Small-spored Alternaria Species Research Articles

Two novel species and a new host record of Alternaria (Pleosporales, Pleosporaceae) from sunflower (Compositae) in Myanmar.

Sunflower (Helianthusannuus L.) is a widely cultivated, fast-growing crop known for its seeds and oil, with substantial ecological and economic importance globally. However, it faces challenges from leaf diseases caused by Alternaria species, which threaten its yield. Three small-spored Alternaria species were isolated from leaf spot and blight symptoms on sunflower in Myanmar. All the species were determined based on morphological characterization and a multi-locus phylogenetic assessment of seven genes, including the internal transcribed spacer of rDNA region (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase second largest subunit (RPB2), translation elongation factor 1-α (TEF1), Alternaria major allergen gene (Alt a 1), endopolygalacturonase gene (EndoPG), and an anonymous gene region (OPA10-2). The results introduced two new Alternaria species, A.myanmarensis sp. nov. and A.yamethinensis sp. nov., and a known species of A.burnsii, firstly reported from sunflower.

Four New Species of Small-Spored Alternaria Isolated from Solanum tuberosum and S. lycopersicum in China.

Small-spored Alternaria species have been frequently isolated from diseased leaves of Solanum plants. To clarify the diversity of small-spored Alternaria species, a total of 118 strains were obtained from leaf samples of S. tuberosum and S. lycopersicum in six provinces of China during 2022-2023. Based on morphological characterization and multi-locus phylogenetic analysis of the internal transcribed spacer of the rDNA region (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), translation elongation factor 1 alpha (TEF1), RNA polymerase second largest subunit (RPB2), Alternaria major allergen gene (Alt a 1), endopolygalacturonase gene (EndoPG) and an anonymous gene region (OPA10-2), seven species were determined, including four novel species and three known species (A. alternata, A. gossypina and A. arborescens). The novel species were described and illustrated as A. longxiensis sp. nov., A. lijiangensis sp. nov., A. lycopersici sp. nov. and A. solanicola sp. nov.. In addition, the pathogenicity of the seven species was evaluated on potato leaves. The species exhibited various aggressiveness, which could help in disease management.

Leaf spot of Lonicera japonica Thunb. (honeysuckle) caused by Alternaria alternata newly reported in China

Lonicera japonica Thunb. (honeysuckle) is widely cultivated as a medicinal herb in China. In recent years, the crop has been affected by a leaf spot disease in Suiyang, Guizhou, China. Disease symptoms included necrotic spots and wilting on leaves. The pathogen responsible for the disease was successfully isolated from symptomatic leaf tissue and identified. Identification based on morphological characteristics suggested that all the recovered fungal isolates belonged to small-spored Alternaria species. Multilocus sequence analyses of the internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), endopolygalacturonase (endoPG), translation elongation factor 1-alpha (tef1), and Alternaria major allergen (Alt a 1) genes, assigned five selected isolates as belonging to Alternaria alternata. Pathogenicity assays confirmed the Alternaria alternata species caused the observed symptoms. To our knowledge, this is the first report of honeysuckle leaf spot caused by A. alternata in China. The results of this study advance our understanding of honeysuckle leaf spot in China and lay the groundwork for developing efficient pre- and post-harvest control measures to stop the spread of the disease.

Alternaria alternata, the Causal Agent of a New Needle Blight Disease on Pinus bungeana.

Pinus bungeana, an endangered and native coniferous tree species in China, has considerable timber and horticulture value. However, little is known about needle diseases in P. bungeana. A needle blight of P. bungeana has been observed in Hebei Province, China. P. bungeana inoculated with mycelial plugs of fungal isolates presented symptoms similar to those observed under field conditions. Ten virulent fungal isolates were identified as a small-spored Alternaria species based on morphological observations. Maximum likelihood and Bayesian phylogenetic analyses carried out with multilocus sequence typing of eight regions (SSU, LSU, ITS, gapdh, tef1, Alt a 1, endoPG, OPA10-2) assigned the pathogen to Alternaria alternata. This is the first report of A. alternata causing needle blight on P. bungeana in China.

Characterization of New Small-Spored Alternaria Species Isolated from Solanaceae in Algeria.

