The Host Stomatal Density Determines Resistance to Septoria gentianae in Japanese Gentian.

Plant stomata represent the main battlefield for host plants and the pathogens that enter plant tissues via stomata. Septoria spp., a group of ascomycete fungi, use host plant stomata for invasion and cause serious damage to agricultural plants. There is no evidence, however, showing the involvement of stomata in defense systems against Septoria infection. In this study, we isolated Septoria gentianae 20-35 (Sg20-35) from Gentiana triflora showing gentian leaf blight disease symptoms in the field. Establishment of an infection system using gentian plants cultured in vitro enabled us to observe the Sg20-35 infection process and estimate its virulence in several gentian cultivars or lines. Sg20-35 also entered gentian tissues via stomata and showed increased virulence in G. triflora compared with G. scabra and their interspecific hybrid. Notably, the susceptibility of gentian cultivars to Sg20-35 was associated with their stomatal density on the adaxial but not abaxial leaf surface. Treatment of EPIDERMAL PATTERNING FACTOR-LIKE 9 (EPFL9/STOMAGEN) peptides, a small secreted peptide controlling stomatal density in Arabidopsis thaliana, increased stomatal density on the adaxial side of gentian leaves as well. Consequently, treated plants showed enhanced susceptibility to Sg20-35. These results indicate that stomatal density on the adaxial leaf surface is one of the major factors determining the susceptibility of gentian cultivars to S. gentianae and suggest that stomatal density control may represent an effective strategy to confer Septoria resistance.

Rapid temporal changes in root colonization by arbuscular mycorrhizal fungi and fine root endophytes, not dark septate endophytes, track plant activity and environment in an alpine ecosystem.

Fungal root endophytes play an important role in plant nutrition, helping plants acquire nutrients in exchange for photosynthates. We sought to characterize the progression of root colonization by arbuscular mycorrhizal fungi (AMF), dark septate endophytes (DSE), and fine root endophytes (FRE) over an alpine growing season, and to understand the role of the host plant and environment in driving colonization levels. We sampled four forbs on a regular schedule from June 26th-September 11th from a moist meadow (3535 m a.s.l) on Niwot Ridge, Rocky Mountain Front Range, CO, USA. We quantified the degree of root colonization by storage structures, exchange structures, and hyphae of all three groups of fungi. AMF and FRE percent colonization fluctuated significantly over time, while DSE did not. All AMF structures changed over time, and the degree of change in vesicles differed by plant species. FRE hyphae, AMF arbuscules and AMF vesicles peaked late in the season as plants produced seeds. AMF hyphae levels started high, decreased, and then increased within 20 days, highlighting the dynamic nature of plant-fungal interactions. Overall, our results show that AMF and FRE, not DSE, root colonization rapidly changes over the course of a growing season and these changes are driven by plant phenology and seasonal changes in the environment.

[Species and ecological control of disease on cultivated Gentiana rigescens in Yunnan].

OBJECTIVE: To find out variety of the fungal diseases of cultivated Gentiana rigescens and provide important basis for prevention. METHODS: The diseases were diagnosed based on field investigate, symptoms observation, pathogen isolation, determination the size of morphological and verification following the Koch's Postulate procedures. RESULTS: Anthracnose (Colletotrichum gloeosporioides), grey mould (Botrytis cinerea), brown spot (Alternaria tenuis), rust (Aecidiumpers), circular spot (Pestalotiopsis), leaf blight (Stemphylium, Ascochyta, Pleospora) and nematodes (Heterodera spp., Meloidogyne spp.) were found on Gentiana rigescens. Anthracnose was the first main disease, the diseased plant rate was over 40% and disease severity was 4 - 5 degree and second disease was rust, incidence of rate was less 10% and other diseases rate was not enough 2%. CONCLUSION: All these diseases on Gentiana rigescens are reported for the first time and Gentiana rigescens is the new host plant of the diseases.

The molecular phylogeny of the white blister rust genus Pustula reveals a case of underestimated biodiversity with several undescribed species on ornamentals and crop plants.

Despite their economic importance, the knowledge of the biodiversity of many plant pathogens is still fragmentary. In this study we show that this is true also for the white blister rust genus Pustula that is parasitic on several genera in the asterids, including sunflower and the gentian, Eustoma. It is revealed that several distinct species exist in Pustula, suggesting that species are mostly host genus specific. No geographic patterns were observed in the occurrence of Pustula, the host range of which includes the Araliaceae, Asteraceae, Gentianaceae, and Goodeniaceae. Evidence points to these becoming hosts as a result of jumps from the Asteraceae, with subsequent host-specific adaptation and speciation. Among the undescribed species are pathogens of economic importance, e.g. the white blister rusts of sunflower, or with still restricted geographical ranges, e.g. Pustula centaurii, which could potentially spread with international seed trade, if no quarantine restrictions are implemented.

Gentiopicrin-producing endophytic fungus isolated from Gentiana macrophylla.

Gentiana macrophylla is a traditional Chinese medicinal plant. Its dominant active constituents are secoiridoids, mainly gentiopicrin. The objective of this study was to determine whether endophytic fungi isolated from this plant produce the bioactive ingredient gentiopicrin. Primary screening was done by Dragendorff's reaction and the strain re-selection was done with thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) to identify the fermentation products of the selected strains. In this study, 20 strains of endophytic fungi were isolated from G. macrophylla, and the extracts from five strains had a positive Dragendorff's reaction. Two strains (QJ16 and QJ18) had a component with the same R(f) value in TLC as that of authentic gentiopicrin and one ingredient of the QJ18 extract had a retention time identical with that of authentic gentiopicrin in HPLC. Therefore, the fungus appears to produce the bioactive ingredient gentiopicrin, as does its host plant, and could be used for the production of gentiopicrin by fermentation.

A peroxiredoxin Q homolog from gentians is involved in both resistance against fungal disease and oxidative stress.

An antifungal protein (GtAFP1) showing antimicrobial activity against phytopathogenic fungi was purified from leaves of Gentiana triflora. The deduced amino acid sequence of the cDNA of the corresponding gene, GtAFP1, showed 94, 75, 72 and 63% amino acid identities with peroxiredoxin Q from Populus balsamifera x P. deltoides subsp. trichocarpa, Sedum lineare, Suaeda maritima and Arabidopsis thaliana, respectively. The GtAFP1 gene is suggested to be present in the genome in one to two copies and was expressed in the leaves, roots and stems. Expression of GtAFP1 was induced by treatment with salicylic acid, but not methyl jasmonate. Recombinant GtAFP1 protein showed not only antifungal activity but also thioredoxin-dependent peroxidase activity. Overexpression of GtAFP1 in tobacco plants improved tolerance not only against fungal diseases but also against oxidative stress. These results indicate that GtAFP1 might act as a disease and oxidative stress defensive gene in plants and could be useful for engineering stress-resistant plants.