Nuclear Ultrastructural Changes and Aggregates of Viruslike Particles in Mungbean Cells Affected by Mungbean Yellow Mosaic Disease

Abstract

Yellow mosaic disease of mungbean in Thailand was caused by a whitefly-transmitted agent, presumably a virus. Ultrastructural changes similar to those previously reported for whitefly-transmitted viruses are associated with the disease. The virus-like particles (VLPs) associated with the disease were isometric, about 15-20 nm in diameter, and often formed loose aggregates that sometimes almost filled the total nuclear volume of infected phloem cells. Mungbean infected by whitefly transmission or by grafting had hypertrophied nucleoli, aggregates of VLPs, and fibrillar bodies in the nuclei of phloem cells as early as 2 days before symptom appearance. In vacuoles or lumens of the partially or fully differentiated infected sieve elements, VLPs occasionally formed aggregates having a double cylindrical arrangement of particles. No VLPs were detected in tissues other than the phloem of infected plants or in any tissues of comparable healthy plants.