ARS | Publication request: SENSITIVITY OF ASCOCHYTA RABIEI BASELINE ISOLATES TO AZOXYSTROBIN, PYRACLOSTROBIN, AND BOSCALID

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2006
Publication Date: N/A

Interpretive Summary: Ascochyta rabiei is a fungus causing Ascochyta blight of chickpea (Cicer arietinum). There is concern that the fungus may be evolving resistance to certain fungicides. Isolates of the fungus that were present prior to the introduction of these fungicides are present in culture collections. These older isolates have been tested for resistance / susceptibility to the fungicides in order to establish baseline data. This baseline data can be used in comparison with the analogous resistance / susceptibility of contemporary isolates.

Technical Abstract: Ascochyta blight (causal agent, Ascochyta rabiei) is the most serious disease of chickpea (Cicer arietinum) in the United States. In North Dakota, application of fungicides is the primary method of Ascochyta blight management. Isolates of A. rabiei were tested to determine baseline sensitivities to two quinone outside inhibiting (QoI) fungicides, azoxystrobin and pyraclostrobin, and one carboximide fungicide, boscalid. Fifty-one isolates collected prior to the 1998 release of azoxystrobin in the United States were tested in an in vitro assay comparing spore germination on potato dextrose agar amended with 0, 0.001, 0.01, 0.1, 1, and 10 ug/ml of technical formulation of each fungicide. The effective fungicide dose that inhibited spore germination by 50% (ED50) was determined for each isolate-fungicide combination. ED50 values of azoxystrobin and pyraclostrobin ranged from 0.018 to 0.034 ug/ml and from 0.0012 to 0.0033 ug/ml with mean values of 0.027 and 0.0023 ug/ml, respectively. ED50 values of boscalid ranged from 0.02 to 0.32 ug/ml with a mean of 0.17 ug/ml.