Although large-spored Alternaria species of the section Porri are considered to be the major agents responsible for leaf spot and blight of Solanaceae, small-spored Alternaria species are also frequently isolated from symptomatic tissues. A survey of the north-western regions of Algeria during the 2017–2018 growing seasons revealed that amongst the 623 Alternaria isolates from tomato, potato, pepper, eggplant and black nightshade, 8% could not be morphologically assigned to either section Porri or section Alternaria. In order to more precisely determine the taxonomic position of these isolates, detailed morphological characterizations and multi-locus phylogenetic analyses were performed. Based on these analyses, the isolates were grouped into four main clades: section Ulocladioides, section Infectoriae, including two new species, section Embellisioides, and section Eureka, including one new species. These isolates were also characterized for their virulence under green-house conditions. They were able to produce leaf spot symptoms on tomato plants but with variable levels.

First Report of Moldy Core of Sweet Tango Apples from New Zealand Caused by Alternaria arborescens.

First Report of Moldy Core of Sweet Tango Apples from New Zealand Caused by Alternaria arborescens.

Alternaria Leaf Spot Caused by Alternaria Species: An Emerging Problem on Ornamental Plants in Italy.

Serious outbreaks of Alternaria leaf spot and plant decay have recently been recorded on several ornamental plants in the Biella Province (Northern Italy). Twenty-two fungal isolates were obtained from Alternaria infected plant tissues from 13 ornamental hosts. All the isolates were identified morphologically as small-spored Alternaria species. Multilocus sequence typing, carried out by means of ITS, rpb2, tef1, endoPG, Alt a 1, and OPA10-2, assigned 19 isolates as Alternaria alternata, two isolates as belonging to the Alternaria arborescens species complex, and one isolate as an unknown Alternaria sp. Haplotype analyses of ornamental and reference A. alternata isolates from 12 countries identified 14 OPA10-2 and 11 endoPG haplotypes showing a relatively high haplotype diversity. A lack of host specialization or geographic distribution was observed. The host range of the studied A. alternata isolates expanded in cross-pathogenicity assays, and more aggressiveness was frequently observed on the experimental plants than on the host plants from which the fungal isolates were originally isolated. High disease severity, population expansion, intraspecies diversity, and increased range of experimental hosts were seen in the emergence of Alternaria disease on ornamentals. More epidemiological and molecular studies should be performed to better understand these diseases, taking into consideration factors such as seed transmission and ongoing climate changes.

First Report of Leaf Spot Caused by Alternaria alternata on Ginseng (Panax ginseng) in China

