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

Abstract

Soybean target spot (Corynespora cassiicola) has become an important disease in most soybean growing regions in Brazil. The sensitivity of 34 isolates of C. cassiicola to 11 fungicides was evaluated based on mycelial growth inhibition (boscalid, carbendazim, cyproconazole, fluopyram, fluxapyroxad, prothioconazole and thiophanate-methyl) or spore germination inhibition (azoxystrobin, picoxystrobin, pyraclostrobin and trifloxystrobin). In addition, the efficacy of five fungicides to control target spot was tested in four field trials carried out during three crop seasons: 2011/2012, 2012/2013 and 2013/2014. Fungal isolates were collected from soybean plants in several soybean growing areas in Brazil. The effective concentration of each fungicide to inhibit fungal growth or spore germination by 50% (EC 50 ) was calculated for all isolates. ABSTRACTgrowth inhibition and pyraclostrobin led to the lowest spore germination percentage, with the lowest EC 50 values. At field experiments, cyproconazole and carbendazim showed target spot control ranging from 26% to 29%. On the other hand, fluxapyroxad and prothioconazole prevented an epidemic of the disease by 45% to 55%, respectively. In general, the efficacy of fungicides in the field reflected the in vitro sensitivity averages. Large sensitivity reduction was detected to benzimidazoles (MBC), indicating that this group of fungicides should no longer be used for target spot control. There was a negative and significant correlation (-0.265) between target spot severity and soybean yield. The pathogen showed variability in sensitivity to the fungicide groups carboxamides (SDHI), triazoles (DMI) and strobilurins (QoI), which denotes a high risk of selection for resistance. RESUMOA mancha-alvo da soja (Corynespora cassiicola) tornou-se uma importante doença na maioria das regiões produtoras de soja no Brasil. A sensibilidade de 34 isolados de Corynespora cassiicola a 11 fungicidas foi avaliada pela inibição do crescimento micelial (boscalida, carbendazim, ciproconazol, fluopiram, fluxapiroxada, protioconazol e tiofanato-metílico) ou inibição da germinação de esporos (azoxistrobina, picoxistrobina, piraclostrobina e trifloxistrobina). Além disso, a eficácia de cinco fungicidas para controlar mancha-alvo foi testada em quatro ensaios no campo, conduzidos durante três safras: 2011/2012, 2012/2013 e 2013/2014. Os isolados do fungo foram coletados de plantas de soja em diversas regiões produtoras de soja do Brasil. A concentração efetiva para inibir o crescimento micelial ou a germinação dos esporos em 50% (EC 50 ), para cada fungicida, foi calculada para todos os isolados. Fluxapiroxada e protioconazol proporcionaram as Teramoto, A.; Meyer, M.C.; Suassuna, N.D.; Cunha, M.G. Sensibilidade de Corynespora cassiicola isolado de soja a fungicidas in vitro e controle químico de mancha-alvo da soja no campo. Summa Phytopathologica, v.43, n.4, p.281-289, 2017. maiores inibições de crescimento micelial do patógeno e piraclostrobina a menor porcentagem de germinação de esporos, com o...

Meta‐analysis of fungicide efficacy on soybean target spot and cost–benefit assessment

“…The relatively low efficacy of CZM observed here could be attributed to the low fungitoxicity of the active ingredient itself or to the reported increased frequency of C. cassiicola isolates with resistance to this active ingredient in local populations of the pathogen (Teramoto et al ., ; Xavier et al ., ).…”

Efficacy of new generation fungicides against Corynespora leaf fall disease of rubber (Hevea brasiliensis)

“…Prosper et al (2018) [15] reported high level efficacy of pyraclostrobin and carbendazim against C. cassiicola in rubber. In another laboratory studies the fungicide pyraclostrobin was observed to be very promising in inhibiting the germination of the spores of C. cassiicola, the causal agent of target spot of soybean (Teramoto et al, 2017) [23] . The nursery studies on the evaluation of fungicides against corynespora leaf fall disease caused by C. cassiicolla revealed that the fungicides pyraclostrobin+ metiram thiophanate methyl, iprodione + carbendazim and mancozeb were effective in containing the disease severity.…”

The fungal pathogen Corynespora cassiicola: A review and insights for target spot management on cotton and Soya bean

“…Resistance to boscalid was found in cucumber C. cassiicola isolates in Japan (Miyamoto et al, 2009(Miyamoto et al, , 2010. HNS or resistant C. cassiicola isolates from Soya bean were reported in Brazil to fluxapyroxad and boscalid fungicides (Teramoto et al, 2017); and in China, the resistance of C. cassiicola isolates from cucumber to boscalid is widespread (Zhu et al, 2019).…”