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Aggregate sheath spot and sheath spot of rice

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Aggregate sheath spot and sheath spot of rice are caused by Rhizoctonia oryzae-sativae (Sawada) Mordue and R. oryzae Ryker & Gooch, respectively. Although sheath spot is usually considered as a minor disease, it can be a very aggressive disease of rice. Aggregate sheath spot was also regarded as minor until the disease became increasingly important in temperate rice-growing regions such as California and south eastern Australia. The potential yield loss caused by both diseases was unknown until recent research clearly demonstrated the potential threat aggregate sheath spot and sheath spot represent to temperate rice industries. Worldwide, aggregate sheath spot and sheath spot have received little attention compared with the disease sheath blight, caused by Rhizoctonia solani. This article reviews the information available on both R. oryzae-sativae and R. oryzae relating to distribution, host range, biology, symptoms, disease cycle, epidemiology, pathogenicity, identification and control methods, yield losses and resistance. This paper is the first comprehensive review of sheath spot and aggregate sheath spot of rice.
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Crop Protection 26 (2007) 799–808
Review
Aggregate sheath spot and sheath spot of rice
V.M. Lanoiselet
a,
, E.J. Cother
b
, G.J. Ash
a
a
E H Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), School of Agricultural and
Veterinary Sciences, Charles Sturt University, Wagga Wagga NSW 2678, Australia
b
NSW Department of Primary Industries, Agricultural Institute Orange NSW 2800, Australia
Received 7 October 2005; received in revised form 21 June 2006; accepted 21 June 2006
Abstract
Aggregate sheath spot and sheath spot of rice are caused by Rhizoctonia oryzae-sativae (Sawada) Mordue and R. oryzae Ryker &
Gooch, respectively. Although sheath spot is usually considered as a minor disease, it can be a very aggressive disease of rice. Aggregate
sheath spot was also regarded as minor until the disease became increasingly important in temperate rice-growing regions such as
California and south eastern Australia. The potential yield loss caused by both diseases was unknown until recent research clearly
demonstrated the potential threat aggregate sheath spot and sheath spot represent to temperate rice industries. Worldwide, aggregate
sheath spot and sheath spot have received little attention compared with the disease sheath blight, caused by Rhizoctonia solani. This
article reviews the information available on both R. oryzae-sativae and R. oryzae relating to distribution, host range, biology, symptoms,
disease cycle, epidemiology, pathogenicity, identification and control methods, yield losses and resistance. This paper is the first
comprehensive review of sheath spot and aggregate sheath spot of rice.
r2006 Elsevier Ltd. All rights reserved.
Keywords: Diseases of rice; Rhizoctonia oryzae;Rhizoctonia oryzae-sativae
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
2. Host range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
3. Biology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
3.1. Mycelium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
3.2. Sclerotia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
3.3. Basidiospores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
4. Symptoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
5. Disease cycle, epidemiology and pathogenicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802
6. Identification/diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804
6.1. Sclerotial and nuclear characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804
6.2. Anastomosis testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804
6.3. Pectic zymogram testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804
6.4. Molecular technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
6.5. Fatty acid testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
7. Control methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
7.1. Chemical control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
7.2. Cultural practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
ARTICLE IN PRESS
www.elsevier.com/locate/cropro
0261-2194/$ - see front matter r2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cropro.2006.06.016
Corresponding author. Tel.: +61 2 69334419; fax: +61 2 69332812.
E-mail address: vlanoiselet@csu.edu.au (V.M. Lanoiselet).
8. Yield losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
9. Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
10. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808
1. Introduction
On rice, Rhizoctonia oryzae-sativae (Sawada) Mordue
causes aggregate sheath spot. R. oryzae-sativae was first
described in Taiwan as Sclerotium oryzae-sativae (Sawada,
1922). Since then, the disease has been reported in many
Asian countries (Ou, 1985), Italy (De Carolis, 1973), India
(Mukherjee et al., 1980), Iran (Rahimian, 1989), Venezuela
(Ceden
˜o et al., 1998), Chile (Ricardo-Madariaga et al.,
1999) and recently in Australia (Lanoiselet et al., 2001). In
the USA, the disease has been reported in California
(Gunnell and Webster, 1984) and also in southern United
States (Rick Cartwright, personal communication). The
teleomorph of R. oryzae-sativae was described as Cerato-
basidium oryzae-sativae by Gunnell and Webster (1987).
