First report of bougainvillea floral bract proliferation disease in Cuba and its association with phytoplasmal infection

Authors: Wei, Wei; PEREZ-LOPEZ, EDEL - University Of Saskatchewan; Zhao, Yan

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2019
Publication Date: 3/1/2020
Citation: Wei, W., Perez-Lopez, E., Zhao, Y. 2020. First report of bougainvillea floral bract proliferation disease in Cuba and its association with phytoplasmal infection. Plant Disease. 104/967. https://doi.org/10.1094/PDIS-09-19-2052-PDN.
DOI: https://doi.org/10.1094/PDIS-09-19-2052-PDN

Interpretive Summary: Bougainvillea is a popular ornamental plant widely cultivated in tropical, subtropical, and temperate areas around the world. Many garden varieties produce eye-catching inflorescences with large, sepal-like bracts surrounding tiny flowers. In May of 2016, blooming bougainvillea plants with abnormal floral arrangement were observed in a garden located at Güines, Mayabeque, Cuba. The affected plants produced inflorescences with densely clustered bracts. Since, in botanical term, floral bracts are modified leaves, ARS scientists suspected that the symptom might be caused by excessive branching and foliage proliferation due to a possible infection by a small bacterium termed phytoplasma. Together with collaborators in Canada, ARS scientists conducted DNA fingerprint analysis on floral bract samples from affected plants and found that the diseased plants were indeed infected by a phytoplasma. The team identified the phytoplasma as 'Candidatus Phytoplasma asteris', which has a very broad host range. Phytoplasmal diseases in bougainvillea were previously reported in other countries such as India and Brazil; however, the disease symptoms displayed by the host plants were strikingly different. The work reported in this communication will be of interest to farmers and extension personnel who are concerned with phytoplasmal disease diagnosis and management.

Technical Abstract: Bougainvillea is a genus of evergreen woody climbers or bushes native to South America. The plants in the genus often produce multiple inflorescences consisting of sepal-like bracts and waxy flowers. Being popular ornamental plants, bougainvilleas are widely cultivated in tropical, subtropical, and temperate areas around the world. Bougainvillea x buttiana refers to a variety of garden hybrids of B. glabra and B. peruviana, and are famous for their attractive inflorescences with large colorful bracts encircling tiny white flowers. In May of 2016, B. x buttiana plants with abnormal floral arrangement were observed in a garden located at Güines, Mayabeque, Cuba. The affected plants produced inflorescences with densely clustered bracts. Since, in botanical term, floral bracts are modified leaves, the symptom was considered a result of excessive branching and foliage proliferation. Such symptom resembled the morphotype of free-branching poinsettia, signaling a possible phytoplasma infection. Floral bract samples were collected from five symptomatic plants and total DNA was extracted from the samples. Polymerase chain reaction (PCR) was carried out using phytoplasma-universal primer pair P1A/16S-SR. All PCR assays with DNA templates from symptomatic plants yielded an amplicon of 1.53 kb, corresponding to a near-full-length phytoplasmal 16S rDNA and a partial 16S-23S RNA intergenic region. No amplicon was generated in PCRs containing DNA templates from symptomless control plants. Confirmatory PCRs were then performed on the same set of DNA samples using phytoplasma universal primers that target a ribosomal protein (rp)-encoding locus, rpsM-rplV-rpsC. An amplicon of expected size (1240 bp) was generated from DNA samples of each of the five symptomatic plants, but not from symptomless control plants. Results from subsequent cloning and nucleotide sequencing of the 16S rDNA and rp amplicons revealed that phytoplasma infection had occurred in the symptomatic B. x buttiana plants. An iPhyClassifier analysis indicated that the infecting phytoplasma strains were closely related to the reference strain of 'Candidatus Phytoplasma asteris'. The phytoplasma was designated as bougainvillea proliferation phytoplasma (BPP). To our knowledge, this is the first report of bougainvillea phytoplasmal disease in Cuba. Phytoplasmal infections in bougainvillea were previously reported in Brazil and India, involving three mutually distinct 'Ca. Phytoplasma' species. Remarkably, the disease symptom described in this communication is strikingly different from the ones from previously reported cases. While the Cuban strains triggered floral bract proliferation, the India strain induced little leaf and yellowing symptoms and the Brazilian strains promoted shoot proliferation. It would be interesting to explore whether the bract proliferation symptom can be exploited as a desirable ornamental trait as in the case of free-branching poinsettia.