Baseline sensitivity of Brazilian Mycosphaerella fijiensis isolates to protectant and systemic fungicides

Black Sigatoka caused by Mycosphaerella fijiensis is a foliar disease that affects banana plants and large amounts of fungicides are required to prevent crop losses. Intensive applications of single-site fungicides can select for fungicide-resistant isolates. The objective of this study was to assess the sensitivity of 60 isolates of M. fijiensis to commonly used fungicides. Using two different protocols, microtiter and Petri plate tests, the effective concentration at which mycelium growth is reduced by 50% (EC50) was determined for thiophanatemethyl, tebuconazole, chlorothalonil and mancozeb. Additionally, partial sequences of the cytochrome b gene were obtained for 46 isolates to detect the G143A mutation, commonly associated with strobilurin resistance. The EC50 values for tebuconazole and thiophanate-methyl ranged from 0.02 to 1.39 and from 0.008 to 8.22 μg mL-1, respectively. For chlorothalonil, the lowest and highest EC50 values were 0.39 μg mL-1 and 53.7 μg mL-1, respectively. For mancozeb, approximately 50% of the isolates had EC50 values greater than 1000 μg mL-1. No mutation was found in the isolates assayed for strobilurin resistance. There was no correlation between sensitivity levels to any fungicide and geographic region. Low EC50 values were estimated for most fungicides but, some isolates had high EC50 values for mancozeb

Characterization of tomato accessions for resistance to early blight

The purpose of this study was to characterize 50 tomato genotypes of the Vegetable Genebank of the FederalUniversity of Viçosa. They were evaluated together with the controls Débora, Fanny and Santa Clara, in a randomized block designwith two replications. The experiment was conducted in a research field of the UFV, from February to May 2007. We evaluated thedisease severity, which is the percentage of diseased leaf area. The severity values were transformed into area under the diseaseprogress curve (AUDPC), improving the result visualization. The analysis of variance and grouping of AUDPC means by the Scott-Knott test at 5 % significance were performed. The accessions BGH-2081, BGH-2034, BGH-700, BGH-2057, BGH-2035, BGH-2054, BGH-2018, BGH-2065, BGH-2008, and BGH-2032 had a lower mean AUDPC than the controls and are therefore indicatedfor future breeding programs

Crop breeding and applied biotechnology

The purpose of this study was to characterize 50 tomato genotypes of the Vegetable Genebank of the Federal University of Viçosa. They were evaluated together with the controls Débora, Fanny and Santa Clara, in a randomized block design with two replications. The experiment was conducted in a research field of the UFV, from February to May 2007. We evaluated the disease severity, which is the percentage of diseased leaf area. The severity values were transformed into area under the disease progress curve (AUDPC), improving the result visualization. The analysis of variance and grouping of AUDPC means by the Scott-Knott test at 5 % significance were performed. The accessions BGH-2081, BGH-2034, BGH-700, BGH-2057, BGH-2035, BGH-2054, BGH-2018, BGH-2065, BGH-2008, and BGH-2032 had a lower mean AUDPC than the controls and are therefore indicated for future breeding programs.O objetivo deste trabalho foi caracterizar 50 subamostras de tomateiro do Banco de Germoplasma de Hortaliças da Universidade Federal de Viçosa (BGH-UFV). Foram avaliadas juntamente com as testemunhas Débora, Fanny e Santa Clara, em experimento em blocos ao acaso, com duas repetições. O experimento ocorreu na Horta de Pesquisas da UFV, no período de fevereiro a maio de 2007. Avaliou-se a severidade da doença, que é a porcentagem da área foliar lesionada. Os valores de severidade foram transformados em área abaixo da curva de progresso da doença (AACPD), possibilitando uma melhor visualização dos resultados. Foi realizada a análise de variância, seguido do agrupamento das médias de AACPD pelo teste de Scott-Knott, a 5% de significância. As subamostras BGH-2081, BGH-2034, BGH-700, BGH-2057, BGH-2035, BGH-2054, BGH-2018, BGH-2065, BGH-2008 e BGH-2032 apresentaram menor média de AACPD em relação às testemunhas, podendo ser utilizadas em futuros programas de melhoramento

Potencial de hibridação entre acessos de tomateiro para pré‑melhoramento quanto à resistência à requeima

