Status and strategies in breeding for rust resistance in wheat

Abstract

Wheat along with rice and maize is fulfilling half of the calories demands of the world. Global Wheat production has increased tremendously since green revolution in 1960's and helped in minimizing hunger and malnutrition. Developing countries, which consume 60% of the global wheat production, have shown a higher yield increase than the developed countries in the past [1]. It was driven by the hunger prevalence in these countries and was attributable to the introduction of high yielding and rusted resistant semi dwarf varieties developed under the collaborative efforts of International and National research systems during the last 50 years. Whereas, climate change and the emergence of new pests and diseases are threatening the food sustainability. The evolution of new races of disease pathogens like stem rust (Ug 99) is of serious concern. In order to feed the ever increasing population we have to increase wheat production at the rate 1.6% which can be achieved by developing high yielding varieties having a good tolerance level for biotic and abiotic stresses.

Genetic analysis of rust resistance genes in global wheat cultivars: an overview

“…Wheat leaf rust fungus can easily spread thousands of kilometers from the initial infection site through its dikaryotic urediniospores, which have been documented to spread both within and between continents [22]. This widespread dispersal has led to the occurrence of epidemics on a continental scale [9].…”

“…Therefore, durable resistance remains effective after widespread deployment over a considerable period of time. This type of resistance is mainly associated with minor genes, also known as slow rusting genes, and is generally controlled by more than one gene during the adult-plant stage rather than the seedling-resistant stage, and shows non-HRs to infection [22]. In wheat cultivars, the presence of a single resistance gene is generally less effective for controlling rust disease, whereas the combination of two or more genes enhances resistance durability.…”

“…In wheat cultivars, the presence of a single resistance gene is generally less effective for controlling rust disease, whereas the combination of two or more genes enhances resistance durability. The genetic basis of durable resistance is the additive effect of partially resistant minor genes, and it is usually polygenic in nature and active in the adult-plant stage [22]. A group of CIMMYT germplasms involving 10-12 different genes were developed by pyramiding 4-5 minor genes; this resulted in a degree of resistance against rust that approaches immunity [22].…”

“…The genetic basis of durable resistance is the additive effect of partially resistant minor genes, and it is usually polygenic in nature and active in the adult-plant stage [22]. A group of CIMMYT germplasms involving 10-12 different genes were developed by pyramiding 4-5 minor genes; this resulted in a degree of resistance against rust that approaches immunity [22]. The Pakistani variety Lyalpur 73 and the South American wheat cultivar are good examples of durable resistance varieties that were developed over 50 years ago and remain rust resistant almost everywhere in the world.…”

“…The combined effect of the leaf rust resistance gene Lr19 with the stem rust resistance gene Sr25 causes wheat flour to appear yellow and enhances the durability of leaf rust resistance in wheat cultivars [26]. When Sr2 is present alone, it does not provide a sufficient level of resistance; however, in combination with the Lr27 gene, it provides a desirable level of stem rust resistance in tall Kenyan cultivars such as Kenya plume and semi-dwarf CIMMYT cultivars Pavon F76, Parula, Kingbird, and Dollarbird [22]. Similarly, the combined effect of Lr34 and Yr18 in the Italian varieties Mentana and Ardito [175] has lead to effective durable resistance to stem rust.…”