The protrusion of sprouts is a major cause of loss of dry onions (Allium cepa L.) during extended storage. Sprouting is conventionally suppressed by treating onions with maleic hydrazide (MH) before harvest. More recently, ethylene was reported to inhibit sprout growth in stored onions, but commercial use of ethylene has been limited. Therefore, the objective of this study was to assess the effectiveness of ethylene on sprout suppression of five commercial cultivars of onions during storage and compare its effectiveness with and without MH treatment. Onions treated with MH were stored for up to 9 months at 1 °C in atmospheres with and without ethylene in a series of experiments conducted over six seasons. Differences in sprout elongation and protrusion were observed during storage in air among the five cultivars. Storage in ethylene was effective in inhibiting sprout elongation and root growth of onion bulbs in all cultivars, with concentrations of 7 µL·L−1 ethylene being more effective than 1 µL·L−1 ethylene. Delaying application of ethylene by 4 months was less effective in inhibiting sprout elongation than continuous treatment. Ethylene provided greater sprout suppression than MH treatments alone and could serve as a replacement for MH.
Charles F. Forney, Kristen Cue, and Sherry Fillmore
Michael A. Jordan, Kenneth McRae, Sherry Fillmore, and Willy Renderos
Volatile compounds contribute to carrot (Daucus carota) flavor. However, effects of postharvest treatments on these compounds are not defined. To characterize treatment effects, fresh carrots (cv. Sunrise) were treated with 0 or 1.0 μL/L 1-methylcyclopropene (1-MCP) at 10 °C for 16 h, then exposed to 0, 0.3, or 1.0 μL/L ozone (O3) at 10 °C for 1, 2, or 4 days, and subsequently stored at 0 °C for up to 24 weeks. Twelve terpenes were identified in the headspace over whole carrots, including dimethylstyrene (22.5%), alpha-pinene (19.1%), caryophyllene (15.8%), beta-pinene (9.1%), p-cymene (8.3%), limonene (7.7%), gamma-terpinene (6.7%), myrcene (4.7%), gamma-terpinolene (4.5%) camphene (1.0%), alpha-phellandrene (0.52%), and sabinene (0.03%). Most terpenes responded similarly to treatments and storage. Immediately after treatment with 1.0 μL/L O3 for 1, 2, or 4 days, total terpene concentrations were 45%, 85%, and 87% greater than concentrations in non-treated controls. Caryophyllene, beta-pinene, and sabinene did not increase in response to the O3 treatment unlike the other terpenes. 1-MCP reduced terpene concentrations by an average of 18%. O3 treatments also stimulated stress volatile production. Ethanol headspace concentrations were 8-, 21-, and 43-times greater than the nontreated controls immediately following treatments with 0.3 nL/L O3 for 4 days or 1.0 μL/L O3 for 2 or 4 days, respectively. However, after 8 weeks, no differences among treatments were observed. Hexanal production also was stimulated by all O3 treatments, being 2- to 11-times greater than controls immediately following treatment. 1-MCP reduced O3-stimulated ethanol and hexanal production by 23% and 8%, respectively.
P. Gordon Braun, Keith D. Fuller, Kenneth McRae, and Sherry A.E. Fillmore
This study evaluated the effects of pre-plant treatments: deep ripping (DR), fumigation (F), deep ripping plus fumigation (DRF), deep ripping plus hog manure compost (DRC), and deep ripping plus fumigation plus hog manure compost (DRFC) in comparison with a non-treated control (NTC) on shoot and root performance of ‘Honeycrisp’ apple trees on M.4 rootstocks in an old orchard site with apple replant disease (ARD). Cylindrocarpon spp., Pythium spp., and Pratylenchus penetrans Cobb, all potential agents of ARD, were present in the orchard soil. Fine-root numbers (1 to 2.9 mm diameter) were significantly greater in the DRC and DRFC treatments than the DR treatment. After 6 years, trunk cross-sectional area (TCSA) and yield were largest for the DRFC treatment followed closely by F. The DR treatment had no effect on TCSA, yield, or yield efficiency when applied alone compared with the NTC. Contrast analysis demonstrated that F was significantly better than non-F for yield in all years and TCSA and yield efficiency in 2007. Also, there was a significant interaction between DR and F treatment in 2005 that significantly reduced yield in the DRF treatment. Contrast analysis showed that compost had a significant positive effect on yield in all three production years and TCSA and yield efficiency in 2007. Yield efficiency in the third production year was largest for F, DRC, and the DRFC treatments. Nutrient analysis revealed that soil phosphorus concentrations in compost-treated plots were double those in other treatments. High phosphorus content of compost may have contributed to the amelioration of ARD symptoms. This study found that in 2007, soil fumigation alone, as conventionally used for ARD control, and composted hog manure were equally effective in increasing yield and yield efficiency of apple trees planted in an ARD soil. The DRFC treatment was the overall best treatment in all years.