Rotating and stacking genes can improve crop resistance durability while potentially selecting highly virulent pathogen strains

Abstract

Rotating crop cultivars with different resistance genes could slow the evolution of virulent strains of fungal pathogens, but could also produce highly virulent pathogen strains. We present a new model that links polycyclic pathogen epidemiology and population genetics in order to predict how different strategies of rotating cultivars with different resistances will affect the evolution of pathogen virulence and the breakdown of crop resistance. We modelled a situation where there were four different resistance genes that can be deployed within each crop cultivar, and four virulence genes that may be present within the pathogen. We simulated four different rotational management strategies: (i) no rotation; (ii) a different gene every year; (iii) a different gene every 5 years; and (iv) a different combination of two stacked genes each year. Results indicate that rotating cultivars can lead to longer periods of disease suppression but also to the selection of highly virulent strains. The efficacy and relative advantage of different resistant cultivar rotation strategies depended on the fitness penalties, initial virulence allele frequencies, and ability of non-virulent pathogen genotypes to grow and reproduce on resistant cultivars. By capturing the essential processes involved, our model provides a useful new tool for investigating the evolutionary dynamics of pathogen virulence and crop resistance breakdown.

Durable resistance or efficient disease control? Adult Plant Resistance (APR) at the heart of the dilemma

“…This is due to the small selection pressure applied to the pathogen population, given that the wt genotype can thrive on cultivars carrying such resistance genes almost as if they were susceptible. This is in accordance with results obtained via different simulation models (Carolan K et al, 2017; Crété R et al, 2020) and confirms one of the mechanisms according to which partially efficient resistance is generally predicted to be more durable than complete resistance (Lecoq H et al, 2004; Stuthman DD et al, 2007; Zhan J et al, 2015). Such phenomena have also been described for pest adaptation to chemicals, where small application doses were shown to slow down the emergence of adapted genotypes (Hobbelen PHF et al, 2014).…”

Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: A compromise between the efficacy and durability of a recently broken‐down resistance gene?

“…Recent landscape‐scale models have investigated the effect of the proportion of fields sown with resistant and susceptible cultivars and their connectivity on the dynamics of resistance breakdown after several generations (e.g., Fabre et al, 2015). In comparisons of different strategies for preventing or delaying the appearance of a “superpathogen", cultivar mixtures appeared to be effective in the long term for pathogens with high mutation rates and high fitness costs (Crété et al, 2020; Rimbaud et al, 2018). Our experimental findings confirm that cultivar mixtures may also be used to extend the lifetime of resistance sources, this time at within‐field scale, through the introduction of heterogeneity.…”

Annual dynamics ofZymoseptoria triticipopulations in wheat cultivar mixtures: a compromise between the efficiency and durability of a recently broken-down resistance gene?

“…Fabre et al ., 2015). In comparisons of different strategies for preventing or delaying the appearance of a ‘superpathogen’, cultivar mixtures appeared to be effective in the long term for pathogens with high mutation rates and high fitness costs (Rimbaud et al ., 2018; Crété et al ., 2020). Our experimental findings confirm that cultivar mixtures may also be used to extend the lifetime of resistance sources, this time at within-field scale, through the introduction of heterogeneity.…”