Rhizoctonia Newsletter
Volume 1, Number 3,
May 5, 1997
Published by the Rhizoctonia Subject-Matter Committee (IRC)
of the International Society for Plant Pathology (ISPP)
IRC Chairman: Baruch Sneh, Department of Botany, Tel Aviv
University, Ramat Aviv, Israel 69978
Editor: Stephen Neate, CSIRO Land and Water,
P.B. No.2 Glen Osmond, SA 5064 Australia
E-mail: stephen.neate@adl.soils.csiro.au
Retirement of Martin Kulik
We regretfully wish to announce the retirement of Martin Kulik as the editor of the Rhizoctonia Newsletter. Martin started work on Rhizoctonia research in a later stage of his professional career, but showed great initiative in promoting interactions among Rhizoctonia researchers. Martin's research interests in Rhizoctonia included the resistance of annual and perennial Medicago sp. to damping off and the potential for use of actinomycetes, cyanobacteria and algae for biocontrol of damping off. Martin has decided to retire from the Soybean and Alfalfa Research Laboratory of the USDA-ARS Beltsville.
Martin together with Baruch Sneh conceived the idea of an international meeting on Rhizoctonia and after organizing the satellite Rhizoctonia meeting in the 1993 ISPP Congress in Montreal, invited interested researchers to a meeting to discuss the idea. From this meeting an Rhizoctonia subject matter committee was established, which eventually became the ISPP International Rhizoctonia Committee (IRC), and the seeds were sown for the Rhizoctonia Symposium in the Netherlands in 1995 and the book, Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Martin was an enthusiastic worker for the Rhizoctonia Committee as well as contributing to the Symposium and book. Martin assumed responsibility to establish, edit and distribute the Rhizoctonia newsletter, serving in that capacity from 1995 until his retirement.
We would like to express our thanks to Martin for his contributions to the Rhizoctonia working group and we wish Martin all the best, success and joy in his future activities and hope that he stays in contact with his old friends and colleagues.
Baruch Sneh
Submissions to Newsletter Wanted
Disappointed that nobody has recognised the real implications of your earth-shattering research finding? Longing to find out who else works in your area of interest? The Rhizoctonia newsletter is your chance to let your colleagues know that you and your research group exist, to obtain help with that seemingly intractable problem, to communicate with a group of people who really care about the ultrastructure of that dolipore septum or the specificity of your molecular probe. The types of articles being sought are descriptions of current research projects, exciting new results, research being undertaken by post graduate students, news about colleagues, and topics for the discussion corner.
Rhizoctonia Web page
The International Society of Plant Pathology Committee on Rhizoctonia now has a web page. The web page contains the charter of the Committee, information about current Committee members with contact details, back issues of the newsletter, links to other web pages of interest or relating to Rhizoctonia, upcoming meetings and hopefully also a section announcing any jobs and scholarships wanted or available.
The site works with Netscape versions 1.2 and later and Microsoft Explorer or any browser that supports tables and inline images which is greater than 95% of the available browsers in use. The URL for the site is
http://www.adl.soils.csiro.au/adl/staff/stephenn/rhizoc/rhizoc.htm
Those with access to the internet should have a look at the page and give constructive feedback on the current content or anything new they would like to see added to the page.
Discussion Corner
I would like to introduce a new segment to the newsletter, the Discussion Corner. What I would like to do is to introduce significant topics related to Rhizoctonia that people may wish to debate and in some cases hopefully reach a consensus on. It will be difficult to get good interactivity because relative infrequency of the newsletter, but I would like to try anyway. What I suggest is that anyone wishing to take up a topic, start an email dialog with the person who submitted it. I would then ask anyone who participates in the dialog to cc their correspondence to me and I will post a summary of who said what in the next newsletter. The success of the discussion and outcomes depend on this cc'ing.
The editor.
