New Disease Reports
New Disease Reports (2009) 19, 42.
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First report of Rhizoctonia oryzae isolated from bordered sheath spot of rice 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: 12 Jun 2009

Rice diseases reduce yields and are a major concern in Myanmar (Naing et al. 2004). In a recent survey, we documented the occurrence of Rhizoctonia oryzae-sativae from diseased rice sheaths in Myanmar (Aye et al., 2009).In this same survey, three isolates from samples of rice plants in Daikoo Township (MWC2) and HleguTownship (MWC3 and MCW5) were collected from plants that displayed oval shaped lesions, 1-3 cm in length with bleached straw coloured centres surrounded by brownish borders (Fig. 1). These symptoms were different from those caused by R. oryzae-sativae (Aye et al., 2009).

Ten days after isolation, mature cultures on potato dextrose agar formed irregular masses of salmon -coloured sclerotia formed at the sub-surface of the medium (Fig. 2).This differed from the tan, irregular globose sclerotia formed by R. oryzae-sativae (Aye et al., 2009). Multinucleate cells were observed under light microscope by hyphal staining with Saffranin O (Fig. 3). According to the morphological criteria, the causal agent was initially identified as R. oryzae.Ribosomal DNA-ITS sequence data of isolate MWC2 (GenBank Accession No. FJ66520) were matched with all other available data sources in GenBank and were found to have up to 98% identity with R. oryzae (EU152861).

A pathogenicity test was completed by inoculating the tillers of 10-week-old rice plants with isolates MWC2, MWC3 and MWC5 (three plants for each isolate). A five-day-old mycelial plug was placed on the stem one cm below the axil of the fully mature leaf and wrapped with parafilm. Similar symptoms to those observed in the field were produced five to seven days after stem inoculation (Fig. 4), while control plants did not produce any symptoms.Koch’s postulates was completed by re-isolating and confirming the identity as R. oryzae. In Australia, yield losses caused by R. oryzae and R. oryzae-sativae were as high as 10% and 20%, respectively (Lanoiselet et al., 2005). Occurrence of bordered sheath spot caused by R. oryzae has been reported in paddy fields of Japan (Inagaki, 1996). However, this is the first report in Myanmar.

Figure1+
Figure 1: Rice stems naturally infected with R. oryzae collected from Myanmar
Figure 1: Rice stems naturally infected with R. oryzae collected from Myanmar
Figure2+
Figure 2: Culture of R. oryzae (MWC2 isolate) on PDA medium
Figure 2: Culture of R. oryzae (MWC2 isolate) on PDA medium
Figure3+
Figure 3: Hyphal characterestics of R. oryzae showing the multinucleate cell
Figure 3: Hyphal characterestics of R. oryzae showing the multinucleate cell
Figure4+
Figure 4: Bordered sheath spot of rice disease symptom expression on artificially inoculated rice stems
Figure 4: Bordered sheath spot of rice disease symptom expression on artificially inoculated rice stems

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.Rhizoctonia oryzae-sativae, causal agent of aggregate sheath spot disease of rice in Myanmar. New Disease Reports [http://www.bspp.org.uk/publications/new-disease-reports/volumes.php] Volume 19.
  2. Inagaki K, 1996. Distribution of strains of rice bordered sheath spot fungus, Rhizoctonia oryzae, in paddy fields and their pathogenicity to rice plants. Annals of the Phytopathological Society of Japan 62, 386-392.
  3. Lanoiselet VM, Cother EJ, Ash GJ, Harper JDI, 2005. Yield loss in rice caused by Rhizoctonia oryzae and R. oryzae-sativae in Australia. Australasian Plant Pathology 4, 175-179.
  4. Naing TAA, 2004. Rice production in Myanmar and effects of intensification on crop health. Kassel, Germany: University of Kassel, PhD Thesis.
This report was formally published in Plant Pathology

©2009 The Authors