RESUMO
Bacterial leaf streak of corn, caused by Xanthomonas vasicola pv. vasculorum, has been present in South Africa for over 70 years, but is an emerging disease of corn in North and South America. The only scientific information pertaining to this disease on corn came from work done in South Africa, which primarily investigated host range on other African crops, such as sugarcane and banana. As a result, when the disease was first reported in the United States in 2016, there was very limited information on where this pathogen came from, how it infects its host, what plant tissue(s) it is capable of infecting, where initial inoculum comes from at the beginning of each crop season, how the bacterium spreads from plant to plant and long distance, what meteorological variables and agronomic practices favor disease development and spread, how many other plant species X. vasicola pv. vasculorum is capable of infecting or using as alternate hosts, and if the bacterium will be able to persist in all corn growing regions of the United States. There were also no rapid diagnostic assays available which initially hindered prompt identification prior to the development of molecular diagnostic tools. The goal of this synthesis is to review the history of X. vasicola pv. vasculorum and bacterial leaf streak in South Africa and its movement to North and South America, and highlight the recent research that has been done in response to the emergence of this bacterial disease.
Assuntos
Xanthomonas , Doenças das Plantas , África do Sul , América do Sul , Zea maysRESUMO
Pectobacterium carotovorum subsp. brasiliense is a newly identified member of the potato soft rot enterobacteriaceae. The pathogenesis of this pathogen is still poorly understood. In this study, an mCherry-P. carotovorum subsp. brasiliense-tagged strain was generated to study P. carotovorum subsp. brasiliense-potato plant interactions. Prior to use, the tagged strain was evaluated for in vitro growth, plasmid stability, and virulence on potato tubers and shown to be similar to the wild type. Four potato cultivars were evaluated for stem-based resistance against P. carotovorum subsp. brasiliense. Confocal laser-scanning microscopy and in vitro viable cell counts showed that P. carotovorum subsp. brasiliense is able to penetrate roots of a susceptible potato cultivar as early as 12 h postinoculation and migrate upward into aerial stem parts. Due to the phenotypic differences observed between tolerant and susceptible cultivars, a comparison of P. carotovorum subsp. brasiliense colonization patterns in these cultivars was undertaken. In the susceptible cultivar, P. carotovorum subsp. brasiliense cells colonized the xylem tissue, forming "biofilm-like" aggregates that led to occlusion of some of the vessels. In contrast, in the tolerant cultivar, P. carotovorum subsp. brasiliense appeared as free-swimming planktonic cells with no specific tissue localization. This suggests that there are resistance mechanisms in the tolerant cultivar that limit aggregation of P. carotovorum subsp. brasiliense in planta and, hence, the lack of symptom development in this cultivar.
Assuntos
Resistência à Doença , Suscetibilidade a Doenças , Pectobacterium carotovorum/patogenicidade , Doenças das Plantas/microbiologia , Solanum tuberosum/microbiologia , Proteínas Luminescentes , Microscopia Confocal , Pectobacterium carotovorum/genética , Pectobacterium carotovorum/crescimento & desenvolvimento , Fenótipo , Doenças das Plantas/imunologia , Raízes de Plantas/imunologia , Raízes de Plantas/microbiologia , Caules de Planta/imunologia , Caules de Planta/microbiologia , Tubérculos/imunologia , Tubérculos/microbiologia , Plasmídeos , Proteínas Recombinantes de Fusão , Solanum tuberosum/imunologia , Virulência , Proteína Vermelha FluorescenteRESUMO
Several Gram-negative-staining, facultatively anaerobic bacterial isolates were obtained from Eucalyptus seedlings showing symptoms of bacterial blight and dieback in Colombia, Rwanda and South Africa. Partial 16S rRNA gene sequencing, together with partial gyrB sequencing, placed the isolates in the genus Pantoea and indicated that they constituted three novel species. Multilocus sequence analysis (MLSA) based on partial sequences of gyrB, rpoB, infB and atpD revealed Pantoea dispersa, Pantoea eucrina and Pantoea cypripedii as their closest phylogenetic relatives. DNA-DNA hybridization studies confirmed the classification of the new isolates as three novel species and phenotypic tests allowed them to be differentiated from their closest phylogenetic neighbours. The names Pantoea rodasii sp. nov. [type strain LMG 26273(T)=BD 943(T) (deposited with the Plant Pathogenic and Plant Protecting Bacteria Collection, South Africa)=BCC 581(T) (deposited with the Bacterial Culture Collection, Forestry and Agricultural Institute, South Africa)], Pantoea rwandensis sp. nov. (type strain LMG 26275(T)=BD 944(T)=BCC 571(T)) and Pantoea wallisii sp. nov. (type strain LMG 26277(T)=BD 946(T)=BCC 682(T)) are proposed.
