In vitro mycelial sensitivity of Macrophomina phaseolina to fungicides

Black root rot, caused by Macrophomina phaseolina (Tass.) Goid., is the most common root disease in soybean fields. This study aimed to determine the in vitro mycelial sensitivity, measured by the IC50 (concentration to inhibit 50% of the fungus mycelial growth) of a M. phaseolina isolate obtained from soybean, to different fungicides (thiram, iprodione, carbendazim, pyraclostrobin, fluquinconazol, tolyfluanid, metalaxyl and penflufen + trifloxystrobin), at six concentrations (0.01 mg L-1, 0.10 mg L-1, 1.00 mg L-1, 10.00 mg L-1, 20.00 mg L-1 and 40.00 mg L-1 of the active ingredient). The 0.00 mg L-1 concentration represented the control, without fungicide addition. The mycelial growth evaluation was performed with the aid of a digital pachymeter, by measuring the colonies diameter, when the fungus growth in the control treatment reached the Petri dish edge. The experimental design was completely randomized, with four replications. Concerning the fungitoxicity of active ingredients, a variation from non-toxic to highly fungitoxic was observed to the M. phaseolina isolate, with IC50 values ranging from 0.23 mg L-1 to > 40.00 mg L-1, being carbendazim the most efficient one (IC50 = 0.23 mg L-1). The fungus showed insensitivity to the active ingredients of fluquinconazole, metalaxyl, thiram and tolyfluanid

Pathogenic fungi found in wheat seeds and medium early maturity, produced in three parts of Rio Grande do Sul, Brazil

Seed samples of wheat harvest in 2010 from Santo Augusto, Passo Fundo and Vacaria, RS; were plated on gerbox acrylic sterilized culture medium PSA (potato, sucrose and agar) plus antibiotics. Were used 400 seeds of each cultivar total of 45 cultivars. Were distributed equally spaced 25 seeds in each seedling with four replications, totaling 100 seeds per replicate. The seeds were incubated at 25 ± 2°C in an incubator with a photoperiod of 12 hours for 12 days. The experimental design was blocks and the experimental unit consists of four gerbox containing 25 seeds each. Was considered to be infected the seed of conidiophore presence and/or conidia of the fungus. The data were transformed to (x+1)1/2 and subjected to analysis of variance and means compared by Tukey test at 5% probability. Fungi F. graminearum and Alternaria spp. were detected in high incidence in most lots, performing at respectively 96.0% and 98.0% of samples, thereafter Bipolaris spp. So too, Drechslera siccans was found in 41.5% of samples showing that their incidence is increasin

Fungos patogênicos detectados em sementes de trigo de ciclo precoce e médio, produzidas em três lugares do Rio Grande do Sul, Brasil

Seed samples of wheat harvest in 2010 from Santo Augusto, Passo Fundo and Vacaria, RS; were plated on gerbox acrylic sterilized culture medium PSA (potato, sucrose and agar) plus antibiotics. Were used 400 seeds of each cultivar total of 45 cultivars. Were distributed equally spaced 25 seeds in each seedling with four replications, totaling 100 seeds per replicate. The seeds were incubated at 25 ± 2°C in an incubator with a photoperiod of 12 hours for 12 days. The experimental design was blocks and the experimental unit consists of four gerbox containing 25 seeds each. Was considered to be infected the seed of conidiophore presence and/or conidia of the fungus. The data were transformed to (x+1)1/2 and subjected to analysis of variance and means compared by Tukey test at 5% probability. Fungi F. graminearum and Alternaria spp. were detected in high incidence in most lots, performing at respectively 96.0% and 98.0% of samples, thereafter Bipolaris spp. So too, Drechslera siccans was found in 41.5% of samples showing that their incidence is increasing.Amostras de sementes de trigo da safra 2010 provenientes de Santo Augusto, Passo Fundo e Vacaria, RS; foram plaqueadas em gerboxes de acrílico, previamente esterilizados e contendo meio de cultura BSA (batata, sacarose e agar) mais antibiótico. Foram utilizadas 400 sementes de cada amostra, totalizando 45 cultivares. As sementes foram incubadas a 25 ± 2 °C em câmara climatizada com fotoperíodo de 12 horas durante 12 dias. O delineamento experimental foi de blocos casualizados e a unidade experimental constituída por 4 gerboxes contendo 25 sementes cada. Foi considerada infectada a semente com presença de conidióforo e/ou conídio do fungo. Os dados foram transformados para (x+1)1/2 e submetidos à análise de variância, e as médias comparadas pelo teste de Tukey a 5% de probabilidade. Os fungos F. graminearum e Alternaria spp. foram detectados em alta incidência na maioria dos lotes, apresentando-se respectivamente em 96.0 % e 98.0 % das amostras analisadas, seguidamente de Bipolaris spp. Assim também, Drechslera siccans foi encontrada em 41,5% das amostras, evidenciando que sua ocorrência vem aumentando

