Sensitivity of Phytophthora nicotianae From Tobacco to Fluopicolide, Mandipropamid, and Oxathiapiprolin

Abstract

Black shank incited by Phytophthora nicotianae is a devastating disease in the production of tobacco. Fungicides have been commonly used for managing the disease; however, there is only a narrow pool of effective fungicides. A few new fungicides became available in recent years, including fluopicolide, mandipropamid, and oxathiapiprolin, which reduced diseases incited by oomycetes under field conditions. Limited information is available regarding sensitivity of P. nicotianae isolates to these new fungicides. Research was conducted to determine effects of the three new fungicides on P. nicotianae isolates from tobacco in Georgia. Studies with 106 isolates indicated that they did not grow when agar medium was amended with the fungicides at the rate of 1 μg/ml. Twenty isolates were used for in vitro studies to determine sensitivity to the fungicides. Fluopicolide, mandipropamid, and oxathiapiprolin inhibited mycelial growth of the isolates with mean EC50 values (effective concentrations that provide 50% growth reduction) of 0.09, 0.04, and 0.001 μg/ml, respectively. EC50 values of fluopicolide, mandipropamid, and oxathiapiprolin for inhibiting sporangial formation were 0.15, 0.03, and 0.0002 μg/ml, respectively. EC50 values for suppressing zoospore germination averaged 0.16, 0.04, and 0.002 μg/ml for fluopicolide, mandipropamid, and oxathiapiprolin, respectively. Results from the study indicated that P. nicotianae isolates from tobacco in Georgia were sensitive to the fungicides, with lower EC50 for oxathiapiprolin than for fluopicolide and mandipropamid. The information on effectiveness and baseline sensitivity of fungicides on P. nicotianae will facilitate monitoring of resistance development in the pathogen population.

Population Structure and Genetic Diversity of Phytophthora nicotianae from Tobacco in Georgia

“…Isolates of P. nicotianae were collected in Georgia from infected tobacco plants in 2013 and 2014, and generation of single-spore isolates and their pathogenicity on tobacco ('K326') was reported previously (Qu et al 2016). Isolates of P. nicotianae were collected in Georgia from infected tobacco plants in 2013 and 2014, and generation of single-spore isolates and their pathogenicity on tobacco ('K326') was reported previously (Qu et al 2016).…”

“…After incubating for 10 days at 25°C, wheat seed fully colonized by mycelium were utilized to inoculate seedlings of tobacco, as described previously (Qu et al 2016). After incubating for 10 days at 25°C, wheat seed fully colonized by mycelium were utilized to inoculate seedlings of tobacco, as described previously (Qu et al 2016).…”

“…After incubating for 7 days at 25°C, colony diameters were measured and effective concentration of mefenoxam for 50% mycelial growth reduction (EC 50 ) was calculated using the previously described methods (Qu et al 2016). Ridomil Gold (45.3% mefenoxam) provided by Syngenta (Greensboro, NC) was used to make a stock solution in sterile distilled water.…”

“…The most widely used fungicide to control tobacco black shank is mefenoxam, and it was only recently that some newer fungicides were demonstrated to be effective alternative or complementary tools to combat the disease (Ji et al 2014;Qu et al 2016). Due to the wide distribution of race 1, reliance on cultivars with resistance to race 0 strains is not sufficient to manage the disease effectively.…”

Mating type and sensitivity of Phytophthora nicotianae from tobacco to metalaxyl and dimethomorph in Henan province, China

“…Stunting, wilting and yellowing of leaves, black lesions at the base of the stem and root necrosis are symptoms associated with this disease (Csinos & Bertrand, ). The most characteristic symptoms are that the pith of stem is dry, brown to black and is separated into plate‐like discs (Qu, Shao, Csinos, & Ji, ). Black shank of tobacco can be effectively managed using an integrated approach that includes cultural practices, chemical control and host resistance (Antonopoulos, Melton, & Mila, ; Csinos & Bertrand, ).…”