Varietal susceptibility of potatoes to internal black spot

Summary

• 1 Experiments were conducted to further test the correlation between black spot index and specific gravity, and to show the effect of field location on the relative response of various varieties to black spot and specific gravity.

• 2 A highly significant positive corelation of 933 was found between black spot index and specific gravity in 1949, using Long Island-grown Katahdin potatoes. We must conclude that there are other factors influencing blackening, but that there is an association between the specific gravity of the tuber and the black spot index.

• 3 The variety trials in 1949-1950 indicate that internal black spot is no longer just a Long Island problem, but is becoming increasingly prevalent throughout New York State.

• 4 The fact that location has an important effect on the incidence of black spot was demonstrated in the 1950–1951 trials. Several of the tested varieties reacted differently in blackening susceptibility when grown in certain counties. However, Ontario consistently blackened more than the other varieties in practically every location, whereas Ashworth, Pontiac and Kennebec showed the least susceptibility to discoloration of any of the varieties tested.

• 5 The most practical recommendations for the control of internal black spot are: (1) careful handling to avoid bruising, especially after very long storage and (2) the use of less susceptible potato varieties.