Prospects of Wheat Breeding for Durable Resistance against Brown, Yellow and Black Rust Fungi

Wheat leaf, stripe and stem rusts have devastating role in reducing crop yield resulting in socio-economic instability many times across the world. The semi-dwarf wheat varieties with race specific resistance could not survive longer due to the evolution of new rust races. However, varieties like Lerma Rojo-64, Yaqui-50 and Lyalpur-73 developed in early part of green revolution retained resistance for longer time due to presence of adult plant resistance (APR) genes. Evolution of new rust races like virulence's Yr9 and Yr27 followed by the emergence of Ug99 and its mutants lead the breeders to revise their breeding strategy. Breeders are now depending on accumulation of minor genes or their use in combination with major genes for durability of rust resistance in wheat varieties. The minor genes/APR genes, Sr2/Yr30, Lr34/Yr18, Lr46/Yr19 are being exploited in wheat breeding at CIMMYT and other places. The germplam with this type of resistance have shown survival consistency over space and time. At Ayub Agriculture Institute, Faisalabad the home of green revolution in Pakistan, this strategy has been adopted since 1995. The partial resistance varieties were crossed in a top cross/back cross scheme and the segregating populations were advanced by selected bulk method, which resulted in the development of material having better yield and rust resistance than the pre-exiting varieties (e.g., Inqlab-91, MH-97). Three varieties, Shafaq-06 and Lasani-08 and AARI-11 from these crosses have been approved for general cultivation. Similarly, the material developed and distributed by CIMMYT, Mexico having this type of resistance is being globally adopted. The SSR markers for above mentioned minor genes are available and can be used as an aid in the early selection of superior genotypes. copyright 2013 Friends Science Publishers