Baseline Sensitivity and Resistance-Risk Assessment of Phytophthora capsici to Iprovalicarb

Abstract

Iprovalicarb has been used to control Phytophthora capsici, a devastating pathogen of many economically important crops. To evaluate the risk of fungicide resistance, 158 isolates of P. capsici were examined for sensitivity to iprovalicarb by measuring mycelial growth. Values of effective concentrations for 50% mycelial growth inhibition varied from 0.2042 to 0.5540 μg/ml and averaged 0.3923 (±0.0552) μg/ml, with a unimodal distribution. This is the first report of P. capsici isolates highly resistant to iprovalicarb (resistance factor >100). Resistance of the isolates was stable through 10 transfers on iprovalicarb-free medium, and most resistant isolates had the same level of fitness (mycelial growth, zoospore production, and virulence) as their corresponding parents, indicating that iprovalicarb resistance was independent from other general growth characters. There was cross-resistance among all tested carboxylic acid amide (CAA) fungicides, including iprovalicarb, flumorph, dimethomorph, and mandipropamid, but not with non-CAA fungicides, including azoxystrobin, chlorothalonil, cymoxanil, etridiazole, metalaxyl, and zoxamide. Based on the present results, resistance risk of P. capsici to CAAs could be moderate and resistance management should be considered.

Using Soil-Applied Fungicides to Manage Phytophthora Crown and Root Rot on Summer Squash

“…To delay the development of resistance, fluopicolide should be used in rotation with fungicides with different modes of action such as mandipropamid or dimethomorph. Cross-resistance to multiple carboxylic acid amide (CAA) fungicides, including dimethomorph and mandipropamid, has been reported in some P. capsici populations (17,25). Therefore, these fungicides should not be used exclusively or in tank mixtures.…”

The cellulose synthase 3 (CesA3) gene of oomycetes: structure, phylogeny and influence on sensitivity to carboxylic acid amide (CAA) fungicides

“…As a consequence the CesA3 enzyme should generally be a suitable target for CAA fungicides in all oomycetes. Several studies reported the high activity of CAAs against Peronosporales (Cohen & Gisi, 2007;Gisi et al 2007;Cohen et al 2008;Zhu et al 2008;Kim et al 2009;Lu et al 2010) but only few studies addressed the insensitivity of the Pythiales against this fungicide class (Albert et al 1988;Stenzel et al 1998;. It is surprising that the CAAs were never tested against representatives of the animal parasitic order Saprolegniales, members of which can cause enormous losses in aquaculture (van West 2006;Phillips et al 2008), or against plant parasitic Albuginales causing white blister rust.…”

“…P. infestans, P. capsici, Bremia lactucae, P. cubensis, P. viticola (Cohen & Gisi 2007;Gisi et al 2007;Cohen et al 2008;Zhu et al 2008;Kim et al 2009;Lu et al 2010) and to some extent in Pythiales (Albert et al 1988;Stenzel et al 1998;. However, comprehensive data about CAA sensitivity of oomycete species outside Peronosporales or Pythiales is lacking.…”

Proteomic analysis on zoxamide-induced sensitivity changes in Phytophthora cactorum

“…Mycelial growth inhibition was used to determine the sensitivity of P. cactorum to zoxamide according to Lu et al's method [22]. For each of the 73 isolates of P. cactorum, a fresh plug (5 mm in diameter) was taken from the growing edge of a CA culture and transferred onto CA amended with zoxamide at 0, 0.02, 0.05, 0.1, 0.15, 0.2, 0.5 and 1.0 mg/L.…”

“…A regression equation was derived by correlating the log of the zoxamide concentration and the probit of the percent inhibition of the average radial mycelial growth of P. cactorum. The effective concentration for 50% inhibition (EC50) of radial mycelia growth of P. cactorum was calculated from this regression equation [22]. A histogram of the EC50 for all isolates was plotted, and the shape of the frequency distribution was analyzed by examining the curve shape, range and mean values of the EC50, as well as the ratio of the highest and lowest EC50 values.…”