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Disease Cycle (disease + cycle)
Selected AbstractsA dynamic simulation model for powdery mildew epidemics on winter wheat,EPPO BULLETIN, Issue 3 2003V. Rossi A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991,98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics. [source] cAMP blocks MAPK activation and sclerotial development via Rap-1 in a PKA-independent manner in Sclerotinia sclerotiorumMOLECULAR MICROBIOLOGY, Issue 1 2005Changbin Chen Summary Sclerotinia sclerotiorum is a filamentous ascomycete phytopathogen able to infect an extremely wide range of cultivated plants. Our previous studies have shown that increases in cAMP levels result in the impairment of the development of the sclerotium, a highly differentiated structure important in the disease cycle of this fungus. cAMP also inhibits the activation of a S. sclerotiorum mitogen-activated protein kinase (MAPK), which we have previously shown to be required for sclerotial maturation; thus cAMP-mediated sclerotial inhibition is modulated through MAPK. However, the mechanism(s) by which cAMP inhibits MAPK remains unclear. Here we demonstrate that a protein kinase A (PKA)-independent signalling pathway probably mediates MAPK inhibition by cAMP. Expression of a dominant negative form of Ras, an upstream activator of the MAPK pathway, also inhibited sclerotial development and MAPK activation, suggesting that a conserved Ras/MAPK pathway is required for sclerotial development. Evidence from bacterial toxins that specifically inhibit the activity of small GTPases, suggested that Rap-1 or Ras is involved in cAMP action. The Rap-1 inhibitor, GGTI-298, restored MAPK activation in the presence of cAMP, further suggesting that Rap-1 is responsible for cAMP-dependent MAPK inhibition. Importantly, inhibition of Rap-1 is able to restore sclerotial development blocked by cAMP. Our results suggest a novel mechanism involving the requirement of Ras/MAPK pathway for sclerotial development that is negatively regulated by a PKA-independent cAMP signalling pathway. Cross-talk between these two pathways is mediated by Rap-1. [source] Phymatotrichum (cotton) root rot caused by Phymatotrichopsis omnivora: retrospects and prospectsMOLECULAR PLANT PATHOLOGY, Issue 3 2010SRINIVASA RAO UPPALAPATI SUMMARY Phymatotrichum (cotton or Texas) root rot is caused by the soil-borne fungus Phymatotrichopsis omnivora (Duggar) Hennebert. The broad host range of the fungus includes numerous crop plants, such as alfalfa and cotton. Together with an overview of existing knowledge, this review is aimed at discussing the recent molecular and genomic approaches that have been undertaken to better understand the disease development at the molecular level with the ultimate goal of developing resistant germplasm. Taxonomy:Phymatotrichopsis omnivora (Duggar) Hennebert [synonym Phymatotrichum omnivorum (Shear) Duggar] is an asexual fungus with no known sexual stage. Mitosporic botryoblastospores occasionally form on epigeous spore mats in nature, but perform no known function and do not contribute to the disease cycle. The fungus has been affiliated erroneously with the polypore basidiomycete Sistotrema brinkmannii (Bres.) J. Erikss. Recent phylogenetic studies have placed this fungus in the ascomycete order Pezizales. Host range and disease symptoms: The fungus infects most dicotyledonous field crops, causing significant losses to cotton, alfalfa, grape, fruit and nut trees and ornamental shrubs in the south-western USA, northern Mexico and possibly parts of central Asia. However, this fungus does not cause disease in monocotyledonous plants. Symptoms include an expanding tissue collapse (rot) of infected taproots. In above-ground tissues, the root rot results in vascular discoloration of the stem and rapid wilting of the leaves without abscission, and eventually the death of the plant. Characteristic mycelial strands of the pathogen are typically present on the root's surface, aiding diagnosis. Pathogenicity: Confocal imaging of P. omnivora interactions with Medicago truncatula roots revealed that infecting hyphae do not form any specialized structures for penetration and mainly colonize cortical cells and eventually form a mycelial mantle covering the root's surfaces. Cell wall-degrading enzymes have been implicated in penetration and symptom development. Global gene expression profiling of infected M. truncatula revealed roles for jasmonic acid, ethylene and the flavonoid pathway during disease development. Phymatotrichopsis omnivora apparently evades induced host defences and may suppress the host's phytochemical defences at later stages of infection to favour pathogenesis. Disease control: No consistently effective control measures are known. The long-lived sclerotia and facultative saprotrophism of P. omnivora make crop rotation ineffective. Chemical fumigation methods are not cost-effective for most crops. Interestingly, no genetic resistance has been reported in any of the susceptible crop species. [source] Physiology and molecular aspects of Verticillium wilt diseases caused by V. dahliae and V. albo-atrumMOLECULAR PLANT PATHOLOGY, Issue 