Genetic variability of Bipolaris oryzae in the Philippines
2007
Garcia, M.R.F. | Dela Paz, M.A.G. | Beligan, G.A. | Ona, I., International Rice Research Inst., DAPO 7777, Metro Manila (Philippines) | Ardales, E., Philippines Univ. Los Banos, College, Laguna (Philippines). Crop Protection Cluster | Goodwin, P.H., University of Guelph, Guelph ON (Canada). Dept. of Environmental Biology | Vera Cruz, C.M., International Rice Research Inst., DAPO 7777, Metro Manila (Philippines)
The genetic diversity of a collection of Bipolaris oryzae isolates from the Philippines was estimated with a Variable Number of Tandem Repeat (VNTR) marker. Several different lesion types were observed in the field but isolates from each lesion type could produce a range of different lesion types when inoculated onto rice cultivar IR72, which is susceptible to B. oryzae. All the isolates originating from different lesion types also belonged to the same VNTR haplotype, supporting the view that the different lesion types were not a result of genetic differences in the fungus. Intensive sampling from a single field showed that the B. oryzae isolates had a continuous range of virulence to IR72. All those isolates had the same VNTR haplotype, except for two, each of which belonged in a separate haplotype. A collection of 325 isolates obtained from multiple locations on the islands of Luzon and Mindanao and from the Visayas island could be divided into 50 VNTR haplotypes giving a somewhat high genetic diversity (Ht) value of 0.89. However, there were 3 or fewer isolates in 39 of the haplotypes , and 80 percent of the isolates belonged to only 8 haplotypes that had 10 to 71 isolates each, indicating a prevalence for clonality. No major relationship between haplotype and geographical location or host variety was observed. These results indicate the rice fields may contain B. oryzae populations with considerable genetic diversity, but the majority of infections arise from a much smaller subset of these that form clonal populations. It appears that most lesions arise from secondary inoculum that is produced asexually. The source of genetic variation resulting in the large number of haplotypes is not known as sexual stage of B. oryzae, Cochliobolus miyabeanus, has not yet been reported in the Philippines.
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