to stem rust of wheat. Wheat community responded instantaneously. Global Ug99 stem rust screening services were launched in 2005 under the shade of Borlaug Global Rust Initiative (BGRI) in Kenya and Ethiopia with purpose to recognize auxiliary sources of resistance. Screening in Kenya and Ethiopia of wheat materials from Asian countries carried out in 2005-06 disclosed a very low frequency of lines resistant to Ug99 and its variants. Considerable achievements have been attained identifying diverse race-specific resistance and adult plant resistance (APR) genes that can be exploited to improve wheat germplasm to contest the hazard. Four more genes namely Sr55, Sr56, Sr57 and Sr58 along with the Sr2 gene, now have been characterized to confer slow rusting. New perspectives on rust control in the future through the development of multiple resistance gene cassettes through cloning of some rust resistance genes opens. The strain spread to eastern and southern Africa and in Iran. Meanwhile evolution has also been observed in the strain generating new variants. Currently, 10 variants in the Ug99 race group have been perceived in twelve countries.  SAARC wheat disease trap nursery has been developed in the vicinity of Iran where Ug99 was perceived in 2007. Data designates that Pgt-Ug99 (TTKSK) reported from Iran in 2007 has not evolved further, nor has it extended to adjacent Pakistan or India to impose any crop failure.