Detection and genetic relatedness of phytoplasmas associated with plant diseases in Thailand

Phytoplasma ribosomal DNA was detected by the polymerase chain reaction (PCR) in diseased plants collected from different parts of Thailand. Among these, bitter gourd phyllody (BGPHY) from Songkhla, South Thailand is a new phytoplasma disease. Restriction fragment length polymorphism (RFLP) patterns from Alu I, Hpa II, Mse I, and Rsa I restriction enzymes indicated 3 phytoplasmas groups. One group contained carpet grass (Axonopus compressus (Sw.) P. Beauv.) white leaf (CGWL), bermuda grass (Cynodon dactylon (L.) Pets.) white leaf (BGWL), sugarcane white leaf(SCWL), and sugarcane green grassy shoot (SCGS). The second group contained sesame phyllody (SESPHY) and sunnhemp phyllody (SUNPHY), and the third group contained periwinkle phyllody (PERPHY) and BGPHY. Only digestion with Mse I permitted differentiation of SCWL from CGWL and BGWL and also from SCGS. Spacer region sequence analysis showed that the 3 groups of phytoplasmas formed distinct phylogenetic clusters. SESPHY was closely related to faba bean phyllody (FABAPHY) while PERPHY and BGPHY were related to the aster yellows agent. Within the white leaf cluster, SCWL and SCGS were more closely related to each other than they were to BGWL and CGWL.