Rice varieties resistant to BPH have been screened on a large scale at the International Rice Research Institute
(IRRI)7. The resistance gene from the indica cultivar Mudgo was named Bph1 and that from the indica cultivar
ASD7 was named bph2. The indica cultivar IR26 harboring the Bph1 gene was bred at IRRI and used as the first
commercial cultivar for controlling BPH. However, a Bph1-vilurent biotype of BPH gradually rended the resistance
gene Bph1 ineffective8. Next, some cultivars such as IR42 harboring bph2 were released for BPH control.
However, they were also rendered ineffective by the appearance of a new virulent BPH biotype9.