Piriformospora Indica, a Cultivable Plant-Growth-Promoting Root
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APPLIED AND ENVIRONMENTAL MICROBIOLOGY, June 1999, p. 2741–2744 Vol. 65, No. 6 0099-2240/99/$04.0010 Copyright © 1999, American Society for Microbiology. All Rights Reserved. Piriformospora indica, a Cultivable Plant-Growth-Promoting Root Endophyte AJIT VARMA,1,2 SAVITA VERMA,2† SUDHA,2 NIRMAL SAHAY,2 BRITTA BU¨ TEHORN,1 1 AND PHILIPP FRANKEN * Max-Planck-Institut fu¨r terrestrische Mikrobiologie, Abteilung Biochemie and Laboratorium fu¨r Mikrobiologie des Fachbereichs Biologie der Philipps-Universita¨t,35043 Marburg, Germany,1 and School of Life Science, Jawaharlal Nehru University, New Delhi 110067, India2 Received 29 June 1998/Accepted 23 December 1998 Piriformospora indica (Hymenomycetes, Basidiomycota) is a newly described cultivable endophyte that col- Downloaded from onizes 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. Fungi interact with plants as pathogens or benefactors and tremula L.) plantlets. After germination or micropropagation, may influence yields in agroforestry and floriculture. Knowl- plantlets of maize (1 week after germination), tobacco and pars- edge concerning plant-growth-promoting cultivable root endo- ley (2 weeks after germination), and A. annua, B. monnieri, and phytes is low (7), and most studies have been conducted with poplar (4 weeks of micropropagation) were placed in pots mycorrhizal fungi. These mutualists improve the growth of (9-cm height by 10-cm diameter) containing expanded clay (2 http://aem.asm.org/ crops on poor soils with lower inputs of chemical fertilizers and to 4 mm in diameter). One gram of wet fungal mycelium was pesticides (2, 9). Arbuscular mycorrhizal (AM) fungi, forming mixed with 100 ml of substrate; in control pots, autoclaved the order Glomales of the Zygomycota (15), occur on the roots mycelium was added. Plants were grown in a growth cham- of 80% of vascular flowering plant species (19), but they are ber under the following constant conditions: 75% relative hu- 2 2 obligate biotrophs and cannot be cultured without the plant. midity, 25°C, 16-h day (300 mmol m 2 s 1), and weekly fertil- In contrast, many ericoid and ectomycorrhizal fungi can be ization with Long Ashton solution (12). Roots of maize and grown in pure culture, but their host spectrum is restricted to tobacco were harvested 4, 7, and 15 days after inoculation and the Ericaceae or to woody plants (14). stained with chlorazol black E (4). Piriformospora indica Verma, Varma, Kost, Rexer & Fran- Colonization was observed under a light microscope. Con- ken, a plant root-interacting fungus, can be easily grown on trol plants contained no fungal structures. When hyphae of on May 9, 2020 by guest various complex and minimal substrates, where it asexually P. indica contacted roots, they developed appressoria (Fig. 1A) forms chlamydospores containing 8 to 25 nuclei (28). Stages of and roots were colonized intercellularly (Fig. 1B). The fungus a sexual life cycle have not been observed. Analysis for taxo- also colonized cortex cells intracellularly, where it formed coils nomic position by molecular methods based on 18S rRNA se- and branches (Fig. 1C) or round bodies (Fig. 1D), but a typical quences and by electron microscopy suggests that this fungus is arbuscule such as that developed by the Glomales (3, 10) was related to the Hymenomycetes of the Basidiomycota. Our ob- not observed. The round bodies, however, might function as jectives in this study were to determine the pattern of root col- storage organs, as has been considered for the intraradical onization by this fungus and to assess its effect on the growth vesicles of the Glomineae (29). P. indica never invaded the of six plant species. stelar tissue nor traversed upwards into the shoot. We did not P. indica is deposited at the Deutsche Sammlung fu¨r Mikro- determine whether P. indica causes invagination of the host organismen und Zellkulturen, Braunschweig, Germany (DSM plasma membrane during colonization, as do many other bio- 11827). The fungus was grown on plates or in liquid culture trophic organisms, or if it interacts with plant roots as a ne- containing a complete medium (21). crotroph or a saprophyte. Seeds of maize (Zea mays L.), tobacco (Nicotiana tabaccum Four weeks after inoculation, whole plants (all species) were L.), and parsley (Petroselinum crispum L. ‘Hamburger Schnitt’) harvested and divided into roots and shoots, and fresh weights were surface sterilized for 2 min in ethanol followed by 10 min of each were determined. The root and shoot biomasses for the in a NaClO solution (0.75% Cl) and washed six times with ster- P. indica treatment were about twice