RUST FUNGI AND HOST PLANT COEVOLUTION: DO PRIMITIVE HOSTS HARBOR PRIMITIVE PARASITES?

Abstract— The classical view of rust phylogeny is that rusts found on ferns and conifers are primitive, while rusts that parasitize angiosperms are advanced. This belief was based on the theory that primitive hosts harbor primitive parasites; that is, it assumed coevolution (co-speciation) of hosts and parasites. A cladistic analysis of 30 genera and 28 characters representative of the major patterns of rust fungi diversity is presented. The results of this analysis suggest that tropical short-cycle rusts on angiosperms form the cladistically basal group of rusts, while the rusts on conifers and ferns (Melampsoraceae sensu lato ) form a nested terminal clade. These results suggest that rusts and their hosts have not undergone a long period of parallel cladogenesis (co-speciation); host transfer has probably been at least as frequent as co-speciation. The cladograms indicate evolutionary trends of spore stages and life history: urediniospores evidently preceded the evolution of aeciospores and pycniospores within Uredinales, and heteroecism is a derived condition which evolved at least several times. This study stresses the importance of making use of independent cladistic analyses of both host and parasite in order to test assumptions of coevolution and host transfer.     

Rusts (Uredinales) of Triticeae: evolution and extent of coevolution, a cladistic analysis

BAUM, B. R. & SAVILE, D. B. O., 1985. Rusts (Uredinales) of Triticeae: evolution and extent of coevolution, a cladistic analysis. Established evolutionary trends in Uredinales as a whole are reviewed, and primitive and advanced characters are presented. The rusts of all Poaceae arc presented in a table that strongly indicates Bambusoideae to be the oldest and Pooideae the youngest subfamily. The rusts of Triticeae and their ecogeography are outlined; the rusts of Cyperaceae, selected as an out-group, are beiefly summarized; and the available characters and character states for rusts of Triticeae are given. Host alternation complicates the analysis. The aerial host (never a grass) is ecologically associated with the unrelated telial (grass) host. There are no appropriate methods to permit analysis of the combined components: aecial host evolution, telial host evolution, rust evolution, and their coevolution. Also, several aecial hosts are unknown. Consequently it was necessary to omit aecial hosts from the analysis. Cladistic analysis of the rusts of Triticeae was performed using five methods and consisted of cycles of tree analysis and modification of character state trees. A cladogram put together from a Dollo and a Wagner cladogram was used as a basis for the classification of rusts given. Subsequently a cladistic analysis of genera of Triticeae, using presence/absence of rusts as characters (Brooks' approach) was performed. The Triticeae cladogram of Baum (1983) was also analysed. Distances between the cladogram generated by various methods and that of Baum were computed for each possible pair, using the method of Robinson & Foulds, and then the resulting distance matrix was reduced in dimensionality by principal components and non-metric multidimensional scaling. The results are discussed in light of the limitation of the analyses and the data. It is concluded that coevolution is limited and that frequent jumps to ecologically associated hosts explain the parallelism in evolution of rusts on Triticeae.     

Phylogenetic analysis of rust fungi (Uredinales) from the Colombian Andean region using 28S ribosomal DNA sequences

Rust fungi (Uredinales, Basidiomycetes) are one of the most diverse and economically important plant-obligated parasites. Taxonomy of this group has been under revision during the last years using molecular techniques to define phylogenetic relationships. In this study we evaluated the phylogenetic affinities of a group of 40 rust fungi obtained from different plants in the Colombian Andean region using sequence analysis of the 28S ribosomal DNA, specifically D1/D2 domains. Comparisons were undertaken with sequences of rust fungi from around the world deposited in the GenBank database. An alignment of sequences was used to build a phylogenetic tree through Maximum parsimony analysis. Our results support the taxonomical validity of families Pucciniaceae, Phakopsoraceae, Phragmidiaceae, Pileolariaceae, Mikronegeriaceae, Coleosporiaceae and Cronartiaceae, while Pucciniosiraceae represents redundant taxa with Pucciniaceae. The analyses indicated that Uropyxidaceae, Raveneliaceae, Chaconiaceae and Pucciniastraceae correspond to polyphyletic families. Melampsoraceae appear to be a basal taxon to the Uredinales. Information obtained in this study will be useful to incorporate a higher number of sequences from tropical rust fungi within global efforts to redefine the taxonomy of order Uredinales. Additionally, we propose to give priority to future phylogenetic studies of taxa: Gerwasia, Hemileia, Phragmidium, Prospodium, Puccinia and Uromyces, genera that include a high number of rust fungi from the tropics.     

