Fitopatologia - Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11741
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Item Variáveis climáticas associadas à incidência de mofo-cinzento em eucalipto(Fitopatologia Brasileira, 2006-03) Mafia, Reginaldo G.; Alfenas, Acelino C.; Ferreira, Eraclides M.; Leite, Fernando Palha; Souza, Flávio Luiz deCom base em dados de infecção natural avaliou-se a incidência do mofo-cinzento, causado por Botrytis cinerea, em 14 clones de Eucalyptus spp. em relação às condições climáticas predominantes em um viveiro clonal localizado em Belo Oriente, Minas Gerais. A temperatura máxima, mínima e média, precipitação pluviométrica e umidade relativa do ar foram coletadas entre 1991 e 2004. A incidência da doença foi avaliada mensalmente em 2004 em todas as fases de produção de mudas clonais de eucalipto. A presença do patógeno foi avaliada na água coletada do efluente de fertirrigação. A incidência do mofo-cinzento correlacionou-se melhor e negativamente com a temperatura máxima. Os resultados indicaram que a temperatura máxima é a variável a ser monitorada para fins de previsão da doença, a qual apresenta alto risco de incidência quando a temperatura máxima registrada for inferior a 27 ºC. Dentre os 14 clones propagados em 2004, o clone 957 (híbrido de Eucalyptus urophylla) apresentou menor incidência da doença, sob condições de infecção natural. Observou-se que o fungo encontra-se comumente associado a mudas de eucalipto e que o desenvolvimento da epidemia é regulado por temperaturas amenas, uma vez que, condições de alta umidade relativa e presença de água livre no hospedeiro ocorrem constantemente, em virtude das freqüentes irrigações requeridas para produção de mudas. Constatou-se que a água reutilizada, coletada no efluente de irrigação, contém inóculo do patógeno.Item Condições de ambiente favoráveis à germinação e à infecção de Puccinia substriata var. penicillariae em diferentes cultivares de milheto pérola(Fitopatologia Brasileira, 2007-09) Costa, Antonio Carlos T.; Carvalho, Aldir O.; Soares, Dartanhã J.; Carmo, Margarida Goréte F.; Pimentel, CarlosA ferrugem do milheto (Pennisetum glaucum), causada por Puccinia substriata var. penicillariae, provoca perdas na produção da forragem. Tendo em vista a escassez de informações sobre a doença no Brasil realizou-se o presente trabalho sobre a sua epidemiologia. Avaliaram-se, em casa-de-vegetação, o período latente médio, a freqüência de infecção e tamanho das lesões da ferrugem em quatro genótipos de milheto: ENA 1, Composto II, BRS 1501 e HKP. In vitro, monitorou-se a germinação dos urediniósporos em diferentes temperaturas (10, 15, 20 e 25ºC), na presença ou não de luz. Após isto, avaliou-se o processo de infecção nos genótipos Guerguera, Souna III, BRS 1501 e ENA 1, em câmara de crescimento, utilizando-se 0, 1, 2, 4, 8 e 12 h de molhamento foliar, na presença ou não de luz, e em casa-de-vegetação, nos genótipos ENA 1, Guerguera e Souna III, utilizando-se 3/4, 1, 2, 4, 6 e 8 h de molhamento foliar. O período latente médio da ferrugem do milheto variou entre 10 e 12 dias, e os urediniósporos germinaram em faixa ampla de temperatura, de 10ºC a 25ºC, na presença ou não de luz, com germinação máxima a 17,5ºC no escuro. Nestas condições, os primeiros esporos germinaram com menos de 45 min. e atingiram taxa máxima, 88,2%, em 1,7 h de incubação. Infecções de folhas foram observadas em plantas submetidas a apenas 45 min de molhamento foliar após a inoculação, porém, com efeito benéfico do escuro e do aumento do período de molhamento foliar.Item Aggressiveness and host specificity of Brazilian isolates of Phytophthora infestans(Plant Pathology, 2004-08) Suassuna, N. D.; Maffia, L. A.; Mizubuti, E. S. G.The population of Phytophthora infestans in Brazil consists of two clonal lineages, US-1 associated with tomatoes and BR-1 associated with potatoes. To assess whether host specificity in these lineages resulted from differences in aggres- siveness to potato and tomato, six aggressiveness-related epidemiological components – infection frequency (IF), incu- bation period (IP), latent period (LP), lesion area (LA), lesion expansion rate (LER) and sporulation at several lesion ages (SSLA) – were measured on detached leaflets of late blight-susceptible potato and tomato plants. Infection frequency of US-1 was similar on potato and tomato leaflets, but IF of BR-1 was somewhat reduced on tomato. Incubation period was longer on both hosts with US-1, although this apparent lineage affect was not significant. Overall there was no host effect on IP. On potato, BR-1 had a shorter LP (110·3 h) and a larger LA (6·5 cm 2 ) than US-1 (LP = 162·0 h; LA = 2·8 cm 2 ). The highest LER resulted when isolates of BR-1 (0·121 cm 2 h −1 ) and US-1 (0·053 cm 2 h −1 ) were inoculated on potato