Navegando por Autor "Vieira, B. S."
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Item Alternaria cichorii in Brazil on Cichorium spp. seeds and cultivated and weedy hosts(Journal of Phytopathology, 2008-08) Barreto, R. W.; Santin, A. M.; Vieira, B. S.Alternaria cichorii was recorded for the first time in Brazil causing leaf spots on endive (Cichorium endivia) in 2003 based on material collected at Catalão, state of Goiás, in 2001. In 2005, A. cichorii was found causing severe leaf‐spotting in an escarole (C. endivia) plantation in Viçosa, state of Minas Gerais and shortly afterwards also in Viçosa, but at a different location, in the weed hosts common sowthistle (Sonchus oleraceus) and spiny sowthistle (Sonchus asper). A description of A. cichorii based on specimens collected in Viçosa is provided herein. The natural occurrence of A. cichorii on weed hosts in Viçosa indicates that it has already become naturalized in Brazil surviving on non‐cultivated composites, complicating disease management. Pathogenicity tests, complementary to those already published, were performed to better elucidate the range of potential alternative hosts in the Asteraceae of this fungus. This involved inoculation of one isolate of A. cichorii obtained from cichory and one obtained from common sowthistle on selected species and cultivars of 10 tribes in the Asteraceae, but concentrated in the Lactuceae. All species included in the test were shown to be susceptible to at least one of the isolates. A high incidence of leaf spot or blight resulted from inoculation of most individuals. All plants of six test species were killed after inoculation with one of the isolates of A. cichorii. Several of the test species have not been previously recorded as hosts for A. cichorii. Surprisingly, the known host‐range for this fungus is restricted to only few members of the Asteraceae (Acroptilon repens, C. endivia, C. intybus, Carthamus tinctorius and Lactuca sativa). Our results indicate that A. cichorii has a wide host range within the Asteraceae and that other cultivated or non‐cultivated members of this family may serve as inoculum reservoirs for this fungus in the absence of cichory, endive or escarole. An attempt to verify if contaminated seeds might be the original source for such geographically distant occurrences of A. cichorii in Brazil was made. Analysis of 24 samples of cichory and endive seeds obtained from dealers in five different Brazilian states showed that 25% of these samples carried A. cichorii with an incidence varying from 0.6% to 13.75%. Such a result highlights the vulnerable situation in Brazil for avoiding introduction of exotic seed‐carried vegetable pathogens. It is known that a very significant proportion of vegetable seeds marketed in Brazil are imported and seed inspection for pathogens is not performed regularly for such material imported for commerce. It is probable that contaminated cichory, endive and escarole seeds served as a vehicle for introduction of this fungus in Brazil and that the fungus has then become naturalized in many vegetable growing areas and is now surviving on other Asteraceae in the absence of cultivated hosts.Item First record of Bremia lactucae infecting Sonchus oleraceus and Sonchus asper in Brazil and its infectivity to lettuce(Journal of Phytopathology, 2006-02) Vieira, B. S.; Barreto, R. W.Bremia lactucae is recorded for the first time causing downy mildew on common sowthistle (Sonchus oleraceus) and spiny sowthistle (Sonchus asper) in Brazil. The disease and etiological agent are described. Pathogencity of sporangia obtained from S. oleraceus was tested on 12 species belonging to the Asteraceae, already recorded in the literature as hosts of B. lactucae, and four commonly cultivated varieties of lettuce. All four cultivars of lettuce, S. oleraceus and S. asper showed symptoms of the disease and sporulation of the pathogen 5 days after inoculation. It has been observed that the disease occurs on Sonchus spp. throughout the year in Vic ̧osa (state of Minas Gerais), being more common on these two hosts than on lettuce. Both weeds are very common invaders of vegetable growing areas in Brazil. This indicates that those two hosts for the fungus may be important inoculum reservoirs for disease occurring in lettuce, highlighting the need for control of these weeds as part of the pro- cedures aimed at controlling this disease. These results are also in agreement with the views that B. lactucae is split into host-specific infraspecific taxa. Lettuce and sowthistles are regarded as closely related, belonging to the same subfamily and tribe in the Asteraceae (Subfamily Cichorioideae: Tribe Lactuceae).Item Liquid fermentation of Colletotrichum truncatum UFU 280, a potential mycoherbicide for beggartick(Australasian Plant Pathology, 2018-05) Lopes, E. A.; Vieira, B. S.; Dias, L. V. S. A.; Langoni, V. D.One isolate of Colletotrichum truncatum was found recently causing severe anthracnose symptoms and leading to the death of beggartick (Bidens pilosa L. and Bidens subalternans DC.), one of the major weeds of Brazilian agriculture. This isolate, namely UFU 280, was selected for development of a mycoherbicide against this weed. Associated of beggartick, one of the, Here, results of a preliminary attempt to develop a protocol for mass production of inoculum (conidia) and fungal biomass of C. truncatum was performed aimed at paving the way for greenhouse and field evaluations of this biocontrol candidate. Isolates of Colletotrichum spp. have been successfully produced in the past to serve as the active ingredients of mycoherbicides. The method of choice has been the production of propagules through liquid fermentation. We assessed the effect of several options of liquid media recipes, type of seeding of medium, pH levels, incubation lengths, incubation temperatures and agitation speeds on the shaking speed on the concentration of conidia obtained per volume of medium. Additionally, a possible effect of the kind of medium utilized over the virulence of the inoculum was also evaluated through an inoculation study. We found that an adequate amount of conidia of C. truncatum (isolate - UFU 280) can be obtained in ME liquid culture medium, adjusted to a pH of 9.0, seeded with a conidial suspension and incubated for 6 days, under a regime of orbital shaking of 150 rpm, at temperatures ranging from 20 to 25 °C. Mortality of beggartick plants using conidia produced in different liquid culture media was of 100%.