Adalberto C. Café-Filho

Progresso do crestamento gomoso e perdas na cultura da melancia

O progresso do crestamento gomoso e as perdas na cultura da melancia foram estudados em ensaios de campo com inoculacao artificial de Didymella bryoniae. Para o estudo do progresso da doenca foram utilizadas duas areas indenes, cada uma com 24 x 32 m, e nenhuma medida de controle foi adotada. Para obtencao das curvas de progresso, quantificou-se a percentagem media de area foliar afetada em uma area de 768 m2, aos 45, 50, 55, 60, 65, 74, 80 e 87 dias apos o plantio (DAP). Ficou demonstrado que a doenca progride segundo o modelo exponencial, mesmo sob condicoes nao muito favoraveis, na ausencia de chuvas e com baixo nivel de inoculo inicial. Os valores maximos de severidade foram observados aos 87 DAP (12,5-13,6% da area foliar doente). No ensaio de perdas, utilizou-se o delineamento experimental de blocos casualizados com cinco tratamentos e quatro repeticoes. Cinco niveis de doenca foram obtidos pela aplicacao de doses decrescentes da mistura clorotalonil e tiofanato metilico (g/100 L de agua): (a) 0,0 g i.a. (testemunha); (b) clorotalonil 25 g + tiofanato metilico 10 g; (c) clorotalonil 75 g + tiofanato metilico; 30 g; (d) clorotalonil 125 g + tiofanato metilico 50 g; (e) clorotalonil 250 g + tiofanato metilico 100 g. A doenca foi avaliada uma unica vez, aos 78 DAP por meio de uma escala de notas de 0 a 9, baseada na porcentagem de area foliar doente. A severidade maxima foi observada aos 78 DAP na testemunha (26,5% de area foliar doente). Houve alta (r=-0,96) correlacao negativa entre os niveis da doenca nas folhas e a producao de frutos, com reducao de ate 19,2% na produtividade da melancia devido ao crestamento gomoso do caule. O controle quimico foi eficiente a partir da dosagem de clorotalonil 125 g + tiofanato metilico 50 g.

Management of wheat blast with synthetic fungicides, partial resistance and silicate and phosphite minerals

Field trials conducted on a yellow-red latossol (pH 6.0), replicated in 2010 and 2011, sought to examine the effect of silicon, phosphite minerals, synthetic fungicides and genetic resistance for wheat blast management (Magnaporthe grisea) in Central Brazil. Disease intensity was measured on cvs. BRS 264 and BR18 subjected to the following Si treatments: pre-plant furrow application of Ca & Mg silicate (300 kg ha-1); post-plant scattered application of Ca & Mg silicate on top of the soil (1 ton ha-1); multiple foliar SiO2 applications (30 g l-1); and non-treated control. Blast incidence and severity were scored. Further experiments were conducted on cv. BR-264, for examination of the effect of potassium phosphite and synthetic fungicides on wheat blast intensity, with the following treatments: K2HPO3 (1ml l-1); epoxinazole + pyraclostrobin (700 ml ha-1); tebuconazole (600 ml ha-1); tebuconazole + trifloxystrobin (750 ml ha-1); and non-treated control. In 2010, disease intensity was lower than in 2011. In the silicate experiments, disease was significantly lower when plants were treated with foliar or furrow silicate. Si applications significantly reduced disease in BRS-264. While BR-18 consistently demonstrated lower disease levels, cv. BRS-264 generally responded more markedly to silicon applications. In the phosphite/fungicide experiment of 2010, all treatments reduced disease when compared with the control, and in 2011 phosphite efficiency was not significantly different from some fungicide treatments. Synthetic fungicides demonstrated an average blast control of 55% by severity values. Yields were increased in the phosphite-treated plots (by 9–80%), in the Si treatments (by 26–92%), and more so, and more consistently, with synthetic fungicides (by 90–121%). Combined results of all field studies, carried out under environmental conditions highly conducive to disease, indicated that control of wheat blast necessitates the joint integration of several alternatives for efficient disease management.