and tomato leaflets, respectively. The highest values of the area under the sporulation capacity curve (AUSC) were obtained for isolates of US-1 inoculated on tomato leaflets (6146) and for isolates of BR-1 on potato leaflets (3775). In general, higher values of LA, LER, SSLA and AUSC, and shorter values of LP were measured when isolates of a clonal lineage were inoculated on their original host than with the opposite combinations. There is evidence that there are quan- titative differences in aggressiveness components between isolates of US-1 and BR-1 clonal lineages that probably con- tribute to host specificity of P. infestans populations in Brazil.Item Biocontrol of tomato late blight with the combination of epiphytic antagonists and rhizobacteria(Biological Control, 2006-09) Lourenço Júnior, Valdir; Maffia, Luiz A.; Romeiro, Reginaldo da Silva; Mizubuti, Eduardo S. G.Control of tomato late blight (LB) in Brazil is heavily based on chemicals. However, reduction in fungicide usage is required in both conventional and organic production systems. Assuming that biological control is an alternative for LB management, 208 epiphytic microorganisms and 23 rhizobacteria (RB) were isolated from conventional and organically grown tomato plants and tested for antagonistic activity against Phytophthora infestans. Based on in vitro inhibition of sporangia germination and detached leaflet bioassays, four EP microorganisms (Aspergillus sp., Cellulomonas flavigena, Candida sp., and Cryptococcus sp.) were selected. These microorganisms were applied either singly or combined on tomato plants treated or not with the RB Bacillus cereus. On control plants, LB progress rate (r), area under disease progress curve, and final disease severity were high. Lowest values of final severity were recorded on plants colonized by B. cereus and treated with C. flavigena, Candida sp. and Cryptococcus sp. There was no reduction on disease severity in plants treated only with RB. Biological control of LB resulted in low values of r and final severity. Integration of biological control with fungicides, cultural practices, and other measures can contribute to manage LB on tomato production systems.Item Validation of decision support systems for tomato early blight and potato late blight, under Brazilian conditions(Crop Protection, 2006-07) Batista, D. C.; Lima, Marcello Arrais; Haddad, Fernando; Maffia, Luiz Antônio; Mizubuti, E. S. G.Early and late blight are the most important foliar diseases of tomato and potato crops in Brazil. Decision support systems (DSS) are important tools in reducing the large amount of fungicides applied to suppress disease intensity. Systems developed for early or late blight were validated in two cropping seasons under Brazilian conditions. For tomato early blight, FAST, CUFAST, and TOMCAST systems were compared in the spring–summer (September–December) (SS) 2002 and summer–autumn (January–April) (SA) 2003. In both seasons, area under disease progress curve (AUDPC) values for FAST (123.2 and 340.3, respectively) and CUFAST (64.0 and 359.2, respectively) did not differ from calendar-based treated plots (82.5 and 225.7, respectively). Plots treated according to TOMCAST were sprayed once and AUDPC values (369.9 and 697.8) in SS and SA seasons, respectively, did not differ from the control plots (397.5 and 836.0, respectively). In SS, four fungicide sprays were recommended by CUFAST and FAST, whereas five were set by fixed calendar treatment; there were no differences in yield loss among treatments. In SA, FAST, CUFAST and calendar, recommended 4, 9, and 11 sprays, respectively. Higher yields were recorded in plots sprayed according to the calendar system compared to control plots, but there were no significant differences between the DSS and the calendar system. For potato late blight, BLITECAST, SIMCAST, NegFry, and Wallin systems were compared in the summer (December–March) and in the autumn (March–June). Despite no late blight developing in the summer, all systems recommended fungicide sprays. In the autumn–winter, late blight was severe but was reduced by fungicide applications according to all DSS, but the number of sprays was similar to the calendar. The AUDPC values in control plots (1193.5) were higher than BLITECAST (19.5), SIMCAST (97.7), NegFry (193.1), Wallin (69.7), and calendar (63.5) but there were no differences among AUDPC values in plots treated according to DSS. The NegFry and Wallin systems recommended five and the calendar six sprays. All DSS were as effective as the calendar treatment in reducing AUDPC. FAST and Wallin were the most effective systems in forecasting tomato early blight and potato late blight, respectively. Decision support systems are potentially useful tools for integrated management of both diseases in Brazil.