Conyza bonariensis as an alternative host for Colletotrichum species in Argentina.

AIMS: This study investigated the diversity of Colletotrichum isolates recovered from Conyza bonariensis leaves through the use of morphological characteristics, growth rate, carbon sources utilization and phylogenetic analysis. METHODS AND RESULTS: In all, 30 Colletotrichum isolates recovered from C. bonariensis leaves showing symptoms of disease were included in the present study. Based on the analysis of morphology and sequences, the isolates were distributed into six Colletotrichum species complexes. The concatenated alignment of GAPDH and ITS sequences showed that 20 out of 30 isolates were included in four species complexes which comprise the most important pathogens causing anthracnose in soybean or anthracnose and stalk rot in maize: C. truncatum, C. orchidearum, C. gloeosporioides and C. graminicola. The remaining 10 isolates were included in the C. boninense and C. destructivum species complexes or could not be assigned to any complex with the available information. CONCLUSION: Weeds belonging to genus Conyza are host to soybean and maize potential pathogenic species of Colletotrichum and could have a role as inoculum reservoir for cross contamination in the agroecosystem. SIGNIFICANCE AND IMPACT OF THE STUDY: The combined use of morphological, kinetics and physiological parameters of growth and phylogenetic analysis in Colletotrichum isolates from Conyza leaves allowed the detection of species complexes previously not identified in Argentina.

Mycobiota of the weed Conyza canadensis (Asteraceae) in Brazil.

Conyza canadensis is a noxious and notably problematic weed in Brazil whose control is greatly challenging due to the appearance, in the last years, of herbicide resistant populations. An investigation regarding the associated pathogenic fungi of this plant was conducted in Brazil aimed at starting a biological control program to help mitigate its economic impact. Ten fungal species were yielded and described: two ascomycetes (Leptosphaerulina conyzicola sp. nov. and Wentiomyces melioloides), five hyphomycete asexual morphs (Alternaria tenuissima, Cercospora conyzicola sp. nov., Cercosporella virgaureae, and Fusarium fujikuroi), two coelomycete asexual morphs (Phoma conyzaphthora sp. nov., Septoria erigerontis), one rust fungus (Aecidium conyzicola sp. nov.), and one oomycete (Basidiophora entospora). Four among the fungi that were collected represent new taxa, and the others represented either new host-records of known fungal species or new geographic records or both, except for C. virgaureae that had already been recorded on C. canadensis in Brazil. None of the discovered species have any potential to be used as a mycoherbicide or to be introduced somewhere else, nevertheless, the knowledge about this mycobiota will help guide the selection of potential biocontrol agents to be introduced in Brazil.

Conyzicola lurida gen. nov., sp. nov., isolated from the root of Conyza canadensis.

A novel Gram-stain-positive, non-spore-forming, pale yellow, irregular rod-shaped bacterium designated strain HWE2-01(T) was isolated from the surface-sterilized root of horseweed (Conyza canadensis). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain HWE2-01(T) belongs to the family Microbacteriaceae and showed sequence similarity levels of 97.1-97.7% with species of the genus Salinibacterium, 95.9-97.6% with species of the genus Leifsonia and 97.1% with Homoserinimonas aerilata. The highest sequence similarity (97.7%) was with Salinibacterium xinjiangense 0543(T). The genomic DNA G+C content of the novel strain was 68.1 mol%. The predominant cellular fatty acid of strain HWE2-01(T) was anteiso-C15 : 0, major menaquinones were MK-10, MK-9 and MK-11, and diagnostic polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The peptidoglycan of the novel strain contained 2,4-diaminobutyric acid, alanine, glycine and glutamic acid. The cell-wall sugars of strain HWE2-01(T) were galactose, mannose and rhamnose. The murein was of the acetyl type. Based on the results of the phenotypic and phylogenetic analysis, strain HWE2-01(T) differed in some respects from other members of the family Microbacteriaceae. Therefore, strain HWE2-01(T) is proposed to represent a novel species of a new genus in the family Microbacteriaceae with the name Conyzicola lurida gen. nov., sp. nov. (type strain = HWE2-01(T) = KCTC 29231(T) = JCM 19257(T)).

Nocardioides endophyticus sp. nov. and Nocardioides conyzicola sp. nov., isolated from herbaceous plant roots.

