Laboratory studies on the effect of gamma radiation on Erwinia amylovora survival on apple fruit
Susceptibility of Erwinia amylovora to gamma irradiation was determined in vitro on test tube cultures and in vivo on apples and pears. Bacterial strains differed in susceptibility to irradiation. Higher doses of irradiation (ca. 80 krad (1 krad = 10 Gy)) were needed to kill the bacterium on fruit compared with test tube cultures (from 20 to more than 50 krad). Fruit with natural populations of E. amylovora collected from a severely blighted orchard, exposed to doses of 140 krad, still contained viable bacteria. Surviving E. amylovora were pathogenic to green 'Bartlett' pears. Five radiation-sensitizing chemicals (used previously against different pathogens on other commodities) were tested against E. amylovora. N-Ethylmaleimide sensitized the bacteium to gamma irradiation. Treatment of natural populations of the bacterium on apples with N-ethylmaleimide eliminated E. amylovora from the apple surface with a gamma irradiation dose one-third lower than the maximum rate tolerable by fruit.