Arthur C. Cameron

1-MCP blocks ethylene-induced petal abscission of Pelargonium peltatum but the effect is transient

Continual exposure to 1.5 m ll 1 ethylene caused 100% petal abscission within 2 h from detached flowers of Pelargonium peltatum (L.) ‘Pink Blizzard’ (ivy geranium) harvested just after the stigmatic lobes had separated. When flowering plants were first pretreated for 2 h with 1 m ll 1 1-MCP, ethylene-induced petal abscission was completely inhibited. However, the effect was transient, since percent abscission increased with time after 1-MCP treatment. Based on percent abscission from detached flowers after a 2-h ethylene exposure, the half-life of 1-MCP activity was about 2, 3 and 6 days after 1-MCP treatment at 25, 20.7, and 12°C, respectively, and there was no evidence for a residual effect after 4 or 5 days at 25 and 20.7°C, respectively. A second application of 1-MCP renewed the inhibitory effect. Following 1-MCP treatment, the force required to separate petals from the flower declined linearly with time. The time until complete loss of the inhibitory effect was strongly temperature dependent, e.g. : 1 day at 25°C versus 3‐4 days at 12°C. The usefulness of 1-MCP as a commercial treatment to prevent petal abscission from Pelargoniums will depend on shipping and storage temperature and application frequency.

Fungistatic effects of carbon dioxide in a package environment on the decay of Michigan sweet cherries by Monilinia fructicola

Fruits of five cultivars of sweet cherry were packaged in low-density polyethylene and stored in air or in carbon dioxide (CO 2 ) ranging from 12 to 50% at 20 C for 7 days, or 0 C for 14 days followed by 20 C for 7 days. Before packaging, one-half of the fruits were arificially wounded and inoculated with conidia of Monilinia fructicola. The incidence of brown rot was recorded daily, and lesion diameters were measured at the end of four of the six experiments

An ethanol biosensor can detect low-oxygen injury in modified atmosphere packages of fresh-cut produce

Abstract Improper package design or temperature abuse during handling may cause fruits and vegetables in modified-atmosphere (MA) packages to be exposed to low, injurious O 2 levels associated with the production of fermentation volatiles, quality loss and eventually product breakdown. A simple and reliable technique to detect low-O 2 injury in packaged products at an early stage would reduce the risk of supplying inferior or unsafe produce to the consumer. The formation of ethanol, a common product of fermentation, has been correlated with low-O 2 injury. A commercial ethanol biosensor, composed of a chromagen and immobilized enzymes: alcohol oxidase and peroxidase, and available as a test strip, was tested for its suitability to detect low-O 2 injury indirectly. In the presence of ethanol, the chromagen was oxidized, resulting in a color change from a dull white to a clear bluish-green. The biosensor detected 10 μl l −1 (≈1 Pa) ethanol in the gas phase at 5°C with a 15-s exposure. The human threshold for ethanol detection is 30 μl l −1 (≈3 Pa). The color change of the biosensor was closely correlated to ethanol partial pressure in MA package headspace over cut lettuce, cut broccoli, cut cauliflower, shredded cabbage and cut carrots, and to that over prepared standard ethanol solutions. The study demonstrated that the biosensor can detect gas-phase ethanol quantitatively and hence indirectly can detect low-O 2 injury in MA lightly processed cut broccoli, cut cauliflower, cut lettuce and shredded cabbage packages. The biosensor detected ethanol in cut carrot packages prior to the establishment of low-O 2 conditions. This ethanol, also detected using gas chromatography, may have been produced as a wound response to cutting.

Oxygen concentration effects on ethylene production by ripening banana tissue

Abstract Ethylene production was studied as a function of O2 concentration in tangential slices of pulp tissue from bananas during ripening over 8 days at 20°C after initiating ripening with ethylene. The half-saturating O2 concentration for ethylene production ([S]0.5[O2]e) remained at 1.7% O2 throughout ripening, even though tissue levels of 1-aminocyclopropane-1-carboxylic acid (ACC) varied substantially during ripening. Oxygen concentrations within peeled banana pulps averaged 0.52 ± 0.013% less than the surrounding air during ripening. A mathematical model established that the depression of O2 concentration caused by respiratory O2 uptake within tangential slices was unlikely to have exceeded 0.046% O2. [S]0.5[O2]e for ethylene production in banana pulp tissue has therefore been estimated accurately, it appears to be independent of tissue ACC levels.

Controlled Flowering of Herbaceous Perennial Plants

We have determined the juvenility, cold (vernalization), photoperiod, and cultural requirements necessary to flower many herbaceous perennials on specific dates and at specified sizes. We identified the long-day (LD) requirement by conducting critical photoperiod experiments in which critical photoperiod is defined as the photoperiod that elicits a complete, rapid, uniform flowering response in a population. The LD requirement for all herbaceous perennials tested can be met by either a continual photoperiod of 16 hours or more, or by four hours of light as an interruption in the middle of the night. Nightinterruption lighting for two hours is adequate for rapid, uniform flowering in some species. Incandescent, cool-white fluorescent, metal halide, and high-pressure sodium lamps effectively promote an LD response; differences among the irradiance levels required for flower induction are horticulturally insignificant. To maintain vegetative growth on quantitative and qualitative LD species, photoperiods should be 10 hours or fewer.