In vitro plant development and root colonization of Coleus forskohlii by Piriformospora indica

The present study was conducted for optimization of in vitro substrates under aseptic conditions for interaction of Piriformospora indica with the medicinal plant Coleus forskohlii. It aims to test the effects of different substrates on P. indica colonization as well as growth parameters of the in vitro raised C. forskohlii. Interaction of in vitro C. forskohlii with root endophyte P. indica under aseptic condition resulted in increase in growth parameters in fungus colonized plants. It was observed that P. indica promoted the plant’s growth in all irrespective of substrates used for co-culture study. The growth was found inferior in liquid compared to semisolid medium as well as there was problem of hyperhydricity in liquid medium. P. indica treated in vitro plantlets were better adapted for establishment under green house compared to the non treated plants due to fungal intervention.     

Impact of Piriformospora indica on tomato growth and on interaction with fungal and viral pathogens

Piriformospora indica is a root endophytic fungus with plant-promoting properties in numerous plant species and induces resistance against root and shoot pathogens in barley, wheat, and Arabidopsis. A study over several years showed that the endophyte P. indica colonised the roots of the most consumed vegetable crop tomato. P. indica improved the growth of tomato resulting in increased biomass of leaves by up to 20%. Limitation of disease severity caused by Verticillium dahliae by more than 30% was observed on tomato plants colonised by the endophyte. Further experiments were carried out in hydroponic cultures which are commonly used for the indoor production of tomatoes in central Europe. After adaptation of inoculation techniques (inoculum density, plant stage), it was shown that P. indica influences the concentration of Pepino mosaic virus in tomato shoots. The outcome of the interaction seems to be affected by light intensity. Most importantly, the endophyte increases tomato fruit biomass in hydroponic culture concerning fresh weight (up to 100%) and dry matter content (up to 20%). Hence, P. indica represents a suitable growth promoting endophyte for tomato which can be applied in production systems of this important vegetable plant not only in soil, but also in hydroponic cultures.     

Piriformospora indica, a Cultivable Plant-Growth-Promoting Root Endophyte

Piriformospora indica (Hymenomycetes, Basidiomycota) is a newly described cultivable endophyte that colonizes roots. Inoculation with the fungus and application of fungal culture filtrate promotes plant growth and biomass production. Due to its ease of culture, this fungus provides a model organism for the study of beneficial plant-microbe interactions and a new tool for improving plant production systems.     

Root colonization by Piriformospora indica enhances grain yield in barley under diverse nutrient regimes by accelerating plant development

The basidiomycete fungus Piriformospora indica colonizes roots of a broad range of mono- and dicotyledonous plants. It confers enhanced growth, improves resistance against biotic and tolerance to abiotic stress, and enhances grain yield in barley. To analyze mechanisms underlying P. indica-induced improved grain yield in a crop plant, the influence of different soil nutrient levels and enhanced biotic stress were tested under outdoor conditions. Higher grain yield was induced by the fungus independent of different phosphate and nitrogen fertilization levels. In plants challenged with the root rot-causing fungus Fusarium graminearum, P. indica was able to induce a similar magnitude of yield increase as in unchallenged plants. In contrast to the arbuscular mycorrhiza fungus Glomus mosseae, total phosphate contents of host plant roots and shoots were not significantly affected by P. indica. On the other hand, barley plants colonised with the endophyte developed faster, and were characterized by a higher photosynthetic activity at low light intensities. Together with the increased root formation early in development these factors contribute to faster development of ears as well as the production of more tillers per plant. The results indicate that the positive effect of P. indica on grain yield is due to accelerated growth of barley plants early in development, while improved phosphate supply—a central mechanism of host plant fortification by arbuscular mycorrhizal fungi—was not observed in the P. indica-barley symbiosis.     

The plant strengthening root endophyte Piriformospora indica: potential application and the biology behind

The successful conversion of plant production systems from conventional resource-exhausting to sustainable strategies depends on knowledge-based management of environmental factors. Root-inhabiting fungi came more and more into focus because their hyphae connect in ideal manner resources and challenges of the surrounding with the plant. A paradigm for such root endophytes is presented by the basidiomycete Piriformospora indica. This fungus possesses a broad host spectrum and positively affects different aspects of plant performance. This so far unique combination of attributes makes P. indica and its close relatives among the Sebacinales very interesting tools for cultivation of various crops. This review will outline the different aspects required to apply this root endophyte in agri- and horticulture concerning plant growth, plant nutrition and plant defence or tolerance thereby explaining what is known about the biological basis for the observed effects. Open questions and challenges for successful inoculum production and application will be discussed.     

