Reduced Sensitivity in Monilinia fructicola to Propiconazole in Georgia and Implications for Disease Management

Abstract

Single-spore isolates of Monilinia fructicola were collected from commercial orchards in South Carolina and Georgia with prolonged past exposure to demethylation inhibitor (DMI) fungicides and from an orchard with no DMI history (baseline population). Sensitivity to propiconazole was determined using the concentration in agar media required to suppress radial growth of mycelium by 50% (EC50. Mean EC50 values from six South Carolina populations were not different from the baseline population (P < 0.05). Two of five populations from Georgia revealed (significantly higher mean EC50 values compared with the baseline population (P < 0.05). Isolates with high (AP5 and AP6) and low (DL71 and DL72) EC50 values were selected to determine disease incidence on peach fruit after protective or curative applications of propiconazole at 0.15 or 0.3 liter/ha (half and full label rate, respectively). Disease incidence was significantly greater on peaches inoculated with AP5 and AP6 after curative treatment with propiconazole at 0.15 liter/ha (P < 0.05). Following protective or curative treatments at 0.3 liter/ha, disease incidence was significantly greater for AP6 but not for AP5. These results suggest that a shift toward reduced sensitivity has developed in some M. fructicola populations from Georgia, and that isolates with reduced sensitivity to propiconazole are more difficult to control in the field. Field testing of DMI fungicides, captan, QoI fungicides, and fenhexamid in experimental orchards) indicated that the DMI fungicides are still among the most efficacious products for brown rot (control, and that new products containing QoI fungicides may be viable disease control alternatives or rotation partners.

Genus Monilinia on pome and stone fruit species

“…to benzimidazoles was first detected, ergosterol inhibitors (DMI fungicides) have become the most efficient and most widely used fungicides against species of this genus (Zehr et al, 1999;Schnabel et al, 2004). They are very efficient in prevention of blossom blight and fruit rot on stone fruit species (Schnabel et al, 2004). Propiconazole, tebuconazole and fenbuconazole have become a standard for chemical control of these species in peach plantations in southeastern parts of the USA.…”

“…Propiconazole, tebuconazole and fenbuconazole have become a standard for chemical control of these species in peach plantations in southeastern parts of the USA. Despite successful use of these fungicides for over 15 years, reduced sensitivity of isolates has been recently detected in several regions in Eastern USA (Zehr et al, 1999;Schnabel et al, 2004).…”

The Cytochrome P450 Lanosterol 14α-Demethylase Gene Is a Demethylation Inhibitor Fungicide Resistance Determinant in Monilinia fructicola Field Isolates from Georgia

“…The first evidence that M. fructicola was able to develop resistance to DMI fungicides was found in laboratory studies (19). However, it took more than two decades after the introduction of DMI fungicides to detect DMI resistance in M. fructicola field populations, and thus far such populations have only been reported in Georgia and New York (21,27). Isolates with documented in vitro resistance from Georgia were harder to control in detached fruit assays (27) compared to sensitive isolates, and follow-up studies showed that label rates of propiconazole cannot control such isolates in the field (2).…”

“…However, it took more than two decades after the introduction of DMI fungicides to detect DMI resistance in M. fructicola field populations, and thus far such populations have only been reported in Georgia and New York (21,27). Isolates with documented in vitro resistance from Georgia were harder to control in detached fruit assays (27) compared to sensitive isolates, and follow-up studies showed that label rates of propiconazole cannot control such isolates in the field (2). Knowledge of the mechanism of DMI resistance in M. fructicola may help in designing antiresistance strategies and may be useful for identifying molecular markers for DMI fungicide resistance.…”

Pest risk assessment ofMonilinia fructicolafor the EU territory and identification and evaluation of risk management options

“…According to Holb and Schnabel (2007), the addition of elemental sulphur to a DMI fungicide is likely to be a relatively inexpensive means to improve brown rot control in peach production areas where reduced sensitivity to DMI fungicides is suspected. According to field testing of DMI fungicides, captan, QoI fungicides, and fenhexamid in experimental orchards in Georgia (Schnabel et al, 2004) indicated that the DMI fungicides were still among the most efficacious products for brown rot control, and that new products containing quinone outside inhibitor (QoI) fungicides may be viable disease control alternatives.…”