R. oryzae Ryker & Gooch causes sheath spot of rice.
This disease was first found in California, Arkansas and
Louisiana and the causal agent was reported as Tricho-
derma sp. (Tullis, 1934). Later, the causal agent was studied
by Ryker and Gooch (1938) and identified as R. oryzae.
Hashioka and Makino (1969) reviewed the distribution of
the R. oryzae and showed that the pathogen was present in
Japan, Cambodia, Thailand, Taiwan, the Philippines, the
USA, West Africa and Brazil. The pathogen is present in
southern United States (Ryker and Gooch, 1938;Ou, 1985)
and also in California (Gunnell and Webster, 1984).
Hashioka and Makino (1969) noted that the pathogen
was commonly found on rice in subtropical and tropical
rice-growing regions and hypothesised that R. oryzae was
restricted to these climates due to its low cold tolerance
threshold to survive over winter. However, sheath spot has
recently been found in south eastern Australia which is well
outside the tropical and sub-tropical regions (Lanoiselet et
al., 2001). The teleomorph of R. oryzae is Waitea circinata
Warcup & Talbot.
R. solani, the causal agent of sheath blight of rice has
already been the subject of comprehensive reviews (Gang-
opadhyay and Chakrabarti, 1982;Sneh et al., 1996).
Several aspects of R. solani will be discussed in order to
underline the important similarities/differences between the
three Rhizoctonia species.
2. Host range
R. oryzae-sativae has been recorded on Oryza cubensis
Eckman ex Gotoh & Okura (perennial wild red rice),
Juncellus serotinus (Rottboell) C. B. Clarke (tidalmarsh
flatsedge) and Zizania latifolia (Griseb.) Turcz. ex Stapf
(Manchurian wild rice) (Mordue, 1974).
R. oryzae also causes root rot of wheat and barley stunt
disease (Neate, 1985;Ogoshi et al., 1990;Burton et al.,
1988). The pathogen has also been isolated from corn and
sorghum (Nakata and Kawamura, 1939;Jones and
Belmar, 1989), oats (Sprague, 1950) and has recently been
reported on pea (Paulitz, 2002). R. oryzae has been found
on rice field weeds such as Echinochloa crusgalli L. Beauv.
subsp. Edulis Honda (barnyard grass) (Ryker and Gooch,
1938;Ou, 1985). R. oryzae can also infect numerous grasses
(Haywood and Martin, 1990) and turfgrasses (Burpee and
Martin, 1992). In a glasshouse experiment, Jones and
Belmar (1989) successfully infected soybean leaves with R.
oryzae. In contrast to R. solani,R. oryzae did not infect
capsicum, eggplant, tomato and beans (Ryker and Gooch,
1938).
3. Biology
3.1. Mycelium
When grown on potato dextrose agar-based medium, R.
oryzae-sativae mycelium is colourless when young, later
turning pale brown (Fig. 4). The cells of the hyphal tips
measure 5–6.5 mm wide and up to 300 mm long. On older
mycelium, the diameter of cells can vary from 3.5 to 7 mm.
Some isolates can produce moniloid cells (21 to 37 6to
11 mm). Hyphal branches are constricted near their point of
emergence (usually the middle of the cell). Hyphal branches
are also septate, just above their point of origin (Mordue,
1974).
R. oryzae was described by Ryker and Gooch (1938) as:
R. oryzae sp. nov. Mycelium superficial and submerged in
culture, hyaline to white, granulate when young, gradually
becoming clear when old. The main mycelial strands are
6–10 mm in width, branching at an acute angle with a slight
constriction at the point of branching and with a septation
a short distance from the point of constriction. The main
hypha is also septate a short distance above the branch.
Later, short celled, much branched hyphae emerge at right
angles from the main branches and ramify through the
substrate. Certain of these, after a few days, develop much
thickened short hyphae with barrel shape cells. These
hyphae intertwine and anastomose, forming masses of
sclerotial cells or pseudo-sclerotia of various sizes and
shape.’ The optimum temperature for R. oryzae hyphal
growth is 32 1C.
