A. Viron attaches to the host cell surface and the envelope is engulfed B. Naked viron inject nucleic acid into the host cell C. Viron attaches to host cell receptor and fuses with membrane D. Nucleocapsids assoicate with membrane and bud through
Direct penetration means letter B. Naked viron inject nucleic acid to the cell wall. This is the stage that occurs when the appressorium develops a long and thin penetration peg. This will have the ability to penetrate the epidermal cell so that the nucleic acid will be placed directly on the host cell.
This is the type of penetration that is usually done by parasitic plants. This is also done by some types of fungi and nematodes. There are instances when this is bad especially when it is a pathogen that is trying to bring a disease to the plant. They inject diseases to the plants the same way. The disease might eventually make the plant grow weaker and die.