Characterization and colonization of endomycorrhizal Rhizoctonia fungi in the medicinal herb Anoectochilus formosanus (Orchidaceae)

Mechanisms associated with the synergistic induction of resistance to tobacco black shank in tobacco by arbuscular mycorrhizal fungi and β-aminobutyric acid

Tobacco black shank (TBS), caused by Phytophthora nicotianae, is one of the most harmful diseases of tobacco. There are many studies have examined the mechanism underlying the induction of disease resistance by arbuscular mycorrhizal fungi (AMF) and β-aminobutyric acid (BABA) alone, but the synergistic effects of AMF and BABA on disease resistance have not yet been studied. This study examined the synergistic effects of BABA application and AMF inoculation on the immune response to TBS in tobacco. The results showed that spraying BABA on leaves could increase the colonization rate of AMF, the disease index of tobacco infected by P.nicotianae treated with AMF and BABA was lower than that of P.nicotianae alone. The control effect of AMF and BABA on tobacco infected by P.nicotianae was higher than that of AMF or BABA and P.nicotianae alone. Joint application of AMF and BABA significantly increased the content of N, P, and K in the leaves and roots, in the joint AMF and BABA treatment than in the sole P. nicotianae treatment. The dry weight of plants treated with AMF and BABA was 22.3% higher than that treated with P.nicotianae alone. In comparison to P. nicotianae alone, the combination treatment with AMF and BABA had increased Pn, Gs, Tr, and root activity, while P. nicotianae alone had reduced Ci, H₂O₂ content, and MDA levels. SOD, POD, CAT, APX, and Ph activity and expression levels were increased under the combined treatment of AMF and BABA than in P.nicotianae alone. In comparison to the treatment of P.nicotianae alone, the combined use of AMF and BABA increased the accumulation of GSH, proline, total phenols, and flavonoids. Therefore, the joint application of AMF and BABA can enhance the TBS resistance of tobacco plants to a greater degree than the application of either AMF or BABA alone. In summary, the application of defense-related amino acids, combined with inoculation with AMF, significantly promoted immune responses in tobacco. Our findings provide new insights that will aid the development and use of green disease control agents.

Isolation and identification of beneficial orchid mycorrhizal fungi in Paphiopedilum barbigerum (Orchidaceae)

Seed germination and seedling development in nearly all orchid species rely on a symbiotic relationship with mycorrhizal fungi; however, this is not the case with all mycorrhizal fungi. This study aims to provide an understanding about the important role of mycorrhiza in seed germination and growth of Paphiopedilum barbigerum. Therefore, we isolated and identified endophytic fungi from the roots of wild P. barbigerum. The beneficial mycorrhizal fungi Epulorhiza sp. FQXY019 and Tulasnella calospora FQXY017 were screened by seed symbiotic germination tests and found to promote seed germination. However, only the seeds inoculated with FQXY019 progressed from the seed germination to rooting stage. This shows that mycorrhizal fungi and P. barbigerum have a specific relation at different growth phases. In addition, we selected FQXY019 and inoculated it into MS medium, B5 medium, OMA medium, and PDA medium. The results showed that FQXY019 co-cultured on PDA significantly promoted the increase in seedling fresh weight, leaf length, and root length (p < .01). Furthermore, it significantly promoted the root number and leaf number of seedlings compared with those co-cultured on MS, B5, and OMA media and control (p < .05). Thus, this study demonstrated the promoting effect of Epulorhiza sp. FQXY019 on seed germination and seedling development, making it an alternative method for the artificial propagation of P. barbigerum.

Diversity and Aggressiveness of Rhizoctonia spp. from Nebraska on Soybean and Cross-Pathogenicity to Corn and Wheat

Rhizoctonia and Rhizoctonia-like species of fungi that cause disease are known to have varying host ranges and aggressiveness. Accurate identification of these species causing disease is important for soybean disease management that relies upon crop rotation. The anamorphic genus Rhizoctonia contains several diverse species and anastomosis groups (AGs) including some known soybean pathogens, such as Rhizoctonia solani, whereas for others the ability to cause disease on soybean has not been well described. The present study was conducted to identify the predominant species and AG of Rhizoctonia from soybean, corn, and wheat fields that are pathogenic on soybean and characterize cross-pathogenicity to common rotational crops, corn and wheat. We surveyed for Rhizoctonia spp. in Nebraska; isolates were identified to species and AG, and aggressiveness was assessed. A total of 59 R. zeae isolates, 49 R. solani, nine binucleate Rhizoctonia, three R. circinata, and two R. oryzae isolates were collected in 2016 and 2017 from a total of 29 fields in 15 counties. The most abundant R. solani AGs were AG-4, AG-1 IB, AG-2-1, AG-3, and AG-5. R. solani AG-4 and R. zeae were found in all three regions of the state (west, central, and eastern). Some isolates that were most aggressive to soybean seedlings were cross-pathogenic on both wheat and corn. In addition, R. zeae was pathogenic on soybean when evaluated at 25°C, which is warmer than temperatures used previously, and isolates were identified that were aggressive on soybean and cross-pathogenic on both corn and wheat.