Phylogenetic positions of rust fungi parasitic on ferns: Evidence from 18S rDNA sequence analysis

Molecular phylogenetic analyses of fern rusts were carried out based on 18S rDNA sequences. We sequenced the 18S rDNAs of fern rusts (Hyalopsora polypodii andUredinopsis intermedia) and non-fern rusts (Aecidium epimedii, Coleosporium asterum, Ochropsora kraunhiae, Puccinia suzutake andPhysopella ampelopsidis) and analyzed their phylogenetic relationships with other members of the Urediniomycetes. Our bootstrapped neighbor-joining tree obtained from these analyses showed that rust fungi were apparently monophyletic at high confidence level (100% bootstrap confidence). In this molecular phylogenetic tree, the two fern rusts did not occupy the basal position within the rust fungal lineage and did not form a monophyletic lineage. Two species of the Cronartiaceae (Peridermium harknessii, Cronartium ribicola) and one species of the Coleosporiaceae (Coleosporium asterum) grouped with the fern rusts. Therefore, our results suggested that the two fern rusts were not primitive. On the other hand,Mixia osmundae, which is parasitic on the primitive fernOsmunda, was phylogenetically far from the fern rusts.     

Introgression of diverse genes for resistance to rusts into an improved wheat variety, Kalyansona

Breeding for resistance to the three rusts of wheat usually requires incorporation of genetically independent factors conferring resistance to each rust. Linked resistance genes in some alien translocation stocks permit concurrent transference of resistance for more than one rust. Alien derived resistances, however, are often reported to be associated with reduced yield and other undesirable characters. In our experience, backcross breeding when given a limited number of backcrosses (3–6) and with suitable selection procedures has resulted in lines giving yields higher or comparable to the recurrent wheat parent Kalyansona and resistance to one, two or all three rusts without any adverse effects. Some of the rust resistant derivatives also show resistance to Neovossia indica (Karnal bunt). The derivatives thus developed when used as parents in a breeding programme have produced several improved cultivars with high yields, superior grains and diversity for resistance to rust pathogens. One of the cultivars, named Vaishali (DL784-3), has been officially released for cultivation in the country.     

On some rust fungi (Uredinales) collected in an Acacia koa–Metrosideros polymorpha woodland, Mauna Loa Road, Big Island, Hawaii

Nine species of rust fungi (Uredinales) were found during a 1-day field study in an Acacia koa–Metrosideros polymorpha woodland in Volcanoes National Park on Big Island, Hawaii. Two species, both found on Acacia koa, are native (endemic) rusts whereas 7 species are nonnative on nonnative hosts, highlighting the high proportion of introduced species in the Hawaiian flora even in more or less natural habitats. One species, Uromyces linearis on Panicum repens, constitutes the first record of this rust for the Hawaiian archipelago, bringing the total to 93 species on the islands, 70 (75.3%) of which are introduced. The species records are annotated with emphasis on the geographic origin of each taxon. In addition, the study has led to the molecular reevaluation of the genus Racospermyces, indicating that it is synonymous with Endoraecium, and six new combinations are proposed for the species previously placed in Racospermyces. The high number of introduced species in Hawaii coupled with the paucity of native species when compared to other global regions is discussed.     

Aphanocladiutn album, a fungus inducing teliospore production in rusts

The hyphomycetous fungus Aphanocladiutn album can grow over and around uredia of the rusts Puccinia coronata, P. hordei, P. graminis f.sp. avenae and P. recondita f.sp. triticina when host plants are kept under very humid conditions, but not on such plants not infected with rusts; uredia are adversely affected and telia develop in their vicinity. Plants inoculated with these rusts and with five isolates of A. album (one from a dead insect) showed: (1) much earlier development of telia on detached and non-detached rusted leaves inoculated with A. album than on corresponding leaves not thus inoculated; (2) telial induction by A. album in some isolates of rust species which hitherto had rarely or never produced telia; (3) precocious telial formation, in comparison with controls, when A. album spores were sprayed on leaves as much as 3 days before and 9 days after rust inoculation, and occasionally after uredia had already matured. As affected leaves remained green until the whole leaf became moribund, senescence is apparently not the factor inducing telia formation. The normal-appearing teliospores of some isolates were induced to germinate, whereas others did not. Rhamnus palaestina inoculated with basidiospores of one isolate of A. album-treated P. coronata f.sp. avenae produced pycnia and fertile aecia. The importance of A. album as a working tool in rust research and as a possible means for biological control of rust epiphytotics is discussed.     

