Carlos Alberto Forcelini

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.

Efeitos da rotação de cultura, de cultivares e da aplicação de fungicida sobre o rendimento de grãos e doenças foliares em soja

A rotacao de culturas e um metodo eficiente e de baixo custo para o controle de doencas de final de ciclo (DFC) da soja (Glycine max). Em experimentos de campo, nas safras 1998/99 e 2000/01, avaliaram-se os efeitos da rotacao de culturas de verao, com os sistemas soja e milho (Zea mays), de diferentes ciclos e cultivares de soja e da aplicacao de fungicidas, sobre a ocorrencia e intensidade das DFC. Na safra 98/99, detectou-se diferenca significativa no rendimento de graos na comparacao da media dos dois sistemas (soja/soja e soja/milho), devido, principalmente, ao controle da podridao-parda da haste, que causou danos em monocultura. Nao houve diferenca significativa para o uso de fungicida na parte aerea na safra 98/99 para o rendimento. Na safra 00/01 nao houve efeito significativo da rotacao para intensidade de oidio e DFC. A aplicacao de fungicidas proporcionou menor severidade do oidio e das DFC, diferindo significativamente da testemunha em todos as cultivares. Em relacao a severidade do oidio e das DFC houve diferencas significativas para a aplicacao de fungicida. A maior resposta em rendimento de graos foi obtida nas cultivares suscetiveis ao oidio. Os maiores rendimentos de graos foram detectados quando a soja foi cultivada em rotacao com o milho e com a aplicacao de fungicidas, principalmente nas cultivares suscetiveis ao oidio, e na safra 00/01 devido a maior precipitacao pluvial onde houve maior severidade de DFC.

Comparação de métodos para detecção de Bipolaris sorokiniana em sementes de cevada

Comparison of methods for the detection of Bipolaris sorokiniana in barley seeds The fungus Bipolaris sorokiniana, the causal agent of the brown spot of barley (Hordeum vulgare), survives as mycelium in infected seeds or saprofiticaly on host plant debris. In lab experiments, various methods for seed testing (blotter test; blotter test + liquid components of the Reis selective medium; PDA medium; tomato paste medium; V-8 medium; Reis selective medium, and the Dodman & Reinke selective medium) were compared regarding the detection of B. sorokiniana in barley seeds. The selective media, especially the Reis medium, were more sensitive than the PDA and the blotter tests. Seed freezing (- 20 °C for 16 h) prior to incubation did not improve the fungus detection and determined similar results for all methods.

Diagrammatic scale for the assessment of blast on wheat spikes

The correct quantification of blast caused by the fungus Magnaporthe oryzae on wheat (Triticum aestivum) spikes is an important component to understand the development of this disease aimed at its control. Visual quantification based on a diagrammatic scale can be a practical and efficient strategy that has already proven to be useful against several plant pathosystems, including diseases affecting wheat spikes like glume blotch and fusarium head blight. Spikes showing different disease severity values were collected from a wheat field with the aim of elaborating a diagrammatic scale to quantify blast severity on wheat spikes. The spikes were photographed and blast severity was determined by using resources of the software ImageJ. A diagrammatic scale was developed with the following disease severity values: 3.7, 7.5, 21.4, 30.5, 43.8, 57.3, 68.1, 86.0, and 100.0%. An asymptomatic spike was added to the scale. Scale validation was performed by eight people who estimated blast severity by using digitalized images of 40 wheat spikes. The precision and the accuracy of the evaluations varied according to the rater (0.82<R2<0.90, -6.12<a<2.94, 0.85<b<1.16), and systematic errors in overestimating or underestimating the disease were not found among the raters, demonstrating that the developed scale is suitable to evaluate blast on wheat spikes.

Efeito da temperatura e de fungicida na transmissão de Bipolaris sorokiniana da semente para plântulas de cevada

The transmission of seed-borne pathogens and the infection of the host plants are influenced by ambient conditions, mainly temperature and soil moisture. This research studied the effects of temperature and fungicide on the transmission of Bipolaris sorokiniana from seeds to above and below ground barley (Hordeum vulgare) plant parts. The rate of transmission and the potential for fungus sporulation on the apice of coleoptiles were also quantified. These studies involved two seed samples (treated or not treated with the fungicide iminoctadine at 70 g a.i./100 kg seed) sown in non-sterilized field soil at five temperatures (10, 15, 20, 25, and 30 oC). An additional trial was conducted in sand soil, at 25 °C, to follow the fungus transmission over a period of 35 days. The relationships of temperature to transmission were represented by quadratic model equations. The observed and estimated fungus transmissions were higher at 18 - 25 oC and 18.1 - 21.3 oC, respectively. The fungus sporulation was also influenced by temperature and reached its maximum at 19.3 oC. The infection of barley coleoptiles initiated ten days after planting and increased steadily for more than 28 days.

Ação do acibenzolar-S-metil aplicado em tubérculos e plantas de batata contra canela preta, incitada por Pectobacterium carotovorum subsp. atrosepticum atípica

Systemic acquired resistance is an important mechanism of resistance to diseases in plants. In this research, the action of acibenzolar-S-methyl (ASM), a benzothiadiazole inductor of resistance in plants, was evaluated regarding tuber sprout and induction of resistance in potato (Solanum tuberosum) plants. At 60, 120, 150, 200, and 250 mg a.i. l -1, ASM did not inhibit bud number. However, in higher concentrations it decreased bud length. In the greenhouse, ASM was applied (60 and 120 mg a.i. l -1) to tubers and plants of the cultivars Asterix, Baronesa, and Monalisa. In the Asterix cultivar, ASM induced resistance to blackleg. In Baronesa cultivar plants, resistance to blackleg was achieved with tuber treatment with ASM. In Monalisa cultivar, the ASM did not induce resistance to the disease. In conclusion, the role of ASM in inducing resistance to blackleg seems to be cultivar specific.