ARTICLE IN PRESS
V.M. Lanoiselet et al. / Crop Protection 26 (2007) 799–808800
3.2. Sclerotia
R. oryzae-sativae sclerotia are globose, white when
young, then become brown when mature and their
diameter can range from 0.5 to 2 mm (Fig. 5) due to their
aggregation (Mordue, 1974). Sclerotia produced within rice
tissue range from 360–1250 mm270–620 mm(Miller and
Webster, 2001).
In culture, R. oryzae sclerotia are salmon colour, waxy,
soft and often sunken in the agar (Fig. 5)(Ryker and
Gooch, 1938;Gunnell, 1986). While single sclerotia are
globose, sclerotia are often produced in formless masses
arranged in a pattern described by Ryker and Gooch as a
crow’s foot pattern. Sclerotia are found at the end of the
season usually inside the infected leaf sheath (Fig. 2).
3.3. Basidiospores
The teleomorph of R. oryzae-sativae (C. oryzae-sativae)
is known to occur on rice plants in the field in California as
whitish hymenia present on the outside of infected leaf
sheaths (Gunnell and Webster, 1987). Even though the
teleomorph exists in the field, the disease is thought to be
mainly monocyclic (Miller and Webster, 2001). Gunnell
and Webster (1987) described the basiodiospores of C.
oryzae-sativae as ‘globose to subglobose to broadly
ellipsoid, occasionally ellipsoid, smooth,
(8–)9–17(–21) (8–)9–16(–19) mm’. These authors also de-
scribe a method to produce fructification in the glasshouse.
Rice plants were inoculated with a mixture of unhulled
rice+rice hulls, colonised with R. oryzae-sativae, by adding
the inoculum on the surface of the water in which the
plants were growing. The rice plants were grown at
temperatures ranging from 24 to 35 1C and were misted
every 2 h.
The teleomorph of R. oryzae (W. circinata) can be found
on, or near, the lesions usually around the heading stage
and especially during rainy or cloudy periods. The
basidiospores produced can initiate secondary infections
(Rush, 1992). Basidiospores are hyaline, oblong or ellipsoid
with one side flattened, occasionally presenting 1–2 septa,
(7–)8–12 3.5–5(–6) mm(Warcup and Talbot, 1962). Hy-
menium was described as: ‘indefinite, formed on small
irregular, cymosely branched clusters initiated on erect
branches from repent hyphae, the subhymenial branches
characteristically involute, contorted or sometimes coiled.’
4. Symptoms
Symptoms of aggregate sheath spot can be easily
confused with symptoms of sheath spot (caused by R.
oryzae) and sheath blight (caused by R. solani). The first
lesions appear on the rice plant near the water line as
water-soaked spots. Lesions are oval 0.5–4 cm long and
present grey-green to straw coloured centres surrounded by
a brown margin. The spots often coalesce, giving the
impression of an aggregation of concentric lesion bands
(Fig. 1). Under favourable conditions, the disease can
progress upward and reach the upper leaf sheaths and even
the panicle. Leaves of infected sheaths usually turn yellow
and die. The fungus can sometimes infect the panicle
rachis, resulting in grain sterility. R. oryzae-sativae can also
infect the culm which may cause it to rot. This symptom
rarely occurs in California (Gunnell and Webster, 1984)
but has been reported in India (Mukherjee et al., 1980).
The pathogen is also thought to infect rice roots (Mordue,
1974).
R. oryzae also causes spot type lesions on the leaf sheaths
(Fig. 2). Typical lesions are oval, 1–3 cm long, occasionally
reaching more than 10 cm. Mature lesions were described
by Ryker and Gooch (1938) as presenting a bleached, straw
colour centre surrounded with a reddish-brown border.
First symptoms are usually located on the lower leaf sheath
above the waterline, very often just below the ligule (Ryker
and Gooch, 1938). Single, upper stem lesions are thought
to be the result of secondary infection caused by
basidiospores (Rush, 1992).
Initial infection of the sheath blight pathogen also causes
water-soaked spots on the leaf sheath of rice plants.
Lesions are oval 2–3 cm long and 1cm in width, light green
and surrounded by a dark brown margin. As with
aggregate sheath spot, the spots coalesce, giving the
impression of an aggregation of concentric lesion bands
(Fig. 3). Under favourable conditions, the pathogen can
ARTICLE IN PRESS
Fig. 1. Aggregate sheath spot symptoms on rice plants caused by Rhizoctonia oryzae-sativae; severely diseased rice plants (a), mature and immature
sclerotia (b).
