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Rhizoctonia Newsletter

Volume 1, Number 2, October 10, 1996

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: Martin M. Kulik, USDA-ARS, Room 101, Building 001,
BARC-West, Beltsville, MD 20705, U.S.A.
E-mail: mkulik@asrr.arsusda.gov

REPORTS OF RESEARCH IN PROGRESS

BIOCONTROL OF RICE SHEATH BLIGHT IN THAILAND

*Mana Kanjanamaneesathian1, Achara Pengnoo, and
Jirasak Kusoljariyawong

Our research work on the biological control of sheath
blight of rice is aimed at devising appropriate and effective
formulations of bacterial antagonists to deter sheath blight
disease development. At present, we have obtained three
bacterial isolates which show remarkable activity in reducing
R. solani mycelial growth on agar. These bacterial isolates
also suppress sheath blight disease development when tested
on rice plant tissue. The rest of the bacterial isolates
which show less activity in both mycelial inhibition and
symptom suppression are being kept for further testing in
case the selected isolates fail to perform in the
screen-house and field tests.

Preliminary work is being carried out to devise means of
using potential bacterial isolates in the form of pellets.
The pellet must be able to float and have dispersive
properties so that the rice plant can be protected from R.
solani infection at the interface of the rice plant and the
water. The performance of a preliminary formulation is being
evaluated in the screen-house.

This research is being carried out using national budget
funds from the Thai government through The Prince of Songkla
University, Hat Yai Campus. The funding is for a period of
one year. The results of this research will be presented at
the ICPP in Scotland. (END)

ROOT AND STOLON ROTS OF WHITE CLOVER IN AUSTRALIA

*Claire McMullen

Rhizoctonia spp. have been widely detected on rotted
roots and stolons of white clover (Trifolium repens) in all
states of Australia. These fungi may have been the cause of
severe stolon rot at the Berry National White Clover
Improvement sites in early 1995.

As part of a current project at the Institute of
Sustainable Irrigated Agriculture, Tatura (Victoria), in
which the impact of root and stolon rots of white clover in
dairy pastures is being looked at, we have isolated a number
of Rhizoctonia spp. from plants growing in our plots at
Tatura. Colonies of these isolates on quarter-strength PDA
have been identified as either Rhizoctonia solani (although
the AG groups have not been identified) or a Rhizoctonia

binucleate species (group 2). So far we have identified two
types of stolon symptoms: S1; which is characterized by a
soft watery rot at the tip of the stolon, and S2; which is
characterized by a black sunken lesion in the stolon itself.
Rhizoctonia solani has been isolated from plants exhibiting
both types of symptoms, while the Rhizoctonia group 2 species
have primarily been associated with only the S1 type of
symptom. Identification of isolates is still being carried
out, and greenhouse pathogenicity tests of these isolates are
due to begin shortly. (END)

THE TOLERANCE OF ANNUAL MEDICS TO RHIZOCTONIA SOLANI
(AG 8) IN RELATION TO ZINC IN AUSTRALIA

*Tania C. Streeter

Medicago species like the cereals, are susceptible to
both Rhizoctonia root rot and zinc deficiency. Both factors
have been overshadowed by other problems, such as Sitona
weevil and medic aphids, and may be possible causes of the
annual medic decline that is being observed throughout
Australia. The increase in Rhizoctonia is believed to be a
result of the employment of minimum tillage methods which
reduce break-up of hyphae in the soil. The increase in zinc
deficiency results from the use of high analysis, phosphatic
fertilizers, which do not contain significant amounts of zinc
as an impurity. Current work has demonstrated that under
zinc deficiency, shoot dry matter decreased with an
increasing level of Rhizoctonia (AG 8). However, when zinc
supply was adequate, no reduction in shoot dry matter was
observed with the addition of Rhizoctonia. This occurred
even though the number of lesions and "spear tips" that
formed increased, as the level of zinc increased. On a per
metre root basis, no significant difference in the amount of
infection occurred between zinc-deficient and zinc-adequate
plants. This study has demonstrated that annual medics are
more tolerant of Rhizoctonia solani (AG 8) when the supply of
zinc is adequate. Studies are currently being performed to
determine if medics that are zinc efficient (i.e. able to
yield well under zinc-deficient conditions) are also more
tolerant to Rhizoctonia and if so, what mechanisms are
involved. This may then allow farmers in
areas prone to both zinc deficiency and Rhizoctonia, to
successfully grow medics that are more tolerant of these
conditions. (END)

A B S T R A C T S O F P U B L I S H E D P A P E R S

Marianne Boysen, Marise Borja, Catalina del Moral, Oscar
Salazar and *Victor Rubio. 1996. Identification at strain
level of Rhizoctonia solani AG 4 isolates by direct sequence
of asymmetric PCR products of the ITS region. Current
Genetics 29, 174-181.