Ginseng (Panax ginseng) is a perennial herbaceous plant and a precious traditional Chinese medicine. P. ginseng is widely cultivated in Asia, particularly the Changbai Mountain area in China (Wang et al. 2019). Alternaria species can grow under a wide range of temperatures that occur worldwide (Konstantinova et al. 2002). Alternaria panax was reported as the main cause of Alternaria leaf spot of ginseng (Deng et al. 2013); however, a small-spored Alternaria species was isolated from leaf spot symptoms during recent surveys. In our study, leaf spot disease of P. ginseng was observed during 2017 in the Fusong district, Jilin, China. The disease was widespread, with 20 to 30% of the fields affected. Leaves of the affected plants showed brown to black necrotic spots. The fungus was isolated from symptomatic leaves on potato dextrose agar and characterized morphologically under the microscope. Colonies of pure cultures were initially dark brown and then turned black after 7 days. Strains (TCS 15013001 and TCS 15013002) were grown on water agar embedded with surface-sterilized ginseng spot tissues under a 12/12-h light/dark cycle at room temperature. Conidia observed on the lesions were dark brown or olive-brown, ovoid or ellipsoid, short beaked, with three to seven transverse and zero to five longitudinal septa, and 14.9 to 36.5 μm (average 25.8 μm) × 5.8 to 17.9 μm (average 12.5 μm). Based on its morphological characteristics, the pathogen was identified as Alternaria sp. (Simmons 2007). Single-spore cultures were obtained, and their genomic DNA was extracted. The rDNA internal transcribed spacer (ITS, GenBank accession nos. MN394879 and MN394880), endopolygalacturonase (endoPG, MN410909 and MN410910), Alternaria major allergen (Alta1, MN410911 and MN410912), and the portion of the histone 3 (H3, MN410913 and MN410914), elongation factor 1-alpha (EF1-α, MN410915 and MN410916), the RNA polymerase II 2nd largest subunit (RPB2, MN410917 and MN410918), and glyceraldehyde 3-phosphate dehydrogenase (gpd, MN410919 and MN410920) gene were amplified from the two isolates, respectively (Woudenberg et al. 2015). Sequence analysis of the two isolates showed 99 to 100% identity to that of A. alternata (MG182428 for ITS, MG598798 for endoPG, MG598796 for Alt a1, MG182429 for H3, KU738723 for EF1-α, KU738707 for RPB2, and KP851761 for gpd). Pathogenicity tests were conducted in a greenhouse. Sixty healthy 2-year-old P. ginseng seedlings grown in potting medium were tested in a greenhouse at 20/26°C and about 90% relative humidity with natural light. Of the plants, 30 were sprayed with spore suspension (1 × 10⁵ spores/ml) until most of the leaves were wet. Control treatments (30 plants) were treated with distilled water. The two isolates were tested, and all test plants were covered with clear plastic bags for 3 days to increase humidity. Each treatment had three replicate plants. Six days after inoculation, leaf spots similar to the original ones developed at inoculation sites for all isolates, and A. alternata was consistently reisolated from the induced symptoms. The pathogenicity test was performed three times. A. alternata causing leaf spot of American ginseng was reported in China (Hill and Hausbeck 2008). Also, leaf spot of Panax notoginseng caused by A. alternata was reported in China (Yang et al. 2018). To our knowledge, this is the first report of A. alternata on P. ginseng in China.

Secondary metabolite profiles of small-spored Alternaria support the new phylogenetic organization of the genus

The group of the small-spored Alternaria species is particularly relevant in foods due to its high frequency and wide distribution in different crops. These species are responsible for the accumulation of mycotoxins and bioactive secondary metabolites in food. The taxonomy of the genus has been recently revised with particular attention on them; several morphospecies within this group cannot be segregated by phylogenetic methods, and the most recent classifications proposed to elevate several phylogenetic species-groups to the taxonomic status of section. The purpose of the present study was to compare the new taxonomic revisions in Alternaria with secondary metabolite profiles with special focus on sections Alternaria and Infectoriae and food safety. A total of 360 small-spored Alternaria isolates from Argentinean food crops (tomato fruit, pepper fruit, blueberry, apple, wheat grain, walnut, pear, and plum) was morphologically identified to species-group according to Simmons (2007), and their secondary metabolite profile was determined. The isolates belonged to A. infectoria sp.-grp. (19), A. tenuissima sp.-grp. (262), A. arborescens sp.-grp. (40), and A. alternata sp.-grp. (7); 32 isolates, presenting characteristics overlapping between the last three groups, were classified as Alternaria sp. A high chemical diversity was observed; 78 different metabolites were detected, 31 of them of known chemical structure. The isolates from A. infectoria sp.-grp. (=Alternaria section Infectoriae) presented a specific secondary metabolite profile, different from the other species-groups. Infectopyrones, novae-zelandins and phomapyrones were the most frequent metabolites produced by section Infectoriae. Altertoxin-I and alterperylenol were the only compounds that these isolates produced in common with members of section Alternaria. None of the well-known Alternaria toxins, considered relevant in foods, namely alternariol (AOH), alternariol monomethyl ether (AME), tenuazonic acid (TeA), tentoxin (TEN) or altenuene (ALT), were produced by isolates of this section. On the other hand, strains from section Alternaria (A. tenuissima, A. arborescens, and A. alternata sp.-grps.) shared a common metabolite profile, indistinguishable from each other. AOH, AME, ALT, TEN, and TeA were the most frequently mycotoxins produced, together with pyrenochaetic acid A and altechromone A. Alternaria section Alternaria represents a substantial risk in food, since their members in all types of crops are able to produce the toxic metabolites.

Chemotaxonomy of Mycotoxigenic Small-Spored Alternaria Fungi - Do Multitoxin Mixtures Act as an Indicator for Species Differentiation?

