Breeding Wheat for Durable Leaf Rust Resistance in Southern Africa: Variability, Distribution, Current Control Strategies, Challenges and Future Prospects

Abstract

Leaf or brown rust of wheat caused by Puccinia triticina (Pt) is one of the most damaging diseases globally. Considerable progress has been made to control leaf rust through crop protection chemicals and host plant resistance breeding in southern Africa. However, frequent changes in the pathogen population still present a major challenge to achieve durable resistance. Disease surveillance and monitoring of the pathogen have revealed the occurrence of similar races across the region, justifying the need for concerted efforts by countries in southern Africa to develop and deploy more efficient and sustainable strategies to manage the disease. Understanding the genetic variability and composition of Pt is a pre-requisite for cultivar release with appropriate resistance gene combinations for sustainable disease management. This review highlights the variability and distribution of the Pt population, and the current control strategies, challenges and future prospects of breeding wheat varieties with durable leaf rust resistance in southern Africa. The importance of regular, collaborative and efficient surveillance of the pathogen and germplasm development across southern Africa is discussed, coupled with the potential of using modern breeding technologies to produce wheat cultivars with durable resistance.

Fusarium Head Blight and Rust Diseases in Soft Red Winter Wheat in the Southeast United States: State of the Art, Challenges and Future Perspective for Breeding

“…Moreover, SR development was much slower on highly resistant cultivars establishing direct correlation of rust development with HTAP resistance. Apart from seedling and APR, wheat cultivars were also found to have slow rusting or partial resistance to LR and SR (Line and Chen, 1995;Singh et al, 2005;Figlan et al, 2020). Similar to APR, slow rusting resistance is controlled by multiple genes with small effects that are race non-specific and more durable (Kolmer, 1996).…”

“…Similar to the approach for FHB resistance, a system-based approach understanding the host plant and their obligate parasites can help to develop resilient breeding strategies. Development of transgenic wheat and exploiting HIGS still need to be largely explored (Figlan et al, 2020). Yin et al (2011) summarized the ability of RNAi technology to suppress the expression pattern of SR fungus gene through the use of barley stripe mosaic virus system.…”

“…Further, gene-deployment strategies to gain durable rust resistance require better understanding of potential pathogen variability. The emergence of new rust races can be constantly scouted by using sophisticated surveillance technology called "field pathogenomics" which uses RNAseq or genomic DNA-based approaches to generate high-resolution NGS data for describing pathogen dynamics (Derevnina and Michelmore, 2015;Figlan et al, 2020). These modern tools show considerable promise to provide insights into the biology, population structure, and pathogenesis of wheat SR and could help formulate breeding decisions while deploying rust resistance genes in SRWW cultivars (Hubbard et al, 2015).…”

“…With the recent achievements on whole-genome sequencing (IWGSC, 2014) and the genome annotation (Appels et al, 2018), the future breeding endeavor of SRWW should orient towards the exploration of high-throughput genomic tools such as field pathogenomics, transgenes, gene cloning, genome editing, NGS, and GBS to gain deeper insights into host and underlying pathogen to achieve durable FHB and rust resistance (Bulli et al, 2016;Dinh et al, 2020;Figlan et al, 2020). Above all, a continued collaboration among wheat breeders for sharing and multi-location screening of the promising germplasm against FHB, LR, and SR resistance will be a key to successful resistance breeding in the southeast US.…”

“…Similarly, SR resistance genes that have been cloned include Yr5/YrSP and Yr7 ( Marchal et al, 2018 ), Yr10 ( Liu et al, 2014 ), Yr15 ( Klymiuk et al, 2018 ), Yr18 ( Krattinger et al, 2009 ), Yr36 ( Fu et al, 2009 ), and Yr46 ( Moore et al, 2015 ). Yr10 is considered the first seedling resistance gene cloned while other genes such as Yr18/Lr34/Sr57/Pm38 , and Yr46/Lr67/Sr55/Pm39 possess multi-pathogen (partial) slow rusting APR functionality against the three wheat rusts and powdery mildew ( Spielmeyer et al, 2005 ; Krattinger et al, 2009 ; Moore et al, 2015 ; Klymiuk et al, 2018 ; Figlan et al, 2020 ). Despite the paucity of success in gene cloning, pathways to engineer genes of interest via high throughput modern genome editing technology have already been unlocked ( Figlan et al, 2020 ) tracking success in powdery mildew resistance ( Wang et al, 2014 ).…”