Localization of tomato yellow leaf curl virus (TYLCV) in susceptible and tolerant nearly isogenic tomato lines

The Israeli isolate of tomato yellow leaf curl virus (TYLCV) is a whitefly-transmitted monopartite geminivirus. We have developed two nearly isogenic tomato breeding lines. Line 52 containing the TYLCV tolerance allele Ty-1, introgressed from the wild tomato species Lycopersicon chilense was tolerant to TYLCV; line 50 containing the ty-1 L. esculentum allele, was sensitive to the virus. The effect of Ty-1 on the establishment of the TYLCV disease was studied by comparing the structural changes and the location of the virus in tissue sections of inoculated leaves from plants of the two lines. A collapse of the spongy mesophyll cells of the susceptible line (but not of the tolerant line) was the first striking cytopathy observed two weeks after inoculation. TYLCV was located in these collapsed cells by in situ hybridization. TYLCV was also found in the phloem and mesophyll cells of both lines, indicating that this virus is not phloem limited in tomato.