Etiologia e intensidade de manchas foliares em cultivares de trigo em três locais do Rio Grande do Sul, Brasil

This study aimed to identify and quantify the causal agents of fungal leaf blights, and compare different assessment methods for disease quantification. The experiments were conducted with 20 medium cycle cultivars in Passo Fundo, Saint Augustus and Vacaria counties with three replications in randomized blocks. For evaluation 20 leaves were collected per plot, at flowering stage. Disease severity was estimated by the percent diseased leaf area and lesions number per leaf. For fungus etiology, twenty five discs of each leaf sample containing a lesion were subjected to a humid chamber. After three days incubation fungi identification was performed under a dissecting microscope. The mean incidence, number of lesions and severity data were subjected to analysis of variance and means compared by the Tukey’s multiple test at 5% significance level. The severity and lesions number were the most efficient criteria to fungal foliar disease, predominantly Bipolaris sorokiniana, Drechslera siccans, D. tritici-repentis and Stagonospora nodorum. The cultivars with the highest incidence rates were not the same as that presented the greatest number of injuries and severity. Join the appearance D. siccans and the resurgence of S. nodorum.O presente trabalho teve por objetivo identificar e quantificar os fungos agentes causais de manchas foliares, além de comparar diferentes critérios fitopatométricos. Os experimentos foram realizados com 20 cultivares de ciclo médio nos municípios de Passo Fundo, Santo Augusto e Vacaria, com três repetições cada, em blocos inteiramente casualizados. A avaliação da incidência foi realizada após a coleta das folhas, na floração, através do exame visual de 20 folhas por amostra. A severidade foi estimada pela percentagem da área foliar doente, e o número de lesões foi avaliado pela quantificação de lesões por folha. Para a identificação dos agentes causais das manchas foliares, vinte cinco discos de cada amostra foram submetidos à câmara úmida. Após três dias avaliou-se a incidência em lupa e no microscópio óptico. As médias obtidas de incidência, número de lesões e severidade foram submetidos à análise de variância e comparados pelo teste de Tukey a um nível de significação de 5%. A severidade em porcentagem e o número de lesões foram os critérios fitopatométricos mais eficientes para avaliar as enfermidades foliares causadas por fungos, predominando Bipolaris sorokiniana, Drechslera siccans, D. tritici-repentis e Stagonospora nodorum. As cultivares que apresentaram as maiores percentagens de incidência não foram as mesmas que apresentaram o maior número de lesões e severidade. Registra-se o aparecimento D. siccans e o ressurgimento de S. nodorum

Etiology and intensity of leaf spot in wheat cultivars at three sites at Rio Grande do Sul, Brazil

This study aimed to identify and quantify the causal agents of fungal leaf blights, and compare different assessment methods for disease quantification. The experiments were conducted with 20 medium cycle cultivars in Passo Fundo, Saint Augustus and Vacaria counties with three replications in randomized blocks. For evaluation 20 leaves were collected per plot, at flowering stage. Disease severity was estimated by the percent diseased leaf area and lesions number per leaf. For fungus etiology, twenty five discs of each leaf sample containing a lesion were subjected to a humid chamber. After three days incubation fungi identification was performed under a dissecting microscope. The mean incidence, number of lesions and severity data were subjected to analysis of variance and means compared by the Tukey’s multiple test at 5% significance level. The severity and lesions number were the most efficient criteria to fungal foliar disease, predominantly Bipolaris sorokiniana, Drechslera siccans, D. tritici-repentis and Stagonospora nodorum. The cultivars with the highest incidence rates were not the same as that presented the greatest number of injuries and severity. Join the appearance D. siccans and the resurgence of S. nodorum