Fusarium Head Blight (FHB) is a disease of great concern in wheat (Triticum aestivum). Due to its relatively narrow susceptible phase and environmental dependence, the pathosystem is suitable for modeling. In the present work, a mechanistic model for estimating an infection index of FHB was developed. The model is process-based driven by rates, rules and coefficients for estimating the dynamics of flowering, airborne inoculum density and infection frequency. The latter is a function of temperature during an infection event (IE), which is defined based on a combination of daily records of precipitation and mean relative humidity. The daily infection index is the product of the daily proportion of susceptible tissue available, infection frequency and spore cloud density. The model was evaluated with an independent dataset of epidemics recorded in experimental plots (five years and three planting dates) at Passo Fundo, Brazil. Four models that use different factors were tested, and results showed all were able to explain variation for disease incidence and severity. A model that uses a correction factor for extending host susceptibility and daily spore cloud density to account for post-flowering infections was the most accurate explaining 93% of the variation in disease severity and 69% of disease incidence according to regression analysis.
do trigo -aspectos epidemiológicos e modelos de previsão. Fitopatologia Brasileira 29: 587-605. 2004. RESUMOA giberela ou fusariose da espiga é, atualmente, uma das mais importantes doenças da cultura do trigo (Triticum aestivum). Epidemias severas têm sido observadas nos últimos anos em diversas regiões do mundo, promovendo perdas na produtividade e na qualidade dos grãos. No Brasil, a giberela alcançou o status de principal doença nas regiões tritícolas, principalmente no Sul do Brasil. A sua natureza esporádica está associada à dependência climática, sendo as mais severas epidemias observadas em anos com maior freqüência de chuvas, durante a fase de florescimento e enchimento de grãos. Poucas são as cultivares com resistência genética aceitável e essas normalmente falham em anos muito favoráveis a epidemias. Medidas de controle com fungicidas têm sido preconizadas, entretanto, a dificuldade reside no momento e na tecnologia de aplicação, para se obter resultados satisfatórios. O melhor entendimento dos fatores que influenciam a dinâmica da doença pode auxiliar no manejo da cultura visando a minimizar os riscos de epidemias. Aspectos como aerobiologia e tipo de inóculo, distribuição espacial e gradiente espacial da doença podem contribuir no conhecimento da associação e a importância de fontes de inóculo local ou distante ao campo. Recentemente, uma grande atenção tem sido dada ao desenvolvimento de modelos de previsão ou de risco de giberela. Tais modelos podem auxiliar na tomada de decisão no acionamento de medidas de controle bem como alertar níveis epidêmicos da doença em uma determinada região, ou mesmo quanto à alta contaminação do trigo com micotoxinas de Fusarium spp.Palavras-chave adicionais: Fusarium graminearum, simulação de epidemias, modelos de risco, distribuição espacial, aerobiologia, Gibberella zeae. ABSTRACT Fusarium head blight of wheat -Epidemiological aspects and forecast modelsFusarium Head Blight (FHB) is one of the most important wheat (Triticum aestivum) diseases worldwide. Severe epidemics have been recently reported in various countries, causing great losses in yield and grain quality. In Brazil, FHB emerged in the last decade as a disease of great concern, mainly in the Southern region. The sporadic nature of the epidcmics is related to strong weather dependence. Epidemic levels are observed in years with a high frequency of rain occurring from flowering to grain filling developmental stages. Most wheat varieties are susceptible and few show acceptable genetic resistance. Fungicides applied at flowering, sometimes, can help in preventing economic losses but their efficacy is dependent on application timing and technology for a good spike covering. A better understanding of the many factors influencing disease occurrence and development is needed for better disease management to minimize risks. Studies on the aerobiology, importance of spore types and spatial and temporal patterns of the disease may contribute to develop hypotheses regarding the association and importance of local ve...
This thesis is devoted to my dearest ones, my family, whose love and trust encouraged me to achieve: My wife, Carmen, for her permanent support and endurance, son, Jose Mauricio, and my daughter, Carmen Alexandra, for their understanding, my parents, Fidel and Antonia, for their foresight, my brothers, for their encouragement, and the Lord, God, for all that has given me.
El grupo Chiliotrichum sensu stricto pertenece a la familia ASTERACEAE, tribu ASTEREAE, subtribu Hintemuberinae, se compone de 17 especies reunidas en ocho géneros: Ayfacophora deserticola, Cabreraea andina, Chiliophyttum densifolium, Chiliotrichiopsis keidelii, C. ledifolia, C. medndodna, Chiliotrichum diffusion, C. fuegianum, Lepidophytlum cupressiforme, Nardophyllum armatum, N. bryoides, N. cabrerae, N. chiliotrichioides, N. genistoides, N. lanatum, Paleaepappus patagonicus y Weigforthia peruviana, y se distribuye en la region Andino-Patagónica del extremo sur de América del Sur. Se discute el grupo Chiliotrichum sensu lato comprendido por el grupo Chiliotrichum sensu stricto mas los géneros Ericameria, Diplostephium, Llerasia, Oritrophium, Parastrephia y Pteronia, con el fin de estabecer los límites del grupo estudiado. Se presenta una clave para la identificación de los géneros del grupo Chiliotrichum sensu stricto, y para cada género se detalla, la lista de sinónimos, especie tipo, descripción, y se elaboraron claves dicotómicas para la identificación de las especies integrantes. Para cada especie se presenta lista sinonímica, descripción ampliada, observaciones, lamina ilustrando aspectos morfólogicos y mapa de distribución geográfica. Adicionalmente, para todas las especies excepto Nardophyllum genistoides y Weigforthia peruviana se presentan láminas con fotografías que ilustran el hábito y hábitat de las especies y complementan las ilustraciones morfológicas.
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