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Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/4/2014 Publication Date: 4/23/2014 Citation: Liu, S.S., Liu, Y. 2014. Reducing injury of lettuce from phosphine fumigation. HortTechnology. 24:188-195. Interpretive Summary: Low temperature fumigation with cylindered pure phosphine free of ammonia has been used successfully in postharvest pest control on some fresh commodities. However, when treatment time is long, low temperature phosphine fumigation injures lettuce. It is not clear what causes the injuries. It is critical to minimize the negative impact on lettuce for commercial use of low temperature phosphine fumigation on lettuce to control tolerant insects that require long treatments. The accumulation of plant volatiles such as carbon dioxide and/or ethylene might be responsible for injuries to lettuce. In this study, we fumigated lettuce with and without absorbents for carbon dioxide and ethylene for 3 days. The presence of the absorbents in phosphine fumigations prevented injuries and helped to retain quality of both head and romaine lettuce. These results are important in developing safe and effective low temperature phosphine fumigation not only on lettuce but also on other sensitive fresh commodities. Technical Abstract: Low temperature fumigation with pure phosphine free of ammonia has been used in recent years for postharvest pest control on some fresh fruits and vegetables. However, long fumigation treatments cause injuries to lettuce. It is unknown what factors contributed to the injuries. It is important to minimize the impact of fumigation on lettuce for commercial use of low temperature phosphine fumigation. We hypothesized that the accumulation of plant volatiles such as carbon dioxide and ethylene may be responsible for the injuries associated with phosphine fumigation, and experimentally determined that absorbents for carbon dioxide and ethylene can prevent or reduce injuries to lettuce in phosphine fumigation. Head lettuce and romaine lettuce were fumigated in fumigation chambers in the presence and absence of CO2 and ethylene absorbents for 3 d at 2ºC. In the absence of the absorbents, significant proportions of head lettuce and romaine lettuce sustained injuries in the form of brown stain, a typical symptom of CO2 injuries, and lettuce quality was reduced significantly as compared with controls. When CO2 and ethylene absorbents were used, injuries to lettuce were completely prevented and there was no reduction in lettuce quality as compared with controls, which indicated that carbon dioxide accumulation was mainly responsible for injuries associated with phosphine fumigation. We also found that the internal quality reduction and injury were strongly related to lettuce weight. External and internal quality and injury were generally tightly correlated. Our findings have important implications for developing safe and effective phosphine fumigation protocols at low temperature for controlling insect pests on fresh commodities, especially when a long treatment time is required. |