Green Rust Formation from the Bioreduction of γ –FeOOH (Lepidocrocite): Comparison of Several Shewanella Species

Green rusts are mixed ferrous/ferric hydroxides that typically form under weakly acidic to alkaline conditions in suboxic environments. The recent identification of green rusts as products of the reduction of Fe(III) oxides and oxyhydroxides by Shewanella putrefaciens, a dissimilatory iron-reducing bacterium (DIRB), suggests that green rusts may play a role in the redox cycling of Fe in many aquatic and terrestrial environments. We examined the potential for green rust formation resulting from the bioreduction of lepidocrocite(γ -FeOOH) by a series of Shewanella species (S. alga BrY, S. amazonensis SB2B, S. baltica OS155, S. denitrificans OS217T, S. loihica PV-4, S. oneidensis MR-1, S. putrefaciens ATCC 8071, S. putrefaciens CN32, S. saccharophilia, and Shewanella sp. ANA-3). All Shewanella species, with the exception of S. denitrificans OS217T, were able to couple the oxidation of formate to the reduction of Fe(III) in lepidocrocite; however there were significant differences among species with respect to the rate and extent of Fe(II) production. Despite these differences, green rust was the only Fe(II)-bearing solid phase formed under our experimental conditions, as indicated by X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy. The formation of green rust by Shewanella species isolated from a wide range of habitats and possessing varied metabolic capabilities suggests that under favorable conditions biogenic green rusts may be formed by a diverse array of DIRB.     

DNA barcoding in the rust genus Chrysomyxa and its implications for the phylogeny of the genus

Chrysomyxa rusts are fungal pathogens widely present in the boreal forest. Taxonomic delimitation and precise species identification are difficult within this genus because several species display similar morphological features. We applied a DNA barcode system based on the ribosomal internal transcribed spacer region (ITS), large subunit (28S) ribosomal RNA gene, mitochondrial cytochrome oxidase 1 (CO1) and mitochondrial NADH dehydrogenase subunit 6 (NAD6) in 86 strains from 16 different Chrysomyxa species, including members of the Chrysomyxa ledi species complex. The nuclear ITS and 28S loci revealed higher resolving power than the mitochondrial genes. Amplification of the full CO1 barcode region failed due to the presence of introns limiting the dataset obtained with this barcode. In most cases the ITS barcodes were in agreement with taxonomic species based on phenotypic characters. Nevertheless we observed genetically distinct (different DNA barcodes) lineages within Chrysomyxa pyrolae and Chrysomyxa rhododendri, providing some evidence for allopatric speciation within these morphologically defined species. This finding, together with the observed pattern of host specificities of the studied rust fungi, suggest that species diversification within the C. ledi species complex might be governed by a set of factors such as specialisation to certain Ericaceae species as telial hosts and to a lesser extent specialization to different spruce species as aecial hosts. Moreover allopatric speciation by geographic disruption of species also seems to take place. When our data were integrated into a broader phylogenetic framework the Chrysomyxa genus unexpectedly was not resolved as a monophyletic group. Indeed the spruce cone rusts C. pyrolae and C. monesis coalesced with the pine needle rusts belonging to the genus Coleosporium, whereas the microcyclic species Chrysomyxa weirii was embedded within a clade comprising the genus Melampsora.     

Inheritance and QTL analysis of durable resistance to stripe and leaf rusts in an Australian cultivar, Triticum aestivum 'Cook'.