those of the controls ile water. Seeds were germinated on water-agar plates (0.8% (Table 1). Expanded clay was used as a substrate for the ex- Bacto Agar; Difco, Detroit, Mich.) at 25°C in the dark. Plant- periment whose results are shown in Table 1; however, similar lets of tobacco, Artemisia annua L., and Bacopa monnieri L. growth responses were also obtained when plants were culti- were grown from calli on a standard medium for micropropa- vated on other substrates, e.g., vermiculite and commercially gation as described by Varma (27). H. Rennenberg (University available garden soils (data not shown). Germinated tobacco of Freiburg) kindly provided micropropagated poplar (Populus seeds also were directly inoculated on water agar by placing disks (1-cm diameter) from complete medium with and with- out the fungus close to the roots. Seedlings were harvested * Corresponding author. Mailing address: Max-Planck-Institut fu¨r after 3 weeks of further incubation in a growth chamber. Root terrestrische Mikrobiologie, Abteilung Biochemie, Karl-von-Frisch- Strasse, 35043 Marburg, Germany. Phone: 49-6421-178 300. Fax: 49- and shoot weights from these seedlings were similar to those 6421-178 309. E-mail: [email protected]. grown in pot cultures (Table 1). † Present address: Walter Reed Army Institute of Research, Wash- Calli of tobacco plants were placed on MS medium without ington, D.C. 20007. any supplements (18) close to agar disks with the fungus. For 2741 2742 VARMA ET AL. APPL.ENVIRON.MICROBIOL. Downloaded from http://aem.asm.org/ on May 9, 2020 by guest FIG. 1. Plant colonization by P. indica. Maize plants were inoculated with P. indica. Roots were harvested 4 (A), 7 (B), and 16 (C and D) days after inoculation, stained, and observed by light microscopy. Bars, 10 mm. (A) A fungal appressorium attached to the root surface. Arrow 1 indicates a hypha leading to the appressorium; arrow 2 indicates a hypha leading away from the appressorium into the plant. (B) A root segment showing intercellular hyphae. Arrows indicate plant cell walls. (C) Cortical cells with coiled and branched intracellular hyphae. (D) Cortical cells showing round bodies. control treatments, the agar disks were empty, and the medium ferred to plastic pots (10-cm height by 6-cm diameter) filled was supplemented with benzyl amino purine (2 mg/liter) and with a mixture of sterile soil and sand (3:1; garden soil from the naphthaleneacetic acid (0.1 mg/liter). Seven replications were Jawaharlal Nehru University campus and acid-washed river carried out, and culture bottles were incubated under the fol- bed sand). Pots were placed in a mist chamber (90% relative lowing controlled conditions: 60% relative humidity, 24°C, humidity, 24°C, 16-h day [1,000 lx]). After 4 weeks, microscop- 16-h day (2,000 lx). Calli of fungus-treated tobacco rooted ical analysis of chlorazol black E-stained roots showed that earlier (within 7 to 10 days) than those of controls supple- 87% 6 10% (mean 6 standard deviation) of the cortex was mented with growth regulators (30 days and later). Biomass colonized by the fungus. The survival rate of P. indica-inocu- production by fungus-treated calli increased by approximately lated plantlets was 95%, but only 57% of untreated plantlets 50% after 4 weeks (Table 1). Six weeks after inoculation, three survived the transfer to pots. plantlets per replication (control and inoculated) were trans- We analyzed culture filtrates to determine whether P. indica VOL. 65, 1999 PIRIFORMOSPORA INDICA 2743 TABLE 1. Growth-promoting effect of P. indica to be species specific (11). In some instances, other fungi were also studied, but those reports concerned only the effect on one Fresh wt (g) Plant Treatment plant and/or the enhancement of plant growth was relatively Shoot Root low (6, 8, 16, 25). We suggest that P. indica is a good candidate a to improve commercial plant production and might be espe- Maize Control 45 6 3.1 48 6 2.5 P. indica 90 6 6.7 75 6 4.8 cially useful in agroforestry and flori-horticulture applications. Research on the cellular and molecular basis of the interaction Tobaccoa Control 4.3 6 0.3 3.4 6 0.2 should contribute to the understanding of the beneficial associ- P. indica 7.8 6 0.5 6.2 6 0.4 ations between plants and fungi. Bacopaa Control 2.7 6 0.1 2.0 6 0.2 We thank H. Rennenberg (Freiburg) for providing us with micro- P. indica 7.8 6 0.4 6.9 6 0.5 propagated poplar plants, as well as P. Bonfante (Torino) and H. Steele (Marburg) for critically reading the manuscript. Artemisiaa Control 8.6 6 0.5 4.0 6 0.3 A. Varma, Sudha, and N. Sahay are thankful to the government of P. indica 15 6 1.2 9.9 6 0.8 India (Department of Biotechnology and University Grant Commis- sion) for partial funding.