V.M. Lanoiselet et al. / Crop Protection 26 (2007) 799–808 801
rapidly progress upward and reach the leaves blades. The
concentric lesions on the leaf blades are not found with
sheath spot and aggregate sheath spot (Fig. 3). Brown
sclerotia are quickly produced on the outside of the
infected plant tissues (Rush and Lee, 1992)(Fig. 3).
5. Disease cycle, epidemiology and pathogenicity
Sheath spot and aggregate sheath spot disease cycles are
very similar to the sheath blight disease cycle. R. oryzae
and R. oryzae-sativae survive the overwintering season as
sclerotia or mycelium present in the soil or in rice crop
debris (Endo, 1931;Mordue, 1974;Gunnell, 1992;Rush,
1992;Miller and Webster, 2001). At the start of the rice-
growing season, when rice fields are flooded, the hydro-
phobic sclerotia float on the water surface, germinate and
infect the rice sheaths at, or just above, the water line
(Ryker and Gooch, 1938). The location of the initial
penetration is subject to controversy. Hashioka and Okuda
(1971) reported that both R. solani and R. oryzae usually
enters through the inner sheath surface whereas experi-
ments by Marshall and Rush (1980) suggested that the
initial penetration occurs though the outer sheath surface.
Pre-penetration and penetration processes of both R. solani
and R. oryzae are similar (Hashioka and Okuda, 1971).
Both fungi form two infection structures; infection
cushions and lobate appressoria. The formation of these
two infection structures was positively correlated. There
was also a high positive correlation between sheath blight
disease severity ratings of the rice cultivar and the number
of infection structures produced by both R. solani and R.
oryzae (Marshall and Rush, 1980). These authors also
ARTICLE IN PRESS
Fig. 2. Sheath spot symptoms on rice plants caused by Rhizoctonia oryzae; healthy plant compared with two severely diseased plants (a), sclerotia in leaf
sheath (b).
Fig. 3. Sheath blight symptoms on rice plants caused by Rhizoctonia solani; early symptom on leaf sheath (a), leaf symptoms (b), mature sclerotia on rice
plants (c). Photos courtesy of Dr. Marco A. Marchetti.
V.M. Lanoiselet et al. / Crop Protection 26 (2007) 799–808802
demonstrated that R. solani can penetrate the outermost
sheaths and, therefore, colonise the culm of a rice cultivar
with a low disease severity rating for sheath blight. R.
oryzae failed to infect the culm of any rice cultivar. On the
resistant cultivars, the infection is stopped by the collapse
of the parenchyma cells surrounding the invaded hyphae.
The study of Marshall and Rush (1980) suggests that the
rice cultivars that are partially resistant to R. solani are also
partially resistant to R. oryzae (Figs. 4 and 5).
Epidemiological studies suggest that both R. oryzae and
R. oryzae-sativae infect the rice plant early in the season
without showing any symptoms (Kadowaki and Isota,
1993b) and that both pathogens are present on the rice
plant during the whole rice-growing season (Kadowaki and
Isota, 1993a). Even though both fungi can sporulate on rice
plants, both diseases are believed to be predominantly
monocyclic (Gunnell, 1986;Miller and Webster, 2001).
W. circinata, the teleomorph of R. oryzae, can be found on,
or near, the lesions usually around the heading stage and
especially in rainy or overcast days. The basidiospores
produced can initiate secondary infections (Rush, 1992).
Although Ryker and Gooch (1938) never observed
ARTICLE IN PRESS
Fig. 4. Comparative picture showing colonies of Rhizoctonia oryzae-sativae (a), R. oryzae (b), and R. solani (c) on 1
4PDA.
Fig. 5. Comparative picture showing sclerotia of Rhizoctonia oryzae-sativae (a), R. oryzae (b) and R. solani (c) on 1
4PDA.
V.M. Lanoiselet et al. / Crop Protection 26 (2007) 799–808 803
R. oryzae sclerotia on rice plants, both R. oryzae and
R. oryzae-sativae produce sclerotia on plants (Mordue,
1974;O’Neill, 1976;Gunnell, 1986). Inagaki et al. (1987)
reported that sclerotia of R. oryzae and R. oryzae-sativae in
plant residue overwintered better than those placed on the
soil.
