Achieving durable rust resistance in wheat through deployment of major and minor genes
Stripe rust and leaf rust have been major constraints to wheat production in Nepal since the 1960s. Several rust epidemics causing hardship for Nepalese wheat growers were due to race changes. Breeding for rust resistance was initiated with establishment of the National Wheat Research Program in 1972, but concerted searches for durable resistance came later with the introduction of wheat genetic resources from CIMMYT, Mexico. The early wheat varieties Nepal 297, Siddhartha, Vinayak, BL1473, BL 1022 and Annapurna series with leaf rust and stripe rust resistance genes Lr13, Lr23, Lr26 and Yr9, and Yr27 in the 1970s and 1980s succumbed to new races within a few years of release. However, Bhrikuti (CMT/COC75/3/PLO/FURY/ANA) with both major and minor gene combinations (Lr10, Lr14a, Lr26/Yr9/Sr31+ and Lr34/Yr18) and released in 1994 was unaffected by Yr9 virulence in 1997 and Yr27 virulence in 2004. This variety with >20 years of leaf rust and stripe rust protection continues to be the most popular wheat variety in Nepal. Three other varieties, Gautam (Siddhartha/Ning8319//Nepal 297) released in 2004, WK 1204 (SW89-3064/Star) released in 2007, and Pasang Lhamu (PGO/SERI) released in 1997 with Lr16, Lr26/Yr9/Sr31, Lr34/Yr18, Lr46/Yr29, Yr7, and Sr2 also remain resistant. The Ug99 resistant varieties Vijay (NL748/NL837), Danphe(KIRITATI//2*PBW65/2*SERI.1B) and Tilottama (Francolin#1 = Waxwing*2/Vivitsi) also possesses APR to the three rusts. Nepalese wheat researchers work closely with the CIMMYT Global Wheat Program and DRRW/BGRI to utilize knowledge and APR germplasm. Strong networks for participatory varietal selection involving women farmers in both the hills and terai help in faster adoption and in establishing varietal diversity. In summary, Nepalese wheat breeders have successfully used APR in protecting wheat crops.