M. C. Meyer

Ferrugem-asiática da soja no Brasil: passado, presente e futuro

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi , is the most severe disease of the crop and can cause yield losses of up to 90%. The disease was first reported in Brazil in 2001. Epidemics of the disease are common in the country, where the fungus can survive year‑round. Regulatory measures to reduce the inoculum between seasons and avoid late-season soybean have been adopted to manage the disease. Disease control has relied mainly on chemical control, but a lower sensibility of the fungus to fungicides has been reported in Brazil. Major‑resistance genes have been mapped and incorporated into the cultivars. With the reduced efficacy of the fungicides, the adoption of integrated measures to control the disease will be important for the sustainability of the crop. This review presents the main changes in the soybean crop system caused by the introduction of the fungus in Brazil, the current management strategies adopted to avoid losses, and the new trends that, together with biotechnological strategies, can improve management in the future.

Reação de cultivares de soja à Corynespora cassiicola

O fungo Corynespora cassiicola, agente causal da mancha-alvo em soja, tem ocorrido com frequencia na regiao Centro-Oeste do Brasil e pode, sob condicoes de alta temperatura e alta umidade, causar serios danos a cultura. O uso de cultivares resistentes ao patogeno e recomendado, porem sao poucas as disponiveis no mercado. Este trabalho foi realizado visando avaliar a reacao de doze cultivares comerciais de soja inoculados com C. cassiicola, em casa de vegetacao e no campo. A severidade foi avaliada utilizando escala diagramatica de severidade da mancha-alvo. As cultivares menos suscetiveis ao patogeno na casa de vegetacao foram BRSGO 7960 e BRS Sambaiba e as mais suscetiveis foram BMX Potencia RR e M-SOY 7908 RR. No campo, as cultivares menos suscetiveis foram M-SOY 8866, M-SOY 7908 RR e BMX Potencia RR e as mais suscetiveis foram BRSGO 8360 e BRS Tracaja.

Fungitoxicidade de grupos químicos sobre Myrothecium roridum in vitro e sobre a mancha-de-mirotécio em algodoeiro

The objective of this work was to evaluate the toxicity of benzimidazoles, triazoles, strobilurins, isoftalonitrils and ditiocarbamats on Myrothecium roridum conidial germination and micelial growth in vitro, and the myrothecium leaf spot severity on cotton plants. On in vitro tests, fungicides were solubilized in PDA media at the following concentrations: 0.1, 1, 10 and 100 mg L -1 . The toxicity of the products were evaluated by the ED50 rate (required for inhibiting 50% of the conidial germination or mycelial growth). In greenhouse tests, the severity of myrothecium leaf spot was quantified by measuring the leaf area affected by the pathogen in cotton plants sprayed before (preventive) and after (curative) the pathogen inoculation. The fungicides thiophanate methyl, carbendazim, metconazole, thiophanate methyl + chlorothalonil, pyraclostrobin + epoxyconazole, pyraclostrobin + metiran, trifloxystrobin + propiconazole, and tebuconazole were highly efficient (ED50<1 mg L -1 ) or efficient (ED50 between 1 and 10 mg L -1 ) inhibiting conidial germination and mycelial growth of M. roridum isolates. In greenhouse tests, fungicides pyraclostrobin + epoxyconazole, tebuconazole, metconazole, and azoxystrobin + cyproconazole are the most efficient against myrothecium leaf spot disease. Preventive treatment is more efficient than curative.

Reação de cultivares de soja à mela (Thanatephorus cucumeris) em campo em dois estádios de desenvolvimento das plantas

Rhizoctonia aerial blight (RAB), caused by the fungus Thanatephorus cucumeris is one of the most damaging diseases of soybean at Roraima, Brazil. The objective of this study was to evaluate the reaction of 15 soybean cultivars to RAB in a cerrado (savannah) ecosystem in the state of Roraima. The percentage of foliar area infected (FAI) and the percentage of pods with disease symptoms (WP) were evaluated on soybean plants at R.5.5 and R.6 growth stages, respectively. There were significative differences among cultivars tested based on Fisher LSD test in both evaluations. The FAI ranged from 1.5% (cv. Padre) to 62% (cv. BR-36) and WP from 8% (cv. UFV-9 and cv. Jucara) to 55 % (cv. BR-36). Significative and positive correlation was observed between the evaluations.

