2 research outputs found
Occurrence, Distribution and Polymerase Chain Reaction-Based detection of resistance to Sterol Demethylation Inhibitor Fungicides in populations of Blumeriella jaapii in Michigan.
The intensive use of site-specific fungicides in agricultural production
provides a potent selective mechanism for increasing the frequency of
fungicide-resistant isolates in pathogen populations. Practical resistance
occurs when the frequency and levels of resistance are great enough to
limit the effectiveness of disease control in the field. Cherry leaf spot
(CLS), caused by the fungus Blumeriella jaapii, is a major disease of
cherry trees in the Great Lakes region. The site-specific sterol demethylation
inhibitor fungicides (DMIs) have been used extensively in the region.
In 2002, CLS control failed in a Michigan orchard that had used the DMI
fenbuconazole exclusively for 8 years. That control failure and our observations
from around the state suggested that practical resistance had developed
in B. jaapii. Field trial data covering 1989 to 2005 for the DMIs
fenbuconazole and tebuconazole supported observations of reduced efficacy
of DMIs for controlling CLS. To verify the occurrence of fungicideresistant
B. jaapii, monoconidial isolates were collected in two surveys
and tested using a fungicide-amended medium. In one survey, 137
isolates from sites with different DMI histories (no known history, mixed
or alternated with other fungicides, and exclusive use) were tested against
12 concentrations of fenbuconazole, tebuconazole, myclobutanil, and
fenarimol. Isolates from sites with no prior DMI use were DMI sensitive
(DMIS = no colony growth at 0.2 \u3bcg/ml a.i.) whereas the isolates from the
site with prior exclusive use showed growth at DMI concentrations 3 to
>100 times higher, and were rated as DMI resistant (DMIR). A second
survey examined 1,530 monoconidial isolates, including 1,143 from 62
orchard sites in Michigan, where DMIs had been used to control CLS.
Resistance to fenbuconazole was detected in 99.7% of the orchard isolates.
All isolates from wild cherry trees were sensitive and isolates from
feral and dooryard trees showed a range of sensitivities. A polymerase
chain reaction (PCR)-based detection method for identifying B. jaapii
and DMIR was developed and tested. The species-specific primer pair (Bj-
F and Bj-R) based on introns in the CYP51 gene of B. jaapii, and the
DMIR-specific primer pair (DMI-R-Bj-F and DMI-R-Bj-R) based on an
insert found upstream of CYP51 in all DMIR isolates, provided an accurate
and rapid method for detecting DMIR B. jaapii. The PCR-based identification
method will facilitate timely decision making and continued
monitoring of DMIR subpopulations in response to management programs
Integration of Copper based and Reduced-Risk Fungicides for Control of Blumeriella jaapii on Sour Cherry
Practical resistance to sterol demethylation inhibitor (DMI) fungicides among populations of
Blumeriella jaapii, the cherry leaf spot (CLS) pathogen, was documented in 2005. In the present
study, strategies to reduce selection for DMI-resistant strains of B. jaapii and adapt to possible
restrictions on the use of chlorothalonil are described. Ten field trials were conducted on the sour
cherry cultivars Balaton and Montmorency to test the efficacy of integrating respiration-inhibitor
and copper-based fungicides into spray programs. Programs that included up to three sprays of
copper-based fungicides were among the most effective for controlling CLS, although leaf phytotoxicity
was sometimes observed. Under high disease pressure, eliminating chlorothalonil
compromised CLS control. \u2018Balaton\u2019 and \u2018Montmorency\u2019 did not differ in the percentage of
leaves with CLS or defoliation resulting from CLS. The physical modes of action of representative
DMI, QoI, and copper-based fungicides were evaluated in a leaf disk assay. Trifloxystrobin,
a QoI fungicide, provided the best protection against infection by B. jaapii. All fungicides were
more effective than water when applied 46 h postinfection, although differences were not statistically
significant in one of two trials. Tebuconazole, a DMI, was the only fungicide that was
more effective than water in preventing resporulation from existing lesions in both trials. Isolates
of B. jaapii, which varied in DMI-sensitivity, all were sensitive to copper in vitro