Role of Genetics, Genomics, and Breeding Approaches to Combat Stripe Rust of Wheat

Abstract

Puccinia striiformis (Pst) is a devastating biotrophic fungal pathogen that causes wheat stripe rust. It usually loves cool and moist places and can cause 100% crop yield losses in a single field when ideal conditions for disease incidence prevails. Billions of dollars are lost due to fungicide application to reduce stripe rust damage worldwide. Pst is a macrocyclic, heteroecious fungus that requires primary (wheat or grasses) as well as secondary host (Berberis or Mahonia spp.) for completion of life cycle. In this review, we have summarized the knowledge about pathogen life cycle, genes responsible for stripe rust resistance, and susceptibility in wheat. In the end, we discussed the importance of conventional and modern breeding tools for the development of Pst-resistant wheat varieties. According to our findings, genetic engineering and genome editing are less explored tools for the development of Pst-resistant wheat varieties; hence, we highlighted the putative use of advanced genome-modifying tools, i.e., base editing and prime editing, for the development of Pst-resistant wheat.

Keywords: Puccina striiformis; fungal pathogen; new breeding strategies; resistance genes; wheat; yellow rust.

Figure 1

World map showing the epidemic years of stripe rust in different countries around the globe.

Figure 2

Historical view of different breeding techniques/procedures used for the development of stripe rust-resistant wheat cultivars. Before the advent of mutation breeding in the first quarter of the nineteenth century, conventional breeding approaches were used for resistance incorporation. Later on, advancement in the breeding approaches has brought us to the era of genome editing. Conventional breeding uses conservative breeding tools for the improvement of the trait of interest. Mutation breeding uses physical/chemical mutagens to introduce variation in a population followed by selection. Genetic engineering utilizes recombinant DNA technology for the alteration of the genetic makeup of plants and when the transfer of gene of interest is required from the distantly related organisms. Marker-assisted breeding uses DNA markers for selection of genes of interest and has the advantage of selecting the desirable plants using seedling or even seed sometimes. Genome editing is a way of making specific changes to the DNA of a cell or organism. An enzyme cuts the DNA at a specific sequence, and when this is repaired by the cell, a change or “edit” is made to the sequence.

Figure 3

Development of stripe rust-resistant wheat variety using the CRISPR/Cas system. The process begins by selecting the cultivars having the S gene to be modified followed by trait improvement through genome editing. The modified plants are used in the breeding program for the development of variety, and in later generation, transgene-free plants are selected. The illustration also discusses the pros and cons of conventional breeding vs. genome editing. The efficiency of conventional breeding techniques is low as compared to genome editing. Similarly, the off-targeting effects of conventional mutations tools are relatively high in comparison to genome editing.