José Maurício Cunha Fernandes

Epidemiology of apple leaf spot

A mancha foliar da macieira (Malus domestica), causada por Colletotrichum spp., e uma das principais doencas da macieira no Sul do Brasil. Estudos sobre sua epidemiologia foram conduzidos em Passo Fundo e Vacaria, RS, no periodo de fevereiro/1998 a outubro/2000. A doenca foi encontrada nos seis pomares amostrados em 1998 e 1999. Isolados do fungo obtidos a partir de lesoes em folhas e frutos corresponderam as especies C. gloeosporioides (75%), C. acutatum (8%) e Colletotrichum sp. (17%). O patogeno sobreviveu em ramos e gemas dormentes, mas nao em folhas caidas ao solo e frutos mumificados. O tratamento de inverno com duas aplicacoes de oxycloreto de cobre (0,3%) reduziu o inoculo do patogeno em gemas (65 a 84,6%) e ramos (85,6 a 93,7%), mas nao diminuiu o progresso inicial da doenca. A severidade da mancha foliar da macieira aumentou a medida que a temperatura ambiente foi elevada de 14 para 26-28 °C. A 34 °C, entretanto, a infeccao foi completamente inibida. A duracao do molhamento foliar requerido para infeccao variou de duas horas a 30 °C para 32 h a 16 °C. A relacao da temperatura (T) e do molhamento foliar (W) com a severidade de doenca (Y) foi representada pela equacao Y = 0,00145[((T-13)1,78)((34,01-T )1,09)] * 25/[1+14 exp(-0,137W)], R2 = 0,73 e P < 0,0001. Atualmente, estas informacoes estao sendo utilizadas para manejo da mancha foliar da macieira e para validacao de um sistema para sua previsao.

Factors affecting density of airborne Gibberella zeae inoculum

Fusarium head blight (FHB) is a disease of increasing concern in the production of wheat (Triticum aestivum). This work studied some of the factors affecting the density of airborne Gibberella zeae inoculum. Spore samplers were placed at the edge of a field in order to observe spore deposition over a period of 45 days and nights in September and October, the period that coincides with wheat flowering. Gibberella zeae colonies were counted for each period and values transformed to relative density. A stepwise regression procedure was used to identify weather variables helpful in predicting spore cloud density. In general, a predominant night-time spore deposition was observed. Precipitation and daily mean relative humidity over 90% were the factors most hightly associated with peak events of spores in the air. Models for predicting spore cloud density simulated reasonably well with the fluctuation of airborne propagules during both night and day, with potential to be integrated into an FHB risk model framework.

Efeito do tratamento de sementes com fungicida sobre o controle de doenças na parte aérea do trigo

Effect of fungicide seed treatment to control foliar diseases of wheat The control of wheat (Triticum aestivum) foliar diseases through seed treatment was evaluated in Passo Fundo, RS, during 1999. The cultivar used in the experiment was OR 1 which is known to be very susceptible to powdery mildew and leaf rust. The response variables yield and test weight were significant (P>0.05) lower in the check than in the treatments. Highest yields were obtained with fluquinconazol + prochloraz at rates of 250.0 g + 51.0 g (2,943 kg/ha) and 125.0 g + 25.0 g (2,864 kg/ha) being, respectively, 132% and 125% higher than the yield in check (1,270 kg/ha). While treatments with triticonazol, difenoconazol and triadimenol yielded 1,908 kg/ha, 1,821 kg/ha and 1,815 kg/ha, respectively. No phytotoxic effects due to fungicide treatments were observed. The powdery mildew and leaf rust control was effective up to 98 DAE (days after emergency) which coincided with the threshold for fungicide spraying. Fungicides were no longer efficient after 108 DAE. Powdery mildew and leaf rust severity, at 118 DAE in the treatments involving fluquinconazol + prochloraz were 6.2% and 33.9%, and in the check 16.5% and 78.0%, respectively. Thus, treating wheat seeds with fungicides, as demonstrated in this work, in association with crop rotations and more resistant cultivars may play an important role in controlling foliar diseases of wheat while reducing production costs and environmental polution.

