Mycoactive acetate esters from apple fruit stimulate adhesion and germination of conidia of the gray mold fungus.

Ethyl acetate, 2-methylbutyl acetate, butyl acetate (BA), and hexyl acetate were detected by solid-phase microextraction and gas-liquid chromatography inside slices of Golden Delicious apple and in water droplets on the skin of slices incubated in sealed glass jars. Conidial adhesion and germination of the gray mold fungus, Botrytis cinerea, was assessed on apple slices after exposure or no exposure to the esters in the headspaces of glass jars. Attached conidia were dislodged by sonication and remaining conidia on apple slices were counted by microscopy. Adhesion generally increased as BA increased to 7.2 microg mL(-1), but declined with greater concentrations. BA at 0-3.6 microg mL(-1) for 24 h stimulated adhesion 2-fold greater compared to that at 4 h. Adhesion stimulated by BA increased as a function of time (0-24 h), showing linear trends (r (2) = 0.99; p = 0.01) during 0-12 h. The four esters were similar in their ability to stimulate adhesion. Germination of conidia exposed to BA increased linearly (r (2) = 0.95-0.98; p = 0.01) during 4-12 h. Conidial adhesion stimulated by BA preceded conidial germination by 2 h. The four esters stimulated conidial germination to similar levels. Results indicated that acetate esters formed in apple fruit are mycoactive, influencing life-cycle events of B. cinerea important to its survival on the fruit. The similar responses of three B. cinerea isolates to four acetate esters suggests a common stimulation mechanism may operate in B. cinerea.

A procedure for quantifying adhesion of conidia of Botrytis cinerea to the skin of apple fruit.

Ultrasonication was evaluated as a nonchemical means to quantitatively remove conidia of Botrytis cinerea from the skin of Golden Delicious apple (Malus domestica Borkh.) fruit. A probe immersed in a suspension of conidia and generating 20 kHz at 150 W for 30- or 60-s pulses destroyed 13.3% or 29% of conidia, respectively. Destruction at 150 W for 10 s or at 30-120 W for up to 60 s was <2%. The procedure for quantifying adhesion of conidia to the skin of fruit consisted of pipetting a 50-microL water droplet containing 5 x 10(4) conidia onto the skinside of a slice of fruit, incubating the slices inside sealed 500 cm3 glass jars, excising a 1 cm diameter piece of skin bearing the droplet, and sonicating the skin in 8 mL of ice-cold water at 150 W for 10 s. The skin was removed, the suspension was centrifuged at 1250 x g for 15 min, and the supernatant was reduced to 1 mL by vacuum suction using a pipet. Conidia were stained with crystal violet and counted in a hemacytometer. Adhesion of conidia to skin was 3.0%, 14.6%, 20.8%, 39.4%, 57.6%, and 73.1% after 0, 2, 4, 8, 12, and 24 h incubation, respectively. Sonication was more effective than two other procedures for recovery of conidia. Conidia on the skin of fruit exposed to 4 microL of butyl acetate in the headspace of glass jars for 4 h at 23 degrees C increased the adhesion of conidia 107% above that for unexposed conidia. Sonication with a programmable power- and time-controlled probe was a simple, rapid, safe, and effective method for quantifying adhesion of B. cinerea conidia to the skin of apple fruit.

Butyl acetate and yeasts interact in adhesion and germination of Botrytis cinerea conidia in vitro and in fungal decay of golden delicious apple.

Butyl acetate is a volatile aroma and flavor compound in apple. Conidia of three strains of Botrytis cinerea, a fungus that causes decay of apple fruit in postharvest storage, had greater adhesion to and greater germination on polycarbonate membrane filters on water inside sealed 500 cc glass jars that were injected with 4 microliters butyl acetate than conidia not so exposed. Conidial germination was highly correlated with conidial adhesion. The yeasts Sporobolomyces roseus and Cryptococcus laurentii, but not Saccharomyces cerevisiae, reduced the adhesion and germination promoting effect of butyl acetate. Conidia did not readily utilize butyl acetate as a food source, as shown by lack of tetrazolium violet reduction, whereas S. roseus and C. laurentii, but not S. cerevisiae did. Butyl acetate added to suspensions of conidia increased the electrical conductivity of the suspensions and increased the loss of 14C from 14C-labeled conidia compared to conidia unexposed to butyl acetate. Uptake of [14C]glucose by conidia was not increased by butyl acetate. Wounds of Golden Delicious apples inoculated with conidia (strain F-J-4) in a dilute solution of butyl acetate had greater decay than unexposed wounds. S. roseus and C. laurentii, but not S. cerevisiae, added with the conidia decreased the incidence or size of decay. Results indicated that butyl acetate increased conidial adhesion, stimulating conidial germination, and some yeasts can reduce this effect.

Assimilation of volatiles from ripe apples by Sporidiobolus salmonicolor and Tilletiopsis washingtonensis.

Sporidiobolus salmonicolor ATCC 623 and Tilletiopsis washingtonensis NRRL Y-2555 grew on carbon resources provided as volatiles by ripe 'Golden Delicious' apples. This ability was not correlated with the reported natural habitats of the 21 species (26 strains) tested. Ethylene, the major volatile produced, was not utilized but butyl acetate, hexyl acetate and hexyl-2-methyl-butanoate (identified by GC-MS) were. These yeasts also assimilated ethanol, butanol, hexanol (Tilletiopsis excepted), acetate, propionate, butyrate and ethyl acetate at appropriately low concentrations. Ethanol and acetate aside, this is the first report of such assimilations by any yeast.