Pathotypic and genetic characterization of Pyricularia grisea, causal organism of rice blast disease, in Myanmar

抄録

Rice blast caused by Pyricularia grisea (perfect state: Magnaporthe grisea) is one of the major fungal diseases of rice in Myanmar and severely affects the yield under favourable environmental condition. Growing resistant cultivar is the most effective control method for this disease. However, the durability of the resistance is limited because of variability of the pathogen. Knowledge of genetic and pathotypic diversity of a plant pathogen in a disease occurrence location is important to produce relatively durable resistant cultivars. Consequently, the objectives of the present study were to determine genetic and pathotypic variations of the collected isolates from Myanmar and compare the relationship between genetic lineages and pathotypes for developing rice blast resistant rice breeding.

Forty-six isolates collected from Myanmar (Aung Ban area and Hmawbi Township) and 26 isolates from Japan (Fukuoka prefecture and Oita prefecture) were obtained in 2011 to 2012, respectively. The population structure of the P. grisea was determined by Rep-PCR using the two primers, Pot2-TIR and MGR586-TIR primers, separately. The combined dendrogram was constructed based on the different fingerprint patterns. Four fingerprint groups (designated Type-A, B, C and D) were identified and indicated that the Myanmar isolates are genetically divergent from Japan isolates; the tested Japan isolates showed a less divergent. The genetic fingerprint group Type-A was dominant in Aung Ban area, on the other hand, Type-C was dominant in Hmawbi region, and all isolates collected from Japan belonged to Type-D.

Pathotypes of the representative isolates from each fingerprint group were randomly selected and examined by using a set of twelve Japanese differential rice cultivars. The rice variety, Aichi asahi (Pia), Kento (Pik) and Tsuyuake (Pik-m) were strongly susceptible to Myanmar isolates and the virulence frequencies on those varieties were 94.1%, 82.4% and 88.2%, respectively. Whereas Fukunishiki (Piz), Pi no. 4 (Pita2) and BL1 (Pib) were resistant to all isolates. Moreover, Toride1 (Piz-t) and K60 (Pik-p) were incompatible to the isolates from Aung Ban area but compatible to most of the isolates from Hmawbi area. Yashiromochi (Pita) was susceptible to most of isolates collected from Aung Ban and resistant to the isolates from Hmawbi area. Nine races (031.0, 032.0, 036.0, 106.4, 122.4, 132.4, 136.4, 432.5 and 437.5) were identified from Myanmar isolates. The races (136.4 and 106.4) and (432.5 and 437.5) were dominant in Aung Ban and Hmawbi, respectively.

The distributions of genetic lineages of P. grisea generated by Rep-PCR were relatively associated to the geographical locations. The resistant genes, Pik-s, Piz, Pita2, Piz-t, Pik-p and Pib, and Piz, Pita, Pita2 and Pib, could be used as the sources of rice blast resistance in breeding programs for rice growing area of Aung Ban and Hmawbi, respectively. Additionally, the resistant genes, Piz, Pita2 and Pib were totally resistant to all tested isolates and those resistant genes could be useful for rice breeding of blast resistant cultivars in Myanmar. The correlations between the pathotypic races and fingerprint groups were not fully agreed because some isolates exhibited complex pathotypic reactions.