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SESSION 3: PATHOGENESIS – EPIDEMIOLOGY AND POPULATION
GENETICS
Fusarium graminearum: Species or Clade?
J. F. Leslie¹, R. L. Bowden²
¹Department of Plant Pathology, Throckmorton Plant Sciences Center, Kansas State University,
Manhattan, Kansas 66506, USA; ²Plant Science and Entomology Research Unit, USDA-ARS,
Throckmorton Plant Sciences Center, Kansas State University, Manhattan, Kansas 66506, USA.
E-mail: jfl@ksu.edu
Fusarium graminearum is a common cause of disease and mycotoxin
contamination of grains such as maize, wheat, barley and rice. Within F.
graminearum there are a number of phylogenetic lineages that some researchers
recognize as distinct phylogenetic species. This hypothesis brings with it the
expectation of other significant differences between the lineages. Yet, there is no
significant difference in the quantitative ability of the strains from any of the tested
lineages to form perithecia or ascospores when crossed with female-fertile tester
strains that were designed for making controlled crosses. Physical and
recombinational maps of F. graminearum are co-linear and similar for members of
at least the tested phylogenetic lineages, and there is no evidence for large
numbers of chromosomal rearrangements segregating in field populations. In
general, biological and phylogenetic species concepts group strains similarly and
into a larger number of groups than those identified on the basis of morphology
alone. In F. graminearum, however, the number of morphological and biological
species is the same, i.e., one. These results could be explained in at least two
ways. The explanation voiced the loudest is that the lineages are incipient species
and that the phylogenetic analysis has caught this group in the act of evolving
from a single species into many. Alternatively, the phylogenetic lineages may be
separate populations that have evolved independently for some time but are still a
part of a single common species, much as Eskimos and Australian aborigines are
in humans. Identifying natural populations where “hybrids” between lineages may
occur under field conditions remains a key to the competitive evaluation of these
hypotheses, with populations of F. graminearum in South America and South
Korea offering, perhaps, the best opportunities to do so.
Keywords: biological species, sexual fertility
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