Breeding wheat for leaf rust resistance: past, present and future

Abstract

Leaf rust of wheat caused by ( Puccinia triticina Eriks) proliferate under optimum weather conditions and causes severe damage. Diseases appeared in form of epidemics pose a real threat to food security rising the cost of food production. Breeding for development of resistant varieties against disease has advantages for ecological and monetary reasons, predominantly for peasants in the developing world. Sufficient research work has been conducted regarding pathogen host interaction mechanism. Two mechanisms of resistance are acquainted very well. Complete resistance function from seedling to adult growth stages whereas partial resistance becomes effective at the pre-booting stage and is more durable. Eighty leaf rust-resistant genes have been documented. Among these leaf rust-resistant genes Lr12, Lr13, Lr22a, Lr34, Lr35, Lr37, Lr46, Lr48, Lr49, Lr67, Lr68, Lr74, Lr75, Lr77 , and Lr78 are adult plant resistant (APR) genes. Fear of genetic erosion is also well known. It means cultivars grown on a wide range with narrow genetic backgrounds and this situation is undesired as it may invite an epidemic. It has been experienced repeatedly in past decades. Wide genetic diversity in parents can promise to achieve maximum output from the breeding programmes. Sources of resistance other than Triticum aestivum are rich in diversity and consequently have been addressed adequately. Usage of relatives of wheat plant as a source of novel genes belonging to genera Triticum , Aegilops , Thinopyrum and Secale has generated more desired output. Molecular markers are being applied to explore diversity in pathogen as well as in host effectively although conventional approaches are being used as well. Status of research work carried in Pakistan has also been discussed in abridged form. This review has been conducted with an objective to summarize research work academic as well as applied, carried to develop strategies to incorporate genetic resistance in wheat against leaf rust.