The impact of potato virus y on the severity of potato early dying

Abstract

The effect of Verticillium dahliae on the severity of Potato Early Dying (PED) and on the potato yield in the presence of Potato Virus Y (PVY) was studied in two potato cultivars, Russet Norkotah and Russet Burbank. Field experiments were conducted at the Hancock Experiment station during the summers of 1991 and 1992 in four row pltos replicated five times per treatment in a randomized block design (RBD). PVY was mechanically inoculated on the foliage both years. Infected seed tubers harvested from infected plants in 1991 were used in additional treatments in 1992. Verticillium dahlia gown on rye grain was spread over soil by hand and incorporated to a depth of 15 cm with a rototiller. Folia infection by PVY resulted in a yield reduction of about 30% and 24% in Russet Norkotah and Russet Burbank respectively in 1991. In 1992, the effect of foliar inoculation treatment was not significant, either in viral symptom expression or on potato yield. This may have been due to environmental conditions including frost damage following inoculation. Plants grown from PVY-infected tubers were found to have very good viral symptoms and to have reduced yield of about 50%. In 1991, V. dahlia alone did not show any effect on the development of PED. However, in 1992 the two levels of the fungus gave good symptom expression of PED and yield losses were 38% and 18% for Russet Norkotah and Russet Burbank respectively. PED severity and yield losses were greater when both diseases were present. The effects of combined diseases on the severity of PED were synergistic and on yield were additive. In 1992 a field experiment was conducted to determine the effect of time of PVY infection on subsequent infection of the progeny tubers. The experiment was established at the Hancock experimental station using four row plots replicated four times per treatment in a RBD. Russet Norkotah and Russet Burbank potato plants were mechanically inoculated with PVY at three or four different dates, respectively. The results showed that earlier infection resulted in a higher number of infected progeny tubers.