Abstract:
Fusarium circinatum and Fusarium subglutinans are two distinct species in the Gibberella
fujikuroi species complex. A genetic linkage map produced from an interspecific cross between
these species was used to identify quantitative trait loci (QTLs) associated with variation in
mycelial growth and morphology of colony margins (CM) in the 94 F1 progeny. Mycelial
growth was assessed by measuring culture size at 25˚C and 30˚C, while CM morphology was
characterized in the parents and assessed in their F1 progeny. In order to test the pathogenicity of
the progeny, Pinus patula seedlings were inoculated and lesion lengths were measured after three
weeks. Seven putative QTLs were associated with mycelial growth, three for growth at 25˚C
and four at 30˚C. One highly significant QTL (P < 0.001) was present at both growth
temperatures. For CM morphology, a QTL was identified at the same position (P < 0.001) as the
QTL responsible for growth at the two temperatures. The putative QTLs accounted for 45 and
41% of the total mycelial growth variation at 25˚C and 30˚C, respectively, and for 21% of the
variation in CM morphology. Only one of the 94 F1 progeny was pathogenic on P. patula
seedlings. This observation could be explained by the genetic constitution of this F1 isolate,
namely that ~96% of its genome originated from the F. circinatum parent. This F1 individual also grew significantly faster at 25˚C than the F. circinatum parent (P < 0.05), as well as more
rapidly than the average growth for the remaining 93 F1 progeny (P < 0.05). However, no
association was found between mycelial growth and pathogenicity at 25˚C. The highly
significant QTL associated with growth at two temperatures, suggests that this is a principal
genomic region involved in mycelial growth at both temperatures, and that the same region is
also responsible for CM morphology.