Resistência de Didymella bryoniae a fungicidas no Brasil

Didymella bryoniae resistance to fungicides in Brazil Gummy stem blight (Didymella bryoniae) is one of the most important diseases of watermelon (Citrullus lanatus) wordwide. Chemical control, although widely adopted, cannot always avoid disease progress in the field. Resistance of the causal agent to some active ingredients has been reported in Europe, Japan and in the United States, but no such study has been done in Brazil. This work reports results of three in vitro assays for fungicide resistance, as measured by the rate of mycelial growth. In the first test, seven isolates were evaluated against nine fungicides at half the recommended commercial doses. Evidence of resistance to Methyl Thiophanate (TM) and Carbendazim (CARB) (Benzimidazoles) as well as to the mixture of Methyl-Thiophanate and Chlorotalonil (TM+CHLO) was detected. No resistance was suggested to Mancozeb, Difenoconazole, Tebuconazole and the mixtures Mancozeb + Difenoconazole or Trifloxistrobine + Propiconazole. The test was repeated with the same seven isolates of D. bryoniae against TM, CARB, TM+CHLO and Copper Oxichlorate at ¼, ½, 1 and 2 times the recommended doses. Only Copper Oxichlorate consistently caused a decrease in the mycelial growth rates with increasing doses. TM had no effect on the mycelial growth rates at any of the concentrations tested, and CARB and TM+CHLO showed very minor effects with increasing product concentrations. Finally, a collection of 31 isolates from seven Brazilian states was tested for resistance against TM at the recommended dose (490 ppm). Eighty-one per cent of the isolates, from most Brazilian states, proved to be highly resistant. Resistant and sensitive isolates were found in the same geographic regions. Considering the prevalence of isolates resistant to both TM and CARB, an evidence of cross-resistance, the use of benzimidazoles should be avoided for gummy stem blight control. Additional keywords: benzimidazoles, sensitivity to fungicides , Ascochyta cucumis.

Controle químico do crestamento gomoso do caule em melancia

This work reports the results of the effects of chemical control and nitrogen-potassium fertilization on gummy stem blight, one of the most important watermelon (Citrullus lanatus) diseases. Two factorial field assays were conducted in Projeto Formoso, Tocantins, in a randomized block design with four replicates. Experimental plots measured 30 x 10 m. Treatments for assay I were (factor a - active ingredients/100 l water or ha): (1) mancozeb (MANC)-160.2 ml, (2) methyl thiophanate (TM)-49 g, (3) carbendazin-500 ml, (4) tebuconazole-20 g, (5) difenoconazole (DIFE)-75 ml, (6) methyl thiophanate-40 g + chlorothalonil -100 g, (7) copper oxychlorate-168 g, (8) trifloxistrobina-87.5 g + propiconazole-87.5 g, (9) mancozeb-80 ml + difenoconazole-37.2 ml, and (10) control. Treatments for factor b were two levels of N-K fertilization: (1) 30-20, and (2) 90-60 kg/ha. Disease severity on leaves was evaluated on a 0 to 9 scale. For the assay II, treatments for factor a were repeated, while treatments for factor b were N-K fertilization levels (kg/ha) 60-40 and 120-80. On both assays, lowest Areas Under Disease Progress Curves (AUDPD), were obtained with MANC + DIFE, TM + chlorothalonil, MANC, trifloxistrobina + propiconazole and copper oxychlorate. Fertilization did not affect disease severity. Larger yields were obtained with TM + chlorothalonil, MANC + DIFE and MANC.

Development and validation of a diagrammatic scale for estimation of anthracnose on sweet pepper fruits for epidemiological studies.

