New Disease Reports
New Disease Reports (2009) 19, 22.
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Rhizoctonia oryzae-sativae, causal agent of aggregate sheath spot disease of rice, found in Myanmar

Seint San Aye 1, Yi Yi Myint 2, Thein Lwin 2 and Masaru Matsumoto 1*

*mmatsu@agr.kyushu-u.ac.jp

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Accepted: 06 Apr 2009

Sheath diseases of rice are widely observed in many rice growing regions of Myanmar. Recently, stem rot of rice caused by Sclerotium hydrophilum was reported in Myanmar (Aye et al., 2009). In addition to the symptoms caused by S. hydrophilum, oval shaped lesions with a straw coloured centre surrounded by a brown margin were observed in paddy rice fields in PyinmanaTownship and Hmawbe, Myanmar (Fig. 1).

Isolation of a suspected fungal pathogen was carried out by culturing the diseased portion on water agar medium and incubating at 28OC. Two days after culturing, rectangular branching of mature hyphae, formation of a septum just after branching and constriction at the branching point were observed by light microscopy (Fig. 2). One-week-old cultures were observed as being white to pale brown coloured with irregularly globose sclerotia on potato dextrose agar (Fig. 3). According to morphological characteristics, the causal agent collected from PyinmanaTownship was initially identified as Rhizoctonia oryzae-sativae.A total of four isolates were collected altogether from Pyinmana (HROS1 and MRSO4) and Hmawbe (JROS2 and KROS3). These were deposited at the Institute of Tropical Agriculture, KyushusUniversity.

Confirmation of the causal agent was completed by sequencing and pathogenicity tests. The rDNA-ITS sequence of HROS1 (GenBank Accession No. FJ 667257) had 99% identity with a reference sequence (AB122144) confirming the isolates’s identity as R.oryzae-sativae (telemorph Ceratorhiza oryzae-sativae). Pathogenicity tests were conducted as described by Aye et al. (2009) with isolate HROS1. Symptoms similar to naturally infected lesions were observed on all inoculated tillers one week after inoculation (Fig. 4).Lanoiselet et al. (2007) reported similar symptoms as ‘aggregate sheath spot’ of rice. Koch’s postulates were completed by re-isolation of R. oryzae-sativae from inoculated plants. This report describes the first evidence of aggregate sheath spot caused by R. oryzae-sativae in Myanmar. Further research activities focused on sheath diseases of rice are needed as a part of an integrated disease management strategy in Myanmar.

Figure1+
Figure 1: Rice hill in Myanmar naturally infected with Rhizoctonia oryzae-sativae
Figure 1: Rice hill in Myanmar naturally infected with Rhizoctonia oryzae-sativae
Figure2+
Figure 2: Hyphal character of Rhizoctonia oryzae-sativae showing (a) the constricted branching of mature hyphae with right angle formation; and (b) the septum near the branch. Bar = 20 μm
Figure 2: Hyphal character of Rhizoctonia oryzae-sativae showing (a) the constricted branching of mature hyphae with right angle formation; and (b) the septum near the branch. Bar = 20 μm
Figure3+
Figure 3: Culture of Rhizoctonia oryzae-sativae on potato dextrose agar medium after one week incubation at 28° C
Figure 3: Culture of Rhizoctonia oryzae-sativae on potato dextrose agar medium after one week incubation at 28° C
Figure4+
Figure 4: Symptoms of aggregate sheath spot on inoculated rice stem.
Figure 4: Symptoms of aggregate sheath spot on inoculated rice stem.

Acknowledgements

The authors acknowledge the Director, Professor Kazuo Ogata, for his valuable suggestions and comments in this research.

References

  1. Aye SS, Myint YY, Lwin T, Matsumoto M, 2009. Stem rot of rice caused by Sclerotium hydrophilum isolated in Myanmar. New Disease Reports [http://www.ndrs.org.uk/] Volume 18.
  2. Lanoiselet VM, Cother EJ, Ash GJ, 2007. Aggregate sheath spot and sheath spot of rice. Crop Protection 26, 799-808.
This report was formally published in Plant Pathology

©2009 The Authors