Gs. Karaoglanidis et al., Fitness of Cercospora beticola field isolates resistant and sensitive to demethylation inhibitor fungicides, EUR J PL P, 107(3), 2001, pp. 337-347
Isolates of Cercospora beticola resistant to fungicides that inhibit sterol
demethylation (DMIs) were collected from sugar beet fields in Northern Gre
ece. Fitness of these isolates was compared to that of DMI-sensitive isolat
es. The parameters measured were competitive ability both under growth cham
ber and field conditions, mycelial growth, spore germination, germ tube len
gth, incubation period, virulence and spore production. The competitive abi
lity under growth chamber conditions was measured for 4 pairs of one resist
ant and one sensitive isolate. Results showed that after 4 disease cycles,
in 2 out of 4 pairs tested, the resistant isolates competed well with the s
ensitive isolates, but in the remaining two pairs the frequency of the resi
stant isolate decreased significantly. The competition experiment in the fi
eld was carried out by inoculating field plots with a conidial suspension c
onsisting of a spore mixture from all the resistant and all the sensitive i
solates used in this study. Results showed that at the end of the growing p
eriod the frequency of the resistant isolates had slightly decreased (P < 0
.05). The measurements of fitness components of individual isolates showed
that the resistant isolates had significantly lower (P < 0.05) virulence an
d spore production than the sensitive isolates, while no significant differ
ences (P > 0.05) to the remaining 4 fitness components, were detected. With
correlation analysis it was determined whether there is a relationship bet
ween values of each fitness component and the level of sensitivity to flutr
iafol of individual isolates. The correlation coefficients for virulence (r
= 0.45) and spore production (r = 0.41) were significantly different from
0 (P < 0.05), indicating that resistance to DMIs affected, to some degree,
the fitness of the resistant isolates.