Reaction of hybrids, inhibition in vitro and target spot control in cucumber

Abstract

The fungus Corynespora cassiicola is the causal agent of target spot in cucumber. Under favorable climatic conditions it can cause serious damage in this horticultural crop. In Brazil, there exists not enough knowledge to determine efficient control measures to the disease. This investigation was carried out to evaluate: a) the reactions of nine cucumber hybrids to C. cassiicola; b) the sensibility of six isolates of C. cassiicola to fungicides in vitro (captan, chlorothalonil, mancozeb, azoxystrobin, difenoconazole, carbendazin, tebuconazole and thiophanate-methyl), used in concentrations of 0, 1, 10, 100 and 1,000 µg mL -1 of active ingredient and c) protective and curative chemical treatments with the same fungicides used in vitro in cucumber plants inoculated with C. cassiicola. The cucumber hybrids were evaluated using the scale of notes and diagrammatic of target spot severity. The more resistant hybrids to the pathogen were Taisho, Nikkey, Yoshinari and Safira. The difenoconazole fungicide caused the most mycelial growth inhibition (MGI) and showed the lowest ED 50 . Thiophanate-methyl was the worst fungicide, it did not inhibit the mycelial growth of the fungus. Azoxystrobin was the most efficient in controlling the disease, although it has to be registered in Ministry of Agriculture, Livestock and Food Supply in Brazil before its recommendation.

In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot

“…Most isolates had EC 50 values above the highest tested concentration (1000 µg mL -1 ), indicating resistance of C. cassiicola to carbendazim and thiophanate-methyl in Brazil. Similar results were obtained in other studies (26,31,33).…”

Sensitivity of Corynespora cassiicola from soybean to carbendazim and prothioconazole

“…Prothioconazole was recommended for soybean in Brazil for the first time in 2010/11. Although some authors considered 1 µg/mL as a cut off for triazoles -C. cassiicola (Teramoto et al, 2011), no baseline data has been published for prothioconazole. Prothioconazole is the only DMI-fungicide that belongs to the chemical group triazolinthione (FRAC, 2013b).…”

“…The range of EC 50 was similar to the one observed for prothioconazole (0.47 µg/mL to 26.44 µg/mL). Teramoto et al (2011) evaluated the sensitivity of five cucumber (Cucumis sativus L.) C. cassiicola isolates from São Paulo and one from Goiás State, Brazil, using mycelium growth inhibition to azoxystrobin, difenoconazole, carbendazim, tebuconazole and thiophanate-methyl and found EC 50 values higher than 50 μg/mL for azoxystrobin, carbendazin and thiophanate-methyl and below 50 μg/mL for difenoconazole and tebuconazole. Benzimidazoles and QoI resistance has been reported for C. cassiicola in cucumber with decrease in its use in Japan (Hasama, 1991;Hasama & Sato, 1996;Date et al, 2004;Takeuchi et al, 2006).…”

Caracterização de isolados de Corynespora cassiicola e avaliação da sensibilidade in vitro a fungicidas

“…No pepineiro, até 2003, a mancha-alvo era considerada uma doença de importância secundária, entretanto, nos últimos anos passou a ser um dos principais patógenos desta cultura ocasionando danos de até 60%, principalmente nos estados de São Paulo, Paraná e Goiás, tanto em cultivo convencional quanto em cultivo protegido (Teramoto et al, 2011). O fungo C. cassiicola foi relatado pela primeira vez causando doença em pepino por Blazquez (1967), no estado da Flórida (Estados Unidos).…”

“…Com o progresso da doença, as manchas crescem, tomando formato arredondado e apresentando centro marrom claro e bordos encharcados de coloração olivácea. Ainda não foram observados sintomas da doença em caule, frutos e raízes (Teramoto et al, 2011).…”