Pyramiding for Resistance Durability: Theory and Practice

Abstract

Durable disease resistance is a key component of global food security, and combining resistance genes into "pyramids" is an important way to increase durability of resistance. The mechanisms by which pyramids impart durability are not well known. The traditional view of resistance pyramids considers the use of major resistance gene (R-gene) combinations deployed against pathogens that are primarily asexual. Interestingly, published examples of the successful use of pyramids in the traditional sense are rare. In contrast, most published descriptions of durable pyramids in practice are for cereal rusts, and tend to indicate an association between durability and cultivars combining major R-genes with incompletely expressed, adult plant resistance genes. Pyramids have been investigated experimentally for a diversity of pathogens, and many reduce disease levels below that of the single best gene. Resistance gene combinations have been identified through phenotypic reactions, molecular markers, and challenge against effector genes. As resistance genes do not express equally in all genetic backgrounds, however, a combination of genetic information and phenotypic analyses provide the ideal scenario for testing of putative pyramids. Not all resistance genes contribute equally to pyramids, and approaches have been suggested to identify the best genes and combinations of genes for inclusion. Combining multiple resistance genes into a single plant genotype quickly is a challenge that is being addressed through alternative breeding approaches, as well as through genomics tools such as resistance gene cassettes and gene editing. Experimental and modeling tests of pyramid durability are in their infancy, but have promise to help direct future studies of pyramids. Several areas for further work on resistance gene pyramids are suggested.

Genetic Engineering for Disease Resistance in Plants: Recent Progress and Future Perspectives

“…Thus, disease resistance conferred by a single R gene often lacks durability in the field because pathogens can evolve to evade recognition by mutating the corresponding avr gene. For improved durability and to broaden the resistance spectrum, multiple R genes are often introduced simultaneously, which is commonly known as stacking (Li et al, 2001;Fuchs, 2017;Mundt, 2018). Resistance conferred by stacked R genes is predicted to be long lasting, as the evolution of a pathogen strain that could overcome resistance conferred by multiple R genes…”

Assessing the Individual and Combined Effects of QTL for Adult Plant Stripe Rust Resistance Derived from Cappelle-Desprez

“…The continuous process of identifying and introgressing multiple sources of resistance with complementary and/or additive effects into wheat cultivars is paramount for the attainment of durability. Mundt [9] mentioned that durability might be linked to gene pyramids involving APR. Although combinations of minor, slow rusting APR genes have enabled cultivars to remain resistant for many years, even when commercialized over large areas [7,10], race specificity for some wheat stripe rust APR genes has been reported [11].…”

Dynamics of Race Structures of the Rice Blast Pathogen Population in Heilongjiang Province, China From 2006 Through 2015

“…The three major resistance genes (Pia, Pii, and Pik) carried by the japonica subset of the CDCs might serve as a core of resistance in cultivars grown in HLJ over the whole period, because the four dominant races detected in 2006 to 2015 were responsible for reactions on the japonica subset carrying the three genes (Table 5). It would also be worthwhile to more thoroughly investigate the core of resistance within a given region and incorporate promising resistance genes into future cultivars to ensure a sustainable level of control over the disease (Dorrance et al 2016;Liang et al 2016;Lin et al 2007;Mundt 2018).…”