Exogenous auxin affects the oxidative burst in barley roots colonized by Piriformospora indica

Beside a cardinal role in coordination of many developmental processes in the plant, the phytohormone auxin has been recognized as a regulator of plant defense. The molecular mechanisms involved are still largely unknown. Using a sensitive chemiluminescence assay, which measures the oxidation of luminol in the presence of H₂O₂ by horseradish peroxidase (HRP), we report here on the ability of exogenously added indole-3-acetic acid (IAA) to enhance the suppressive effect of the root endophyte Piriformospora indica on the chitin-elicited oxidative burst in barley roots. Thus, the potential of P. indica to produce free IAA during the early colonization phase in barley might provide the symbiont with a means to interfere with the microbe-associated molecular patterns (MAMP)-triggered immunity.     

Synergy between Glomus fasciculatum and a beneficial Pseudomonas in reducing root diseases and improving yield and forskolin content in Coleus forskohlii Briq. under organic field conditions

Root rot and wilt, caused by a complex involving Fusarium chlamydosporum (Frag. and Cif.) and Ralstonia solanacearum (Smith), are serious diseases affecting the cultivation of Coleus forskohlii, a crop with economic potential as a source of the medicinal compound forskolin. The present 2-year field experiments were conducted with two bioinoculants (a native Pseudomonas monteilii strain and the exotic arbuscular mycorrhizal (AM) fungus Glomus fasciculatum) alone and in combination under organic field conditions in order to evaluate their potential in controlling root rot and wilt. Combined inoculation of P. monteilii with G. fasciculatum significantly increased plant height, plant spread, and number of branches; reduced disease incidence; and increased tuber dry mass of C. forskohlii, compared to vermicompost controls not receiving any bioinoculants. Increase in tuber yields was accompanied by an increase in plant N, P, and K uptake. Co-inoculation of P. monteilii with G. fasciculatum significantly improved the percent AM root colonization and spore numbers retrieved from soil. This suggests P. monteilii to be a mycorrhiza helper bacterium which could be useful in organic agriculture. The forskolin content of tubers was significantly increased by the inoculation treatments of P. monteilii, G. fasciculatum, and P. monteilii + G. fasciculatum.     

Patterns of interaction between Populus Esch5 and Piriformospora indica: a transition from mutualism to antagonism

Piriformospora indica (Sebacinaceae, Basidiomycota) is an axenically cultivable, plant growth promoting root endophyte with a wide host range, including Populus. Rooting of Populus Esch5 explants started within 6 days after transfer to WPM medium. If such plantlets with roots were inoculated with P. indica, there was an increase in root biomass, and the number of 2nd order roots was increased significantly. A totally different observation was recorded when the explants were placed into WPM with pre-grown P. indica. The interaction led to complete blocking of root production and severely inhibited plant growth. Additionally, branched aerial roots appeared which did not penetrate the medium. On contact with the fungal colony or the medium, the ends of the aerial roots became inflated. Prolonged incubation stimulated the fungus to colonize aerial parts of the plant (stem and leaves). Mycelium not only spread on the surface of the aerial parts, but also invaded the cortical tissues inter- and intracellularly. Detached Populus leaves remained vital for 4 - 5 weeks on sterile agar media or on AspM medium with pre-grown P. indica. When the fungus was pre-grown on culture media such as WPM, containing ammonium as the main source of nitrogen, leaves in contact with the cultures turned brownish within 4 - 12 h. Thereafter, the leaves bleached, and about one day later had become whitish. Thus, cultural conditions could alter the behaviour of the fungus drastically: the outcome of the interaction between plant and fungus can be directed from mutualistic to antagonistic, characterized by fungal toxin formation and extension of the colonization to Populus shoots.     