Under natural conditions, survival of mycelium from
plant residue was higher than that of sclerotia placed on
the soil. Cold tolerance of mycelia and sclerotia of R.
oryzae is low (Hashioka and Makino, 1969). Kim and Kim
(1988) reported that overwintered sclerotia collected from
rice fields survived an extra 2 months when placed at room
temperature. Miller and Webster (2001) demonstrated that
straw management practices such as burning or bailing
stubble could reduce the number of sclerotia present in
soils. They also showed that disease incidence was not
always correlated with the number of sclerotia present in
the seedbed. The authors concluded that the level of
sclerotial inoculum present early in the season was not the
only factor affecting the final disease incidence, and
suggested that mycelium present in floating straw debris
may also play an important role in primary infections.
Lanoiselet et al. (2005a) demonstrated that both R. oryzae
and R. oryzae-sativae could overwinter as mycelium on
straw debris, regardless of whether the straw was left on the
ground or buried. Mycelium of R. oryzae-sativae present
on rice straw was also found to be able to produce
sclerotia, from saprophytic growth, during the overwinter-
ing period. The authors concluded that overwintered
hyphal fragments of R. oryzae-sativae present in the straw
debris would very likely supplement the sclerotia as a
primary source of inoculum.
Ray and Pan (1989) studied the effect of temperature,
soil moisture and soil pH on sclerotial germination of R.
oryzae-sativae. The optimal conditions for sclerotial
germination were at 30 1C and 75% soil moisture. Sclerotia
germinated well when incubated at 20–30 1C, but germina-
tion was better between 30 and 40 1C. Up to 12 germ tubes
were produced per sclerotium. When incubated in natural
soils, a fungistatic effect was observed, resulting in delayed
sclerotial germination, then sudden sclerotial germination,
reduced number of germ-tubes and poor to nil soil
colonisation.
Endo (1940) tested the pathogenicity of several Chinese
isolates and noted differences between isolates. Several
authors reported that isolates of R. oryzae-sativae were less
aggressive than R. oryzae on rice plants (Shangzhi and
Mew, 1987;Kim and Yu, 1990).
Jones and Belmar (1989) reported that in contrast to R.
solani,R. oryzae did not seem to spread from one plant to
another. The authors were unable to retrieve sclerotia from
plant residue or from soil samples. The fungus was only
isolated from plant residue as mycelium or from lesions on
rice plants, suggesting that in Texas, R. oryzae might
overwinter as mycelium on plant residues.
In contrast to sheath blight of rice, aggregate sheath spot
is not favoured by high nitrogen applications (Gunnell,
1986). Recent field trials suggest that aggregate sheath spot
might be favoured by potassium deficient soils (Williams
and Smith, 2001).
6. Identification/diagnosis
Several Rhizoctonia spp. including multi-nucleate species
comprising several anastomosis groups of R. solani and R.
zeae are known to cause sheath lesions on rice plants. In
addition, several bi-nucleate Rhizoctonia spp. including R.
oryzae-sativae, are also known to cause sheath spot on rice
(Sneh et al., 1991). Leaf sheath diseases of rice are relatively
difficult to diagnose due to the similarity of the symptoms,
especially when the lesions are young (Matsumoto et al.,
1997). Over time, a lot of identification techniques have
been developed to identify Rhizoctonia spp. These methods
includes morphological examination (Duggar, 1915;Butler
and Bracker, 1970) and nuclear staining (Parmeter and
Whitney, 1970), anastomosis testing (Parmeter et al., 1969),
pectic zymogram testing (Sweetingham et al., 1986;Neate
and Cruickshank, 1988), molecular techniques (Jabaji-
Hare et al., 1990;Johanson et al., 1998) and fatty acid
profiling (Matsumoto et al., 1996;Lanoiselet et al., 2005c).
6.1. Sclerotial and nuclear characteristics
R. oryzae-sativae and R. oryzae can be identified on the
basis of the nuclear condition and the structure of their
sclerotia. The rapid stain, Safranin O, reported by Bandoni
(1979) can be used to rapidly determine the number of
nuclei per cell, R. oryzae-sativae being binuclear and R.
oryzae being multinucleate. R. oryzae-sativae sclerotial cells
are globose, 13–30 mm in diameter (Mordue, 1974) while R.
oryzae sclerotial cell shape is variable but are usually
9–19 0.5 mm in diameter, forming chains (Gunnell, 1986).
