Association of phytoplasmas with tapping panel dryness syndrome of Hevea brasiliensis: A pathological perspective to unresolved mystery?

Tapping panel dryness is a serious disorder impairing the synthesis of latex in the laticifer cells of the soft bark region of para rubber, Hevea brasiliensis. Decades of research did not yield conclusive evidence for the causative factor of this disorder. Soft bark region of the bark is rich in latex vessels and phloem sieve tubes. Semi- and ultrathin sections of this region demonstrated blockage of sieve tubes and shrunken latex vessels. Presence of pleomorphic bodies in the size range of 400–2,000 nm was depicted in scanning electron microscopy images. Confocal laser scanning electron microscopy with DAPl staining compared the healthy and diseased soft bark region. Diseased sample exhibited fluorescence in the sieve tubes with thick callose deposition. Presence of phytoplasmas in tapping panel samples dryness affected bark samples was confirmed by amplification and sequencing of 16S rRNA gene region with universal primers. The sequence of the phytoplasma from clone RRll 105 was submitted to NCBl with accession number KP025809.