Hyphal Fusion Frequency
(This discusssion topic is submitted by Hans Schneider, irs.hazen@pi.net)
Historically, AG 2 is the only subgroup subdivided according to hyphal fusion frequency (FF). This still holds for the discrimination between AG 2-1 and AG-2-2. However, since the first reports it has been found that FF is time consuming, laborious and may lead to ambiguous results and many isolates have remained unassigned to an AG subgroup. In addition, it has been observed that low-frequency fusion, bridging, can occur between AG 2 isolates and isolates belonging to AG 3, AG 8, AG 11 and AG BI The host range of AG 2-2 isolates is remarkably different from AG 2-1 isolates. On the basis of ITS rDNA analysis it has been shown that AG 2-2 are genetically distinct from AG 2-1 isolates. Also pectic zymograms which have with some groups been related to pathogenicity, show distinct different pectic enzyme patterns for AG 2-1 and AG 2-2.
Therefore, it is questionable whether hyphal fusion frequency remains a reliable criterion to determine subgroups within AG 2 and whether AG 2-2 still has to regarded as a subgroup of AG 2, rather than a distinct AG.
To my opinion it is better to consider AG 2-2 a distinct AG, rather than a subgroup of AG 2 and to use other methods than FF to distinguish subgroups within AG 2. Pectic zymograms seem to be a suitable tool.
AG coding
(This discusssion topic is submitted by Hans Schneider, irs.hazen@pi.net)
Let us reach consensus with respect to AG coding. The book of Sneh et. al, 1996 refers to AG 1, AG 2, etc. Latest papers, e.g. MacNish et al., 1997 (Mycological Research) use the form AG-1 and AG-2. Which is it going to be?.
Abstracts
Characterization of Rhizoctonia solani AG 2 isolates causing bare patch in field grown tulips in the Netherlands. European Journal of Plant Pathology (1997) 103: 265-279.
J.H.M. SCHNEIDER, M.T. SCHILDER, and G. DIJST
Address: Institute of Sugar Beet Research (I.R.S.)
(snr author) P.O. Box 32
NL-4600 AA Bergen op Zoom
The Netherlands
Phone: 31 164 274400
Fax: 31 164 250962
Email: irs.hazen@pi.net (place J Schneider's name in the subject field)
During a spring survey in 1991, 130 isolates of R. solani were collected in 25 commercial flower bulb fields from diseased plants occurring in bare patches. On the basis of hyphal fusion frequency and pathogenicity to flower bulbs, tulip isolates were provisionally assigned to AG 2-t to distinguish these isolates from AG 2-1 isolates which were non-pathogenic to bulbs. Hyphal fusion frequency of a subgroup of 7 AG 2-t isolates was highly variable when paired with 7 AG 2-1 isolates (2-75%), thus making assignment of AG 2-t isolates to AG 2-1 inconclusive. The mean hyphal fusion frequency among AG 2-t isolates was 65% (+/- 6%) indicating AG 2-t to be a relatively homogeneous group. Hyphal fusion frequency among AG 2-1 isolates was highly variable with a mean 51%(+/-25%) indicating AG 2-1 to be a heterogeneous group. The optimum growth temperature for AG 2-t and AG 2-1 isolates on malt peptone agar was 20-25 C. The host range of AG 2-t and two AG 2-1 isolates comprised tulip, iris, hyacinth and lily at both 9 and 18 C, and cruciferous, sugarbeet and lettuce seedlings at 18 C. Six other AG 2-1 isolates were pathogenic to cruciferous seedlings, but not to any of the bulbous crops. The tested narcissus, Tagetes patula, tomato, potato, wheat, leek and maize cultivars were not susceptible to AG 2-t and AG 2-1 isolates. Statistical analysis using a proportional-odds model revealed significant differences in aggressiveness between R. solani AG 2-t isolates and differences in susceptibility between tulip and iris cultivars. At 18 C, but not at 9 C, isolates representing AG 2-2, AG 4, AG 5 and AG BI were pathogenic to bulbous crops. In addition to bare patch causing AG 2-t isolates, other anastomosis groups may cause disease in field grown tulips. For the development of optimal crop rotation schedules, the impact of bulb rot causing isolates under field conditions needs further study.
