Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850.
Phytopathology. 2021 Jul;111(7):1095-1103. doi: 10.1094/PHYTO-09-20-0427-R. Epub 2021 Sep 7.
Streptomycin (STR) has been used to control citrus huanglongbing (HLB) caused by ' Liberibacter asiaticus' (CLas) via foliar spray. Here, we studied the residue dynamics of STR and its effect on CLas titers in planta applied by foliar spray and trunk injection of 3-year-old citrus trees that were naturally infected by CLas in the field. After foliar spray, STR levels in leaves peaked at 2 to 7 days postapplication (dpa) and gradually declined thereafter. The STR spray did not significantly affect CLas titers in leaves of treated plants as determined by quantitative PCR. After trunk injection, peak levels of STR were observed 7 to 14 dpa in the leaf and root tissues, and near-peak levels were sustained for another 14 days before significantly declining. At 12 months after injection, moderate to low or undetectable levels of STR were observed in the leaf, root, and fruit, depending on the doses of STR injected, with a residue level of 0.28 µg/g in harvested fruit at the highest injection concentration of 2.0 µg/tree. CLas titers in leaves were significantly reduced by trunk injection of STR at 1.0 or 2.0 g/tree, starting from 7 dpa and throughout the experimental period. The reduction of CLas titers was positively correlated with STR residue levels in leaves. The in planta minimum effective concentration of STR needed to suppress the CLas titer to an undetectable level (cycle threshold ≥36.0) was 1.92 µg/g fresh weight. Determination of the in planta minimum effective concentration of STR against CLas and its spatiotemporal residue levels in planta provides the guidance to use STR for HLB management.
链霉素（STR）已被用于通过叶面喷施来控制由‘亚洲韧皮杆菌’（CLas）引起的柑橘黄龙病（HLB）。在这里，我们研究了 STR 在田间自然感染 CLas 的 3 年生柑橘树上通过叶面喷施和树干注射的残留动态及其对植株中 CLas 滴度的影响。叶面喷施后，STR 在叶片中的浓度在施药后 2 至 7 天（dpa）达到峰值，此后逐渐下降。定量 PCR 测定结果表明，STR 喷雾处理并未显著影响处理植株叶片中的 CLas 滴度。树干注射后，STR 水平在叶片和根组织中于 7 至 14 dpa 达到峰值，在接近峰值水平持续 14 天，然后显著下降。注射后 12 个月，根据 STR 注射剂量的不同，STR 可在叶片、根和果实中观察到中等至低水平或无法检测到的残留，在最高注射浓度 2.0 µg/株时，收获果实中的残留水平为 0.28 µg/g。从 7 dpa 开始，STR 树干注射可显著降低叶片中的 CLas 滴度，剂量为 1.0 或 2.0 g/株，整个实验期间均如此。CLas 滴度的降低与叶片中 STR 残留水平呈正相关。抑制 CLas 滴度至无法检测水平（循环阈值≥36.0）所需的 STR 体内最小有效浓度为 1.92 µg/g 鲜重。测定 STR 对 CLas 的体内最小有效浓度及其在植株中的时空残留水平为 STR 用于 HLB 管理提供了指导。
