Host Diversification May Split Epidemic Spread into Two Successive Fronts Advancing at Different Speeds

Abstract

Host diversification methods such as within-field mixtures (or field mosaics, depending on the spatial scale considered) are promising methods for agroecological plant disease control. We explore disease spread in host mixtures (or field mosaics) composed of two host genotypes (susceptible and resistant). The pathogen population is composed of two genotypes (wild-type and resistance-breaking). We show that for intermediate fractions of resistant hosts, the spatial spread of the disease may be split into two successive fronts. The first front is led by the wild-type pathogen and the disease spreads faster, but at a lower prevalence, than in a resistant pure stand (or landscape). The second front is led by the resistance-breaking type, which spreads slower than in a pure resistant stand (or landscape). The wild-type and the resistancebreaking genotype coexist behind the invasion fronts, resulting in the same prevalence as in a resistant pure stand. This study shows that host diversification methods may have a twofold effect on pathogen spread compared to a resistant pure stand (or landscape): on one hand they accelerate disease spread, and on the other hand they slow down the spread of the resistancebreaking genotype. This work contributes to a better understanding of the

The proportion of resistant hosts in mixtures should be biased towards the resistance with the lowest breaking cost

“…Monovirulent pathogens therefore have a net transmission rate (1 − c i ) β , i = 1, 2. The idea of a cost as a counterpart of the ability of breaking a resistance gene originated as a theoretical hypothesis to explain the often-observed persistence of virulence polymorphism in pathogen populations, both in agricultural and in wild ecosystems [ 5 , 13 , 25 – 31 ]. Such a cost has been demonstrated and measured in a number of parasites, including bacteria [ 32 , 33 ], fungi [ 34 – 40 ], viruses [ 41 – 46 ], nematodes [ 47 ] and oomycetes [ 48 ].…”

Evolution and spread of multiadapted pathogens in a spatially heterogeneous environment

“…Many different situations could generate this type of spatial heterogeneity. For instance, in agriculture, the use of different resistant varieties in crops could be a way to manipulate the spatial distribution of host resistance to a specific pathogen Clin et al, (2022) ; Gilligan, (2008) ; Hamelin et al, (2022) ; Mikaberidze et al, (2015) ; Mundt, (2002) . In animal species, the use of different vaccines at different locations could also generate a spatial mosaic of immunity McLeod et al, (2021) .…”

Tolerant crops increase growers’ yields but promote selfishness: how the epidemiology of disease resistant and tolerant varieties affect grower behaviour

“…Epidemiological models have long been used to identify strategies that optimise the deployment of resistant crop (reviewed in Rimbaud et al (2021)),Very often the focus is pathogen evolutionary dynamics and the breakdown of resistance traits (van den Bosch & Gilligan (2003), Fabre et al (2012), Watkinson-Powell et al (2020), Rimbaud et al (2018)). This builds on a long history of models aiming to explain gene-for-gene polymorphisms in host and pathogen populations, stretching back to theoretical work which is now nearly fifty years old (Leonard (1977)) although is still of current interest (Tellier & Brown (2007), Clin et al (n.d.), Hamelin et al (2022)). However, no studies have compared the epidemiological consequences of using tolerant versus resistant crop at the population scale, despite tolerant and resistant crop having significantly distinct effects on other growers.…”