An F4-derived F6 recombinant inbred line population (n = 148) of a cross between the durable stripe (yellow) rust (caused by Puccinia striiformis) and leaf (brown) rust (caused by Puccinia triticina) resistant cultivar, Triticum aestivum 'Cook', and susceptible genotype Avocet-YrA was phenotyped at several locations in Canada and Mexico under artificial epidemics of leaf or stripe rusts and genotyped using amplified fragment length polymorphism (AFLP) and microsatellite markers. Durable adult plant resistance to stripe and leaf rusts in 'Cook' is inherited quantitatively and was based on the additive interaction of linked and (or) pleiotropic slow-rusting genes Lr34 and Yr18 and the temperature-sensitive stripe rust resistance gene, YrCK, with additional genetic factors. Identified QTLs accounted for 18% to 31% of the phenotypic variation in leaf and stripe rust reactions, respectively. In accordance with the high phenotypic associations between leaf and stripe rust resistance, some of the identified QTLs appeared to be linked and (or) pleiotropic for both rusts across tests. Although a QTL was identified on chromosome 7D with significant effects on both rusts at some testing locations, it was not possible to refine the location of Lr34 or Yr18 because of the scarcity of markers in this region. The temperature-sensitive stripe rust resistance response, conditioned by the YrCK gene, significantly contributed to overall resistance to both rusts, indicating that this gene also had pleiotropic effects.     

Accumulation of genes for susceptibility to rust fungi for which barley is nearly a nonhost results in two barley lines with extreme multiple susceptibility

Nonhost resistance is the most common type of resistance in plants. Understanding the factors that make plants susceptible or resistant may help to achieve durably effective resistance in crop plants. Screening of 109 barley (Hordeum vulgare L.) accessions in the seedling stage indicated that barley is a complete nonhost to most of the heterologous rust fungi studied, while it showed an intermediate status with respect to Puccinia triticina, P. hordei-murini, P. hordei-secalini, P. graminis f. sp. lolii and P. coronata ff. spp. avenae and holci. Accessions that were susceptible to a heterologous rust in the seedling stage were much more or completely resistant at adult plant stage. Differential interaction between barley accessions and heterologous rust fungi was found, suggesting the existence of rust-species-specific resistance. In particular, many landrace accessions from Ethiopia and Asia, and naked-seeded accessions, tended to be susceptible to several heterologous rusts, suggesting that some resistance genes in barley are effective against more than one heterologous rust fungal species. Some barley accessions had race-specific resistance against P. hordei-murini. We accumulated genes for susceptibility to P. triticina and P. hordei-murini in two genotypes called SusPtrit and SusPmur, respectively. In the seedling stage, these accessions were as susceptible as the host species to the target rusts. They also showed unusual susceptibility to other heterologous rusts. These two lines are a valuable asset to further experimental work on the genetics of resistance to heterologous rust fungi.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-004-1319-1Abbreviations ff. spp Formae speciales - RIL Recombinant inbred line - DC Double cross - DC-S Progeny produced by selfing of double-cross plants     

Phylogenetic studies in <Emphasis Type="Italic">Ravenelia esculenta</Emphasis> and related rust fungi

Ravenelia esculenta Naras. and Thium. is a rust fungus, which infects mostly thorns, inflorescences, flowers and fruits of Acacia eburnea Willd. Aecial stages of the rust produce hypertrophy in infected parts. DNA of the rust fungus was isolated from aeciospores by ‘freeze thaw’ method. 18S rDNA was amplified and sequenced by automated DNA sequencer. BLAST of the sequence at NCBI retrieved 96 sequences producing significant alignments. Multiple sequence alignment of these sequences was done by ClustalW. Phylogenetic analysis was done by using MEGA 3.1. UPGMA Minimum Evolution tree with bootstrap value of 1000 replicates was constructed using these sequences. From phylogenetic tree it is observed that Ravenelia esculenta and the genus Gymnosporangium share a common ancestry, though Ravenelia esculenta is autoecious on angiosperm and the genus Gymnosporangium is heteroecious with pycnia, aecia on angiosperm and uredia, telia on gymnosperm. Two major clades are recognized which are based on the nature of aecial host (gymnosperm or angiosperm). These clades were also showing shift from pteridophytes to angiosperms as telial hosts. The tree can be interpreted in the other way also where there is separation of 14 families of Uredinales depending upon nature of teliospores, nature of aeciospores and structure of pycnia. These studies determine the phylogenetic position of Ravenelia esculenta among other rust fungi besides broad separation of Uredinales into two clades. These studies also show that there is phylogenetic correlation between molecular and morphological data. This is first report of DNA sequencing and phylogenetic positioning in genus Ravenelia from India.     

