晚熟柑橘越冬保果新药剂筛选研究

Screening of new reagents for preventing fruit-drop on late-maturing Citrus

【目的】筛选防止晚熟柑橘冬季落果的新药剂。【方法】以‘塔罗科’血橙和‘清见’橘橙为供试品种,以2,4-D为药剂对照(TCK)、以只喷咪鲜胺和乳化剂为空白对照(CK),以前期试验初步筛选出的2甲4氯钠(T1)、2甲4氯二甲铵盐(T2)、2甲4氯苯氧乙酸(T3)为药剂处理,在冬季对试验树果实进行喷布,调查落果率,成熟采收时分析果实药剂残留及品质。【结果】与空白对照落果率(‘塔罗科’血橙为34.65%、‘清见’橘橙为82.52%)相比,4种药剂均能显著降低落果率,虽然T1、T2、T3落果率高于2,4-D,但它们之间无显著差异;无论是‘塔罗科’血橙还是‘清见’橘橙,4种药剂处理后果肉中的药剂残留量均远远低于果皮,T1、T2和T3在果肉中的药剂残留量明显低于2,4-D,且所有处理果皮和果肉的药剂残留量均在国家规定范围之内。各药剂处理间的果实品质多数指标无显著差异。【结论】T1、T2、T3有望作为2,4-D的替补药剂用于防止晚熟柑橘冬季落果,且农药残留更低。

[ Objective ] Fruit drop is severe in late-maturing citrus varieties during winter anti early spring seasons. Therefore, how to address the fruit drop problem is very important for the late-maturing citrus in- dustry. 2,4-dichlorophenoxyacetic acid （2,4-D） is the best effective reagent preventing citrus preharvest drop, but the toxicity of 2,4-D residues has been a concern and also controversial for a long time, and 2,4- D has been limited or forbidden to be used on citrus fruits in many countries or regions. There are no sub- stitutes for controlling citrus preharvest drop. Thus, it is necessary to investigate the efficacy of some new reagents, which have a no or low toxicity to humans and animals, on preventing fruit-drop of the late-ma- turing citrus. [Methods]This experiment was executed at the Citrus Research Institute, Chinese Academy of Agricultural Sciences during the 2014--2015 seasons. Seven year old ＇Tarocco＇ blood orange （Citrus sinensis ＇Tarocco＇） and ＇Kiyomi＇ tangor （Citrus sinensis x Citrus unshiu Marc.） growing under the same conditions were used as experimental materials, and fifty trees were divided into five test groups. Using 2, 4-D as a positive control （TCK）, the resistance of three preliminary screened chemicals [2- methyl- 4- chloro-sodium （T1）, 2-methyl-4-chloro-dimethgl amine salt （T2） and 2-methyl-4-chloro-phenoxy ace-tic acid （T3）] against citrus preharvest drop were investigated. Prochloraz and TritonX- 100 were used as a blank control （CK）. At four different times, sprays of reagents were applied to ＇Tarocco＇ blood orange and ＇Kiyomi＇ tangor every 20-30 days on sunny days from Nov. 2014 to Jan. 2015. The fruit drops of each tree were investigated every two weeks, and the dropped fruit were removed from the orchard. The fruit drops were divided into two types including physiological fruit drop and pathological fruit drop, and only the data of the physiological fruit drops were analyzed in this study. To evaluate mature fruit quality, the soluble solid content （TSS）, titration acid （TA）, vitamin C and fruit chromatic aberration etc were analyzed using a PAL-1 hand-held refractometer, naoh neutral titration, 2,6-dichloroindophenol titration, and chroma meter CR-10, respectively. The reagent residues in the peel and pulp were also determined using QuEChER combined with UPLC-MS/MS. All the treatments were repeated 3 times. [Results ]The results showed that 2,4-D and three tested reagents significantly reduced the fruit-drop. And the percentage fruit drop of both varieties was very low before the low temperatures arrived. In test groups, the fruit drop ratios of ＇Tarocco＇ blood orange and ＇Kiyomi＇ tangor were 15.42%-19.79% and 10.80%-18.89%, respective- ly. The accumulative fruit drop ratio of CK was very high at the end of the experiment and that of 34.65% and 82.52% were observed in ＇Tarocco＇ blood orange and ＇Kiyomi＇ tangor, respectively. The data showed that the fruit-drop rates of all treatments were significantly lower than that of CK, while there were no significant differences between 2,4-D and the three tested reagents. The reagent residues of the fruit pulp were lower in both varieties than that of the fruit peel. In the pulp of the ＇ Tarocco＇ blood orange, the residues of 2,4-D residue were 0.013 0 mg. kg-1 and that of T1 was only 0.002 3 mg＂ kg-~. The residues of T2 and T3 were not detected. But in the peel, the reagent residues of 2,4-D were 2.2-4.7 times as much as that of the other three treatments. Similarly, in the pulp of ＇ Kiyomi＇ tangor, the reagent residues of 2,4- D were the highest among all the treatments, and the reagent residues of TCK were 0.081 0 mg·kg^-1. In the peel, the reagent residues of T2 were the highest （0.082 4 mg. kg-1）, and that of 2,4-D was the lowest （0.060 8 mg. kg-~）. The GB2763--2014 results showed that the largest residues in the citrus of 2,4-D were 1 mg-kg-＇, and that of 2-methyl-4-chloro- sodium were 0.1 rag-kg i. Thus, the presented reagent residues in the pulp and peel after treatment with T1, T2, T3 and 2,4-D were within the standards set by our country. For the fruit chromatic aberration, when compared with 2,4-D, the L value, a value and b val- ue of the two varieties had no significant differences after treatment with T 1, T2 and T3, and there were no significant differences among most indexes for the fruit quality. [ Conclusion ] The results showed that 2,4- D and the three tested reagents significantly reduced the fruit-drop in both of ＇Tarocco＇ blood orange and ＇Kiyomi＇ tangor, compared to the control. Moreover, the reagent residues in the pulp and peel were under the national standards of the PRC, and the qualities of the fruit had no significant differences. Thus, T 1, T2 and T3 reagents should be effective substitutes for 2,4-D in preventing fruit-drop of late-maturing citrus.