Biotic Stress and Crop Improvement: A Wheat Focus Around Novel Strategies - Crop Improvement: New Approaches and Modern Techniques - page 251

chromosomes 3BL and 2DS which ultimately reduced the disease spread (Sukh-
winder-Singh et al. 2012 ).
Rusts(Leaf,StemandYellow)
Of the total 215 million hectares area planted to bread and durum wheat globally
about 44 % (95 million hectares) are in Asia. Sixty-nine million hectares are in Chi-
na, India and Pakistan. Most of the farmers are classed as “poor” or “small” farm-
ers and hence food security plus production stability are of significant importance.
Stem rust has been under control since the green revolution times of the mid-sixties.
Leaf rust (caused by Puccinia triticina ) and yellow rust (caused by Puccinia strifor-
mis ) however have the potential to affect production levels up to 60 and 43 million
hectares respectively in Asia if susceptible cultivars were grown (Singh et al. 2004 ).
Though fungicidal applications offer control their use is an added cost to farmers
besides being unsafe environmentally. Hence growing resistant cultivars is the most
effective and efficient control strategy (Rizwan et al. 2008 ). These major stresses
have to be simultaneously addressed.
Rusts have remained very dynamic pathogens that have consistently existed as
a major wheat-breeding objective globally. Currently major attention is given to
stem rust and yellow rust is a close second that should not be a reason to look at
leaf rust with complacency. The conventional picture details numerous genes for all
three rusts in the Wheat Rust compilation (McIntosh et al. 2003 ). Genes have been
identified from within conventional wheat cultivars and also from alien species.
The resource of the D genome Ae. tauschii is of interest for this presentation and its
contributions to yellow rust and stem rust shall be elucidated. An in depth coverage
of leaf rust has been made by Dubin and Brennan ( 2009 ) in the IFPRI 2020 Vision
Initiative Report hence it is not covered here.
Stripe or Yellow Rust
Stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici , is an important
foliar disease of wheat. It occurs in wheat growing areas of temperate, moist and
cool regions in all continents except Antarctica (Chen 2005 ). Its wider prevalence is
a global threat to wheat production inflicting about 30-100 % grain losses besides
affecting the quality of grain and forage (Chen 2005 ). In China, India and Paki-
stan; the top wheat producers in Asia where 59.3 million hectares are under wheat
cultivation, stripe rust prevails in 24.8 million hectares i.e., ∼ 40 % of wheat
grown area (Singh et al. 2004 ). The deployment of stripe rust resistant genes is the
most effective method to protect wheat productivity and several stripe rust resistant
genes have been deployed successfully in the past. So far 84 Yr genes have been
designated in wheat out of which 36 genes have temporary designations (McIn-
tosh et al. in MacGenes 2010 ). Additionally, 52 QTLs have also been identified