A cross section representation of both sclerotia can be
found on page 289 of Ou (1985).
6.2. Anastomosis testing
R. oryzae-sativae belongs to the anastomosis group AG-
B(b) indicating that R. oryzae-sativae is capable of hyphal
fusion with other species belonging to the AG-B(b) group.
The anastomosis tester isolate for AG-Bb is the Japanese
isolate, C-455 (ATCC76135). R. oryzae belongs to the
anastomosis group WAG-O. The anastomosis tester isolate
for WAG-O is the Japanese isolate C-521 (ATCC76154).
These isolates and other anastomosis tester isolates can be
obtained from the American Type Culture Collection,
12301 Parklawn, Rockville, MD 20852, USA (Sneh et al.,
1991).
6.3. Pectic zymogram testing
Sweetingham et al. (1986) demonstrated that the
electrophoresis of extractable proteins enables the predic-
tion of the pathogenicity of Rhizoctonia isolates. Neate and
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Cruickshank (1988) showed that there was a relationship
between anastomosis groups and zymograms. However, to
date, most of this work has focused on R. solani isolates.
6.4. Molecular technique
A PCR-based diagnostic technique has been developed
by Johanson et al. (1998) to distinguish between R. oryzae-
sativae,R. oryzae and R. solani isolates causing leaf sheath
diseases of rice. Primers GMRS-3 (specific for R. solani),
GMRO-3 (R. oryzae) and GMROS-6 (R. oryzae-sativae)
permitted the successful detection of the pathogens in rice
tissues as early as 2 days after inoculation.
6.5. Fatty acid testing
In 1996, Matsumoto et al. described a new total cellular
fatty acid analysis protocol and successfully differentiated
between isolates of R. solani AG 1-IA,AG 2-2-IIIB,R.
oryzae, R. oryzae-sativae and R. fumigata.Lanoiselet et al.
(2005c) used a modified method, which permitted a clear
differentiation between the R. oryzae-sativae and R. oryzae
species, regardless of the isolates’ country of origin.
7. Control methods
7.1. Chemical control
Kataria et al. (1991) demonstrated that cyproconazole
and tolclofos-methyl have a strong activity against the
mycelial growth of R. oryzae in vitro, but have moderate
effectiveness again the pathogen when applied to rice
seedlings as a preventive application. A recent study
(Lanoiselet et al., 2005b) found that pyraclostrobin and
propiconazole were strong inhibitors of both pathogens in
vitro and that both fungicides reduced disease development
in the field, but failed to increase rice yield. The fungicide
Quadris
s
(azoxystrobin) has been registered for the
control of aggregate sheath spot in California. Californian
rice-growers are currently advised to regularly monitor
aggregate sheath spot progression up the leaf sheaths and
to use Quadris
s
if the disease threatens the upper sheath
leaves (Webster and Greer, 2004). In Missouri, azoxystro-
bin and propiconazole are registered for the control of both
aggregate sheath spot and sheath spot (Wrather, 2005
http://aes.missouri.edu/delta/muguide/ricfol.stm). The fun-
gicide Quilt
s
contains both active ingredients and is
labelled for all three Rhizoctonia species. Quilt
s
is
currently registered in several southern US states, including
Arkansas, Texas and Missouri but it is not registered in
California (http://www.greenbook.net).
7.2. Cultural practices
In California, chemical control and straw management
practices aimed at reducing the carryover of R. oryzae-
sativae inoculum are currently recommended practices
(Lanoiselet et al., 2005a). Miller and Webster (2001)
demonstrated that straw management practices such as
burning or bailing stubble could reduce the number of R.
oryzae-sativae sclerotia present in the soils but they also
showed that disease incidence was not always correlated
with the number of sclerotia present in the seedbed. The
authors reported a decrease in disease incidence when rice
straw was incorporated into soil in autumn compared with
a late spring incorporation.
R. oryzae-sativae has only been reported on rice,
perennial wild red rice, tidalmarsh flatsedge and Manchur-
ian wild rice (Mordue, 1974) so any crop following a rice
crop is likely to break the disease cycle of aggregate sheath
spot. R. oryzae has been reported on wheat and barley
(Neate, 1985;Ogoshi et al., 1990;Burton et al., 1988). In
Australia, these crops are commonly grown following rice
but it remains unknown if, under Australian conditions,
both crops are carry-over hosts of the pathogen. To date,
in Australia, R. oryzae has never been reported on any crop
other than rice.
