Impact of ploidy and pathogen life cycle on resistance durability

10.1101/2021.05.28.446112 ◽

2021 ◽

Author(s):

Meline Saubin ◽

Stephane De Mita ◽

Xujia Zhu ◽

Bruno Sudret ◽

Fabien HALKETT

Keyword(s):

Life Cycle ◽

Plant Pathogens ◽

Life Cycles ◽

Strong Impact ◽

Pathogen Population ◽

Host Alternation ◽

Resistance Breakdown ◽

Resistance Durability ◽

The Impact ◽

Population Collapses

The breeding of resistant hosts based on the gene-for-gene interaction is crucial to address epidemics of plant pathogens in agroecosystems. Resistant host deployment strategies are developed and studied worldwide to decrease the probability of resistance breakdown and increase the resistance durability in various pathosystems. A major component of deployment host strategies is the proportion of resistant hosts in the landscape. However, the impact of this proportion on resistance durability remains unclear for diploid pathogens with complex life cycles. In this study, we modelled pathogen population dynamics and genetic evolution at the virulence locus to assess the impact of the ploidy (haploid or diploid) and the pathogen's life cycle (with or without host alternation) on resistance durability. Ploidy has a strong impact on evolutionary trajectories, with much greater stochasticity and delayed times of resistance breakdown for diploids. This result emphasizes the importance of genetic drift in this system: as the virulent allele is recessive, positive selection on resistant hosts only applies to homozygous (virulent) individuals, which may lead to population collapses at low frequencies of the virulent allele. We also observed differences in the effect of host deployment depending on the pathogen's life cycle. With host alternation, the probability that the pathogen population collapses strongly increases with the proportion of resistant hosts in the landscape. Therefore, resistance breakdown events occurring at high proportions of resistant hosts frequently amount to evolutionary rescue. Last, life cycles correspond to two selection regimes: without host alternation (soft selection) the resistance breakdown is mainly driven by the migration rate. Conversely, host alternation (hard selection) resembles an all-or-nothing game, with stochastic trajectories caused by the recurrent allele redistributions on the alternate host.

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Ultrastructural analysis of “Sensory” surface nerve endings and “putative” neurotransmitter sites in Schistosoma mansoni Miracidia

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100156791 ◽

1989 ◽

Vol 47 ◽

pp. 962-963

Author(s):

Betty Ruth Jones ◽

Steve Chi-Tang Pan

Keyword(s):

Nervous System ◽

Life Cycle ◽

Schistosoma Mansoni ◽

Snail Host ◽

Complex Life Cycle ◽

Rational Approach ◽

Effective Control ◽

The Social ◽

Social And Economic Development ◽

Basic Biology

INTRODUCTION: Schistosomiasis has been described as “one of the most devastating diseases of mankind, second only to malaria in its deleterious effects on the social and economic development of populations in many warm areas of the world.” The disease is worldwide and is probably spreading faster and becoming more intense than the overall research efforts designed to provide the basis for countering it. Moreover, there are indications that the development of water resources and the demands for increasing cultivation and food in developing countries may prevent adequate control of the disease and thus the number of infections are increasing.Our knowledge of the basic biology of the parasites causing the disease is far from adequate. Such knowledge is essential if we are to develop a rational approach to the effective control of human schistosomiasis. The miracidium is the first infective stage in the complex life cycle of schistosomes. The future of the entire life cycle depends on the capacity and ability of this organism to locate and enter a suitable snail host for further development, Little is known about the nervous system of the miracidium of Schistosoma mansoni and of other trematodes. Studies indicate that miracidia contain a well developed and complex nervous system that may aid the larvae in locating and entering a susceptible snail host (Wilson, 1970; Brooker, 1972; Chernin, 1974; Pan, 1980; Mehlhorn, 1988; and Jones, 1987-1988).

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A freeze-fracture-etched study of the physarum polycephalum plasma membrane during early formation of the macroplasmodial stage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100147570 ◽

1993 ◽

Vol 51 ◽

pp. 346-347

Author(s):

Randolph W. Taylor ◽

Henrie Treadwell

Keyword(s):

Plasma Membrane ◽

Life Cycle ◽

Growth Phase ◽

Filter Paper ◽

Physarum Polycephalum ◽

Freeze Fracture ◽

Petri Dish ◽

Wire Screen ◽

Wide Mouth ◽

Sterile Filter

The plasma membrane of the Slime Mold, Physarum polycephalum, process unique morphological distinctions at different stages of the life cycle. Investigations of the plasma membrane of P. polycephalum, particularly, the arrangements of the intramembranous particles has provided useful information concerning possible changes occurring in higher organisms. In this report Freeze-fracture-etched techniques were used to investigate 3 hours post-fusion of the macroplasmodia stage of the P. polycephalum plasma membrane.Microplasmodia of Physarum polycephalum (M3C), axenically maintained, were collected in mid-expotential growth phase by centrifugation. Aliquots of microplasmodia were spread in 3 cm circles with a wide mouth pipette onto sterile filter paper which was supported on a wire screen contained in a petri dish. The cells were starved for 2 hrs at 24°C. After starvation, the cells were feed semidefined medium supplemented with hemin and incubated at 24°C. Three hours after incubation, samples were collected randomly from the petri plates, placed in plancettes and frozen with a propane-nitrogen jet freezer.

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