Association of a Phytoplasma with Pistachio Witches’ Broom Disease in Iran

Pistachio is an important crop in Iran, which is a major producer and exporter of pistachio nuts. The occurrence of a new disease of pistachio trees, characterized by the development of severe witches’ broom, stunted growth and leaf rosetting, was observed in Ghazvin Province. A phytoplasma was detected in infected trees by polymerase chain reaction (PCR) amplification of rRNA operon sequences. Nested PCR with primer pairs P1/P7 and R16F2n/R16R2 was used for specific detection of the phytoplasma in infected trees. To determine its taxonomy, the random fragment length polymorphism (RFLP) pattern and sequence analysis of the amplified rRNA gene were studied. Sequencing of the amplified products of the phytoplasma 16S rRNA gene indicated that pistachio witches’ broom (PWB) phytoplasma is in a separate 16S rRNA group of phytoplasmas (with sequence homology 97% in Blast search). The unique properties of the DNA of the PWB phytoplasma indicate that it is a representative of a new taxon.