Department of Plant Pathology, National Chung Hsing University, Taichung 402, Taiwan.
Department of Horticulture, National Chung Hsing University, Taichung 402, Taiwan.
Plant Dis. 2021 May;105(5):1539-1545. doi: 10.1094/PDIS-10-20-2304-RE. Epub 2021 Apr 7.
It has long been established that phytoplasma infection is the cause of the free-branching phenotype in poinsettia. However, relatively little is known about the ecology of the pathogen in planta. The present study evaluated the infection pattern of poinsettia branch-inducing phytoplasma (PoiBI) and its association with the poinsettia phenotype during cutting propagation. The presence of this pathogen in the poinsettia variety Luv U Pink was determined using PCR and sequence analysis. The infection density of PoiBI in distinct tissue types of different plant segments were then determined using quantitative PCR coupled with plasmid-based standard curves. Both vegetative-stage and flowering-stage plants were tested. The results showed that, despite being considerably variable among plants, the infection densities of PoiBI tend to be higher in source leaves located in the lower parts of the plant. The densities were consistently lower in tissues located at the top of the plants, regardless of the tissue type. Analysis of the infection densities among samples collected from six stock plants used in commercial production also revealed significantly different levels of PoiBI load. An association between PoiBI infection density in the stock plants and the level of branching in cutting-propagated plants (derived from the stock plants) was also observed; stock plants with low infection densities tended to produce smaller proportions of plants exhibiting higher degrees of branching both before and after pinching. These data suggest that uneven distribution of PoiBI within and among stock plants may lead to the production of cuttings with variable phytoplasma densities which may, in turn, affect the phenotypic uniformity of the plants produced. Overall, findings from the present work add to the understanding of PoiBI's ecology and could provide implications to commercial poinsettia production.
已证实，植原体感染是一品红自由分枝表型的原因。然而，对于病原体在植物体内的生态学相对知之甚少。本研究评估了一品红诱导分枝植原体（PoiBI）在扦插繁殖过程中的感染模式及其与一品红表型的关系。使用 PCR 和序列分析确定一品红品种 Luv U Pink 中是否存在这种病原体。然后使用定量 PCR 结合基于质粒的标准曲线确定不同植物段不同组织类型中 PoiBI 的感染密度。对营养阶段和开花阶段的植物进行了测试。结果表明，尽管在植物之间存在很大差异，但位于植物下部的源叶中 PoiBI 的感染密度往往较高。无论组织类型如何，位于植物顶部的组织中的密度始终较低。对商业生产中使用的六个母株采集的样本的感染密度进行分析，也揭示了 PoiBI 载量存在明显差异。还观察到母株中 PoiBI 感染密度与扦插繁殖植物（源自母株）分枝程度之间存在关联；感染密度较低的母株在掐尖前后产生的表现出较高分枝程度的植物比例较小。这些数据表明，PoiBI 在母株内和之间的分布不均可能导致扦插具有不同的植原体密度，这反过来可能影响所生产植物的表型均匀性。总体而言，本研究的结果增加了对 PoiBI 生态学的理解，并可能对商业一品红生产产生影响。
