Effectiveness of isofetamid, a new succinate dehydrogenase inhibitor fungicide, in the control of grapevine gray mold

Cien. Inv. Agr. 41(3):365-374. 2014 www.rcia.uc.cl crop protection DOI: 10.4067/S0718-16202014000300009 research paper Effectiveness of isofetamid, a new succinate dehydrogenase inhibitor fungicide, in the control of grapevine gray mold Carlos M. Piqueras, Bernardo A. Latorre, and René Torres Facultad de Agronomía e Ingeniería Forestal and Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile. Casilla 306-22, Santiago, Chile. Abstract C.M. Piqueras, B.A. Latorre, and R. Torres. 2014. Effectiveness of isofetamid, a new succinate dehydrogenase inhibitor fungicide, in the control of grapevine gray mold. Cien. Inv. Agr. 41(3):365-374. Gray mold is an important disease in grapevines in Chile, and its control depends primarily on the use of fungicides with a single-site mode of action. Botrytis cinerea has a high risk of developing resistance against such fungicides. Therefore, novel chemical options are needed to achieve satisfactory control of gray mold. Isofetamid is a new succinate dehydrogenase inhibitor (SDHI) fungicide with a single-site of action that inhibits cellular respiration and appears to be a new option in the chemical treatment against gray mold. The aim of this study was to determine the effectiveness of isofetamid in controlling grapevine gray mold in Chile. Field trials undertaken in three different commercial vineyards showed that isofetamid controls gray mold to a similar extent as fenhexamid. During 2012 and 2013, 10 B. cinerea isolates were obtained from commercial vineyards in central Chile to determine their sensitivity to isofetamid. The median inhibitory concentration of isofetamid varied between 0.3-10.0 µg mL-1 and 0.6 to >10 µg mL-1 for mycelium and conidia, respectively. The efficacy of isofetamid against B. cinerea in apple bioassays varied between 61-100% and 37.5-100% for mycelium and conidia, respectively. The results of this study demonstrate that isofetamid is a highly effective fungicide against B. cinerea. Key words: chemical control, fenhexamid, fungicides, isofetamid, SDHI, Vitis vinifera. Introduction Gray mold, caused by Botrytis cinerea, is the most important disease in table grapes (Vitis vinifera) in Chile and other countries (Bulit and Dubos, 1988; Latorre, 1986). It is a polycyclic disease with abundant inoculum production during spring, summer, and autumn, leading to difficult control. The use of fungicides with a single-site mode of action favors the developReceived May 22, 2014. Accepted October 26, 2014. Corresponding author: 11444 - 9 Piqueras.indd 365 ment of resistant strains of B. cinerea (Leroux et al., 2007). Integrated control strategies are suggested for gray mold, and crop cultural practices (e.g., leaf removal, cluster thinning, and vigor management) and chemical control are the most frequent sustainable plant control strategies used by farmers (Broome et al., 1995; Molitor et al., 2011). Chemical control strategies are primarily applied at flowering, beginning of berry touch (prebunch closure) and between veraison and harvest, which are critical grapevine growth periods of gray 12-12-14 15:04 366 ciencia e investigación agraria mold infection (Latorre et al., 2001). Several fungicides with different sites of action have been introduced with the aim of controlling gray mold. Some of these fungicides have multiple sites of action (e.g., captan, chlorothalonil), while others have a single-site of action (e.g., boscalid, cyprodinil, fludioxonil, fenhexamid, fluazinam, pyraclostrobin, pyrimethanil) (Chatzidimopoulos et al., 2013; FRAC, 2013). Currently, chemical control in Chile relies mainly on fungicides with a single-site mode of action (Latorre and Torres, 2012). Consequently, the risk of resistance development is medium to high (FRAC, 2013; Kim et al., 2012), and antiresistance strategies are needed to prevent the rapid appearance of resistant B. cinerea strains. These resistance management strategies include limiting the number of applications per growing season, rotation of fungicides with different modes of action, and the use of pre-packed mixtures or tank mixing of fungicides with different modes of action (Forster and Staub, 1996). Isofetamid is a new fungicide currently under worldwide development and is manufactured by Sumitomo (Japan). It belongs to the phenyl-oxoethyl thiophene amide chemical group (FRAC, 2013) and has a single-site mode of action that inhibits fungal respiration by blocking electron transport, which is achieved by reducing the activity of the succinate dehydrogenase at complex II in the electron chain in the inner mitochondria membrane (FRAC, 2013). This new fungicide and the more commonly known fungicide boscalid are succinate dehydrogenase inhibitors (SDHIs) (Avenot and Michailides, 2010; FRAC, 2013). The objectives of this study were i. to determine baseline sensitivity of B. cinerea to isofetamid and ii. to determine the effectiveness of isofetamid against grapevine gray mold under field conditions. Material and methods Isolates Isolates of B. cinerea were collected from V. vinifera vineyards located between the Aconcagua valley and Los Angeles (Table 1). Pure isolates were cultured in potato dextrose Table 1. Effectiveness of isofetamid against gray mold in apples and baseline sensitivity of Botrytis cinerea to isofetamid. Isolates Origin Median effective concentration, EC501 µg mL-1 Gray mold control2 % Mycelium Conidia Mycelium Conidia bc1 Santiago 5.3 0.6 100.0 100.0 bc4 Los Andes nd 5.2 96.0 48.0 bc5 Viluco 10.0 5.3 76.0 94.6 bc6 Nancagua 2.5 4.5 65.5 nd bc7 Nancagua 0.6 2.7 100.0 nd bc8 Nancagua 0.3 nd 100.0 37.5 bc9 Requinoa 0.8 10.0 100.0 100.0 bc10 Nancagua 1.4 3.7 100.0 100.0 bc11 Casablanca 3.0 >10 61.0 93.4 bc12 Los Angeles 2.3 6.6 100.0 91.4 EC50 was determined in vitro using MM and YBA media for mycelium and conidia, respectively. Performed in Granny Smith apples at label concentration of isofetamid (0.4 µg mL -1). nd: not determined. 1 2 11444 - 9 Piqueras.indd 366 12-12-14 15:04 VOLUME 41 Nº3 OCTOBER – DECEMBER 2014 agar acidified with 96% 0.5 mL L -1 lactic acid (APDA). Hyphal tips were transferred to fresh APDA plates and incubated at 22 °C for 4 days. Isolates were maintained in APDA at 20 °C until use. Fungicides In this study, the following fungicides were used: isofetamid (IKF-5411 40 SC, Sumitomo, Japan) and fenhexamid (Teldor 50 WP, Bayer Chile). Mycelium and conidia sensitivity The sensitivity of the mycelium of B. cinerea isolates to isofetamid was assayed using minimal agar media (MM) containing 10 g of glucose, 1.5 g of K 2HPO4, 2 g of KH2PO4, 1 g of (NH4)2SO4, 0.5 g of MgSO4·7H2O, 2 g of yeast extract, and 12.5 g of agar (Hu et al., 2011). The plates were supplemented with 0.1, 0.5, 1.0, 3.0, 5.0, and 10.0 µL L-1 isofetamid. A mycelial plug (5 mm diameter) was placed at the center of the plates, with three replicates for each isofetamid conc (...truncated)