A novel option for control of Rhizoctonia solani AG-4 in bean and cucumber with host-resistance inducing chemicals
HANS R. KATARIA, BETTINA WILMSMEIER AND HEINRICH BUCHENAUER
Address: Institut fuer Phytomedizin, Universitaet
Hoheiiheim, D-70593 Stuttgart, Germany
Email: kataria@uni-hohenheim.de
Five salicylic acid derivatives, three nicotinic acid derivatives, four butyric acid derivatives, one benzothiazol compound (Bion), one amino acid analogue (DL-norvaline), and one glucose-polysaccharide (lichenin - from the lichen Cetraria islandica) were evaluated as soil drench (aqueous solutions of 2 mM or less) against damping-off and seedling rot of bean and cucumber caused by Rhizoctonia solani AG 4 isolate in greenhouse and climate room pot experiments. Only 5-nitrosalicylic acid, o-acetylsalicylic acid, 2,6-dichloro-iso-nicotinic acid, 2-amino-iso-butyric acid and lichenin proved effective in preventing damping-off and seedling rot and gave up to 60-70% disease control in bean and up to 30-40% control in cucumber without showing any apparent phytotoxic effect on seedling growth. These five compounds have proved consistently effective in disease control in bean in several repeated tests in both greenhouse and climate room, but gave generally weak and variable disease control in cucumber. Disease control was considerably augmented in both crops when soil was applied with either of these five compounds in mixtures with Pseudomonas fluorescens (strain # W36) cell suspensions. These compounds had no or very negligible effects on mycelial growth of R. solani on PDA plates at concentrations of 2 mM or less, and hence control the disease by inducing resistance in plants to the pathogen. As far as we know, this is the first report of successful disease control against Rhizoctonia fungi by host-resistance inducing chemicals and opens new interesting opportunities for controlling these and other root-infecting fungal pathogens with non-toxic chemical inducers of resistance used either alone or in compatible mixtures with Pseudomonas fluorescens.
We gratefully thank Prof. Baruch Sneh for providing the isolate of R. solani AG 4 (isolate # Rsl3) used in this study.
Research in Progress
Research at McGill University, Canada
Researchers: Dr. Suha J.-Hare,
Students currently enrolled: Christian Archambault (Ph.D.), Lingru Xue (Ph.D.) and Catherine Jacques (M.Sc.).
Address: Department of Plant Science, Macdonald Campus of McGill University, 21,111 Lakeshore Rd., Ste.- Anne-de-Bellevue, Quebec, Canada.
E-mail: share@nrs.mcgill.ca
Our projects are concerned with understanding the mechanisms of biological control of R . solani. We have concentrated our efforts in the past three years on the molecular and biochemical aspects of mycoparasitism and induced resistance. We are interested in understanding the process of mycoparasitism using Stachybotrys elegans as the mycoparasite of R. solani, and the role of non-pathogenic binucleate Rhizoctonia in systemic acquired resistance (SAR).
Mycoparasitism: The results below are the work of two Ph.D. and 1 M.Sc. students (Christian Archambault, Russell Tweddell and Catherine Jacques).
We have concentrated our efforts on the characterization of the cell wall hydrolytic enzymes 1,3-B-glucanase produced by Stachybotrys elegans, a good mycoparasite of R. solani. Two 1,3-B-glucanases (94 kDa and 75 kDa) have been purified and characterized to homogeneity. Although both enzymes cause rapid cell wall lysis of R. solani, the 75 kDa glucanase is biologically more active. C. Archambault is currently cloning the 75 kDa 1,3-B-glucanase gene. Once this is achieved, expression of this glucanase in transgenic plants will be attempted. Since it is commonly known that synergistic action between glucanases and chitinases can lead to greater cell wall lysis than the use of either enzymes alone, C. Jacques (M.Sc. student) is working on purifying several chitinases from S. elegans. Maximum chitinase activity was estimated at 3 to 5 days. Native gels containing glycol chitin as the substrate demonstrated the presence of four different bands showing chitinase activity. The chitinases are currently being purified by ammonium sulfate precipitation, ion exchange chromatography and size exclusion chromatography.
Systemic acquired resistance (SAR): The results below represent the work of Lingru Xue, a Ph.D. student.
