S. C. Bhardwaj

Ug99-Future Challenges

Stem or black rust of wheat was a disease of past until the emergence of Ug99, a race of Puccinia graminis f. sp. tritici in Uganda in 1999. The peculiar feature of this race is its virulence to Sr31 which was conferring resistance to various diseases in wheat covering about 40 % of the world’s acreage under wheat. Since then this race has evolved seven more variants, five of which have virulence to Sr31 and different combinations of other Sr genes like Sr24 and Sr36. This group of races have further spread to Kenya, Ethiopia, Sudan, Yemen, Iran Tanzania, Zimbabwe, Mozambique and South Africa. With a call from Noble Laureate Dr. Norman Borlaug in 2005, the entire world stood up to fight this menace. Under the umbrella of Borlaug Global Rust Initiative (BGRI), Durable Rust Resistance in Wheat (DRRW) started functioning with funding from many donors. Before the Sr31 virulences could spread further, more than 2,50,000 lines of wheat from almost all the wheat-growing countries had been evaluated in Kenya and Ethiopia and many have been found resistant against Ug99 group of races . It may not be threat in main wheat belt of North Western Plains Zone of India; however, management strategy is in place, if there is an independent mutation for Sr31 to secure the wheat in stem rust prone areas. Already a sizeable area is under Ug99 group resistant wheat in Peninsular and Central India.

A new variant 5R9-7 of Puccinia triticina on emmer and durum wheats in India

Emmer and durum wheats are generally resistant to leaf (brown) rust in many countries including India, where pathotypes specialized to these wheats rarely occur. During 2006, widespread prevalence of leaf (brown) rust was recorded on Emmer wheat. A new pathotype, 5R9-7(DBBGB), of Puccinia triticina was associated with leaf rust on many of the popular cultivars, which was avirulent to most of the bread wheat accessions tested; including Agra Local, a susceptible host to wheat rusts in India. Pathotype 5R9-7(DBBGB) was found to be virulent to Lr2c, Lr14a, Lr18 and Lr20. Resistance sources to this pathotype based on evaluation of Indian and exotic wheat germplasm, its avirulence/virulence structure, adult plant response of important tetraploid wheat material and other attributes are described.

'HS628'-A Potential Genetic Stock for Resistance to New Virulent Pathotypes of Black, Brown and Yellow Rusts of Wheat (Triticum aestivum L.)

Three rusts of wheat viz., leaf / brown (Puccinia recondita sp. tritici), stripe / yellow (Puccinia striiformis sp tritici), stem / black (Puccinia graminis sp. tritici) are very devastating diseases causing huge losses to the wheat crop worldwide with India no exception. The 1BL.1RS translocation derived wheat varieties carrying Yr9/Lr26/Sr31/Pm8 gene complex provided protection against losses due to leaf and stripe rusts in India till 1995. However, the evolution of pathotype (pt) 46S119 virulent to Yr9 and Yr2 resistance genes has changed the whole scenario (Nayar et al., 1996). After breakdown of Yr9 based resistance, some protection against stripe rust was rendered by “Attila” germplasm derived wheat varieties that had Yr27 effective against pt. 46S119, was succumbed with new variant 78S84 (Prashar et al., 2007). Recently five new highly virulent pathotypes of stripe rust viz., 46S117, 110S119, 238S119, 110S247 and 110S84 have been identified in India (Gangwar et al., 2015). Due to emergence of these pathotypes , Yr12 became susceptible to pts. 110S84, 110S119, 110S247 and 238S119. Joss-Cambier carrying Yr11 gene, also became susceptible to the new pts. 110S84 and 238S119 in addition to 46S119 pathotype (Bhardwaj et al. Pers. Comm). Another gene Yr14 is also defeated by the new virulent pt. 110S119.

Efficiency of double haploid production in wheat through wide hybridization and embryo rescue

The effect of haploid induction in wheat F1s by Zea mays, Imperata cylindrica and growth environments was investigated. Doubled Haploid (DH) plant production via maize and I. cylindrica technique from field grown LWH x VL616 F1 plants was equally efficient. In second environment, four F1 hybrids viz. LWH x VL616, HPW266 x Yr15 (CN25087), HS490 x HI1563 and Local Red x WHD938 were grown in greenhouse conditions and pollinated with maize. Efficiency of DH production was considerably high from greenhouse grown F1s as compared to field grown F1s. We also report an efficient protocol for DH production in bread wheat.

Near-isogenic lines in NP 4 background carrying the genes Lr13, Lr18, Lr19 and Lr26 as locally adapted differentials for Indian pathotypes of wheat leaf rust

A backcross programme was conducted to transfer 13 of the Lr genes present in the leaf rust differentials being currently used in India viz., Lr1, Lr2a, Lr2c, Lr3a, Lr9, Lr10, Lr13, Lr15, Lr17a, Lr18, Lr19, Lr20 and Lr26 in the background of wheat variety NP 4 having desired agronomic traits. Homozygous resistant lines carrying these genes singly have been developed through six backcrosses and subsequent selection. Nine of these lines have already been reported. Present communication reports the remaining four lines carrying the genes Lr13, Lr18, Lr19 and Lr26. These lines being locally adapted and early maturing are easy to maintain under Indian conditions, and can be widely used for virulence analysis and genetic studies.

Molecular marker assisted back cross breeding for effective transfer of Lr19 in wheat (Triticum aestivum L.)

The gene Lr19, derived from Agropyron elongatum provides effective resistance against leaf rust in Northern India. To develop improved wheat lines in the background of HS240, HS295, rust resistance from FLW20 possessing Lr19 was involved to generate back cross populations and confirm resistance through host-pathogen interaction and molecular marker. The SCAR marker SCS265512 was used to validate Lr19 in back cross plants transferred from FLW20. Results of HPI test and molecular marker assisted validation for Lr19 showed 88–93 percent consistency, indicating that both the techniques are mutual exclusive for effective selection of Lr19. Fixed gene populations are now ready for station trials.