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Invasion and colonization of mature apple fruit by a transformant ofErwinia amylovoratagged with bioluminescence genes fromVibrio fischeriwas examined. The transformant was deposited on cut surfaces of fruit stems, wounds on the shoulders and calyces, injured fruit-bearing twigs of harvested apple fruit, and cut fruit flesh. After incubation in closed stainless steel or plastic boxes at 25°C, fruit were periodically observed with a two-dimensional luminometer. The presence of the transformant in luminous areas was confirmed by isolating it on selective media.E. amylovora, when deposited in fruit stems: (1) can invade mature as well as immature apple fruit; (2) vertically and horizontally spreads and colonizes along vascular bundles, increasing its population; (3) reaches the calyx end and the flesh just under the exocarp within 3-4 days after inoculation; (4) when deposited on cut fruit flesh, irrespective of its maturity, can easily increase its population and survive 2-4 weeks or more at 25°C; and (5) even at the time of fruit maturation, can migrate within twigs rapidly and reaches the abscission layers between fruit-bearing twigs and fruit stems. [ABSTRACT FROM AUTHOR]