One of the mechanism by which BNR suppresses disease is related to immunization leading to systemic acquired resistance (SAR). Enzymatic activity of chitinases, glucanases, peroxidases and PAL were estimated in (i) BNR-protected bean seedlings and (ii) in bean seedlings infected with R. solani. Activities of these defense enzymes were significantly higher in protected bean tissues than in infected and control tissues. To test whether the increase in enzyme activities is correlated with increases in their mRNA transcripts, total RNA was extracted from bean hypocotyls and cotyledons, and subjected to Northern analyses with the appropriate homologous cDNA probes. The results revealed that mRNA accumulation encoding for each of the above enzymes was higher in protected than in infected tissues. The kinetic of mRNA accumulation is consistent with that detected for enzyme activities. These results clearly demonstrate that protection of bean seedlings with BNR is due to the activation of host-defense mechanism not only at the enzyme level but also at the transcriptional level.
New PhD project (and a plea for help)
Molecular and genetic characterisation of AG-2 subgroups of Rhizoctonia solani in Australia.
Postgraduate Student:
Mr Ben Stodart stodart.ben@pi.sa.gov.au
SARDI, Plant Research Centre, Waite Precinct
GPO Box 397 Adelaide 2000, Australia.
Project supervisors:
Dr D. Whisson whisson.dara@pi.sa.gov.au
Dr S. Neate stephen.neate@adl.soils.csiro.au
Dr E. Scott escott@waite.adelaide.edu.au
Aims
- To identify molecular markers specific to the subgroups of Rhizoctonia solani AG-2.
- To use the markers to elucidate the evolution and population dynamics of this fungal pathogen in the soil in Australia.
- To examine the host range and pathogenicity of Australian AG-2 isolates and attempt to correlate this with the molecular data.
Proposal:
To achieve the above aims, genomic DNA will be examined by both RAPD-PCR and RFLP analysis. We hope to isolate and prepare an appropriate DNA probe for the detection of AG-2 subgroups directly from soil samples by the method of Whisson, Herdina and Francis (1996).
The pathogenicity of AG-2 subgroups will be examined on a range of different host and results correlated with those from other studies, as well as with our own molecular data. Further to this, the association of AG-2 subgroups with other AG's will be examined. We hope that this will further the knowledge of origin of AG-2 subgroups in Australian soils.
We hope to obtain AG-2 isolates from not only South Australian sites but as many different regions as possible. Any assistance with obtaining isolates of AG-2 would be greatly appreciated.
Completed PhD and Masters Theses
Submitted by Dr. A. I. Roy
Assam Agricultural University
Jorhat-785 013
INDIA
Ph.D.Theses
Bhagawati, Rupankar (1994). Effect of ecological factors on the survival of Trichoderma species in relation to suppressing the incidence of sheath blight of rice.
Das, B.C. (1991). Antagonism of Aspergillus terreus on Rhizoctonia solani and its effect on the incidence of sheath blight of rice.
Bhattacharyya, Ashok (1995). Biochemical and physiological changes in chemical induced resistant rice plant against sheath blight.
M.Sc(Ag) Theses
Borah (Rajbongshi), Kiran (1992). Integrated management of sheath blight of rice with mycoparasite and chemical.
Gogoi, Robin 1989). Biological control of sheath blight of rice with Aspergillus terreus.
Boruah, Nabajyoti (1991). Effect of calcium on the incidence of sheath blight of rice caused by Rhizoctonia solani.
Pathak, D. (1990). Effect of herbicides on the growth and sclerotial survival of Rhizoctonia solani Khehn.
ICPP98 Edinburgh
The Rhizoctonia Committee has been communication with the International Congress of Plant Pathology Organising Committee for nearly two years. The ICPP Committee has decided that there will not be sessions devoted to specific pathogens, but that individual researchers should make their contributions through the scientific program they have arranged. Details of the ICPP98 scientific program can be obtained within the web page located at
http://www.bspp.org.uk/icpp98.htm
or by contacting
ICPP98 Congress Secretariat
c/o Meeting Makers
50 George Street
Glasgow G1 1QE
Scotland, UK.
Tel: +44 141 553 1930
Fax: +44 141 552 0511
e-mail:icpp98@meetingmakers.co.uk
It is anticipated that there will be two evening meetings associated with Rhizoctonia, one for scientific matters and one for business. Further information on these evening meetings will be published in future copies of this newsletter.