Utilization of the cropgro-soybean model to estimate yield loss caused by Asian rust in cultivars with different cycle

In recent years, crop models have increasingly been used to simulate agricultural features. The DSSAT (Decision Support System for Agrotechnology Transfer) is an important tool in modeling growth; however, one of its limitations is related to the unac- counted-for effect of diseases. Therefore, the goals of this study were to calibrate and validate the CSM CROPGRO-Soybean for the soybean cultivars M-SOY 6101 and MG/BR 46 (Conquista), analyze the performance and the effect of Asian soybean rust on these cultivars under the environmental conditions of Vicosa, Minas Gerais, Brazil. The experimental data for the evaluation, testing, and adjustment of the genetic coefficients for the cultivars, M-SOY 6101 and MG/BR 46 (Conquista), were obtained during the 2006/2007, 2007/2008 and 2009/2010 growing seasons. GLUE (Generalized Likelihood Uncertainty Estimation) was used for the estimation of the genetic coefficients, and pedotransfer functions have been utilized to estimate the physical characteristics of the soil. For all of the sowing dates, the early season cultivar, M-SOY 6101, exhibited a lower variance in yield, which represents more stability with regard to the interannual climate variability, i.e., the farmers who use this cultivar will have in 50% of the crop years analyzed, a higher yield than a late-season cultivar. The MG/BR 46 (Conquista) cultivar demonstrated a greater probability of obtaining higher yield in years with favorable weather conditions. However, in the presence of the Asian soybean rust, yield is heavily affected. The early cultivar, M-SOY 6101, showed a lower risk of being affected by the rust and consequently exhibited less yield loss considering the scenario D90 (condensation on the leaf surface occurs when the relative humidity is greater than or equal to 90%), for a sowing date of November 14.

Avaliando a taxa de expansão de lesões de Bipolaris sorokiniana em trigo

Symptoms of spot blotch caused by Bipolaris sorokiniana in wheat (Triticum aestivum) first appear as small, dark lesions onthe upper side of the leaf. As the lesions expand, they become oval with a dark brown center and a yellow hallo. Under favorable weather conditions, leaf lesions coalesce and kill large areas of the leaf surface. The effect of temperature on the lesion expansion rate of B. sorokiniana was examined in eight wheat cultivars. Digital images of lesions of B. sorokiniana for each temperature were captured in each cultivar and stored in an electronic format. A specific computer program, called AreaScan, was used to measure the area of individual lesions. Lesion growth ratewas not uniform among cultivars.The wheat cultivar BR 18 showed the slowest lesion growth rate. The cultivars Embrapa 15 and Embrapa 16 showed the fastest lesion growth rates, while BR 15, BR 23, BR 35, Embrapa 40, andEmbrapa 49 had a moderate rate. The relationship between temperature and lesion expansion rate was described by a mathematical function, such as y=(a+bx)/(1+cx+dx2), where y is the response, x the temperature, and a,b,c, and d the parameters. Nocturnal temperature of 23 oC and diurnal of 30 oC proved to be the most favorable for lesion expansion. Selecting wheat cultivars with partial resistance to spot blotch is strategic for growing wheat in tropical and subtropical regions. Finally, the methodological approach used in this study for determining lesion growth rate may play an important role for selecting for this genetic trait.

Disease Risk, Spatial Patterns, and Incidence-Severity Relationships of Fusarium Head Blight in No-till Spring Wheat Following Maize or Soybean

The first large-scale survey of Fusarium head blight (FHB) in commercial wheat fields in southern Brazil was conducted over three years (2009 to 2011). The objectives were to: (i) evaluate whether increased FHB risk is associated with within-field maize residue; (ii) determine the spatial pattern of FHB incidence; and (iii) quantify the relationship between FHB incidence and severity. FHB was assessed in a total of 160 fields between early milk and dough. Incidence ranged from 1.0 to 89.9% (median = 25%) and severity from 0.02 to 18.6% (median = 1.3%). FHB risk was neither lower nor higher in wheat following maize than in wheat following soybean. Only 18% of fields were classified as having aggregated patterns of FHB-symptomatic spikes. A binary power law description of the variances was consistent with an overall random pattern of the disease. These results conform with the hypothesis that FHB epidemics in southern Brazil are driven by sufficient atmospherically-transported inoculum from regional sources. The incidence-severity relationship was coherent across growing season, growth stage, and previous crop; one common fitted curve described the relationship across all observations. Estimating severity from incidence may be useful in reducing the workload in epidemiological surveys.