Necrotrophic as well as saprophytic small-spored Alternaria (A.) species are annually responsible for major losses of agricultural products, such as cereal crops, associated with the contamination of food and feedstuff with potential health-endangering Alternaria toxins. Knowledge of the metabolic capabilities of different species-groups to form mycotoxins is of importance for a reliable risk assessment. 93 Alternaria strains belonging to the four species groups Alternaria tenuissima, A. arborescens, A. alternata, and A. infectoria were isolated from winter wheat kernels harvested from fields in Germany and Russia and incubated under equal conditions. Chemical analysis by means of an HPLC-MS/MS multi-Alternaria-toxin-method showed that 95% of all strains were able to form at least one of the targeted 17 non-host specific Alternaria toxins. Simultaneous production of up to 15 (modified) Alternaria toxins by members of the A. tenuissima, A. arborescens, A. alternata species-groups and up to seven toxins by A. infectoria strains was demonstrated. Overall tenuazonic acid was the most extensively formed mycotoxin followed by alternariol and alternariol mono methylether, whereas altertoxin I was the most frequently detected toxin. Sulfoconjugated modifications of alternariol, alternariol mono methylether, altenuisol and altenuene were frequently determined. Unknown perylene quinone derivatives were additionally detected. Strains of the species-group A. infectoria could be segregated from strains of the other three species-groups due to significantly lower toxin levels and the specific production of infectopyrone. Apart from infectopyrone, alterperylenol was also frequently produced by 95% of the A. infectoria strains. Neither by the concentration nor by the composition of the targeted Alternaria toxins a differentiation between the species-groups A. alternata, A. tenuissima and A. arborescens was possible.

Identification and Characterization of Alternaria iridiaustralis Causing Leaf Spot on Iris ensata in China

In 2016, a severe leaf spot disease was found on Iris ensata Thumb. in Nanjing, China. The symptom was elliptical, fusiform, or irregularly necrotic lesion surrounded by a yellow halo, from which a small-spored Alternaria species was isolated. The fungus was identified as Alternaria iridiaustralis based on morphological characteristics. The pathogenicity tests revealed that the fungus was the causal pathogen of the disease. Phylogenic analyses using sequences of ITS, gpd, endoPG, and RPB2 genes confirmed the morphological identification. This study is the first report of A. iridiaustralis causing leaf spots on I. ensata in China.

Alternaria alternata, the causal agent of leaf blight of sunflower in South Africa

Sunflower (Helianthus annuus L.) is an important oilseed crop in South Africa, and is grown in rotation with maize in some parts of North West, Limpopo, Free State, Mpumalanga and Gauteng provinces. Alternaria leaf blight is currently one of the major potential disease threats of sunflower and is capable of causing yield losses in all production regions. Alternaria helianthi was reported as the main cause of Alternaria leaf blight of sunflower in South Africa; however small-spored Alternaria species have been consistently isolated from leaf blight symptoms during recent surveys. The aim of this study was to use morphological and molecular techniques to identify the causal agent(s) of Alternaria blight isolated from South African sunflower production areas. Alternaria helianthi was not recovered from any of the sunflower lesions or seeds, with only Alternaria alternata retrieved from the symptomatic tissue. Molecular identification based on a combined phylogenetic dataset using the partial internal transcribed spacer regions, RNA polymerase second largest subunit, glyceraldehyde-3-phosphate dehydrogenase, translation elongation factor and Alternaria allergen gene regions was done to support the morphological identification based on the three-dimensional sporulation patterns of Alternaria. Furthermore, this study aimed at evaluating the pathogenicity of the recovered Alternaria isolates and their potential as causal agents of Alternaria leaf blight of sunflower. Pathogenicity tests showed that all the Alternaria alternata isolates tested were capable of causing Alternaria leaf blight of sunflower as seen in the field. This is the first report of A. alternata causing leaf blight of sunflower in South Africa.

