1. Diaz-Moreno, F. 1965. El virus del amarillamiento de las papas. Cienc. Nat. 8: 25–37.
2. Dowley, L.J. 1973. Effects of primary and secondary infection with potato virus X (PVX) on yield, size, chemical composition, blight resistance and cooking quality of potato variety Kerr’s Pink. Potato Res. 16: 3–9.
3. Fernow, K.H. 1967. Tomato as a test plant for detecting mild strains of potato spindle tuber virus. Phytopathology 57: 1347–1352.
4. Hooker, W.J. and R.F. Fronek. 1961. The influence of virus Y infection on early blight susceptibility in potato. Conf. Potato Virus Dis. Proc., 1960 4: 76–81.
5. Horsfall, J.G., and R.W. Barratt. 1945. An improved grading system for measuring plant disease. Phytopathology 35: 655.