Growth of Arabidopsis seedlings on high fungal doses of Piriformospora indica has little effect on plant performance,stress, and defense gene expression in spite of elevated jasmonic acid and jasmonic acid-isoleucine levels in the roots

The endophytic fungus Piriformospora indica colonizes the roots of many plant species including Arabidopsis and promotes their performance, biomass, and seed production as well as resistance against biotic and abiotic stress. Imbalances in the symbiotic interaction such as uncontrolled fungal growth result in the loss of benefits for the plants and activation of defense responses against the microbe. We exposed Arabidopsis seedlings to a dense hyphal lawn of P. indica. The seedlings continue to grow, accumulate normal amounts of chlorophyll, and the photosynthetic parameters demonstrate that they perform well. In spite of high fungal doses around the roots, the fungal material inside the roots was not significantly higher when compared with roots that live in a beneficial symbiosis with P. indica. Fifteen defense- and stress-related genes including PR2, PR3, PAL2, and ERF1 are only moderately upregulated in the roots on the fungal lawn, and the seedlings did not accumulate H₂O₂/radical oxygen species. However, accumulation of anthocyanin in P. indica-exposed seedlings indicates stress symptoms. Furthermore, the jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile) levels were increased in the roots, and consequently PDF1.2 and a newly characterized gene for a 2-oxoglurate and Fe²⁺-dependent oxygenase were upregulated more than 7-fold on the dense fungal lawn, in a JAR1- and EIN3-dependent manner. We conclude that growth of A. thaliana seedlings on high fungal doses of P. indica has little effect on the overall performance of the plants although elevated JA and JA-Ile levels in the roots induce a mild stress or defense response.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis>-mediated salinity tolerance in <Emphasis Type="Italic">Aloe vera</Emphasis> plantlets

Piriformospora indica, a root endophytic fungus, has been reported to promote growth of many plants under normal condition and allow the plants to survive under stress conditions. However, its impact on an important medicinal plant Aloe vera L. has not been well studied. Therefore, this study was undertaken to investigate the effect of P. indica on salinity stress tolerance of A. vera plant. P. indica inoculated and non-inoculated A. vera plantlets were subjected to four levels of salinity treatment- 0, 100, 200 and 300 mM NaCl. The salinity stress decreased the ability of the fungus to colonize roots of A. vera but the interaction of A. vera with P. indica resulted in an overall increase in plant biomass and greater shoot and root length as well as number of shoots and roots. The photosynthetic pigment (Chl a, Chl b and total Chl) and gel content were significantly higher for the fungus inoculated A. vera plantlets, at respective salinity concentrations. Furthermore, the inoculated plantlets had higher phenol, flavonoid, flavonol, aloin contents and radical scavenging activity at all salinity concentrations. The higher phenolic and flavonoid content may help the plants ameliorate oxidative stress resulting from high salinity.     

Piriformospora indica?rescues growth diminution of rice seedlings during high salt stress

Piriformospora indica association has been reported to increase biotic as well as abiotic stress tolerance of its host plants. We analyzed the beneficial effect of P. indica association on rice seedlings during high salt stress conditions (200 and 300 mM NaCl). The growth parameters of rice seedlings such as root and shoot lengths or fresh and dry weights were found to be enhanced in P. indica-inoculated rice seedlings as compared with non-inoculated control seedlings, irrespective of whether they are exposed to salt stress or not. However, salt-stressed seedlings performed much better in the presence of the fungus compared with non-inoculated control seedlings. The photosynthetic pigment content [chlorophyll (Chl) a, Chl b, and carotenoids] was significantly higher in P. indica-inoculated rice seedlings under high salt stress conditions as compared with salt-treated non-inoculated rice seedlings, in which these pigments were found to be decreased. Proline accumulation was also observed during P. indica colonization, which may help the inoculated plants to become salt tolerant. Taken together, P. indica rescues growth diminution of rice seedlings under salt stress.     

Endophytic fungus Serendipita indica increased nutrition absorption and biomass accumulation in Cunninghamia lanceolata seedlings under low phosphate

Cunninghamia lanceolata is important forest tree species in southern China, and its successive plantations resulted in degradation of soil fertility in pure stands, causing decline in forest productivity. How to improve productivity in C. lanceolata pure stands is a tough task. Usage of mycorrhizal fungi might be a plausible access to the task. The objective is to study the possibility of the endophytic fungus Serendipita indica (named formerly as Piriformospora indica) in culture of C. lanceolata. Seeds were sowed in plastic pots with river sand. When seedlings had two true leaves, hyphae suspension solution of S. indica was added to near the roots of seedlings in each plastic pot. Such pots with seedlings were placed in a greenhouse and normal management was carried out for the seedlings. Symbiosis effects on root development, nutrition uptake and allocation, and biomass accumulation of C. lanceolata seedlings under low phosphate were investigated. The results showed that S. indica could symbiose with C. lanceolata. The symbiosis did not result in significant changes in root system architecture under low phosphate, but significantly increased nitrogen and phosphorus levels in leaves under low phosphate. Although the symbiosis did not significantly increased nitrogen allocation in leaves under low phosphate, it significantly increased phosphorus allocation in leaves. The interaction between S. indica and C. lanceolata resulted in increase in total biomass under low phosphate and changes in biomass allocation between shoots and roots. The results suggested that S. indica helps host plants to absorb more nutrients under low phosphate and to allocate more nitrogen and phosphate to leaves, promoting plant growth; the fungus might be used in pure stands of C. lanceolata because of its large-scaled axenic culture.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis>, a cultivable root endophyte with multiple biotechnological applications