Lanoiselet et al. (2005a) studied the effect of burning
stubble on the survival of laboratory-produced sclerotia of
R. oryzae-sativae. Experiments revealed that even if a large
proportion of sclerotia present on the soil were killed,
many of them survived the stubble burning regardless of
whether it was a cold burn or a hot burn, and burning
certainly did not eradicate the entire inoculum. The
authors underlined the importance of managing rice straw
to reduce the inoculum and concluded that burning rice
straw greatly contributed to keeping the disease at a
relatively low level in Australian rice fields.
8. Yield losses
In Australia, field trials showed that aggregate sheath
spot caused yield losses as high as 20% and sheath spot
reduced yields by up to 10% (Lanoiselet et al., 2005b). In
Uruguay, potential yield losses on cultivar Tacuari,
ranging from 4% to 9%, have been attributed to aggregate
sheath spot (S. Avila, personal communication).
9. Resistance
Gunnell and Webster (1984) attributed the increase in
both incidence and severity of aggregate sheath spot in
California to the introduction of semi-dwarf rice cultivars.
In 1986, Gunnell reported the effect of cultural practices on
aggregate sheath spot in California and stated that with the
exception of cultivar S-201, Californian semi-dwarf culti-
vars were more susceptible than tall cultivars. A field trail
in Australia in 2003–04 showed that Australian semi-dwarf
cultivars were also more susceptible than a tall Australian
cultivar (Lanoiselet et al., 2005b). Research from Uruguay
suggests that varietal susceptibility to aggregate sheath spot
also exists among Uruguayan rice cultivars and breeding
lines (S. Avila, personal communication).
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V.M. Lanoiselet et al. / Crop Protection 26 (2007) 799–808 805
Gunnell (1986) reported that, under natural inoculation,
time of maturity did not affect disease severity. It is not
known if rice is more susceptible to R. oryzae-sativae at a
particular growth stage but symptoms do not appear
before the late tillering (Gunnell, 1986) to heading stage
(Kadowaki and Isota, 1995).
Good levels of resistance to aggregate sheath spot were
found in Oryza rufipogon and successfully transferred into
long grain germplasm during the 1990s (McKenzie et al.,
1994). The resistance from O. rufipogon is also effective
against sheath spot and stem rot. While short and long
grains germplasm with good levels of resistance are
currently available, further work is currently under way
in California to improve some of the agronomic character-
istics associated with these germplasm (J. Oster, personal
communication).
It should be noted that US researchers have recently
found semi-dwarf lines presenting high level of partial
resistance to R. solani. These researchers have also noticed
that tall and late maturing lines seem to be more resistant
to R. solani than other lines (Milton Rush, personal
communication). The partial resistance in the tall lines is
attributed to their ‘open’ canopy structure. The climatic
conditions occurring late in the rice-growing season are
thought to explain the partial resistance in the late
maturing lines.
10. Conclusion
Compared with sheath blight of rice, research on both
sheath spot and aggregate sheath spot has not been very
comprehensive. However, aggregate sheath spot is clearly
becoming increasingly important in temperate rice-growing
regions. Furthermore, the recent report of the potential
yield losses caused by both diseases has demonstrated the
potential threat both diseases represent to temperate rice
industries.
The US rice industry currently relies on fungicides to
control both diseases, while in Australia, no fungicide is
registered for the control of any of the diseases of rice
present in the country. Recent advances clearly demon-
strate the important of rice straw management as both
pathogens survive the intercropping season on rice straw
(but also in soil) as mycelium and sclerotia. In contrast to
California, where rice is grown as a monoculture, in
Australia, wheat and barley are commonly grown follow-
ing rice. To date, it remains unknown if, under Australian
conditions, both crops are carry-over hosts of R. oryzae.
Further epidemiological research should, therefore, focus
on this area of research.
To date, the Californian rice growing industry is the only
one with an advanced breeding program focusing on
developing cultivars resistant to aggregate sheath spot and
sheath spot. The Australian rice breeding program does
not focus on any disease of rice due to a general feeling that
the local industry is disease free and that quality issues are
more important. A screening program should, therefore, be
developed and integrated with the current rice breeding
program to prevent the release of a rice cultivar very
susceptible to either aggregate sheath spot or sheath spot.
