GENETIC DIVERSITY OF THE PHYTOPLASMA ISOLATES ASSOCIATED WITH ALMOND WITCHES' BROOM IN IRAN*

Almond witches' broom (AWB) is an economically important disease associated with Candidatus Phytoplasma phoenicium, a phytoplasma belonging to the pigeon pea witches' broom group (16SrIX). Induction of different symptoms under natural conditions and after graft inoculation of bitter almond seedlings suggests genetic diversity of Keman 1, Kerman 2, Moshkan, Neyreez 1, Neyreez 2 and Sanandaj isolates of AWB in Iran. Restriction fragment length polymorphism, percent sequence homology and phylogenetic analysis were used for further assessment of genetic diversity among these isolates. RFLP analysis of P1/P7 PCR products (1.8 kbp) using AluI,haeIII, HhaI, HinfI, HpaII, Msel, TaqI and TasI revealed that Moshkan and Kerman 2 isolates are distinguishable from other isolates because of the different dijestion patterns produced by Cfo1 1 and Hinf1 enzymes, respectively. On this basis Moshkan isolate fell into group 1, Moshkan isolate into group 2 and Kerman1, Neyreez1, Neyreez2 and Sanandaj isolates into group 3. Percent homology of SR sequences differentiated AWB isolates. Moshkan isolate being distinctly different from the othes. Phylogenetic tree constructed with 16S rRNA gene and SR sequences also indicated genetic diversity of AWB isolates.Results of the present study shows that the 600 base pairs of rRNA gene operon following 1200 bp of the 5' start end of rRNA operon is the preffered fragment for studing genetic diversity of AWB phytoplasma. In the present stuy AWB disease is reported for the first time from Kerman and Sanandaj almond growing areas of Iran.