Characterization of Actinidia virus 1, a new member of the family Closteroviridae encoding a thaumatin-like protein.

A new member of the family Closteroviridae was detected in Actinidia chinensis grown in Italy, using next generation sequencing of double-stranded RNA. The virus isolate, named Actinidia virus 1 (AcV-1) has a genome of 18,848 nts in length, a structure similar to the unclassified persimmon virus B (PeVB) and contains 12 open reading frames (ORFs) greater than 6 KDa, one carrying two papain-like leader proteases, a methyltransferase, a helicase and an RNA-dependent RNA polymerase domain. Additional ORFs code for homologs of heat shock protein 70, heat shock protein 90 and a coat protein. Curiously, AcV-1 and PeVB genomes code for a thaumatin-like protein, a peculiarity unreported for other viruses. In phylogenetic analyses both viruses group in a distinct clade evolutionarily related to closteroviruses. The final taxonomic position of AcV-1 within the family Closteroviridae is yet to be clarified.

Specific detection of D- and M-isolates of plum pox virus by immunoenzymatic determination of PCR products.

Molecular techniques based on the polymerase chain reaction (PCR) can provide rapid and sensitive diagnosis of plum pox virus (PPV), the causal agent of the devastating 'sharka' disease of stone fruit trees. The present study compared routine polymerase chain reaction (PCR) procedures against a new system, PCR-ELISA (Boehringer Mannheim), which enables immunoenzymatic detection of PCR products. The results show that this hybridisation system ensures fast and more sensitive detection of PPV associated with stone fruit trees and herbaceous hosts. Strain-specific capture probes were also designed to identify the two major PPV isolates, D and M, without subsequent restriction fragment length polymorphism analysis of the PCR products. Optimisation of all parameters involved in the PCR-ELISA procedure are discussed and its advantages reported.

Occurrence of Peach Latent Mosaic Viroid in Stone Fruits and Its Transmission with Contaminated Blades.

Peach latent mosaic viroid (PLMVd) is widely distributed (approximately 55%) in peach germplasm from Europe, Asia, North America, and South America. PLMVd, or a closely related viroid, was occasionally detected in cherry, plum, and apricot germplasm from countries in Europe or Asia. The cherry isolate of PLMVd is 337 nucleotides in length and is 91 to 92% homologous to PLMVd isolates from peach. Molecular hybridization experiments demonstrated that PLMVd is not related to the agent of peach mosaic disease. PLMVd was readily transmitted (50 to 70%) by contaminated blades to green shoots and lignified stems of peach GF-305 plants. These results indicate that the viroid may be transmitted in orchards with contaminated pruning equipment.

Rice tungro bacilliform virus DNA independently infects rice after Agrobacterium-mediated transfer.

In nature, rice tungro disease is caused by an RNA and a DNA virus complex, but we have obtained an independently infectious clone of rice tungro bacilliform virus (RTBV) DNA. Infectivity could be demonstrated only when a more than unit-length copy was cloned in the Agrobacterium binary vector Bin 19 and agroinoculated into rice plants. Rice plants thus agroinfected with cloned RTBV DNA showed typical symptoms of tungro disease, presence of viral DNA and bacilliform particles, and could be used as a source of virus to infect healthy plants by the green leafhopper (Nephotettix virescens). The importance of this infectious clone in understanding the molecular biology of RTBV and the rice tungro disease is discussed.