SUMMARY A diagrammatic scale for the evaluation of anthracnose severity on sweet-pepper fruits, intended for epidemiological field studies was developed. One hundred symptomatic fruits were collected, photographed, and the images were digitally processed to quantify the percentage diseased area of one half of the fruit surface. Anthracnose symptoms ranged from apparently sound, healthy fruits, to fruits displaying more than 90% diseased area. Fruits were separated into nine classes, from class 0 (0% diseased area, sound fruits) to class 8 (81% or more diseased area), roughly following Horsfall and Barratt (1945) midpoint values. Validation was done with additional images of naturally-infected fruits, collected from a grower’s field, presented to 12 raters, half of them experienced and the other half relatively inexperienced. Evaluators’ subjective ratings, with and without use of the scale, were compared statistically to the actual severity values (calculated by Quant R software) by linear regression analysis, and the variance of absolute errors. The t-test was applied to check the null hypotheses of linear coefficient = 0 and angular coefficient b = 1. Use of the scale consistently improved accuracy and precision of all raters, bringing scores close to the real severity values. In addition, the scale proved easy to use in field experiments, allowing sequential evaluations in the same plots and fruits, as needed in temporal dynamic studies, and avoiding destructive sampling of infected fruit.

Reaction of melon genotypes to the gummy stem blight and the downy mildew

The gummy stem blight (Didymella bryoniae) and the downy mildew (Pseudoperonospora cubensis) are two foremost melon (Cucumis melo) diseases, considering their effects on yield and fruit quality. Despite the importance of such diseases, relatively few studies have been done so far on the identification of resistance sources to D. bryoniae and P. cubensis in Brazil. This work aimed at evaluating the resistance of commercial melon genotypes to the gummy stem blight and the downy mildew. Firstly, the most aggressive and representative D. bryoniae isolate was selected. Subsequently, the resistance of 86 melon genotypes to stem infection was studied upon greenhouse conditions by inoculating with the previously selected isolate. Afterwards, the resistance to mildew and leaf infection by D. bryoniae of 28 melon genotypes was evaluated in the field, under natural infection. In the greenhouse, all 86 melon genotypes were infected and showed stem infection symptoms caused by D. bryoniae four days after inoculation. Nevertheless, a significant variation on the resistance levels of the melon genotypes was found. Under field conditions and natural inoculation, genotypes Taslaki and Sary Juliabi were the most susceptible to leaf infection by D. bryoniae, significantly differing from the other genotypes. The lowest levels of susceptibility were identified in genotypes Perlita Busle S1, Valenciano Eliptico, Glaver, MR1, and 2526. All genotypes were susceptible to the downy mildew, albeit differing in susceptibility levels.

Management of strawberry anthracnose by choice of irrigation system, mulching material and host resistance

We studied, by means of field experiments, the combined effects of irrigation system, mulching material and genetic resistance on the incidence of strawberry anthracnose caused by Colletotrichum acutatum. All trials involved artificial inoculation with fruits colonized by the pathogen. One experiment examined the effects of drip irrigation, overhead sprinkler irrigation, and localized low-pressure tape irrigation, and the effects of grass (Brachiaria sp.) and plastic (polyethylene) mulches, in a split plot, randomized complete block design with four replicates. Lower disease incidence, indicating lower pathogen dispersal, was verified with low-pressure tape and drip irrigation. Flower blight and fruit rot incidence in drip-irrigated plots was minimal (ca. 2% of the disease levels in the plots otherwise irrigated). Grass mulch reduced flower blight in the sprinkler system (up to 80%), but had no significant effect when disease levels were already low due to use of other irrigation systems. A second experiment compared the effects of grass mulch, pine (Pinus elliotti) mulch, and plastic mulch with overhead sprinkler irrigation on strawberry cultivars partially resistant (‘Dover’) and susceptible (‘Campinas’) to the disease in a factorial completely randomized design (CRD). Both organic mulches reduced flower blight and diseased fruit incidence by up to 76% compared to the plastic mulch treatment, especially in the early stages of the epidemics. ‘Dover’ had 70% lower incidence of flower blight than ‘Campinas’, and the effects of organic mulches were more pronounced in ‘Campinas’. A third experiment, with all three irrigation systems combined with inoculated and non-inoculated plots, estimated yield effects due to disease and irrigation system. All plots were covered with plastic mulch in a CRD with six treatments. This experiment clearly confirmed the higher flower blight and fruit rot incidences when sprinkler irrigation was used. In inoculated treatments, fruit yield was significantly reduced in tape-irrigated plots, and more so in sprinkler-irrigated plots. In drip-irrigated plots yield was reduced by only 1%. Overall, our results confirm the importance of cultural and genetic factors as valuable means of strawberry anthracnose management. Adoption of localized irrigation systems, the use of organic mulches and choice of a partially resistant cultivar significantly reduced disease levels in field plots. The importance of water splash for C. acutatum dispersal and its dependency on the soil mulch characteristics are the likely causes for the results observed.

