An AFLP marker that differentiates biotypes of the Asian rice gall midge (Orseolia oryzae, Wood-Mason) is sex-linked and also linked to avirulence

In an attempt to identify a specific marker for biotype 2 of the Asian rice gall midge (Orseolia oryzae, Wood-Mason). we used AFLP (amplified fragment length polymorphism) fingerprinting. We identified an AFLP marker that is specifically amplified in biotypes 1, 2 and 5 of the rice gall midge, but n ot in biotype 4. Biotypes 1, 2 and 5 are avirulent to hosts bearing the Gm2 resistance gene (found in rice variety Phalguna), whereas biotype 4 is vir ulent to Gm2, Based on the sequence of this AFLP marker, SCAR (sequence cha racterized amplified region) primers were designed and used in combination with previously developed SCAR primers to distinguish effectively all five biotypes in a multiplex PCR-based assay. The inheritance pattern of this ma rker in the progenies of inter-biotype crosses between biotypes 1, 2 and 4 shows that the marker can be amplified by PCR from all Fl females, irrespec tive of the biotype status of their parents. However, the marker is present only in those male progenies whose mother was of a Gm2 avirulent biotype. The specific amplification of this marker in the avirulent biotypes and its pattern of inheritance show that avirulence with respect to carriers of th e Gm2 gene in rice gall midge is sex-linked.