Genetic diversity and structure of Bipolaris oryzae and Exserohilum rostratum populations causing brown spot of rice in Burkina Faso based on genotyping-by-sequencing

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Résumé

In recent years, Brown spot disease of rice (BSR) has been observed on leaves and
seeds of rice in all rice-growing areas of Burkina Faso. Bipolaris oryzae and
Exserohilum rostratum are the main fungal species isolated from BSR infected
tissues and they are frequently observed in the same field. However, we are lacking
information on the genetic diversity and population structure of these fungi in
Burkina Faso. The mode of reproduction is also unknown. The genetic diversity of
isolates of B. oryzae (n=61) and E. rostratum (n=151), collected from major ricegrowing
areas of Burkina Faso, was estimated using genotyping-by-sequencing
(GBS). The mean values for nucleotide diversity (p) were 1.9 x10-4 for B. oryzae and
4.8 x10-4 for E. rostratum. There is no genetic differentiation between the
geographical populations of each species. The analysis of molecular variance
revealed that 89% and 94% of the genetic variances were within the populations
of B. oryzae and E. rostratum, respectively. For each species, four genetic clusters
were identified by two clustering methods (DAPC and sNMF). The distribution of
these genetic groups was independent of the geographical origin of the isolates.
Evidence of recombination was detected in the populations of B. oryzae and E.
rostratum. For B. oryzae balanced mating type ratios were supporting sexual
reproduction. For E. rostratum overrepresentation of MAT1-2 isolates (79%)
suggested a predominant asexual reproduction. This study provides important
information on the biology and genetics of the two major fungi causing brown
spot disease of rice in Burkina Faso.

Mots-clés

linkage disequilibrium, mating type, recombination, reproduction, rice disease, fungal pathogen