To better understand the nature of maize dwarf mosaic virus (MDMV) and its interaction with susceptible and resistant corn hybrids, the purification of MDMV and its physical properties were re-evaluated and a rapid assay procedure was developed.

The virus was purified by chloroform clarification and differential and sucrose density-gradient centrifugation. Corn tissue was homogenized in 0.1 M sodium citrate plus 0.5% mercaptoethanol. The virus was resuspended after high speed centrifugation in 0.005 M sodium citrate, pH 7.0. Purified virus has an ultraviolet absorption spectrum typical for filamentous viruses having 5% RNA, shows birefringence, has an A260/280 of 1.18, and a sedimentation coefficient of 160-162 S. The virus is filamentous and appears to be a member of the potato virus Y group. A yield of 9.0-23.0 llg of virus/g fresh weigh.t of field-grown, mechanically inoculated Hy X Cl03 was determined by analytical sucrose density-gradient centrifugation. This represents a yield of purified virus of approximately 25% of that in the clarified sap. Results obtained from the density-gradient analysis were comparable to but more sensitive than those from the microprecipitin test and a systemic infectivity assay. The systemic infectivity assay on corn, analyzed by maximum likelihood and log log transformation, showed a yield of purified virus of 0.4% of that in the crude sap.