Assessment of variation in Aceria cajani using analysis of rDNA ITS regions and scanning electron microscopy: implications for the variability observed in host plant resistance to pigeonpea sterility mosaic disease

Aceria cajani on pigeonpea (Cajanus cajan) is the vector of the agent of pi geonpea sterility mosaic disease (PSMD), a very damaging virus-like disease in the Indian subcontinent. PCR was used to amplify A. cajani nuclear ribo somal DNA (rDNA) internal transcribed spacers (ITS) and associated rDNA gen es. They were assessed for variation in this genome region by nucleotide se quencing and RFLP. A. cajani-specific rDNA primers are described. Several A . cajani populations were collected from pigeonpea plants from various PSMD endemic locations in India, Nepal and Myanmar. No significant variation wa s identified in rDNA regions, or in morphological features. These results s uggest strongly that A. cajani on pigeonpea across the Indian subcontinent constitutes one species and that no other Aceria species and probably no A. cajani biotypes that differ in vectoring ability are involved in the trans mission of the agent of PSMD. The implications of these findings for the va riability observed in PSMD-resistant pigeonpea genotypes across various loc ations in India are discussed.