Résumé
Understanding the mode of temporal maintenance of plant pathogens is an
important domain of microbial ecology research. Due to the inconspicuous
nature of microbes, their temporal maintenance cannot be studied directly
through tracking individuals and their progeny. Here, we suggest a series
of population genetic analyses on molecular marker variation in
temporally-spaced samples to infer about the relative contribution of
sexual reproduction, off-season survival and migration in the temporal
maintenance of pathogen populations. We used the proposed approach to
investigate the temporal maintenance of wheat yellow rust pathogen,
Puccinia striiformis f.sp. tritici (PST), in the Himalayan region of
Pakistan. Multilocus microsatellite genotyping of PST isolates revealed
high genotypic diversity and recombinant population structure across all
locations, confirming the existence of sexual reproduction in this region.
The genotypes were assigned to four genetic groups, revealing a clear
differentiation between zones with and without Berberis spp., the
alternate host of PST, with an additional subdivision within the Berberis
zone. The lack of any differentiation between samples across two sampling
years, and the very few re-sampling of multilocus genotypes over-years at
a given location was consistent with limited over-year clonal survival,
and a limited genetic drift. The off-season over-summering population in
the Berberis zone, likely to be maintained locally, served as a source of
migrants contributing to the temporal maintenance in the non-Berberis
zone. Our study hence demonstrated the contribution of both sexual
recombination and off-season over-summering survival to the temporal
maintenance of the pathogen. These new insights into the population
biology of PST highlight the general usefulness of the analytical approach
proposed.