Linkage mapping of genes for resistance to leaf,stem and stripe rusts and ω-secalins on the short arm of rye chromosome 1R

Summary The genes controlling resistance to three wheat rusts, viz., leaf rust (Lr26), stem rust (Sr31) and stripe or yellow rust (Yr9), and -secalins (Sec1), located on the short arm of rye chromosome 1R, were mapped with respect to each other and the centromere. Analysis of 214 seeds (or families derived from them) from testcrosses between a 1BL.1RS/1R heterozygote and Chinese Spring ditelocentric 1BL showed no recombination between the genes for resistance to the three rusts, suggesting very tight linkage or perhaps a single complex locus conferring resistance to the three rusts. The rust resistance genes were located 5.4 ± 1.7 cM from the Sec1 locus, which in turn was located 26.1 ± 4.3 cM from the centromere; the gene order being centromere — Sec1 — Lr26/Sr31/Yr9 — telomere. In a second test-cross, using a different 1BL.1RS translocation which had only stem rust resistance (SrR), the above gene order was confirmed despite a very large proportion of aneuploids (45.8%) among the progeny. Furthermore, a map distance of 16.0 ± 4.8 cM was estimated for SrR and the telomeric heterochromatin (C-band) on 1RS. These results suggest that a very small segment of 1RS chromatin is required to maintain resistance to all three wheat rusts. It should be possible but difficult to separate the rust resistance genes from the secalin gene(s), which are thought to contribute to dough stickiness of wheat-rye translocation lines carrying 1RS.     

The rust fungi of <Emphasis Type="Italic">Luzuriaga</Emphasis> (Luzuriagaceae) with description of a new species, <Emphasis Type="Italic">Puccinia luzuriagae-polyphyllae</Emphasis>

Three species of rust fungi (Uredinales), Puccinia perforans, P. fuegiana (= Uromyces skottsbergii), and Aecidium callixenis have been described on members of Luzuriaga (Luzuriagaceae). Puccinia luzuriagae-polyphyllae is added as a new species on Luzuriaga polyphylla from Chile. The rust had been confused hitherto with P. perforans occurring on L. radicans. Both species differ from P. fuegiana on L. marginata by the absence of a uredinial state and several telial characters. The investigated collections of Puccinia species on Luzuriaga indicate that each is restricted to a single host species. A determination key is presented.     

Phylogenetic relationships of sugarcane rust fungi

The phylogenetic positions of Puccinia spp. infecting sugarcane (a complex hybrid of Saccharum spp.) were determined using 38 newly generated rust sequences and 26 sequences from GenBank. Rust specimens on sugarcane were collected from 164 locations in 23 countries and identified based on light microscopy. The morphology for all samples matched that of Puccinia kuehnii or P. melanocephala, the orange and brown rust pathogens of sugarcane, respectively. Nuclear ribosomal DNA sequences (rDNA) including portions of the 5.8S rDNA, the complete internal transcribed spacer 2 (ITS2) and 5′ region of the large subunit (nLSU) rDNA were obtained for each species along with 36 additional rust taxa. Despite a shared host, the two Puccinia spp. on sugarcane are not closely related within the Pucciniales. Phylogenetic analyses place P. melanocephala most closely to P. miscanthi, P. nakanishikii, and P. rufipes infecting Miscanthus sinensis, Cymbopogon citratus, and Imperata cylindrica, respectively. Puccinia kuehnii is basal to a clade of Poaceae-infecting rusts including P. agrophila, P. polysora, P. substriata, and Uromyces setariae-italicae infecting Schizachyrium spp., Zea mays, Digitaria spp., and Urochloa mosambicensis, respectively. Light and scanning electron microscopy images highlight morphological differences distinguishing the two sugarcane-infecting species. This study confirms the separation of rust species infecting Poaceae from Cyperaceae- and Juncaceae-infecting rusts and also provides support for the presence of an additional group that includes P. kuehnii and other grass-infecting relatives.     