Epidendrumradicans Fungal Community during Ex Situ Germination and Isolation of Germination-Enhancing Fungi

Orchids exhibit varying specificities to fungi in different microbial environments. This pilot study investigated the preference of fungal recruitment during symbiotic germination of Epidendrum radicans Pav. ex Lindl. Two different orchid substrates were used for ex situ seed baiting: pine bark and rotten oak leaf, with Basidiomycota and Ascomycota as the respective dominant groups. Both substrates promoted seed germination, with a higher protocorm formation rate on pine bark (65.75%). High-throughput sequencing characterized the fungal communities of germinated protocorms. Basidiomycota was the dominant group in protocorms that symbiotically germinated on both substrates. The family-level community structures of endophytic fungi in protocorms that symbiotically germinated on both substrates were close to those of protocorms that germinated in vitro on MS1 medium. For protocorms, the dominant fungal groups recruited from substrates differed at the genus level; from pine bark, they were genera belonging to unclassified Sebacinales (41.34%), Thanatephorus (14.48%) and Fusarium (7.35%), while, from rotten oak leaf, they were Rhizoctonia (49.46%), Clitopilus (34.61%), and Oliveonia (7.96%). Four fungal isolates were successfully obtained and identified as belonging to the family Tulasnellaceae, genera Ceratobasidium and Peniophora, which could promote seed germination to the seedling stage. The data indicate that endophytic fungi for E. radicans germination on two different substrates are affected at the genus level by the substrate, with a degree of specificity at the family level.

Mycorrhizal Compatibility and Germination-Promoting Activity of Tulasnella Species in Two Species of Orchid (Cymbidium mannii and Epidendrum radicans)

In nature, Orchidaceae seeds establish a relationship with orchid mycorrhizal fungi to obtain essential nutrients for germination. The orchids, Cymbidium mannii and Epidendrum radicans, have significant ornamental and economic value. We isolated and cultured mycorrhizal fungi from C. mannii, E. radicans, and C. goeringii roots. Three strains of fungi, Tulasnella calospora (Tca), T. asymmetrica (Tas), and T. bifrons (Tbi), were identified using ITS-rDNA sequencing. Their mycorrhizal compatibility, germination-promoting effects, and symbiosis with the seeds of C. mannii and E. radicans were studied in vitro using various concentrations of oatmeal agar (OA) medium. Tca exhibited significant seed-germination-promoting effects on C. mannii (92.1%) and E. radicans (84.7%) on 2.0 and 4.0 g/L OA, respectively. For Tbi and Tas, the highest germination percentages were observed on 4.0 g/L OA in E. radicans (73.60% and 76.49%, respectively). Seed germination in C. mannii was enhanced by high oatmeal concentrations (8.0 and 12.0 g/L) during symbiosis with Tas, whereas Tbi had no effect regardless of OA concentration. Tca exhibited high compatibility with C. mannii and E. radicans, and the oatmeal concentration of the medium affected this compatibility. The findings of this study will aid in the propagation of endangered orchid species for conservation and commercial purposes using mycorrhizal technology.

Evolutionary and genomic comparisons of hybrid uninucleate and nonhybrid Rhizoctonia fungi

The basidiomycetous fungal genus, Rhizoctonia, can cause severe damage to many plants and is composed of multinucleate, binucleate, and uninucleate species differing in pathogenicity. Here we generated chromosome-scale genome assemblies of the three nuclear types of Rhizoctonia isolates. The genomic comparisons revealed that the uninucleate JN strain likely arose by somatic hybridization of two binucleate isolates, and maintained a diploid nucleus. Homeolog gene pairs in the JN genome have experienced both decelerated or accelerated evolution. Homeolog expression dominance occurred between JN subgenomes, in which differentially expressed genes show potentially less evolutionary constraint than the genes without. Analysis of mating-type genes suggested that Rhizoctonia maintains the ancestral tetrapolarity of the Basidiomycota. Long terminal repeat-retrotransposons displayed a reciprocal correlation with the chromosomal GC content in the three chromosome-scale genomes. The more aggressive multinucleate XN strain had more genes encoding enzymes for host cell wall decomposition. These findings demonstrate some evolutionary changes of a recently derived hybrid and in multiple nuclear types of Rhizoctonia.