Efeito do substrato na morfologia de conídios de Bipolaris sorokiniana e da densidade de inóculo na intensidade da mancha marrom em cevada

The fungus Bipolaris sorokiniana causes brown spot, a barley (Hordeum vulgare) disease, worldwide. Identification of the fungus is based mainly on the morphology of its conidia, whose size and septation may be altered by many factors. This research studies the effect of growing substrates on the size, septation, and morphology of conidia, as well as the relationship of inoculum density to disease intensity. The various substrates included six culture media, seeds, and fresh leaves of barley, wheat (Triticum aestivum), rye (Secale cereale), and triticale (Triticum secalotricum). Conidia formed in culture media (68,2 × 21,9 mm; 5,7 pseudosepta) and on seeds (78,3 × 20,4 mm; 7,2 pseudosepta) were shorter, wider, and with less septa than those from leaf lesions (92,9 × 18,2 mm; 7,7 pseudosepta). The effect of the inoculum density (ID) on disease intensity (DI) was tested by applying spore suspensions (2.5 x 103, 5.0 x 103, 10.0 x 103, 15.0 x 103, and 20.0 x 103 conidia/ml) to plants of the barley cultivar BR-2. The ID/DI relationship was represented by a quadratic model equation, in which the maximum values of 183 lesion/leaf and 79% disease severity were obtained with 16.500 and 14.000 conidia/ml, respectively. The number of conidia required for one leaf lesion was estimated in 50 to 90.

Freqüência de Alternaria dauci E Cercospora carotae como agentes da queima das folhas da cenoura em Passo Fundo, RS

Carrot (Daucus carota) leaf blights can be induced by both Alternaria dauci and Cercospora carotae fungi. In an attempt to establish a spray advisory system for such disease, the frequency of each pathogen was determined in carrot fields located in Passo Fundo (RS), from August/98 to December/99. The incidence of each fungus on seeds, seedlings, and adult plants (leaves and petioles), as well as the number of airborne propagules captured by spore trapping devices, were quantified. The seed-borne inoculum in nine carrot cultivars ranged from zero to 5.75% for A. dauci and from zero to 1.25% for C. carotae. Only A. dauci was found in greenhouse grown seedlings of the carrot cultivars Forto (3.7%) and Gigante Flakker (17.1%). The fungus A. dauci occurred during the whole year in the field, and was isolated from 81% of foliar lesions and 81.9% from petioles. On the other hand, C. carotae was found from June to December in 40.4% of diseased leaves and 33.4% of petioles. The number of airborne spores of A. dauci reached 207/week/cm2 at the harvest. Alternaria dauci was shown to be the main pathogen causing carrot leaf blight in local conditions. Therefore, adoption of control strategies should be A. dauci oriented.

Lesion expansion of barley net blotch and its interaction with seed treatment.

Experimentos foram conduzidos na FAMV/UPF, em 2002, com o objetivo de avaliar a influencia do tratamento de sementes no processo de expansao de lesao pela mancha-reticular da cevada (Hordeum vulgare). Utilizaram-se as cultivares BR 2 e MN 698, com e sem tratamento de sementes com o fungicida triadimenol (40 g i.a./100 kg sementes), combinado com aplicacoes foliares de um fungicida triazol (tebuconazole) e uma combinacao de triazol e estrobirulina (epoxiconazole + piraclostrobim), sob uma ou duas aplicacoes, em diferentes estadios fenologicos da planta. O tamanho das lesoes e a severidade da doenca foram avaliadas aos 62, 79, 88, 95, 103 e 111 dias apos a semeadura. O tamanho da lesao foi significativamente menor nas plantas a partir de sementes com baixa incidencia do patogeno, de sementes tratadas e plantas pulverizadas com fungicidas foliares. O numero de aplicacoes, se uma ou duas, e o tipo de fungicida nao influenciaram o tamanho das lesoes. A severidade da mancha-reticular foi pequena, especialmente sob tratamento de sementes. Evidenciou-se o efeito restritivo do tratamento de sementes sobre o crescimento das lesoes, o qual e um componente importante de epidemias por manchas foliares em cevada.

Lesion expansion by barley leaf spots and its interaction with fungicidal sprays

Brown spot and net blotch, caused by the fungi Bipolaris sorokiniana and Pyrenophora teres, respectively, are the main leaf spots of barley (Hordeum vulgare). The rate of lesion expansion is an important epidemiological component of leaf spots and should be taken into account for disease management. Through greenhouse and field trials, lesion expansion was assessed in barley cultivars, under preventive and curative sprays of triazol (cyproconazole + propiconazole) and strobylurin (azoxystrobin) fungicides. In the greenhouse, the average area of brown spot lesions increased from 2.2 to 4.9 mm2, most of which occurred between 14 and 30 days after inoculation. The cultivars MN 698 and EMB 128 showed a higher rate of lesion expansion than BR 2, EMB 127, EMB 129, and MN 684. A single preventive spray of fungicide averted infection by B. sorokiniana for over 21 days. In contrast, curative sprays carried out at one, two, four, six, eight, ten, or 12 days after inoculation, although inhibiting fungus sporulation, also resulted in initial lesions that were larger (up to 0.68 mm2) and more numerous (up to 3.9 per leaf). In the field, only the spray programs initiated at 46 to 60 days after plant emergence were able to reduce lesion size and the area under the disease progress curve (AACPD) for net blotch, which increased grain yield. Because fungicides had little or no curative effect on lesion expansion, fungicidal sprays based on disease severity should be reevaluated.