Molecular diversity and allergenic profiles of Alternaria spp. from desert environments in Arizona

This study examined the genetic diversity of small-spored Alternaria species in the southwest desert of the USA by sampling 552 isolates from different habitats (soil and plant debris) in different locations (urban and an undisturbed desert). To estimate the genetic diversity, Amplified Fragment Length Polymorphism (AFLP) fingerprinting analysis was performed for all isolates. Strains representative of the sampled genotypic diversity (n = 125) were further characterized according their sporulation pattern and the capability to produce allergens. Morphological characterization assigned the majority of the strains to the Alternaria alternata and Alternaria tenuissima morpho-groups with only two isolates assigned to the Alternaria arborescens morpho-group. AFLP fingerprinting differentiated the A. arborescens morpho-groups, but could not distinguish between the A. alternata and A. tenuissima morpho-groups. Western blot analysis showed that a large number of allergenic proteins were produced by strains. These proteins were not specific for any morpho-group nor source of isolation. A hierarchical analysis of molecular variance was performed on the AFLP data to quantify molecular variation and partition this variation among sampled locations and habitat. No statistically significant differentiation among locations and habitat was detected indicating a lack of population structure across environments.

Alternaria Species and Their Associated Mycotoxins.

The genus Alternaria includes more than 250 species. The traditional methods for identification of Alternaria species are based on morphological characteristics of the reproductive structures and sporulation patterns under controlled culture conditions. Cladistics analyses of "housekeeping genes" commonly used for other genera, failed to discriminate among the small-spored Alternaria species. The development of molecular methods achieving a better agreement with morphological differences is still needed. The production of secondary metabolites has also been used as a means of classification and identification. Alternaria spp. can produce a wide variety of toxic metabolites. These metabolites belong principally to three different structural groups: (1) the dibenzopyrone derivatives, alternariol (AOH), alternariol monomethyl ether (AME), and altenuene (ALT); (2) the perylene derivative altertoxins (ATX-I, ATX-II, and ATX II); and (3) the tetramic acid derivative, tenuazonic acid (TeA). TeA, AOH, AME, ALT, and ATX-I are the main. Certain species in the genus Alternaria produce host-specific toxins (HSTs) that contribute to their pathogenicity and virulence. Alternaria species are plant pathogens that cause spoilage of agricultural commodities with consequent mycotoxin accumulation and economic losses. Vegetable foods infected by Alternaria rot could introduce high amounts of these toxins to the human diet. More investigations on the toxic potential of these toxins and their hazard for human consumption are needed to make a reliable risk assessment of dietary exposure.

Identification and Enumeration of Small-Spored Alternaria Species Associated with Potato in the U.S. Northwest.

A number of Alternaria spp. have been isolated from potato worldwide but only Alternaria solani and A. alternata have been described as pathogenic to this host in the United States. These taxa are easily differentiated based on conidial morphology but species delimitation among the small-spored Alternaria spp. associated with potato are much more challenging. Accurate identification methods for small-spored Alternaria spp. are necessary so that a more thorough understanding of Alternaria epidemiology can be obtained. Isolations of Alternaria fungi from lesions on potato leaves collected in the U.S. Northwest were made between 2008 and 2011. Large-spored taxa (putatively A. solani), were isolated less frequently than small-spored taxa (putatively A. alternata sensu lato), except in 2010. Colletotrichum coccodes was isolated from necrotic lesions in 2008 to 2010 but not in 2011. Frequency of isolation ranged from 0.05 (5%) to 0.11 (11%) during the 3 years the fungus was detected. Anonymous genomic region OPA1-3, previously used for Alternaria systematics, allowed for the discrimination of phylogenetic lineages among 210 small-spored isolates. When OPA1-3 was restricted using enzyme ApaI, 65 isolates (31%) displayed a restriction banding pattern consistent with previously characterized morphospecies A. alternata and A. tenuissima and 145 (69%) displayed a restriction banding pattern consistent with the previously characterized morphospecies A. arborescens. Morphological characterization of a subsample of 59 small-spored Alternaria isolates randomly selected with each restriction pattern was compared with phylogenetic lineage. In all, 54 (92%) isolates were consistently assigned to the same group by both methods. Three isolates exhibited conidial morphologies that were inconsistent with any described morphospecies. A small number of isolates were identified as A. arbusti (infectoria group) via sequencing of the glyceraldehyde-3-phosphate-dehydrogenase locus and BLAST searches.