Assuntos
Eucalyptus/microbiologia , Pantoea/classificação , Pantoea/isolamento & purificação , Anaerobiose , Técnicas de Tipagem Bacteriana , Análise por Conglomerados , Colômbia , DNA Girase/genética , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Dados de Sequência Molecular , Tipagem de Sequências Multilocus , Hibridização de Ácido Nucleico , Pantoea/genética , Pantoea/fisiologia , Filogenia , RNA Ribossômico 16S/genética , Ruanda , Análise de Sequência de DNA , África do SulRESUMO
Pineapple (Ananas comosus) is native to South America and widely planted as a fruit crop in the tropics and sub-tropics. This plant is susceptible to a number of fungal diseases of which the most severe is fusariosis. The disease is caused by Fusarium guttiforme and occurs only in South and Central America. The occurrence of a similar disease on pineapples in South Africa has prompted a re-evaluation of the Fusarium sp. associated with pineapple fruit rot. Phylogenetic relationships of isolates from pineapples collected in Brazil and South Africa were assessed based on sequence data for the translation elongation factor-1-α, histone H3 and ß-tubulin gene regions. Analyses showed that the South African isolates represent a species distinct from Brazilian isolates. The South African isolates are characterised by a concentration of aerial mycelium at the centres of the colonies, different to the Brazilian isolates that have an even distribution of aerial mycelium. Both phylogenetic and morphological data show that the disease on pineapple in South Africa is caused by a new Fusarium species described here as F. ananatum sp. nov.
Assuntos
Ananas/microbiologia , Fusarium/classificação , Gibberella/classificação , Doenças das Plantas/microbiologia , Brasil , Frutas/microbiologia , Proteínas Fúngicas/genética , Fusarium/genética , Fusarium/isolamento & purificação , Gibberella/genética , Gibberella/isolamento & purificação , Dados de Sequência Molecular , Fator 1 de Elongação de Peptídeos/genética , Filogenia , África do SulRESUMO
Bacteria isolated from eucalyptus leaves and shoots showing symptoms of blight and die-back collected in Uganda, Uruguay and Argentina and from maize displaying brown stalk rot symptoms in South Africa were tentatively placed in the genus Pantoea on the basis of phenotypic and biochemical tests. These isolates, together with two strains (LMG 2558 and LMG 2560) previously assigned to Pantoea agglomerans based on protein electrophoregrams but later excluded from this species, were further investigated using molecular techniques. 16S rRNA gene sequencing and multilocus sequence analyses (MLSA) revealed that the strains were phylogenetically closely related to Pantoea agglomerans, Pantoea stewartii and Pantoea ananatis. MLSA and amplified fragment length polymorphism analysis placed the strains into four separate clusters, not containing any of the type strains of species of the genus Pantoea. DNA-DNA hybridization confirmed the classification of the isolates into four novel species, for which the names Pantoea vagans sp. nov. (type strain R-21566T=LMG 24199T=BCC 105T=BD 765T), Pantoea eucalypti sp. nov. (type strain R-25678T=LMG 24197T=BCC 076T=BD 769T), Pantoea deleyi sp. nov. (type strain R-31523T=LMG 24200T=BCC 109T=BD 767T) and Pantoea anthophila sp. nov. (type strain LMG 2558T=BD 871T=NCPPB 1682T) are proposed.
Assuntos
Eucalyptus/microbiologia , Pantoea/classificação , Pantoea/isolamento & purificação , Doenças das Plantas/microbiologia , Zea mays/microbiologia , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , Argentina , Técnicas de Tipagem Bacteriana , Análise por Conglomerados , Impressões Digitais de DNA , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Genótipo , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Pantoea/genética , Filogenia , Folhas de Planta/microbiologia , Brotos de Planta/microbiologia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , África do Sul , Uganda , UruguaiRESUMO
Post-hail-associated dieback of Pinus patula and P. radiata trees, induced by Sphaeropsis sapinea (=Diplodia pinea), is a common and important disease in commercial pine plantations. Two morphotypes, A and B, have been described for this fungus based on differences in cultural characteristics, conidial morphology, and virulence among isolates from the north central United States. The existence of the two described morphotypes was later verified through the use of random amplified polymorphic DNA (RAPD) analyses, and the morphotypes were designated as the A and B RAPD marker groups. The objective of this study was to characterize a set of S. sapinea isolates from South Africa, Indonesia, and Mexico using RAPD analysis and DNA sequencing of the internal transcribed spacer (ITS) region of the ribosomal DNA operon. Sizes of conidia and culture morphology were, furthermore, used to compare the three groups of S. sapinea isolates that emerged from the RAPD analysis. Two of the RAPD groups included isolates from the United States, representing the A and B morphotypes, while the third RAPD group accommodated Indonesian and one Mexican isolate. ITS sequences of all the S. sapinea isolates were highly homologous and resolved only the A and B RAPD groups. The ITS sequences of the isolates in the third RAPD group were the same as those of the A RAPD group. Conidia of isolates representing the A and B morphotypes were approximately the same size, but those of the third RAPD group were significantly longer. RAPD analysis enabled us to identify a third group of S. sapinea that is different from the well-recognized A and B groups. Isolates in this third RAPD group also have a distinct morphological characteristic and thus represent a third discrete morphological group, which we refer to as the C morphotype of S. sapinea.