Influência da temperatura e da umidade relativa do ar na esporulação de Magnaporthe grisea em trigo

O fungo Magnaporthe grisea (Anamorfo Pyricularia grisea) e o agente causal da brusone do trigo (Triticum aestivum), uma doenca limitante a cultura do trigo no Brasil em regioes produtoras localizadas acima do paralelo 24 °S. O objetivo do presente trabalho foi estudar o efeito da temperatura e da umidade relativa do ar na esporulacao de M. grisea. O numero medio de conidios foi determinado em raquis de plantas de trigo previamente colonizados com o fungo e expostos em câmaras de crescimento sob temperaturas de 23 e 28 oC, e com umidade relativa do ar de 80, 85, 90, 95 e 100%. A determinacao do numero de conidios produzidos foi feita apos 24, 48, 72 e 96 horas de exposicao em cada combinacao de temperatura e umidade. Os efeitos da temperatura e da umidade foram significativos (P 90%) e a temperatura se encontra ao redor de 28 oC, a producao de conidios de M. grisea e favorecida.

Using lesion density to characterize wheat leaf rust epidemics

Wheat leaf rust caused by Puccina triticina is an important disease affecting wheat (Triticum aestivum) worldwide. Disease symptoms are normally shown on the upper leaf surface, but they can be observed in the leaf sheaths. In this work, epidemic rate and lesion distribution were characterized for the development of a simulation model. Diseased leaves were collected at regular intervals during the 2006 and 2007 seasons, in Tamandare do Sul, RS. Two commercial wheat fields were used for sampling. A digital image was obtained for each sampled leaf. Software was used to assist counting and determining the exact location of leaf rust lesions. The quantification of the number of lesions was made on individual leaves. The data set representing the epidemic progress was adjusted to a logistic model with three parameters. A descriptive analysis indicated that the position of leaf rust lesions followed a random pattern at the beginning of the epidemic, shifting to an aggregate pattern as the epidemic advanced in time. The cubic log- polynomial model successfully predicted portions of leaf area more likely to bear lesions. Further exploration of these techniques could help the statistical modeling of host-pathogen relationships. Moreover, the model can be used to generate a useful diagrammatic scale with gradients of severity.

Climate Suitability for Magnaporthe oryzae Triticum Pathotype in the United States

Wheat blast, caused by the Triticum pathotype of Magnaporthe oryzae, is an emerging disease considered to be a limiting factor to wheat production in various countries. Given the importance of wheat blast as a high-consequence plant disease, weather-based infection models were used to estimate the probabilities of M. oryzae Triticum establishment and wheat blast outbreaks in the United States. The models identified significant disease risk in some areas. With the threshold levels used, the models predicted that the climate was adequate for maintaining M. oryzae Triticum populations in 40% of winter wheat production areas of the United States. Disease outbreak threshold levels were only reached in 25% of the country. In Louisiana, Mississippi, and Florida, the probability of years suitable for outbreaks was greater than 70%. The models generated in this study should provide the foundation for more advanced models in the future, and the results reported could be used to prioritize research efforts regarding the biology of M. oryzae Triticum and the epidemiology of the wheat blast disease.

Controle da ferrugem da folha e da mancha bronzeada da folha de trigo pelo uso de fungicidas em tratamento de sementes

The control of leaf rust and tan spot of wheat by seed treatment with fungicides was evaluated during 1998 in Passo Fundo, RS. Except for treatments including triadimenol and iprodione, leaf rust and tan spot severity in above ground parts of wheat plants was drastically reduced by the fluquinconazole fungicide used.