SYMPTOMATOLOGY, ETIOLOGY AND TRANSMISSION OF CHICKPEA PHYLLODY DISEASE IN PAKISTAN

摘要

Chickpea (Cicer arietinum) plants of two types, kabuli and desi, showing phytoplasma disease-like symptoms were observed for the first time in Pakistan during 2005. The major symptoms were floral virescence, phyllody and extensive proliferation of the branches. Light microscopy of hand-cut sections of symptomatic stems treated with Dienes' stain showed blue areas in the phloem region of diseased plants but not in apparently normal ones. Phytoplasma-like pleomorphic bodies were observed in the sieve cells of symptomatic chickpea stems by transmission electron microscopy, but not in the sieve tubes of healthy plants. Amplification from diseased plants of a 16S rDNA fragment 1800 bp in size with phytoplasma primers P1 and P7, confirmed that they hosted a phytoplasma RFLP profiles and complete sequencing of the R16F2n/R16R2 region showed that the associated phytoplasma had 100% sequence identity in this rDNA region to 16SrII-D subgroup phytoplasmas. Chickpea phyllody disease was transmitted from diseased to healthy chickpea plants by grafting and through the leafhopper Orosius orientalis. Sap inoculation trials were unsuccessful and transmission by Aphis craccivora, Myzus persicae, Empoasca devastans and an unidentified brown leafhopper failed to produce disease symptoms.