Alternaria section Alternaria: Species, formae speciales or pathotypes?

The cosmopolitan fungal genus Alternaria consists of multiple saprophytic and pathogenic species. Based on phylogenetic and morphological studies, the genus is currently divided into 26 sections. Alternaria sect. Alternaria contains most of the small-spored Alternaria species with concatenated conidia, including important plant, human and postharvest pathogens. Species within sect. Alternaria have been mostly described based on morphology and / or host-specificity, yet molecular variation between them is minimal. To investigate whether the described morphospecies within sect. Alternaria are supported by molecular data, whole-genome sequencing of nine Alternaria morphospecies supplemented with transcriptome sequencing of 12 Alternaria morphospecies as well as multi-gene sequencing of 168 Alternaria isolates was performed. The assembled genomes ranged in size from 33.3–35.2 Mb within sect. Alternaria and from 32.0–39.1 Mb for all Alternaria genomes. The number of repetitive sequences differed significantly between the different Alternaria genomes; ranging from 1.4–16.5 %. The repeat content within sect. Alternaria was relatively low with only 1.4–2.7 % of repeats. Whole-genome alignments revealed 96.7–98.2 % genome identity between sect. Alternaria isolates, compared to 85.1–89.3 % genome identity for isolates from other sections to the A. alternata reference genome. Similarly, 1.4–2.8 % and 0.8–1.8 % single nucleotide polymorphisms (SNPs) were observed in genomic and transcriptomic sequences, respectively, between isolates from sect. Alternaria, while the percentage of SNPs found in isolates from different sections compared to the A. alternata reference genome was considerably higher; 8.0–10.3 % and 6.1–8.5 %. The topology of a phylogenetic tree based on the whole-genome and transcriptome reads was congruent with multi-gene phylogenies based on commonly used gene regions. Based on the genome and transcriptome data, a set of core proteins was extracted, and primers were designed on two gene regions with a relatively low degree of conservation within sect. Alternaria (96.8 and 97.3 % conservation). Their potential discriminatory power within sect. Alternaria was tested next to nine commonly used gene regions in sect. Alternaria, namely the SSU, LSU, ITS, gapdh, rpb2, tef1, Alt a 1, endoPG and OPA10-2 gene regions. The phylogenies from the two gene regions with a relatively low conservation, KOG1058 and KOG1077, could not distinguish the described morphospecies within sect. Alternaria more effectively than the phylogenies based on the commonly used gene regions for Alternaria. Based on genome and transcriptome comparisons and molecular phylogenies, Alternaria sect. Alternaria consists of only 11 phylogenetic species and one species complex. Thirty-five morphospecies, which cannot be distinguished based on the multi-gene phylogeny, are synonymised under A. alternata. By providing guidelines for the naming and identification of phylogenetic species in Alternaria sect. Alternaria, this manuscript provides a clear and stable species classification in this section.

A new Alternaria species from grapevine in China

Twelve Alternaria strains were isolated from pedicels and rachis from different parts of grapevines in China. In a phylogenetic analysis, nine showed a close relationship with Alternaria longipes, and are described as a new species, A. viniferae sp. nov., but the other four clustered with A. alternata and A. arborescens within the alternata species-group. The new species can clearly be separated from other related small-spored Alternaria species based on sequences of portions of the glyceraldehyde-3-phosphate dehydrogenase (gpd) and Alternaria major allergen (Alt a 1) genes as well as by distinctive morphology.

Characterization of Alternaria species associated with leaf blight of sunflower in China

Nine Alternaria species have been reported to be associated with sunflower leaf blight worldwide, and A. helianthi has been recognized as the most prevalent and damaging species. However, the population structure of Alternaria species causing leaf blight of sunflower in China had not been examined thoroughly prior to this study. During 2010 to 2013, a total of 272 Alternaria isolates were obtained from infected sunflower leaves in 11 provinces, autonomous regions, and municipalities of China. Based on morphological traits and sequence analyses of the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) and the partial coding sequences of the histone 3 gene, 227 (83.5 %) isolates were identified as belonging to Alternaria tenuissima, the remainder 45 isolates were grouped to A. alternata (16.5 %). Compared with the ITS regions of rDNA, sequence analyses of the partial coding sequences of histone 3 gene displayed a critical role in discrimination of the small-spored Alternaria species. Phylogenetic analysis of the partial coding sequence of histone 3 gene clearly divided the representative Alternaria isolates into two main clades, A. tenuissima and A. alternata. The pathogenicity of A. tenuissima and A. alternata on detached leaves of sunflower cv. Gankui No.2 did not significantly differ between the two species or among isolates from different geographical origins. Our results indicate that the population structure of Alternaria species associated with sunflower leaf blight differed from that reported previously in China since A. helianthi was not found in this study. In addition, this is the first report about A. tenuissima causing leaf blight on sunflower in China.