Piriformospora indica is a wide-host root-colonizing endophytic fungus which allows the plants to grow under extreme physical and nutrient stress. The fungus can be cultivated on complex and minimal substrates. It belongs to the Sebacinales in Basidiomycota. P. indica has a vast geographical distribution and is reported from Asia, South America and Australia. The fungus is interesting for basic research as well as biotechnological applications because: (i) it functions as a plant promoter and biofertilizer in nutrient-deficient soils, (ii) as a bioprotector against biotic and abiotic stresses including root and leaf fungus pathogens and insect invaders, (iii) as a bioregulator for plant growth development, early flowering, enhanced seed production, and stimulation of active ingredients in medicinal plants (iv) as well as a bio-agent for the hardening of tissue-culture-raised plants. Positive interaction are established for many plants of economic importance in arboriculture, agro-forestry, flori-horticulture including Orchids, and those utilized for energy production and paper industry. P. indica also interacts with members of bryophyte, Aneura pinguis, pteridophyte, Pteris ensiormis, Gymnosperms (Pinus halepensis) and a large number of angiosperms (145 tested till date) including the model plant Arabidopsis thaliana and other members of the mustard family. Similar to arbuscular mycorrhizal fungi, P. indica stimulates nutrient uptake in the roots and solubilizes insoluble phosphatic and sulphur components in the soil. The interaction of P. indica with the model plants Arabidopsis thaliana and barley (Hordeum vulgare L.) is used to understand the molecular basis of this beneficial plant/microbe interaction. We describe the current knowledge about the molecular basis of the interaction of plants with P. indica. An attempt is made to compare it with pathogenic and mycorrhizal plant/microbe interactions and also propose possible biotechnological applications.     

Pathogenicity of Pythium aphanidermatum to Chrysanthemum in Combined Inoculations with Belonolaimus longicaudatus or Meloidogyne incognita

Rooted cuttings of ''Iceberg'' chrysanthemum in steamed soil were inoculated with the nematodes Belonolaimus longicaudatus, and Meloidogyne incognita, alone and combined with Pythium aphanidermatum, a fungus pathogen of chrysanthemum. B. longicaudatus alone severely restricted the root system; with P. aphanidermatum also present, plant weight and height were further reduced and onset of symptoms was earlier. M. incognita + fungus interaction was similar but less intense. The fungus suppressed egg production of M. incognita but not the reproduction of B. Iongicaudatus. However, all three pathogens combined significantly suppressed reproduction of both nematodes and caused greatest inhibition of plant growth.     

Effects of Etomopathiogenic Nematodes on Meloidogyne javanica on Tomatoes and Soybeans

Two Hawaiian isolates of Steinernema feltiae MG-14 and Heterohabditis indica MG-13, a French isolate of S. feltiae SN, and a Texan isolate of S. riobrave TX were tested for their efficacy against the root-knot nematode, Meloidogyne javanica, in the laboratory and greenhouse. Experiments were conducted to investigate the effects of treatment application time and dose on M. javanica penetration in soybean, and egg production and plant development in tomato. Two experiments conducted to assess the effects of entomopathogenic nematode application time on M. javanica penetration demonstrated that a single application of 10⁴ S. feltiae MG-14 or SN infective juveniles per 100 cm³ of sterile soil, together with 500 (MG-14) or 1,500 (SN) second-stage juveniles of M. javanica, reduced root penetration 3 days after M. javanica inoculation compared to that of a water treatment. Entomopathogenic nematode infective juveniles applied to assess the effects on M. javanica egg production did not demonstrate a significant reduction compared to that of the water control treatment. There was no dose response effect by Steinernema spp. On M. javanica root penetration or egg production. Steinernema spp. did not affect the growth or development of M. javanica-infected plants, but H. indica MG-13-treated plants had lower biomass than untreated plants infected with M. javanica. Infective juveniles of S. riobrave TX, S. feltiae SN, and MG-14 but not those of H. indica MG-13 were found inside root cortical tissues of M. javanica-infected plants. Entomopathogenic nematode antagonism to M. javanica on soybean or tomato was insufficient in the present study to provide a consistent level of nematode suppression at the concentrations of infective juveniles applied.     