Abstract: The relatedness of nine isolates of Rhizoctonia
solani, belonging to anastomosis group (AG) 4, and one
isolate of AG 1 was determined by comparative sequence
analysis based on direct sequencing of PCR-amplified
ribosomal DNA (the internal transcribed spacer (ITS) region
and the 5.8 s ribosomal DNA). The 5.8 s rDNA is completely
conserved, but both ITS regions show variation among strains.
AG 1 was an outgroup based on anastomosis ability and RFLP
analyses. Phylogenetic analyses based on the ITS sequences
suggest that the analyzed AG 4 strains can be divided into
three groups that correlate with habitat and virulence. (END)


*Maria C. Julian, Fons Debets and *Jaap Keijer. 1996.
Independence of sexual and vegetative incompatibility
mechanisms of Thanatephorus cucumeris (Rhizoctonia solani)
Anastomosis Group 1. Phytopathology 86, 566-574.

Abstract: The soilborne plant pathogen Thanatephorus
cucumeris (anamorph Rhizoctonia solani) is a basidiomycete
that occurs worldwide and causes damage to a large variety of
agricultural crops. The lack of knowledge of the genetic
basis of incompatibility in T. cucumeris hampers the
development of environmentally friendly control measures for
this plant pathogen. To clarify incompatibility mechanisms
in T. cucumeris, sexual and vegetative compatibility were
investigated simultaneously in anastomosis group (AG) 1.
Sporulation was induced in vitro for a field isolate
belonging to AG 1, and single spores were isolated, giving
rise to homokaryotic colonies. The homokaryons were paired,
and the contact area between isolates was studied macro- and
microscopically. Mating processes (formation of
heterokaryotic tufts between paired homokaryons) occurred
independently from vegetative incompatibility processes
(lysis of anastomosed cells), showing that in T. cucumeris AG
1 sexual and vegetative incompatibility are two mechanisms
that operate independently. Vegetative incompatibility was

variable and irreproducible, indicating vegetative
compatibility in T. cucumeris AG 1 is a complex mechanism.
Furthermore, heterokaryotization of homokaryotic mycelium
(Buller phenomenon) was observed. A novel phenomenon is
described, consisting of the spontaneous lysis of thePage 4
cells of some of the homokaryotic progeny of the field
isolate. (END)


The following abstracts are from two papers authored or
co-authored by Roland T. V. Fox. Roland is a Crop Protection
Lecturer in the School of Plant Sciences, The University of
Reading, U.K. His research interests include the development
of very rapid, accurate methods for the diagnosis of plant
pathogens, and improving the methods for controlling
soilborne plant pathogens and biological control of weeds
using soilborne pathogens.

*Fox, R. T. V. 1990. Rapid methods for diagnosis of soil-
borne plant pathogens. Soil Use and Management 6:179-184.

Abstract: Root diseases are often hard to identify or
quantify visually, particularly by the inexperienced, so
several modern methods of diagnosis from other branches of
biology have been modified for soil-borne plant pathogens.
Though very sensitive, most of these techniques are slower
and more laborious than the routine inspection of plants for
disease symptoms, yet they need less expertise and are
consistently accurate. Apart from immunology, most
laboratory diagnostic procedures have so far proved ill-
suited for field use, as they are neither sufficiently
flexible nor portable. Despite the rapid detection and
identification of numerous viruses by routine enzyme-linked
immunosorbent assays (ELISA), there have been until recently
few suitable protocols adapted for fungi. DNA hybridization
forms the basis of another group of fairly rapid diagnostic
techniques which will probably be restricted to the
laboratory for some while yet. Nevertheless, DNA techniques
have proved valuable in various investigations, such as
unravelling the phylogeny of some species of soil-borne
pathogens. For the foreseeable future, methods based on
antibodies and DNA probes are likely to extend their
domination of detection and diagnosis techniques. By making
recognition easier, these techniques play complementary roles
in expanding our understanding of the biology, taxonomy, and
ecology of soil-borne pathogens. (END)


Dusunceli, F., and *Fox, R. T. V. 1992. Accuracy of methods
for estimating the size of Thanatephorus cucumeris
populations in soil. Soil Use and Management 8:21-26.