First report of Alternaria brassicicola on Crambe abyssinica in Goiás state, Brazil

ofseed having inedible oil content of about 38 %. Low water requirement,short crop cycle of about 90 days, rusticity, and the possibility ofcultivating between main cropping seasons, has attracted attentionfor its use as feed stock for biodiesel production. It is estimated thatin 2009 the crop was raised on about 10000 ha.In May 2009, at Rio Verde –GO lower leaves of plants (FMSBrilhante cultivar) showed initially grey necrotic spots (Fig1A), andas the disease progressed, they were covered with concentric zonesand encircled with a chlorotic halo. Severely affected leaves showedpremature senescence (Fig 1B). Intense dark sporulation was observedon the lesions. The clavate conidia produced on dark elongateconidiophores (Fig. 1C) with transverse and longitudinal septa wereformed in chains (Fig. 1D). The fungus was identified as

Temporal and spatial dynamics of watermelon gummy stem blight epidemics

The effect of the distance of initial inoculum on the intensity of watermelon gummy stem blight, caused by Didymella bryoniae, was studied in a naturally-infected rainfed commercial field. The shorter the distance from the focus, the sooner was disease onset and the earlier maximum disease levels were achieved. Maximum disease incidences were reached earlier than maximum severities, but eventually destructive levels were observed for both disease incidence and severity. Disease progressed at similar rates, irrespective of the radial distance from the focus. A detailed study of the disease temporal progress was conducted in inoculated rainfed experimental fields with commercial genotypes Crimson Sweet (susceptible, S) and Riviera (moderately resistant, R). The Gompertz model best described the disease progress curves, and estimated apparent infection rates were 0.049 and 0.020 respectively for S and R genotypes. In addition, spatial pattern studies were conducted during the dry season in overhead irrigated experimental plots, inoculated with point-source foci. Disease intensity gradients were better explained by the Exponential model than by the Power Law model. Gummy stem blight distribution was classified as aggregated by the Ordinary Runs procedure. Two different spatial autocorrelation methods (2DCorr and LCOR) revealed strong short distance spatial dependencies. Long distance positive correlations between quadrats were observed along with periods of higher progress rates. The dynamic patterns of the epidemics of gummy stem blight in watermelon described here are consistent with epidemics of polycyclic diseases with splash-dispersed spores.

Impact of anthracnose on the yield of soybean subjected to chemical control in the north region of Brazil

Losses due to soybean anthracnose, caused by Colletotrichum truncatum, have not been systematically quantified in the field, and the efficacy of chemical control of this disease is not known. This study shows an estimate of losses associated with the disease in soybean crops in the north of the country. Two trials with cv. M9144 RR were carried out in commercial fields in Tocantins State in the 2010/2011 and 2011/2012 growing seasons, in randomized blocks, with four replicates. Foliar applications were performed on plants at R1/R2 and R5.2 stages, employing CO2-pressurized equipment and application volume of 200 L ha-1. Nine fungicides and one untreated control were compared, and the disease gradients in the two seasons were obtained. The percentage of infected pods was calculated at the R6 stage. Grain yield ranged from 3,288 to 3,708 kg/ha in the untreated plots in 2010/2011 and 2011/2012, respectively, and from 3,282 to 4,110 kg/ha in the treated plots. In the 2010/2011 season, only azoxystrobin + cyproconazole significantly reduced the disease incidence, compared to untreated control plots, not differing from the remaining treatments. In the 2011/2012 season, there were no significant differences between treated and untreated plots. Highly significant correlations (p < 0.01) were found between yield and soybean anthracnose incidence on pods in both years (r = -0.85). For each 1% increment in the disease incidence, c. 90 kg/ha of soybean grain were lost. The current study determined that significant losses due to anthracnose occur in commercial crops in the north of the country and highlighted the limitation of chemical control as anthracnose management method.