When does spatial diversification usefully maximise the durability of crop disease resistance?

Abstract

Abstract1 Maximising the durability of crop disease resistance genes in the face of pathogen evolution is a 2 major challenge in modern agricultural epidemiology. Spatial diversification in the deployment of 3 resistance genes, where susceptible and resistant fields are more closely intermixed, is predicted 4 to drive lower epidemic intensities over evolutionary timescales. This is due to an increase in the 5 strength of dilution effects, caused by pathogen inoculum challenging host tissue to which it is not 6 well-specialised. The factors that interact with and determine the magnitude of this spatial effect are 7 not currently well understood however, leading to uncertainty over the pathosystems where such a 8 strategy is most likely to be cost-effective. We model the effect on landscape scale disease dynamics 9 of spatial heterogeneity in the arrangement of fields planted with either susceptible or resistant 10 cultivars, and the way in which this effect depends on the parameters governing the pathosystem 11 of interest. Our multi-season semi-discrete epidemiological model tracks spatial spread of wild-type 12 and resistance breaking pathogen strains, and incorporates a localised reservoir of inoculum, as well 13 as the effects of within and between field transmission. The pathogen dispersal characteristics, 14 any fitness cost(s) of the resistance breaking trait, the efficacy of host resistance, and the length 15 of the timeframe of interest, all influence the strength of the spatial diversification effect. These 16interactions, which are often complex and non-linear in nature, produce substantial variation in the 17 predicted yield gain from the use of a spatial diversification strategy. This in turn allows us to 18 make general predictions of the types of system for which spatial diversification is most likely to be 19 cost-effective, paving the way for potential economic modelling and pathosystem specific evaluation. 20 1 These results highlight the importance of studying the effect of genetics on landscape scale spatial 21 dynamics within host-pathogen disease systems. 22

Combining single-gene-resistant and pyramided cultivars in agricultural landscape compromises the benefits of pyramiding in most, but not all, productions situations

“…Our work goes a step beyond as we considered that adapted pathogen can experience a fitness cost on any host or exclusively for its unnecessary virulence. In previous modeling studies, authors followed either the first (Sapoukhina et al, 2009;Lo Iacono et al, 2012;Nilusmas et al, 2020;Watkinson-Powell et al, 2020;Clin et al, 2021Clin et al, , 2022 or the second approach (Fabre et al, 2009(Fabre et al, , 2015Djidjou-Demasse et al, 2017b;Rimbaud et al, 2018a;Rousseau et al, 2019). Here, for the first time, we compared the two evolutionary scenarios, shading light on the implications of the structure of the host-pathogen interaction matrix on the performance of simple vs. hybrid resistant deployment strategies.…”

“…According to Leonard (1977), this fitness cost, could be counterbalanced by the advantage a of an adapted pathogen on hosts with corresponding gene of resistance (Table 1). It follows that the adapted pathogen may 1) experience the same fitness cost on any host it can infect, with θ > 0 and a = 0 (Sapoukhina et al, 2009;Lo Iacono et al, 2012;Nilusmas et al, 2020;Watkinson-Powell et al, 2020;Clin et al, 2021Clin et al, , 2022; 2) experience a fitness cost only for its unnecessary virulence, with θ = a > 0 (Fabre et al, 2009(Fabre et al, , 2015Djidjou-Demasse et al, 2017b;Rimbaud et al, 2018a;Rousseau et al, 2019); 3) not experiencing a fitness cost on any host, with θ = 0 and a = 0 (Van Den Bosch and Gilligan, 2003;Ohtsuki and Sasaki, 2006;Lo Iacono et al, 2013;Wingen et al, 2013;Pacilly et al, 2018Pacilly et al, , 2019. For the SP, the fitness costs are multiplicative on every host.…”

Prospects for Durable Resistance Against an Old Soybean Enemy: A Four-Decade Journey from Rpp1 (Resistance to Phakopsora pachyrhizi) to Rpp7

“…Once an SBR resistant cultivar/line is developed through either conventional, gene editing or transgenic approaches, the deployment of such cultivars (each cultivar having different genetic make-up as well as containing individual or a set of different resistance genes) or multi-lines (several lines having the same genetic make-up except bearing different resistance genes) at individual farm or regional level could be a cornerstone of disease resistance durability [111,129,130].…”

Taking Advantage of Pathogen Diversity and Immune Priming to Minimize Disease Prevalence in Host Mixtures: A Model

“…Under these conditions, pathogen populations often evolve and break down resistance genes after a few years, while a breeding program may require a least a decade (Brown, 2015;Zhan et al, 2015). More lasting control methods will require managing genetic resistances in time (Bargués-Ribera and Gokhale, 2020;Nilusmas et al, 2020), and/or in space (Fabre et al, 2012(Fabre et al, , 2015Djidjou-Demasse et al, 2017;Papaïx et al, 2018;Rimbaud et al, 2018b,a;Rousseau et al, 2019;Watkinson-Powell et al, 2019;Burdon et al, 2020).…”