Compatibility of <Emphasis Type="Italic">Piriformospora indica</Emphasis> and <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> as dual inoculants in black pepper (<Emphasis Type="Italic">Piper nigrum</Emphasis> L.)

The compatibility of two biological inoculants, Trichoderma harzianum, a mycoparasitic biological control fungus and Piriformospora indica, a root colonizing plant-growth promoting endophytic fungus was evaluated using tissue cultured black pepper plantlets. We report, for the first time, the ability of P. indica to colonize black pepper, a perennial climber. T. harzianum inhibited the growth of P. indica in an in vitro dual culture plate assay. Simultaneous inoculation with both biological inoculants of tissue cultured black pepper plantlets negatively influenced root colonization by P. indica. However, when P. indica was applied initially followed 30 days later by T. harzianum, there was increased root colonization by the root endophyte P. indica and beneficial effects were found on the growth of the black pepper plants. The present study also showed that the efficacy of inoculation of the two fungal biological agents can be increased by sequential application of P. indica at the hardening stage followed by T. harzianum during transplanting into a soil-sand mixture.     

Constitutive overexpression of the sucrose transporter SoSUT1 in potato plants increases arbuscular mycorrhiza fungal root colonization under high, but not under low, soil phosphorus availability

The sucrose transporter SUT1 functions in phloem loading of photoassimilates in solanaceous plant species. In the present study, wildtype and transgenic potato plants with either constitutive overexpression or antisense inhibition of SUT1 were grown under high or low phosphorus (P) fertilization levels in the presence or absence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices. At a low soil P fertilization level, the extent of AM fungal root colonization was not different among the genotypes. In all plants, the AM symbiosis contributed significantly to P uptake under these conditions. In response to a high soil P fertilization level, all genotypes showed a decrease in AM fungal root colonization, indicating that the expression level of SUT1 does not constitute a major mechanism of control over AM development in response to the soil P availability. However, plants with overexpression of SUT1 showed a higher extent of AM fungal root colonization compared with the other genotypes when the soil P availability was high. Whether an increased symbiotic C supply, alterations in the phytohormonal balance, or a decreased synthesis of antimicrobial compounds was the major cause for this effect requires further investigation. In plants with impaired phloem loading, a low C status of plant sink tissues did apparently not negatively affect plant C supply to the AM symbiosis. It is possible that, at least during vegetative and early generative growth, source rather than sink tissues exert control over amounts of C supplied to AM fungi.     

Susceptibility of Several Common Subtropical Weeds to Meloidogyne arenaria,M. incognita,and M. javanica

Experiments were conducted in the greenhouse to assess root galling and egg production of three root-knot nematode species, Meloidogyne arenaria, M. incognita, and M. javanica, on several weeds common to Florida agricultural land. Weeds evaluated were Amaranthus retroflexus (redroot pigweed), Cyperus esculentus (yellow nutsedge), Eleusine indica (goosegrass), Portulaca oleracea (common purslane), and Solanum americanum (American black nightshade). Additionally, although it is recommended as a cover crop in southern regions of the U.S., Aeschynomene americana (American jointvetch) was evaluated as a weed following the detection of root galling in a heavy volunteer infestation of an experimental field in southeastern Florida. Weeds were propagated from seed and inoculated with 1000 nematode eggs when plants reached the two true-leaf stage. Tomato (Solanum lycopersicum ‘Rutgers’) was included as a positive control. Aeschynomene americana and P. oleracea roots supported the highest number of juveniles (J₂) and had the highest number of eggs/g of root for all three species of Meloidogyne tested. However, though P. oleracea supported very high root levels of the three nematode species tested, its fleshy roots did not exhibit severe gall symptoms. Low levels of apparent galling, combined with high egg production, increase the potential for P. oleracea to support populations of these three species of root-knot nematodes to a degree that may not be appropriately recognized. This research quantifies the impact of P. oleracea as a host for M. arenaria, M. incognita, and M. javanica compared to several other important weeds commonly found in Florida agricultural production, and the potential for A. americana to serve as an important weed host of the three species of root-knot nematode tested in southern regions of Florida.