A New Phytoplasma Infecting Lettuce in Iran

Lettuce phyllody (LP) is an economically important disease of romaine lettuce (Lactuca sativa) in vegetative crop and seed crop fields in the Fars Province of Iran. Wild lettuce phyllody (WLP) occurs also in epidemic proportions in wild lettuce (L. serriola) during the fall in Iranian central and southern provinces, especially in Fars. Among various leafhopper species tested, Neoaliturus fenestratus successfully transmitted agents of LP and WLP to lettuce, wild lettuce, periwinkle, and sowthistle directly after field collection or after 5 to 7 days of feeding on diseased source plants. With primer pair P1/P7 in polymerase chain reaction (PCR), target DNA fragments (1.8 kbp) were amplified from total nucleic acid samples extracted from diseased lettuce and wild lettuce plants, but not from healthy counterparts. On the basis of disease symptoms, leafhopper transmission, and positive reaction in phytoplasma-specific PCR, Iranian lettuce and wild lettuce phyllodies agents have phytoplasmal etiology. Phylogenetic and putative restriction site analysis of 16S/23S rDNA spacer region (SR) indicated that LP and WLP phytoplasmas are members of pigeon pea witches'-broom (16SrIX) group and are closely related. Reciprocal transmission of LP phytoplasma to wild lettuce and WLP phytoplasma to lettuce by the same leafhopper species and induction of similar symptoms in common hosts are other evidences that agents of LP and WLP may be related or identical phytoplasmas. This is the first report of lettuce as a new host in pigeon pea witches'-broom group and N. fenestratus as a vector of a pigeon pea witches'-broom group phytoplasma. In other countries, phytoplasmas of aster yellows group (16SrI) are commonly associated with phytoplasmal lettuce diseases (2) and Macrosteles quadrilineatus leafhopper is reported as the vector (1). Relatedness of WLP phytoplasma to 16SrIX group was previously reported (3). On the basis of the results of this study, wild lettuce and sowthistle are two reservoirs of LP phytoplasma. References: (1) D. Errampalli et al. Phytopathology 76:1084, 1986. (2) I.-M. Lee et al. Ann. Rev. Microbiol. 54:221, 2000. (3) E. Verdin et al. Int. J. Syst. Bacteriol. Evol. Microbiol. 53:833, 2003.