New rice cultivars and new management techniques are
regularly introduced and some of these changes may well
favour aggregate sheath spot and/or sheath spot. Patho-
gens are also capable of evolving and adapting to altered
environments, underlining the critical importance of
monitoring diseases and their development regularly on a
long term basis.
Acknowledgements
The authors thank Dr. Jeffrey Oster, Plant Pathologist at
the Rice Experiment Station, Biggs, CA, USA, for sharing
his knowledge on both diseases. Financial support to V.M.
Lanoiselet from the Australian Centre for International
Agricultural Research is gratefully acknowledged.
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Further reading
Oster, J., 2001. Rice Pathology. Rice Experiment Station Progress Report.
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ARTICLE IN PRESS
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... The second group of isolates belonged to R. oryzae-sativae (teleomorph: Ceratobasidium oryzaesativae), showing small globose and pale brown sclerotia with slower growth of mycelia, as described by Vongphachanh et al. (2016); and Sandoval and Cumagun (2019). The third isolate group corresponds with the previous reports of Lanoiselet et al. (2007) and Aye et al. (2009); in which tiny round reddishbrown to black sclerotia were identified as S. hydrophilum. This was the first report of S. hydrophilum associated with sheath blight disease symptoms of rice in Thailand. ...
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... Penyakit bercak pelepah pertama kali dilaporkan di Amerika Serikat pada tahun 1984 pada tanaman gandum dan kemudian penyakit dilaporkan menyebar luas ke kawasan California, Australia, India, Italia, Bangladesh, Uruguay serta kawasan Asia Tenggara (Lanoiselet et al., 2007). Jamur R. oryzae dilaporkan menyerang beberapa kultivar padi di Myanmar selain serangan dari spesies Rhizoctonia yang lain (Aye et al., 2009). ...
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... ShB symptom development is a common phenomenon in the presence of suitable conditions; the disease is able to advance upward and move to the uppermost leaf sheaths and sometime panicle (Fig. 1c). The leaves adjoining to the infected sheaths become turn yellow and die 28 . The collapse of the rice plants caused by an excessive fungal infection was observed in the non-transformed WT plants after 30 dpi, while the transgenic plant lines overexpressing the AtNPR1 gene restricted the vertical growth of the pathogen and facilitated to sustain the sheath and leaf architecture (Fig. 1d). ...
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Rhizoctonia oryzae-sativae, a binucleate species of the form-genus Rhizoctonia, was identified as the cause of aggregate sheath spot on rice (Oryza sativa L.) in Venezuela. The disease was observed on rice plants cultivated in Barinas, Guarico and Portuguesa states, where its incidence and severity have increased during the past few years. On potato-dextrose-agar (Difco PDA), the fungus produced colonies that formed undifferentiated sclerotia. The colonies, whose hyphae averaged 6.04 (5-7)(mu in diameter, were initially white and later turned light-brown. The sclerotia appeared individually and aggregated and were observed irregularly globose, brown to grayish-brown and constituted by globose cells interspersed with undifferentiated hyphae. One hundred sclerotia averaged 1.9 (1.6-2.2) x 1.2 (0.9-1.5) mm. The globose sclerotial cells measured 20.7 (13-28) x 16.7 (12-23) (mu m, HCl-Giemsa staining revealed mainly binucleate hyphal cells, however occasionally cells showing 1, 3 and 4 nuclei were seen. The fungus frequently anastomosed with the culture ATCC 52545 of R. oryzae-sativae isolated from rice in California. Inoculations done on plants of rice 'Cimarron' produced symptoms similar to those observed in the field. R. Oryzae-sativae was continuously isolated from experimentally infected plants confirming the Koch's postulates.
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A description is provided for Rhizoctonia oryzae-sativae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Oryza sativa ; has been found on O. cubensis, Juncellus serotinus and Zizania latifolia [Zizania aquatica] . DISEASE: Lesions with pale centres and distinct brown margins develop on sheaths. They are usually small (0.5-1 cm) but several may occur together. Attack on culms results in browning, lodging and death. Can also infect roots. GEOGRAPHICAL DISTRIBUTION: China, Japan; Malaya, Sri Lanka, Taiwan, Vietnam. TRANSMISSION: Soil-borne. Is capable of overwintering in soil as sclerotia or mycelium; also in stubble and other crop residues (11, 801).
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