Effects of the mycorrhizal fungus Ceratobasidium sp. AR2 on growth and flavonoid accumulation in Anoectochilus roxburghii

Background

Anoectochilus roxburghii is a traditional Chinese medicine with potent medicinal activity owing to the presence of secondary metabolites, particularly flavonoids. A. roxburghii also maintains a symbiotic relationship with mycorrhizal fungi. Moreover, mycorrhizal fungi can induce metabolite synthesis in host plants. However, little is known about the role of mycorrhizal fungi in promoting the accumulation of flavonoid metabolites in A. roxburghii.

Methods

A. roxburghii and the isolated fungus Ceratobasidium sp. AR2 were cocultured. The portion of A. roxburghii above the medium treated with or without AR2 was studied by transcriptome and target metabolome analyses.

Results

AR2 promoted the growth and development of A. roxburghii. The contents of total flavonoid, rutin, isorhamnetin, and cyanidin-3-glucoside chloride were increased compared with those in uninoculated cultures. Transcriptome analysis suggested that 109 unigenes encoding key enzymes were potentially associated with changes in flavonoids. Quantitative real-time polymerase chain reaction of fourteen flavonoid-related unigenes showed that most flavonoid biosynthetic genes were significantly differentially expressed between inoculated and uninoculated plantlets.

Conclusion

The isolate AR2 could significantly promote the growth and development of A. roxburghii and the accumulation of flavonoids. Overall, our findings highlighted the molecular basis of the effects of mycorrhizal fungi on flavonoid biosynthesis in A. roxburghii and provided novel insights into methods to improve the yield and quality of A. roxburghii.

Embryology of Anoectochilus roxburghii: seed and embryo development

BACKGROUND

Anoectochilus roxburghii is known for its medicinal properties, culinary interests, and ornamental applications in Asian countries. Recent studies focus mainly on its phytochemical properties and little is known about its reproductive biology, especially seed and embryo development. This study documents the major developmental events in seed and embryo development of A. roxburghii upon pollination.

RESULTS

Morphological and histological studies revealed that upon pollination embryo and seed development is completed in 40 days. Ovular primordia are at the megaspore mother cell stage at the time of anthesis. Embryo development proceeds after a successful fertilization. A. roxburghii has a single cell suspensor. It elongates but not extended beyond the seed coat. A distinct cell gradient is present within the embryo proper with smaller cells located towards the chalazal end of the seed. Proteins and lipids are the major storage products within the embryo proper cells. At the stage of early globular embryo, the inner seed coat has degenerated and thus a carapace is absent at maturity. A limited deposition of lignin is detected in the mature seed coat.

CONCLUSIONS

The seed of A. roxburghii matures rapidly. At maturity, the embryo proper has a well-differentiated apical zone with little constraints impose by the seed coat. These characters indicate adaptations to fast germination that may ensure a successful colonization in the shaded forest understory.

Remote tropical island colonization does not preclude symbiotic specialists: new evidence of mycorrhizal specificity across the geographic distribution of the Hawaiian endemic orchid Anoectochilus sandvicensis

BACKGROUND AND AIMS

For symbiotic organisms, their colonization and spread across remote oceanic islands should favour generalists. Plants that form obligate symbiotic associations with microbes dominate island ecosystems, but the relationship between island inhabitance and symbiotic specificity is unclear, especially in the tropics. To fill this gap, we examined the mycorrhizal specificity of the Hawaiian endemic orchid Anoectochilus sandvicensis across multiple populations encompassing its entire geographic distribution.

METHODS

By molecular phylogenetic approaches we identified the mycorrhizal fungi associated with A. sandvicensis across its entire geographic distribution and determined the relationship of these fungi to others found elsewhere around the globe. With richness estimators, we assessed the mycorrhizal specificity of A. sandvicensis within and among islands. We then tested whether geographic proximity of orchid populations was a significant predictor for the presence of particular mycorrhizal fungi and their community composition.

