Mechanical transmission of maize rough dwarf virus

Vascular puncture inoculation (VPI) and host developmental variables were modified to improve transmission of a maize rough dwarf virus isolate from Spain (MRDV-SP) to Pioneer hybrid 3379. MRDV-SP transmission at >90% resulted when sequentially, kernels were soaked in tap water at 30°C for 2.5 hr, incubated for 4 hr at 21°C, inoculated along both sides of the embryo axis by VPI, additionally incubated at 30°C for 48 hr and then planted in soil. However, variations among replications remained significant and indicated that this inoculation procedure did not resolve all factors affecting consistent transmission. Placement of inoculated kernels in different emergence or growth environments after the 48 hr postinoculation incubation at 30°C did not significantly improve MRDV-SP transmission. To investigate virus transmission by VPI, inbred Pa405 and 'Spirit' swectcorn kernels were inoculated with maize dwarf mosaic virus (MDMV-A) or mock-inoculated with purple ink, respectively. Based on the distribution of mosaic patterns in MDMV-infected seedling leaves of inbred Pa405 and the permeation of the purple dye in 'Spirit' sweetcorn,vec.icorn kernels after VPI, we hypothesize that the vibrating pins of the engraving tool in VPI efficiently created suitable wounds in cell membranes for virus infection.