First Report of a Phytoplasma Associated with Cactus Witches'-Broom in Yunnan (China)

Sixteen samples from naturally infected cactus (Opuntia linguiformis D.Griffiths) with symptoms of witches'-broom were collected from 5 different sites in Yunnan Province. Symptoms were typified by the production of many young cladodia (the flat leaf like stem), closely bunched together on the old cladodium (Fig. 1).

Diseased and healthy plants were tested by PCR amplification for phytoplasma-specific 16S rDNA. Total nucleic acid was extracted from young cladodia by the method of Ahrens & Seemuller (1992) and used as the template in a nested PCR reaction using primers R16mF2/R16mR1 and R16F2/R2 (Lee & Gundersen, 1998). A 1.2 kbp DNA fragment was amplified from 11 diseased plants but not from known healthy or symptomless plants. The 1.2 kbp DNA fragment was purified, cloned and sequenced and the sequence deposited in the EMBL Database (Accession No. AJ293216). Using a multiple alignment program (DNAMAN Version 4.0) the sequence showed a high similarity with members of the 16SrII group of phytoplasmas (Lee & Gundersen, 1998). The highest homologies were with 16S rDNA of faba bean phyllody phytoplasma (99.7%) (Accession No. X83432), a member of the 16Sr group, subgroup C, and a cactus witches'-broom phytoplasma found in Mexico (99.4%) (Genbank accession No. AF200718). This is the first report of a phytoplasma associated with a disease in cactus from Yunnan (China).