The full life cycle of Leptosphaeria maculans completed on inoculated oilseed rape incubated under controlled conditions
2018
Bousset-Vaslin, Lydia | Ermel, Magali | Lebreton, Lionel
Because epidemics of successive cropping seasons are not independent, epidemiological studies need to encompass the processes occurring during the transmission of epidemics from one season to the next. With Leptosphaeria maculans, infected stubble allows carry-over of the fungus. Generation experiments using recurrent selection on field plots are a useful means of comparing the effects of selection pressures. However, the full life cycle of the fungus, from plant infection to the next generation of ascospores, has not yet been achieved under controlled conditions. Studies were undertaken to achieve an experimental set-up with sexual reproduction under controlled conditions. Cankered oilseed rape stems were produced under controlled conditions, after inoculation with a mixture of 12 isolates across both mating types. Stems were cut longitudinally and attached to styropore plates. Stem halves were incubated outside or in climate chambers regularly soaked in tap water to ensure maturation. Incubation was stopped when mature pseudothecia were observed. In all three independent experiments, more stem halves had pseudothecia when incubated under controlled conditions (30-100%) than incubated outside (0-80%). To the authors' knowledge, this is the first study achieving the full life cycle of the fungus under controlled conditions, from infection of the plant to mature pseudothecia. This opens up the prospect of running experiments year-round to better understand inoculum production, to compare fungal fitness, or to run generation experiments with exotic pathogen populations.
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