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The food-borne human pathogen Listeria monocytogenes survived and its populations increased on cv. Delicious apple slices at 10 or 20°C in air or controlled atmosphere of 0.5% O2 and 15% CO2, but did not grow at 5°C. Controlled atmosphere had no significant effect on the survival or growth of L. monocytogenes. The pathogen populations declined over time when grown in various concentrations of apple juice and the decline was greater as the concentration of the juice decreased. Populations of L. monocytogenes inoculated into decayed apple tissue continually increased on fruit decayed by Glomerella cingulata but did not survive after 5 days on fruit decayed by Penicillium expansum. The pH of the decayed area declined from pH 4.7 to 3.7 in the case of P. expansum, but in the case of G. cingulata the pH increased from pH 4.7 to 7.0. This pH modification may be responsible for affecting the growth of the food-borne pathogen. Storage temperature, as well as the absence of postharvest pathogens such as G. cingulata, is important for maintaining the safety of fresh-cut apples.

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As a part ofthe environmental air quality assessment studies, we have conducted spectral characterizations of steady state fluorescence and canopy level reflectance measurements in responses to the air quality treatments. These studies have been carried out under well watered and restricted soil moisture regimes. Our primary objective was to evaluate fluorescence technique for the nondestructive assessment ofplants grown in elevated CO2. elevated 03, and both elevated CO2 and 03 environments under normal and restricted soil moisture conditions. The experimental field site is located atthe South Farm, USDAIBARC, Beltsville, Maryland. Weused field open-top chamber systems to simulate four altered combinations oftropospheric CO2 and 03 environments under well watered and restricted soil moisture conditions. The simulated gaseous environments included: 1) charcoal-filtered (CF) ambient air as the control chamber; 2) elevated CO2 consisted of CF ambient air plus 150 10 il/1 C02; 3) elevated 03 that consisted of Non-Filtered (NF) ambient air and addition of35 5 nIJl 03; and 4) high CO2 and 03 chamber which consisted ofNF ambient and additions of 150 10 il/l CO2 and 35 5 nl/l 03. The CO2 was supplied for 18 hours (3 :00 to 21 :00 h EST) per day from a CO2 bulk tank. In theelevated 03 treatment chambers, 35 5 nI/i 03 was supplied during seven hour period from 9:00 to 16:00 h EST per day. Both gases were supplied for the entire growing season from early July to late-October. Two soybean cultivars 'Essex' and 'Forrest' were planted in the OTC. Fluorescence images were acquired at F450, F550, F680, and F740. The results showed that fluorescence responses of 'Essex' and 'Forrest' were significantly different in all four bands. Restricted soil moisture treatment had significant effects in that means for F450 and F550 bands significantly increased in both cultivars. The increases in fluorescence intensities at F450 and F550 for 'Essex' due to restricted soil moisture were much greater than those of 'Forrest'. At F680 and F740 bands, only 'Essex' was significantly affected by soil moisture treatment. The most significant effects ofelevated CO2 and 03 were observed at F450 and F550 bands. Means for elevated 03 in ambient air in both cultivars were significantly higher in both soil moisture regimes. However, no significant differences between CF and NF+C02+03 within a soil moisture treatment were observed. Means for CF+C02 was significantly lower for both cultivars under well watered soil condition at F450. In general, none ofthe treatment means were significantly affected by elevated 03 treatments at F680 and F740. Although visible stress symptoms such as chiorosis, discoloration, or necrosis were not evident in the leaves used in this study, F450 and F550 fluorescence images depicted the effects ofelevated 03, partial compensation ofelevated 03 effects by the elevated CO.,, and positive physiological effects ofelevated CO2. Plant stresses that cause localized damage may not be easily detected with small field of view point meas...

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