New biotypes of brown planthopper in Thailand

In the early 1970s, only biotype-1 of brown planthopper (BPH) was prevalent in the rice growing regions of Thailand. All rice varieties grown during the time had no resistance to BPH. RD9, the first improved variety with resistance to the insect, released in 1975 and became widely grown in the farmers field in 1976. Since then, several other high yieldjng varieties with incorporated BPH resistance genes were developed and released. During the last three years, outbreaks of BPH in the central regions of the country have been reported. Some varieties which have previously shown resistance to the pest were severely damaged by the heavy planthopper infestations. Biotype identification using field colledted BPH form two central provinces, Chainat and phitsanulok, revealed the presence of biotype-3 and three new biotyes in the insect population. The newly identified biotypes were designated as biotypes-5(t), biotype-6(t) and biotype-7(t). BPH resistance genes Bphl, Bph3 and Bph4 conveyed resistance to biotype-3. Bph1 is susceptible to all the new biotypes. While Bph3 and Bph4 genes govern resistance to biotype-5(t), only Bph6 showed resistance to biotype-6(t). All four genes, Bph1, bph2, Bph3 and bph4, showed susceptibility to biotype-7(t).Summary (En