Mancha de mirotécio em algodoeiro causada por Myrothecium roridum

ABSTRACT Myrothecium leaf spot caused by Myrothecium roridum Tode ex Fr.was observed on cotton fields in Maranhao State, Brazil, causing yieldreduction of up to 60%. Disease symptoms are lesions with concentricnecrotic rings, with salient structures (sporodochia) irregularly distributed.Symptoms were observed on petioles, bracts, leaves and bolls of cottoncultivars Deltapine Acala 90, Fibermax 966 and Sure Grow 821. Thepathogen was isolated and cultivated on potato-dextrose-agar (PDA)medium. The pathogenicity was evaluated on detached healthy bollsfrom cotton cv. Fibermax 966 (R6 vegetative stage), previouslydisinfested. Thirteen isolates of M. roridum were tested, which included Meyer, M.C., Silva, J.C. da, Maia, G.L., Bueno, C.J., Souza, N.L. Myrothecium leaf spot of cotton caused by Myrothecium roridum . SummaPhytopathologica , v.32, n.4, p.390-393, 2006. RESUMO A mancha de mirotecio causada por Myrothecium roridum Tode exFr. foi observada em lavouras de algodao no sul do Maranhao, causandoreducoes de produtividade de ate 60%. Os sintomas da doenca sao lesoesnecroticas, circulares, com estruturas salientes, os esporodoquios, dedistribuicao irregular. Foram observadas lesoes nos peciolos, bracteas,folhas e macas de algodoeiro cv. Deltapine Acala 90, Fibermax 966 eSure Grow 821. O isolamento do fungo foi realizado em meio de culturabatata-dextrose-agar (BDA). O teste de patogenicidade foi realizado emmacas sadias, destacadas de algodoeiro cv. Fibermax 966, no estadiovegetativo R6, previamente desinfestadas. Foram testados 13 isoladosde

Soybean green stem and foliar retention syndrome caused by Aphelenchoides besseyi

Soybean, the most important agricultural product in Brazil, is widely cultivated all over the country. The occurrence of green stem and foliar retention (GSFR) has been reported since the beginning of the soybean cultivation in Brazil and its potential causes were attributed to severe attack of stinkbugs or plant nutritional disorders. About two decades ago, a new type of GSFR was reported in Brazilian tropical regions of soybean production, also of an unknown cause. Several possible causes were investigated, but the presence of the nematode Aphelenchoides sp. in symptomatic plants was frequently observed. Koch’s postulates were conducted to check whether this nematode could be the cause of the syndrome. Specimens of Aphelenchoides sp. were isolated from soybean plants and multiplied in colonies of the fungus Fusarium sp. in PDA culture medium. Nematode suspensions were inoculated onto healthy soybean plants and the typical GSFR symptoms were observed. The nematode was recovered from the inoculated plants. Based on both morphological and molecular data, we suggest that Aphelenchoides besseyi is the causal agent of GSFR of soybeans in Brazil, a syndrome popularly known as “Soja Louca II”.

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

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. Fluxapyroxad and prothioconazole provided the greatest mycelial Teramoto, A.; Meyer, M.C.; Suassuna, N.D.; Cunha, M.G. In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot. Summa Phytopathologica, v.43, n.4, p.281-289, 2017.

Ciclo de vida de Heterodera glycines raça 9 em soja no Estado do Maranhão

The soybean cyst nematode Heterodera glycines causes great yield losses to soybean in Brazil. There are 11 races occurring in Brazil and, in the Maranhao State, only the race 9 was reported. The objective of this work was to establish the life cycle of a H. glycines race 9 population, on soybean, under tropical weather conditions. The experiment was carried out on a wired greenhouse at Embrapa Soybean - Balsas Experimental Station, Maranhao, Brazil. The average temperature was 28,7 oC in the soil and 31,7 oC in the air, and the relative humidity of the air was 49,8 %. Seedlings of soybean cultivar BRS Sambaiba were transferred to pots containing sandy soil infested with 4000 eggs of H. glycines race 9. The numbers of females and cysts per plant root were evaluated at 17, 20, 23, 26, 29 and 32 days after soil infestation. The average number of female increased significantly between the 17th and 29th days after soil infestation, and started decrease on 32nd day, when start to appear the first cysts. In these experimental conditions, H. glycines race 9 ended its life cycle in 29 days after soil infestation. In this way, it is possible to occur three to four generations of the nematode during the soybean cycle in Balsas, Maranhao, Brazil.

Meta-analytic modeling of the decline in performance of fungicides for managing soybean rust after a decade of use in Brazil

An apparent decline of fungicide performance for the control of soybean rust in Brazil has been reported but the rate at which it has occurred has not been formally quantified. Control efficacy and yield response to three fungicides applied as single active ingredients (a.i.)-azoxystrobin (AZOX), cyproconazole (CYPR), and tebuconazole (TEBU)-and four applied as mixtures-AZOX+CYPR, picoxystrobin + CYPR, pyraclostrobin + epoxiconazole, and trifloxystrobin + prothioconazole (TRIF+PROT)-were summarized using network meta-analytic models fitted to mean severity and yield data from 250 trials (10-year period). The effect of year was tested on both variables in a meta-regression model. Overall control efficacy ranged from 56 to 84%; the three single-a.i. fungicides performed the poorest (56 to 62%). Yield increase for single-a.i. fungicides was as low as 30% but ranged from 47 to 65% for the premixes. Significant declines in both variables were detected for all fungicides except TRIF+PROT. For TEBU, control efficacy (yield response) declined the most: 78% (18%) to 54% (8%) from 2004-05 to 2013-14. The recent surge of resistant populations of Phakopsora pachyrhizi to both demethylation inhibitor and quinone outside inhibitor fungicides is likely the driving force behind a significant decline after 4 years of fungicide use.