Two resistance modes to Clover yellow vein virus in pea characterized by a green fluorescent protein-tagged virus

This study characterized resistance in pea lines PI 347295 and PI 378159 to Clover yellow vein virus (ClYVV). Genetic cross experiments showed that a single recessive gene controls resistance in both lines. Conventional mechanical inoculation did not result in infection; however, particle bombardment with infectious plasmid or mechanical inoculation with concentrated viral inocula did cause infection. When ClYVV No. 30 isolate was tagged with a green fluorescent protein (GFP) and used to monitor infection, viral cell-to-cell movement differed in the two pea lines. In PI 347595, ClYVV replicated at a single-cell level. but did not move to neighboring cells, indicating that resistance operated at a cell-to-cell step. In PI 378159, the virus moved to cells around the infection site and reached the leaf veins, but viral movement was slower than that in the susceptible line. The viruses observed around the infection sites and in the veins were then recovered and inoculated again by a conventional mechanical inoculation method onto PI 378159 demonstrating that ClYVV probably had mutated and newly emerged mutant viruses can move to neighboring cells and systemically infect the plants. Tagging the virus with GFP was an efficient tool for characterizing resistance modes. Implications of the two resistance modes are discussed.