Abstract: The accuracy of assays based on galactosidase and
the enzyme-linked immunosorbent assay specific to
Thanatephorus cucumeris were compared with techniques based
on soil dilution plating and baiting in sterilized field
soil. Although soil dilution plating is reasonably
quantitative, it requires substantial time, material and
labour. Plant baits gave inconsistent results in the
estimation of T. cucumeris populations in the soil. Enzyme-
linked immunosorbent assay (ELISA) using monoclonal
antibodies is suitable for detecting the presence of a
range of anastomosis groups (AGs) of T. cucumeris in soil
samples, but more quantitative applications seem to be
limited to a very narrow range of concentrations of the
fungus (0-10 ug/g). Monoclonal antibody ELISA could be used
if the soil samples are routinely further diluted, provided
the range of concentrations is uniformly low. An assay of B-
galactosidase permits estimations of a more adequate range of
concentrations (0-500 ug/g) and may be used in defined
experiments using uninoculated soil samples. (END)

S U M M A R I E S O F C O M P L E T E D S T U D I E S

Influence of culture substrate on the pathogenicity of
Rhizoctonia solani to seeds and seedlings of Medicago sativa

*Martin M. Kulik

Summary: A study was undertaken to determine whether culture
substrate had a significant effect on the pathogenicity
towards Medicago sativa L. exhibited by isolates of
Rhizoctonia solani Khn. Nineteen isolates of this fungus,
which varied in their pathogenicity, were cultured on potato
dextrose agar (PDA), Czapek's-Dox agar (Cz-Dox) with pectin
substituted for sucrose, and on 1.5% water agar (WA).
Cultures were comminuted in a blender and used to infest
sterile soil substitute, which was placed in pots. The pots
were planted with alfalfa seeds 72 hours after being placed
on a greenhouse bench. Initial seedling stand counts were
made seven days after planting, and final counts were made 28
days after planting. After seven days, the amount of pre-
emergence damping-off that had occurred was significantly
affected by the substrate upon which the isolates had been
grown. Twelve isolates from PDA were significantly more

pathogenic than when they were grown on either Cz-Dox or WA.
Ten isolates from Cz-Dox were significantly more pathogenic
than when they were grown on WA. After 28 days, only seven
isolates from PDA were significantly more pathogenic than
when they were grown on either of the other two substrates.
These data clearly show that substrate can have a significant
effect on the level of pathogenicity exhibited by isolates of
R. solani in pot experiments. In addition, it appears that
this fungus can utilize pectin as a source of carbon and agar
as a source of carbon plus the other nutrients required for
its growth. (END)

13th TRIENNIAL CONFERENCE OF THE EUROPEAN
ASSOCIATION FOR POTATO RESEARCH

BR> *R. Wustman recently attended the 13th Triennial
Conference of the European Association for Potato Research.
A number of contributions to that conference which deal with
Rhizoctonia can be found in: Abstracts of Conference Papers,
Posters and Demonstrations. 13th Triennial Conference of the
European Association for Potato Research (EAPR), Veldhoven,
The Netherlands. 14-19 July 1996.

The book of abstracts may be obtained from: Scientific
Committee EAPR96, P.O. Box 20, 6700 AA, Wageningen, The
Netherlands. (END)

PUBLICATION OF THE RHIZOCTONIA BOOK

The eagerly anticipated book, "Rhizoctonia Species:
Taxonomy, Molecular Biology, Ecology, Pathology and Disease
Control," has just been published. It consists of 577 pages
devoted to an introduction by Akira Ogoshi and 49 chapters
that cover the following six topics: Taxonomy and Evolution;
Genetics and Pathogenicity; Plant-Pathogen Interactions;
Ecology, Population and Disease Dynamics; Characterization of
Isolates, Disease Occurrence and Management in Various Crops;
Control of Diseases.

This book is sold and distributed in the United States
and Canada by: Kluwer Academic Publishers, 101 Phillip Drive,
Norwell, MA 02061, U.S.A. In all other countries, it is sold
and distributed by Kluwer Academic Publishers Group, P. O.
Box 322, 3300 AH Dordrecht, The Netherlands. The price of
this book is Dfl 345 (US $244).

The book editors, Baruch Sneh, Suha Jabaji-Hare, Stephen
Neate, and Gerda Dijst, are to be commended on producing a
book that will be of tremendous value to everyone interested
in Rhizoctonia species. (END)

REQUEST FOR CONTRIBUTIONS TO THE
RHIZOCTONIA NEWSLETTER

The editor solicits articles that would be of interest
to readers of this newsletter: Research in progress or
concluded, changes in assignments, promotions, meetings, etc.

Please limit your contribution to one page, single-spaced,
and set the right-hand margin at 4 cm to prevent the text
from "wrapping around."

Send your contribution to the editor either by e-mail or
by air mail. My e-mail and postal addresses are given near
the top of the first page of this issue. (END)


LIST OF COLLEAGUES WHO RECEIVE THE RHIZOCTONIA
NEWSLETTER VIA E-MAIL

To avoid having subscribers to the newsletter inundated with
electronic or other junk mail, this list has not been duplicated in
this web reproduction of the newsletter. Requests for the list can
be directed to a Committee member who will submit the case for
assessment by the full Committee.