First Report of Group 16SrXII Phytoplasma Associated with Papaya Yellows in Taiwan.

Abstract

Phytoplasmas have been reported to cause various disorders in papaya (Carica papaya L.), including dieback, mosaic, and yellow crinkle in Australia, Nivun Haamir dieback in Israel, and bunchy top-like disease in Cuba (1). Papaya is an economically important crop in Taiwan, and therefore, is monitored for viral infections. In 2005, papaya plants showing chlorosis, yellows and shriveling of leaves, dieback and lateral growth of branches, bending of apical branches, latexosis of fruits, and brown necrosis in phloem tissues were observed in southern Taiwan. Examination by an electron microscope revealed the presence of pleomorphic phytoplasma cells in sieve tubes of the phloem of petioles and leaf veins of diseased plants. Total DNA was extracted individually from at least three diseased plants at each location with a commercial DNA preparation kit (Axygen Scientific, Union City, CA) and used for amplification of the phytoplasma 16S rRNA gene in PCR with universal primer pairs P1 and Tint (3). The full-length 16S rRNA gene has been amplified and cloned. Sequence analysis revealed that the fragment was 1,581 bp long (GenBank Accession No. AJ919994) and shared 99.6% sequence identity with that of the 'Candidatus Phytoplasma solani' reference strain (GenBank Accession No. AF248959). A virtual restriction fragment length polymorphism analysis of the 16S rDNA sequence amplified from the R16F2n/R16R2 primers (2) was performed with iPhyClassifier (4) and pDRAW32. In silico restriction analysis identified the studied papaya phytoplasma as a subgroup 16SrXII-A strain. The sequence had 97 to 98% sequence identity with papaya phytoplasmas of the 16SrXII group in Australia (GenBank Accession No. Y10095), Israel (GenBank Accession No. AY903951), and Cuba (GenBank Accession No. AY725234). The disease incidence was 30 to 35% during the 2006 to 2010 growing seasons, and field surveys indicated that the disease has spread to central Taiwan with sporadic occurrence in recent years. To our knowledge, this is the first report of phytoplasma associated with papaya yellows in Taiwan.