KEY RESULTS

We found that each population of A. sandvicensis forms specific associations with one of three fungi in the genus Ceratobasidium and that the closest relatives of these fungi are globally widespread. Based on diversity indices, A. sandvicensis populations were estimated to partner with one to four mycorrhizal taxa with an estimated total of four compatible mycorrhizal fungi across its entire distribution. However, the geographic proximity of orchid populations was not a significant predictor of mycorrhizal fungal community composition.

CONCLUSIONS

Our findings indicate that the colonization and survival of plant species on even the most remote oceanic islands is not restricted to symbiotic generalists, and that partnering with few, but cosmopolitan microbial symbionts is an alternative means for successful island establishment. We suggest that the spatial distribution and abundance of symbionts in addition to island age, size and isolation should also be taken into consideration for predictions of island biodiversity.

Seed germination and development of orchid seedlings (Cyrtopodium saintlegerianum) with fungi

Abstract Fungi of Rhizoctonia complex are mycorrhizal of orchids and may to germinate yours seeds and development the seedlings. In this context, our objective was to select a fungal isolate to promote seed germination and seedling development of Cyrtopodium saintlegerianum. Pelotons were found in the roots and three mycorrhizal fungi were isolated. We tested mycorrhizal isolates obtained from C. saintlegerianum roots and six mycorrhizal fungi from other orchids as well three pathogenic isolates (of rice and bean) to germinate the seeds in oatmeal-agar medium. Seeds not inoculated were used as control. The isolates En07 (Waitea circinata), Cs10 (Tulasnella sp.) and Ro88 (Rhizoctonia oryzae) were efficient to promote seed germination, but only En07 differing statistically of the control. The non-specific isolate En07 promoted germination in 81% of seeds and the specific isolate (Cs10) promoted 60%, evidencing the non-specificity mycorrhizal association in this orchid during germination. Axenic seedlings were inoculated with four mycorrhizal fungi (non-inoculated seedlings - control). After six months, the isolates En07 and Cs10 were efficient in the interaction with the seedlings, but did not differ to the control. Therefore, our results suggested that fungi of the Rhizoctonia complex can be used in the germination and seedling development of C. saintlegerianum.

Adaptation and tolerance mechanisms developed by mycorrhizal Bipinnula fimbriata plantlets (Orchidaceae) in a heavy metal-polluted ecosystem

The adaptation and performance of orchid mycorrhizae in heavy metal-polluted soils have been poorly explored. In the present study, proteomic and metabolic approaches were used to detect physiological changes in orchid roots established in a heavy metal-polluted soil and to ascertain whether mycorrhizal fungi affect the metabolic responses of roots. Young Bipinnula fimbriata plantlets were established in control and heavy metal-polluted soils in a greenhouse. After 14 months, exudation of root organic acids, phenolics, percentage of mycorrhization, mineral content, and differential protein accumulation were measured. More root biomass, higher root colonization, and higher exudation rates of citrate, succinate, and malate were detected in roots growing in heavy metal-polluted soils. Higher accumulation of phosphorus and heavy metals was found inside mycorrhizal roots under metal stress. Under non-contaminated conditions, non-mycorrhizal root segments showed enhanced accumulation of proteins related to carbon metabolism and stress, whereas mycorrhizal root segments stimulated protein synthesis related to pathogen control, cytoskeleton modification, and sucrose metabolism. Under heavy metal stress, the proteome profile of non-mycorrhizal root segments indicates a lower induction of defense mechanisms, which, together with the stimulation of enzymes related to carotenoid biosynthesis and cell wall organization, may positively influence mycorrhizal fungi colonization. The results point to different metabolic strategies in mycorrhizal and non-mycorrhizal root segments that are exposed to heavy metal stress. The results indicate that root colonization by mycorrhizal fungi is stimulated to alleviate the negative effects of heavy metals in the orchids.

Increase in Artemisia annua Plant Biomass Artemisinin Content and Guaiacol Peroxidase Activity Using the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis

The main objective of this study was to investigate Artemisia annua plant property variations in terms of plant biomass, glandular trichome numbers, artemisinin production and Guaiacol peroxidase (GPOX) activity when plants are in mutualism with AMF. According to the results, A. annua mutualism with AMF significantly increased the most important and pharmaceutically relevant factors of fresh and dry plant biomass. This increase, especially in the biomass of plant herba (leaves), was 30% higher during the vegetation period and remained high (29% higher than for control) when plants were harvested at the end of the vegetation period. Similar differences in dry biomass were also detected. Glandular trichomas numbers increased by 40%, and the artemisinin content by 17% under AMF colonization. No effects due to AMF on chlorophyll variations were detected, while GPOX enzyme concentrations increased significantly under AMF colonization. Altogether the Artemisia plant properties with high pharmaceutically importance (fresh and dry biomass of leaves and artemisinin, number of trichomes and the artemisinin content) were significantly improved by AMF, the application in Artemisia cultivation can be an effective and cheap method. The high GPOX activity under AMF colonization indicate an enhanced oxidative stress alleviation, therefore a higher resistance to water deficiency, mechanisms important under climate conditions with low water supply where Artemisia is usually cultivated.

