为了深入了解柑橘黄龙病湿热蒸汽快速热处理时韧皮部的升温特性,针对柑橘黄龙病细菌位于韧皮部的特点,构建了室内和田间试验装置,主要包含加热罩、湿热蒸汽发生装置、树体表面和韧皮部温度采集装置.通过比较热处理前后韧皮部温度变化,作物恢复程度差异和黄龙病病菌浓度变化,分析获取湿热蒸汽快速热处理合理参数组合.室内试验选用1 a生柑橘树,研究了树体表面温度为55~65℃,蒸汽输送压力为0.015和0.03 MPa,不保温和保温处理30 s对于韧皮部升温和作物恢复的影响.试验结果:树体表面温度为65℃及以上时,作物都因热损而死亡,采用60℃作为热处理温度阈值,有利于韧皮部温度提高.较高的蒸汽输送压力(如0.03 MPa),虽有利于作物所在环境温度的快速升高,但其作用于韧皮部的传热时间短,韧皮部温度并没有得到有效提高,而加热后的30 s保温处理普遍有利于韧皮部温度提高.田间试验选用9 a生柑橘树,研究了树体表面温度为60℃,蒸汽输送压力为0.03 MPa,保温时间30 s的组合参数对于黄龙病病菌浓度和作物恢复的影响.试验结果:4棵染病柑橘树经过热处理,其中2棵恢复到未染病状态,2棵病菌浓度降低.2棵未经过热处理的染病柑橘树,其病菌浓度没有变化.室内和田间试验结果表明:湿热蒸汽快速热处理能有效促进染病柑橘树的生命力恢复,明显降低病菌浓度;对于柑橘黄龙病田间湿热蒸汽快速热处理,不能只关注树体表面温度的快速提高,而应关注韧皮部温度的有效提高;热处理应考虑直接蒸汽加热和关闭蒸汽后保温的综合影响,为了增加韧皮部传热,应尽量选取较高升温上限和较低输送压力.研究结果为柑橘黄龙病田间热处理防治提供参考.%The citrus Huanglongbing (HLB), caused by the bacterium limited in the phloem, Candidatus Liberibacter spp, is a highly destructive citrus disease for the worldwide citrus industry. Until now, the field thermotherapy has showed effect in HLB control. However, all sorts of thermotherapies only focus on the canopy temperature without considering the inner bark or phloem temperature. In this study, indoor and field steam treatment system consists of enclosure, circumstance temperature monitoring system, outer and inner bark temperature testing system. Temperature distribution of outer and inner bark when heating up with different steam supplying pressure and heat preserving time showed that: 1) For the 1-year-old plants, the 65 was the deadly outer temperature limit. The confirmation of deadly outer bark temperature was the most important in℃field heat treatment. Based on the inner bark temperature increasing effect, the outer temperature of 60 was better than℃lower temperature for inner bark temperature increasing. For achieving the higher outer temperature, more heating time is needed, which allows more heat transfer from the outer to inner bark. For the 9-year-old plants, the 60 ℃ was the better outer temperature without obvious heat damage to the plants. 2) For effective control of HLB, the inner bark temperature was more important than the outer bark temperature. The heat preserving time following steam treatment is beneficial for inner bark temperature increasing. The preserving temperature increase from the treatment with higher transfer pressure was higher than lower pressure. However, based on the total heating effect of inner bark, comprehensively considering the temperature increase from treatment and the following heat preserving, the lower pressure was the better choice. 3) For the 9-year plants, after field heat treatment with the 60 ℃-0.03 MPa-30 s, the results of quantitative polymerase chain reaction (qPCR) after treatment showed significant change in the 'Ca.L.asiaticus' bacterial titer, combined with vigorous growth from all 4 treated infected trees. The qPCR testing also confirmed that 2 previously infected plants with heat treatment showed no detectable levels of'Ca.L.asiaticus', while untreated infected plants remained highly infected. 4) Based on the steam treatment, it was concluded that the procedure should be as follows: Based on the inner bark temperature increase, first of all, confirm the deadly outer temperature of the specific plant; then, compare the heating effect with different combination of the steam supplying pressure and the following heat preserving time. As a conclusion, from the view of heat transfer, the best steam treatment parameters should be determined based on the analysis of inner bark temperature increase.
展开▼