Morphology, phylogeny and pathogenicity of Alternaria species, involved in leaf spot disease of sunflower in northern Iran

Leaf spot disease of sunflower is one of the most important foliar diseases on this crop worldwide. Several fungal groups are known to cause leaf spot disease on sunflower. Species of the genus Alternaria are the most common and serious leaf spot causing fungi on this crop. Leaf spot disease is the most destructive foliar diseases on sunflower in northern Iran; however, the identity of the causal agent remains unknown. The present study was aimed to characterise the identity of the causal agent of the disease by means of morphological and molecular data as well as to evaluate the pathogenicity of the responsible species. For this purpose, a total number of 97 fungal isolates were recovered from sunflower leaves with leaf spot disease symptoms from the sunflower fields in northwestern zone of Iran. All of the isolates were identified as Alternaria alternata based on cultural and morphological characteristics. A subset of isolates was subjected to phylogenetic analysis using sequence data from ITS-rDNA region, gpd and rpb2 genes. Sequence data from ITS-rDNA and gpd did not discriminate A. alternata from the other small-spored Alternaria species. A phylogeny inferred using sequence data from rpb2 gene clustered our isolates in several sub-clades within a single monophyletic clade. Sequence data for the type strain of the other small-spored Alternaria species has to be included in phylogenetic analysis, in order to make sure, whether the observed variations in rpb2 gene sequences are an indication for the population variation in sunflower isolates of A. alternata or define species boundaries among the small-spored Alternaria species. The results of pathogenicity assay on sunflower plants (cultivar Euroflor) under greenhouse condition revealed that A. alternata is pathogenic on sunflower.

Characterization of Alternaria isolates from the infectoria species-group and a new taxon from Arrhenatherum, Pseudoalternaria arrhenatheria sp. nov.

The infectoria species-group within the genus Alternaria was originally conceived by Simmons in 1993 and was based upon common morphological characteristics that included the development of conidial chains with primary, secondary, and tertiary branching resulting in substantial three-dimensional complexity. These characters can overlap to varying degrees with numerous taxa in another Alternaria group, the alternata species-group, making species-group differentiation difficult. However, members of the infectoria species-group are also distinguished from other small-spored Alternaria species based upon colony characteristics that typically include white or nearly white floccose colonies on DRYES medium and clumps of sporulation islands on low sugar media such as V8 agar, PCA, and weak PDA. In addition, the infectoria species-group contains representatives that are known to produce teleomorphs (Lewia), whereas the members of the alternata species-group and other Alternaria species-groups are strictly asexual. In this study, an assemblage of isolates recovered from varied hosts from the west coast of the United States were examined based upon morphological characters and compared to previously described members of the infectoria species-group. These isolates and members of the infectoria species-group typically produce arachnoid vegetative hyphae with multiple primary conidiophores, whereas other small-spored Alternaria species produce primary conidiophores predominately directly from the agar surface. Additionally, molecular phylogenetic analyses resolved these isolates and members of the infectoria species-group as distinctly nested amongst other sexual taxa in Allewia (Embellisia anamorph) and Macrospora (Nimbya anamorph) and phylogenetically distant to asexual lineages of Alternaria. One taxon among these isolates was novel and clustered with the asexual A. rosae in a distinct clade basal to all other members of the infectoria species-group. A new genus is proposed, Pseudoalternaria gen. nov. and a new taxon is described, Pseudoalternaria arrhenatheria sp. nov.. Moreover, a second taxon is reclassified, Pseudoalternaria rosae comb. nov.