2 2006EMILIE F. FRADIN SUMMARY Introduction:,Verticillium spp. are soil-borne plant pathogens responsible for Verticillium wilt diseases in temperate and subtropical regions; collectively they affect over 200 hosts, including many economically important crops. There are currently no fungicides available to cure plants once they are infected. Taxonomy:, Kingdom: Fungi, phylum: Ascomycota, subphylum, Pezizomycotina, class: Sordariomycetes, order: Phyllachorales, genus: Verticillium. Host range and disease symptoms:, Over 200 mainly dicotyledonous species including herbaceous annuals, perennials and woody species are host to Verticillium diseases. As Verticillium symptoms can vary between hosts, there are no unique symptoms that belong to all plants infected by this fungus. Disease symptoms may comprise wilting, chlorosis, stunting, necrosis and vein clearing. Brown vascular discoloration may be observed in stem tissue cross-sections. Pathogenicity:,Verticillium spp. have been reported to produce cell-wall-degrading enzymes and phytotoxins that all have been implicated in symptom development. Nevertheless, evidence for a crucial role of toxins in pathogenicity is inconsistent and therefore not generally accepted. Microsclerotia and melanized mycelium play an important role in the disease cycle as they are a major inoculum source and are the primary long-term survival structures. Resistance:, Different defence responses in the prevascular and the vascular stage of Verticillium wilt diseases determine resistance. Although resistance physiology is well established, the molecular processes underlying this physiology remain largely unknown. Resistance against Verticillium largely depends on the isolation of the fungus in contained parts of the xylem tissues followed by subsequent elimination of the fungus. Although genetic resistance has been described in several plant species, only one resistance locus against Verticillium has been cloned to date. Useful website:,http://cbr-rbc.nrc-cnrc.gc.ca/services/cogeme/ [source] Well-being changes in response to 30 years of regional integration in Maya populations from Yucatan, MexicoAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2001Francisco D. Gurri Infant mortality rate (IMR), overall frequency of linear enamel hypoplasia (LEH), sexual dimorphism in LEH, age of onset of LEH, and age at menarche were used as indicators to test the hypothesis that the origin and development of the tourist industry and increased state participation on Maya subsistence agriculturists in the early 1970s had improved the well-being of the Maya. Two historical moments where inferred from the data. The first was derived from cheap and effective immunization and sanitation campaigns that reduced IMR from 143.4/1,000 live births in the early 1960s to 97.4 in the early 1970s. State participation broke the undernutrition,disease cycle enough to reduce LEH frequencies significantly (from 71.9% in individuals born before 1971 to 51.5% in those born in 1971 or after, ,2 = 55.72; 1 df; , = 0.00001) and to eliminate the sex difference in LEH expression (from a 14.8% LEH difference between men and women before 1971 [Male/Female Odds Radio = 0.45, , significant at 0.05] to a nonsignificant 2% difference). Improvement in overall living conditions reflected in a "modern stage" infant mortality regime and an almost disappearance of LEHs, resulted from gradual improvements in living conditions that did not become apparent until the 1980s. Trends in the age at menarche are not statistically significant, probably due to methodological limitations. However, if overall living conditions continue to improve or stay as they are today, accelerations in maturation should become noticeable. Am. J. Hum. Biol. 13:590,602, 2001. © 2001 Wiley-Liss, Inc. [source] Factors affecting the development of Botrytis cinerea (grey mould) on linseed (Linum usitatissimum) buds, flowers and capsulesANNALS OF APPLIED BIOLOGY, Issue 1 2002S A M FERRYMAN Summary A key was produced to describe 10 stages of development of linseed buds, flowers and capsules. Botrytis cinerea conidia germinated more rapidly and germ tubes grew longer on linseed stigmas, petals and mature senescing capsules than on green leaves, sepals and immature capsules. The proportion of conidia which germinated increased and the germ tubes continued growing for longer in the presence of linseed pollen and flower petal extracts. In controlled environment and field experiments, the response of buds, flowers and capsules to inoculation with B. cinerea changed with stage of development; few pre-flowering buds developed symptoms (brown lesions, then grey mould), but high proportions of flowering and post-flowering buds did so. Few immature green capsules developed symptoms and the proportion of capsules which developed symptoms increased as they matured. The presence of linseed pollen decreased the incubation period from inoculation with spore suspensions to appearance of B. cinerea symptoms on buds. A disease cycle was produced to suggest the changes in susceptibility of linseed to infection by B. cinerea conidia during bud, flower and capsule development. [source] | ||||||||||