The objective of this work was to evaluate parents with hybridization potential for pre‑breeding of tomato (Solanum lycopersicum) for resistance to late blight. Six tomato accessions (BGH‑2102, BGH‑2117, BGH‑2127, BGH‑2130, BGH‑2332, and BGH‑2343) were used as resistant parents and 15 F1 hybrids originated from these parents. The design was a randomized complete block with three replicates. The plants were inoculated with a mixture of Phytophthora infestans sporangia, the etiological agent oflate blight, at a concentration of 5x103 sporangia mL‑1. The area under the disease progress curve was used to evaluate resistance. Diallelic analysis was performed, considering the effect of genotypes as fixed. The general and specific combining ability of the accessions was estimated. The resistance pattern of the parents and of most of the F1 was the same as that of the resistant controls. The following were observed: additive genetic variability among the parents, predominance of nonadditive gene effects, and bidirectional dominance deviations in the control of the trait. The frequency of favorable and divergent alleles for late blight resistance is higher in the BGH‑2117, BGH‑2127, and BGH‑2343 accessions.O objetivo deste trabalho foi avaliar genitores com potencial de hibridação para o pré‑melhoramento do tomateiro (Solanum lycopersicum) quanto à resistência à requeima. Foram utilizados seis acessos de tomateiro (BGH‑2102, BGH‑2117, BGH‑2127, BGH‑2130, BGH‑2332 e BGH‑2343) como genitores resistentes e 15 híbridos F1 originários destes genitores. Utilizou-se o delineamento de blocos ao acaso, com três repetições. As plantas foram inoculadas com uma mistura de esporângios de Phytophthora infestans, agente etiológico da requeima, na concentração de 5x103 esporângios mL‑1. A área abaixo da curva de progresso da doença foi utilizada para avaliar a resistência. Realizou-se a análise dialélica, tendo-se considerado o efeito de genótipos como fixo. Estimou-se a capacidade geral e específica de combinação dos acessos. O padrão de resistência dos genitores e da maioria dos F1 foi o mesmo que o das testemunhas resistentes. Foram observados: variabilidade genética aditiva entre os genitores, predominância de efeitos gênicos não aditivos e desvios de dominância bidirecional no controle do caráter. A frequência de alelos favoráveis e divergentes para resistência à requeima é maior nos acessos BGH‑2117, BGH‑2127 e BGH‑2343

Agrupamento de curvas de progresso de requeima, em tomateiro originado de cruzamento interespecífico

The objective of this work was to estimate the progress curves of late blight in tomato genotypes, and to identify tomato genotype groups resistant to this disease. Twenty-five hybrid tomatoes, originated from crosses between four fresh market cultivars, one access from the Banco de Germoplasma de Hortaliças (BGH) of Universidade Federal de Viçosa (UFV), and five F8 lines (Solanum lycopersicum x Solanum habrochaites), selected as late blight resistance source, were evaluated. Plants were inoculated with a sporangium mixture of Phytophthora infestans, and then, six evaluations for late blight severity were carried out every three days. The exponential model was fitted to the data of late blight severity percentage, and the obtained parameter estimates – initial incidence of disease (yo )and progress rate of disease (r) – were submitted to the multivariate analysis of variance (Manova). The means of these estimates, obtained for each genotype, were submitted to the cluster analysis. An optimal number of eight distinct groups was observed, which made it possible to identify the genotypes belonging both to the resistant and susceptible groups. The experimental hybrids Ikram x 73 A, Nemo-Netta x 133 A, Ikram x 163 A and Nemo-Netta x 163 A showed the smaller rate of disease progress and, therefore, higher late blight resistance.O objetivo deste trabalho foi estimar curvas de progresso de requeima, em genótipos de tomateiro, e identificar grupos de genótipos resistentes à doença. Foram avaliados 25 híbridos de tomateiro, originados de cruzamentos entre quatro variedades comerciais, um acesso do Banco de Germoplasma de Hortaliças (BGH), da Universidade Federal de Viçosa (UFV), e cinco linhagens F8 (Solanum lycopersicum x Solanum habrochaites), estas últimas selecionadas como fonte de resistência à requeima. As plantas foram inoculadas com uma mistura de esporângios de Phytophthora infestans e, em seguida, foram realizadas seis avaliações quanto à severidade de requeima, a intervalos de três dias. Ajustou-se o modelo exponencial aos dados de percentagem de severidade de requeima, e as estimativas obtidas quanto à incidência inicial da doença (yo) e taxa de progresso da doença (r) foram submetidas à análise de variância multivariada (Manova). As médias dessas estimativas, para cada genótipo, foram submetidas à análise de agrupamento. Observou-se um número ótimo de oito grupos distintos, o que possibilitou identificar genótipos resistentes e suscetíveis. Os híbridos experimentais Ikram x 73 A, Nemo-Netta x 133 A, Ikram x 163 A e Nemo-Netta x 163 A apresentaram a menor taxa de progresso de requeima e, portanto, maior resistência à doença