Global risk levels for corn rusts (Puccinia sorghi and Puccinia polysora) under climate change projections

Common rust (Puccinia sorghi) and southern rust (Puccinia polysora) are two of the most important foliar corn diseases worldwide. These fungi have caused severe economic loss to corn yields worldwide. The current and future potential distribution of these diseases was modelled with CLIMEX using the known current geographic locations of the rusts, growth and stress indices. The models were run under the A2 scenario using CSIRO‐Mk3·0 and MIROC‐H for 2050 and 2100. The current projection shows areas with marginal to optimal suitability in all the continents. The models for future projections display a general reduction in the Southern hemisphere and increase in the Northern hemisphere, especially for the southern rust. The overlay of the General Circulation Models produce an estimation of the common areas under risk for future climate conditions for the simultaneous occurrence for both corn rusts, with a reduction of the medium‐ and high‐risk categories by 2100. This study highlights the possible effects of climate change at a global level for common and southern rust, as well as the risk of occurrence of both diseases in common areas for future climate that could be particularly harmful for crops.     

Origin and evolution of conifer rusts in the light of continental drift

Many genera and species of present-day aecial rusts on seed plants are derived directly or indirectly from a limited group of these pathogens on northern conifers, whereas conifer rusts are believed to have descended from their progenitors on ferns. It is worth noting that only the Pinaceae, Taxodiaceae and Cupressaceae serve as alternate hosts to an extensive rust flora on ferns and angiosperms which are distributed predominantly in the northern hemisphere. Numerous conifers in the southern hemisphere do not bear rusts, except a few endemic species on Araucariaceae in Malaysia and south central Chile.Such a disjunctive distribution of conifers and their specialized rusts is attributed now to extensive continental drift. Evidence indicates that the breakup of the primary land mass Pangaea into northern Laurasia and southern Gondwanaland, with successive splitting and drifting of these supercontinents, has also scattered ancient land faunas and floras.Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland. Plant Introduction Investigation Paper No. 29.     

甘肃锈菌名录

报道了甘肃省的锈菌计24属150种,主要基于作者1992、2003和2005年在祁连山及其邻近地区所采的标本。涉及的地区包括祁连山系的冷龙岭、走廊南山和乌鞘岭、敦煌、安西、嘉峪关、酒泉、民勤等荒漠地区、阿尼玛卿山东部地区以及渭河、洮河和白龙江流域。早期采集者邓叔群、相望年、余积厚、张天宇等在天水等地采集的少量标本也作了引证。本名录总共引证了约600号标本,绝大多数标本是首次被引证。所有标本保藏在北京中国科学院菌物标本馆(HMAS)。本名录包括锈菌和寄主植物名称及采集地(仅列县、市名),所引标本号均为HMAS的馆藏编号。目前对甘肃的菌物区系仍知之甚少,本名录仅作今后进一步深入研究的基础资料。     

Cryptic diversity and significant cophylogenetic signal detected by DNA barcoding the rust fungi (Pucciniaceae) of Cyperaceae–Juncaceae

Plants play important roles as habitat and food for a tremendous diversity of specialist animals and fungi. The disappearance of any plant species can lead to extinction cascades of its associated biota. In consequence, documenting the diversity and specificity of plant-associated organisms is of high practical relevance in biodiversity conservation. Here, we present the first large-scale molecular investigation into the diversity, host specificity, and cophylogenetic congruence of an especially rich plant–fungal association, the rust fungi (Pucciniaceae) of Cyperaceae and Juncaceae. Using the largest rust fungi DNA barcoding dataset published to date (252 sequences, 82 taxa), we reject the presence of a global ITS2-28S barcode gap, but find a local gap in Cyperaceae–Juncaceae rusts, and suggest the existence of many cryptic species in North America, with some broadly circumscribed species possibly corresponding to >10 cryptic species. We test previous hypotheses of correlations between the phylogenies of rust fungi and their Cyperaceae–Juncaceae hosts using a combination of global-fit and event-based cophylogenetic methods. A significant cophylogenetic signal is detected between rusts and their hosts, but the small number of cospeciations argues for preferential host jumps as the driving process behind these correlations. In addition, temporal congruence between the origin of major Carex clades and their rusts suggests that host diversification may have promoted parasite diversification. Finally, we discuss the relevance of rust infection patterns to the systematics of Cyperaceae, highlight some taxonomic problems uncovered by the analyses, and call attention to the promise of DNA barcoding for bridging knowledge gaps in poorly studied plant-associated microorganisms.