RESUMO
Complex life strategies are common among plant pathogens belonging to rust fungi (Uredinales). The heteroecious willow rust Melampsora larici-epitea produces five spore stages and alternates on larch (Larix). To shed light on the epidemiology of this pathogen, amplified fragment length polymorphisms (AFLPs) were used to determine the genetic diversity and genetic structure of rust samples collected from coppice willow (Salix) plantations at three UK sites (LA, CA and MC) over three sampling dates (September 2000, July 2001 and September 2001). Of the total of 819 isolates, 465 were unique AFLP phenotypes and there was a shift in genotype diversity between the two seasons (0.67 in 2000 and 0.87-0.89 in 2001). No phenotypes were common between the two seasons within a site, suggesting that the rust did not overwinter as an asexual stage within plantations. A temporal analysis detected large amounts of genetic drift (F(S) = 0.15-0.26) between the two seasons and very small effective population sizes (N(e) = 2-3) within sites. These results all point to a new colonization of the plantations by the rust in the second season (2001). The F(ST)-analogue values were Phi(CT) = 0.121, Weir and Cockerham's theta = 0.086 and the Bayesian estimate theta(B) = 0.087-0.096. The results suggest that the sources of inoculum were somewhat localized and the same sources were mainly responsible for disease epidemics in LA and CA over the two seasons. The relatively low F(ST)-values among sites (0.055-0.13) suggest the existence of significant gene flow among the three sampled sites.
Assuntos
Basidiomycota/genética , Deriva Genética , Variação Genética , Salix/microbiologia , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , DNA Fúngico/genética , Ecossistema , Fluxo Gênico , Genótipo , Fenótipo , Doenças das Plantas/microbiologia , Dinâmica Populacional , Estações do Ano , Análise de Sequência de DNA , Esporos Fúngicos/genética , Reino UnidoRESUMO
Genetic diversity among 51 isolates of the mycoparasite Sphaerellopsis filum from Melampsora rusts on willow and poplar was examined using AFLP. Genetic variation was relatively low among the isolates (Nei & Li's similarities > or =90). Genetic diversity calculated using Shannon index was 0.119 at Loughgall, Northern Ireland, 0.109 at Markington, northern England, 0.039 at Craibstone, Scotland, and 0.015 at Long Ashton, southwest England. At Long Ashton, 14 out of 16 isolates shared the same AFLP bands. Two genotypes were found at both Markington and Loughgall. The low genetic diversity and a high rate of clonality suggested that asexual reproduction plays a major role in S. filum epidemics. Sequence information was also obtained from the ITS-5.8S region of the ribosomal DNA from the S. filum isolates derived from willow and poplar rusts and six isolates derived from other sources. ITS sequences were identical among all the 51 isolates from willow and poplar rusts. ITS analysis placed S. filum isolates from Melampsora spp. on willow and poplar, Puccinia coronata on grass and Melampsora sp. on Euphorbia sp. into one clade and the isolates from blackberry rust Phragmidium violaceum and larch rust Triphragmiopsis laricinum into another. Nucleotide sequence differences between the two groups were 8.4-10.4 %. The ITS-5.8S sequences obtained in this study were compared with those deposited in the GenBank database.
Assuntos
Ascomicetos/genética , Variação Genética , Polimorfismo Genético , RNA Ribossômico 5,8S/genética , Ascomicetos/classificação , Ascomicetos/isolamento & purificação , DNA Fúngico/genética , DNA Ribossômico/genética , Inglaterra , Dados de Sequência Molecular , Filogenia , RNA Fúngico/genéticaRESUMO
The 5' end of the large subunit (LSU) region and the entire internal transcribed spacer (ITS) region of ribosomal DNA were sequenced from 11 species or special forms of Melampsora on Salix, and three species on Populus. For all the species, except for M. larici-epitea and M. coleosporioides, the sequences in both the examined regions were identical within a species. Within M. larici-epitea, f. sp. larici-epitea typica and f. sp. larici-retusae shared the same sequences which slightly differed from that of f. sp. larici-daphnoides. In the LSU region, M. larici-epitea, M. capraearum and the stem-infecting form on S. viminalis shared the same sequence and the Far-Eastern species M. epiphylla differed from them only slightly (p distance 0.006), indicating that they may share a common ancestral lineage. M. amygdalinae and M. coleosporioides formed a distict group (bootstrap value 100% for combined ITS and LSU data). M. larici-epitea and M. ribesii-purpurea, both belonging to the M. epitea complex, appeared to be distinct. The molecular data also suggest that the differences in certain characteristics, such as the thickness of teliospore walls and host specificity, may have evolved relatively recently.
Assuntos
Basidiomycota/classificação , DNA Ribossômico/genética , Salicaceae/microbiologia , Basidiomycota/genética , Evolução Biológica , DNA Fúngico/análise , DNA Fúngico/química , DNA Fúngico/genética , DNA de Plantas/química , DNA de Plantas/genética , DNA Ribossômico/química , DNA Espaçador Ribossômico/genética , Filogenia , Doenças das Plantas/microbiologia , Salicaceae/genéticaRESUMO
The mycoparasite Sphaerellopsis filum (teleomorph Eudarluca caricis) was applied simultaneously with Melampsora larici-epitea on to willow leaf discs using eight concentrations of conidia. Inoculum densities were quantified and the numbers of uredinia of the rust, pycnidia and conidia of S. filum and rust spores produced per leaf disc were measured 13 d after inoculation (first assessment). Higher S. filum inoculum densities resulted in more rust uredinia being infected, but did not reduce the number of uredinia produced. The ratios of infected rust pustules: S. filum conidia applied were in a range of 0.25-0.31 when less than 20 S. filum spores were inoculated on to a leaf disc (0.95 cm2). Suppressive effects of S. filum on rust spore production were more obvious in the second assessment, carried out 23 d after inoculation. Inoculum densities of S. filum were significantly (P < 0.001) correlated with the frequency of uredinia infected (% variance accounted for [VAF] = 85.8), the number of S. filum pycnidia (% VAF = 81.4), S. filum spores produced (% VAF = 72.3) and rust spore production (% VAF = 48.6). Rust spore production was significantly (P < 0.001) negatively correlated with the frequency of uredinia infected (% VAF = 51.1), the number of S. filum pycnidia (% VAF = 42.0) and the number of S. filum spores produced (% VAF = 40.6). The best correlation was found between the number of pycnidia and the number of S. filum spores produced (% VAF = 88.8).