Mycorrhizal compatibility and symbiotic seed germination of orchids from the Coastal Range and Andes in south central Chile

Little is known about Orchidaceae plants in Chile and their mycorrhizal associations, a key issue for designing protective actions for endangered species. We investigated root fungi from seven terrestrial orchid species to identify potential mycorrhizal fungi. The main characteristics of Rhizoctonia-like fungi were observed under light microscopy, and isolates were identified through PCR-ITS sequencing. Molecular identification of fungal sequences showed a high diversity of fungi colonizing roots. Fungal ability to germinate seeds of different orchids was determined in symbiotic germination tests; 24 fungal groups were isolated, belonging to the genera Tulasnella, Ceratobasidium, and Thanatephorus. Furthermore, dark septate and other endophytic fungi were identified. The high number of Rhizoctonia-like fungi obtained from adult orchids from the Coastal mountain range suggests that, after germination, these orchids may complement their nutritional demands through mycoheterotrophy. Nonetheless, beneficial associations with other endophytic fungi may also co-exist. In this study, isolated mycorrhizal fungi had the ability to induce seed germination at different efficiencies and with low specificity. Germin ation rates were low, but protocorms continued to develop for 60 days. A Tulasnella sp. isolated from Chloraea gavilu was most effective to induce seed germination of different species. The dark septate endophytic (DSE) fungi did not show any effect on seed development; however, their widespread occurrence in some orchids suggests a putative role in plant establishment.

The carbon and nitrogen ecophysiologies of two endemic tropical orchids mirrors those of their temperate relatives and the local environment

Orchids are one of the most widely distributed plant families. However, current research on the ecophysiology of terrestrial orchids is biased towards temperate species. Thus, it is currently unknown whether tropical terrestrial orchids belong to similar trophic guilds as their temperate relatives. To examine the ecophysiologies of two tropical terrestrial orchids, I analysed the carbon and nitrogen stable isotope compositions and nitrogen concentrations of the Hawaiian endemics Anoectochilus sandvicensis and Liparis hawaiensis. I compared these values with those of surrounding vegetation and their temperate relatives. I found that A. sandvicensis was consistently enriched in the heavy isotope of nitrogen (15N) and had higher nitrogen (N) concentrations than surrounding vegetation, and these values were even higher than those of its temperate relatives. Carbon stable isotope composition among populations of A. sandvicensis varied by island. These results point to local environment and evolutionary history determining the ecophysiology of this species. Whereas L.hawaiensis was also enriched in 15N and had on average higher N concentrations than surrounding vegetation, these values were not significantly different from temperate relatives, indicating that evolutionary history may be a stronger predictor of this orchid species' ecophysiology than environment. I suggest that both Hawaiian species are potentially partially mycoheterotrophic.

Phylogenetic relationships of Rhizoctonia fungi within the Cantharellales

Phylogenetic relationships of Rhizoctonia fungi within the order Cantharellales were studied using sequence data from portions of the ribosomal DNA cluster regions ITS-LSU, rpb2, tef1, and atp6 for 50 taxa, and public sequence data from the rpb2 locus for 165 taxa. Data sets were analysed individually and combined using Maximum Parsimony, Maximum Likelihood, and Bayesian Phylogenetic Inference methods. All analyses supported the monophyly of the family Ceratobasidiaceae, which comprises the genera Ceratobasidium and Thanatephorus. Multi-locus analysis revealed 10 well-supported monophyletic groups that were consistent with previous separation into anastomosis groups based on hyphal fusion criteria. This analysis coupled with analyses of a larger sample of 165 rpb2 sequences of fungi in the Cantharellales supported a sister relationship between the Botryobasidiaceae and Ceratobasidiaceae and a sister relationship of the Tulasnellaceae with the rest of the Cantharellales. The inclusion of additional sequence data did not clarify incongruences observed in previous studies of Rhizoctonia fungi in the Cantharellales based on analyses of a single or multiple genes. The diversity of ecological and morphological characters associated with these fungi requires further investigation on character evolution for re-evaluating homologous and homoplasious characters.