Two Gram-stain-positive, non-motile, non-spore-forming, rod-shaped actinobacterial strains were isolated from the surface-sterilized roots of mugwort (Artemisia princeps) and horse-weed (Conyza canadensis), and subjected to taxonomic characterization. 16S rRNA gene sequence analysis indicated that the isolates, designated MWE 3-5(T) and HWE 2-02(T), should be placed in the genus Nocardioides of the family Nocardioidaceae. The strains were closely related to Nocardioides hankookensis DS-30(T), which exhibited 16S rRNA gene sequence similarity values of 97.99 and 99.09 % with strains MWE 3-5(T) and HWE 2-02(T), respectively. The genome relatedness of N. hankookensis DS-30(T) with strain MWE 3-5(T) was 35.8 %, and that with strain HWE 2-02(T) was 36.4 %, whereas that between the two isolates was 43.2 %. Strains MWE 3-5(T) and HWE 2-02(T) possessed MK-8(H4) as the major isoprenoid quinone, and ll-diaminopimelic acid in the cell-wall peptidoglycan. The main fatty acids were iso-C16 : 0, iso-C17 : 0 and C18 : 1ω9c for strain MWE 3-5(T) and iso-C16 : 0, 10-methyl C18 : 0 and C18 : 1ω9c for strain HWE 2-02(T). Based on phenotypic, genotypic and phylogenetic studies, the following two novel species are proposed: Nocardioides endophyticus sp. nov. (type strain, MWE 3-5(T) = KCTC 29122(T) = JCM 18532(T)) and Nocardioides conyzicola sp. nov. (type strain, HWE 2-02(T) = KCTC 29121(T) = JCM 18531(T)).

Studies on the diversity of arbuscular mycorrhizal fungi and the efficacy of two native isolates in a highly alkaline anthropogenic sediment.

A field survey of the arbuscular mycorrhizal status of herbaceous plant species was conducted in a highly alkaline anthropogenic sediment resulting from the disposal of waste from an acetylene and polyvinyl chloride factory. Most plant species found at the site were mycorrhizal and the dominant mycotrophic plant species was Conyza bilbaoana. Fungal species richness was assessed by identification of spores extracted from the sediment and from continuously propagated trap pot cultures. All of the six species of arbuscular mycorrhizal fungi (AMF) found were from the genus Glomus. Glomus intraradices and G. mosseae were found in field-collected sediment samples and also occurred most frequently in trap cultures. To test the symbiotic effectiveness of these two fungi, seedlings of C. bilbaoana were inoculated with either native G. intraradices BEG163 or G. mosseae BEG198 and non-native G. intraradices BEG75 or G. mosseae BEG25 isolates in sterile and non-sterile sediment collected from the study site. All four isolates were able to colonise C. bilbaoana. However, AMF native to the target sediments were generally more effective than the non-native fungi in promoting plant establishment and growth under highly alkaline conditions. The non-native G. intraradices was, however, more effective than the non-native G. mosseae. The results of this study suggest the use of adapted AMF as inoculants for phytorestoration of alkaline anthropogenic-stressed sediments.

Role of reactive oxygen species and antioxidants in plant disease resistance.

Membrane damage caused by the non-specific fungal toxin fusaric acid was less on pretreated than on control leaves when tobacco leaves were pretreated with anti-senescence plant hormones, such as kinetin, benzyladenine or the anti-ozonant N-[2-(2-oxo-1-imidazolidinyl)]ethyl-N'-phenylurea. Similarly, the necrosis caused by mercuric chloride was reduced by the above anti-senescence agents. In addition, in in vitro tests, leaves from selected paraquat-tolerant tobacco plants were less sensitive to Alternaria alternata (Fr) Keissler infection than those of the control paraquat-sensitive tobacco leaves. Paraquat-tolerant Conyza canadensis (L) Cronq weeds naturally selected in vineyards in Hungary showed similar inhibition of senescence to paraquat-tolerant tobacco, expressed as more green leaves and slower development. In accordance with this, the paraquat-tolerant Conyza leaves remained almost symptomless, while paraquat-sensitive plants showed severe symptoms after infection with Botrytis cinerea Pers. Oxidative burst (accumulation of hydrogen peroxide) was attenuated in TMV-infected leaves of Xanthi-nc tobacco as a result of treatment with salicylic acid or in leaves where systemic acquired resistance (SAR) had been induced by a previous TMV infection. Accordingly, superoxide dismutase (SOD) activity was higher in Xanthi tobacco leaves with SAR than without SAR. However, in NahG tobacco, in which SAR cannot develop, there was no augmentation of SOD activity. All the above data support the significance of delayed senescence and antioxidants in the resistance of plants to biotic and abiotic necrosis-inducing agents.