Marker‐assisted breeding for rust management in wheat

Leaf rust, stripe rust and stem rust are the three important rusts of wheat. While stripe rust is confined to the cooler regions of North West India, stem rust requires a comparatively higher temperature to develop thus confined to Central and peninsular India. Leaf rust on the other hand occurs almost everywhere, wherever wheat is grown in India. Breeding for rust resistance is important for preventing the losses caused by the rust pathogen Puccinia spp. Over the years, judicious deployment of rust resistance genes has kept the rusts under control in India. However, continuous evolution of new virulent races of leaf, stem and stripe rusts have led to breakdown of many effective rust resistance genes. In view of the continuous evolution of new rust races, search and utilization of new rust resistance genes is essential. Resistance breeding using MAS technology have eliminated the creation of artificial rust epiphytotic for selection of rust resistance genes. Marker based selection has aided in incorporation of not only single but multiple genes for rust resistance. Three popular wheat varieties, HD2967, HD2733 and HD2932 were improved for rust resistance by incorporating rust resistance genes, Lr19 , Lr24 , LrTrK , Sr26 , Yr5 , Yr10 and Yr15 . Apart from seedling resistance genes some APR genes such as Lr34 , Lr46 , Lr67 and Lr68 were also introgressed in these varieties to impart durable rust resistance. In some varieties such as HD2733 and HD3059 APR and seedling resistance genes were also combined. Several wheat varieties developed through MAS breeding have already replaced the old susceptible wheat varieties. Marker assisted backcross breeding can produce improved versions of the popular varieties or Near isogenic lines in shorter period of time. NILs may also be used effectively to deploy diverse genes in a given geographical area. Multiple NILs of a mega variety carrying different rust resistance genes can help in managing the rust disease by preventing the build up and spread of inoculums.