Attenuated Mutants of Lily mottle virus Obtained by Tissue Culture of Lily Bulb.

Abstract

Attenuated mutants of Lily mottle virus (LMoV), which caused severe mosaic on the leaves and flowers of lily plants, were obtained by tissue culture of the lily bulb. The bulb scales of ‘Morino-otome’ derived from Lilium × formolongi and L. rubellum, infected with the virulent LMoV isolate ML61, were cultured on MS medium containing 1 g·L⁻¹ picloram for 0, 1 and 2 months and transplanted to MS medium for regeneration. Eleven regenerated plants, which showed markedly milder symptoms than the plants infected only with ML61, were selected. To assess the pathogenicity of the virus population in each selected plant, sap from their leaf was inoculated in seedlings of L. × formolongi ‘White Lancer’, which is sensitive to ML61. Two virus populations, LMm76-2 and LMm93, caused no or extremely mild symptoms in ‘White Lancer’. LMm76-2 and LMm93 showed a certain ability to cross-protect plants from infection by LMoV-ML61. Comparison of the 1,374 bp nucleotide sequence of HC-pro (helper component proteinase) gene among clones of each virus populations revealed some nucleotide mutations. There were three nucleotide mutations in the common sequence of each clone between LMm76-2 and LMm93. The mutation from C to U at the 808th position in the HC-pro gene was unique to attenuated mutants, resulting in one amino acid substitution from Cys to Arg at position 270 in the HC-pro protein.