Transmission of viral RNA and DNA to maize kernels by vascular puncture inoculation

Vascular puncture inoculation (VPI) is an effective technique for transmiss ion of maize viruses without using arthropods or other biological vectors. It involves using a jeweler's engraving tool to push minuten pins through a droplet of virus inoculum, toward the major vascular bundle in the scutell um of germinating kernels. Here, VPI is shown to be useful for introducing RNA and DNA viral genomes into maize. Maize dwarf mosaic potyvirus (MDMV) v irions, MDMV genomic RNA, foxtail mosaic potexvirus (FoMV) genomic RNA and maize streak geminivirus (MSV) DNA were introduced into kernels by VPI, and infection rates determined. At high concentrations, both MDMV virion and g enomic RNA preparations produced 100% infection of susceptible maize. Howev er, MDMV genomic RNA was transmitted with about 100-fold lower efficiency t han virions. FoMV genomic RNA and MSV DNA were transmitted at lower efficie ncy than the MDMV RNA, and the highest transmission rates were about 50%. R ibonuclease A pretreatment prevented genomic MDMV and FoMV RNA transmission , but not MDMV virion transmission indicating the viral RNA was the infecti ous entity. Proteinase K (ProK) pretreatment reduced transmission of MDMV R NA suggesting that integrity of the viral genomic protein bound covalently to the viral RNA may be important for efficient transmission. (C) 2001 Else vier Science B.V. All rights reserved.