Phytoplasmas are dangerous bacteria severely infecting agricultural production worldwide. In the present study, the identification of phytoplasmas infecting tomato plants showing symptoms such as small leaves, flower abnormalities, stunting, witches' broom, and reddening was performed. Five plants, two symptomatic and three asymptomatic, were tested to verify phytoplasma infection. Total DNA isolated from 5 leaf samples was used as a template for PCR reactions. The phytoplasma agents were confirmed in the two symptomatic samples. BLASTn search of 16S rRNA of two sequences shared identity similarity of 99.84% with ‘Candidatus Phytoplasma australasia’. Computer-simulated virtual RFLP profiles show that the 16S rRNA sequences is identical to the reference pattern of the 16SrII-D subgroup, with a similarity coefficient of 1.00. Based on BLAST, virtual RFLP, and phylogenetic dendrogram, the identified phytoplasma strains are enclosed in the 16SrII-D subgroup. This is the first report of tomato witches' broom disease related to 16SrII-D subgroup phytoplasma strains in the Antalya province of Türkiye.
Tobacco (Nicotiana tabacum) is among the agricultural products with the highest added value in Turkey. Although frequently associated with its negative effects on human health, it also provides important contributions to the Turkish economy with the employment it creates in rural areas and continues to be a strategic product. Many postgraduate theses and studies related to the sociological and economic importance of the production of this plant, which is of great importance for our country, have been carried out. However, there are very limited studies on plant diseases in tobacco production areas in Turkey. Phytoplasma is one of the important plant pathogens that cause yield loss in tobacco. Since available data on phytoplasma diseases on tobacco was very scarce worldwide, field surveys to collect samples showing phytoplasma infection-like symptoms such as yellowish color changes, leaf blisters, proliferation, dwarfism, and other physical abnormalities were carried out in Çanakkale and Balıkesir provinces of Turkey from June to August 2021. The presence of phytoplasmas in six samples was confirmed by 16S ribosomal DNA amplification by nested-PCR using universal phytoplasma primer sets, which also suggested the pathogen associated with the symptoms on tobacco. According to phylogenetic study and virtual-RFLP analysis using AluI and MseI endonuclease enzymes, the six Turkish tobacco phytoplasma strains all belong to group 16SrXII and have more than 99% nucleotide sequence identity with some members of ‘Candidatus Phytoplasma solani’ of the taxonomic subgroup ‘stolbur’ (16SrXII-A). Genetic distances analysis indicated that group 16SrI was more closely related to 16SrXII than 16SrVI, in agreement with the groups clustering in the phylogenetic tree. Neutrality tests found that 16SrI and 16SrXII groups are experiencing expanding or bottleneck selections, probably due to new mutations in the 16S rRNA gene fragment. Meanwhile, 16SrVI populations are shown to be undergoing balancing selections, indicating that its isolates have evolved for a long time.
The pathogens associated with citrus Huanglongbing symptoms, including yellowing and mottled leaves in Citrus maxima, an important economic crop on Hainan Island of China, were identified and characterized. In the study, detection, genetic variation and phylogenetic relationship analysis of the pathogens were performed based on 16S rRNA and β-operon gene fragments specific to phytoplasma and Candidatus Liberibacter asiaticus. The results indicated that the pathogens—such as phytoplasma strains of CmPII-hn belonging to the 16SrII-V subgroup and CmPXXXII-hn belonging to the 16SrXXXII-D subgroup, as well as Candidatus Liberibacter asiaticus strains CmLas-hn—were identified in the diseased plant samples, with numbers of 12, 2 and 6 out of 54, respectively. Among them, mixed infection with the 16SrII-V subgroup phytoplasma and Candidatus Liberibacter asiaticus was found in the study, accounting for 7.4% (four samples). The phytoplasma strains of CmPII-hn—Tephrosia purpurea witches’ broom, Melochia corchorifolia witches’ broom and Emilia sonchifolia witches’ broom—were clustered into one clade belonging to the 16SrII-V subgroup, with a 99% bootstrap value. The phytoplasma strains of CmPXXXII-hn and Trema tomentosa witches’ broom belonging to 16SrXXXII-D, and the other 16SrXXXII subgroup strains were clustered into one clade belonging to the 16SrXXXII group with a 99% bootstrap value. There were 16 variable loci in the 16S rRNA gene sequences of the tested 16SrXXXII group phytoplasma strains, of which two bases had an insertion/deletion. The strains of Candidatus Liberibacter asiaticus, identified in the study and the strains that had been deposited in GenBank, were in one independent cluster with a 99% bootstrap value. To our knowledge, this is the first report showing that Citrus maxima can be infected by 16SrII-V and16SrXXXII-D subgroup phytoplasmas in China. Moreover, this is also the first report in which the plants are co-infected by 16SrII-V subgroup phytoplasmas and Candidatus Liberibacter asiaticus. More comprehensive and detailed identification and characterization of the pathogens associated with the diseased symptoms in Citrus maxima on the island in China would be beneficial for epidemic monitoring and for the effective prevention and control of related plant diseases.
Grapevine Bois noir (BN) is associated with ‘Candidatus Phytoplasma solani’. It has been recorded in vineyards throughout Europe as well as in different countries in Asia, where it now constitutes a threat to Iranian viticulture. BN is strictly dependent on ‘Ca. P. solani’ strains, wild host plants, and insect vectors. The molecular typing of ‘Ca. P. solani’, based on the nonribosomal gene tuf and the two hypervariable markers vmp1 and stamp, is valuable for the reconstruction and clarification of the pathways of BN spread. In this study, an RFLP analysis was performed on the vmp1 gene, and a single-nucleotide polymorphism analysis confirmed new vmp types in ‘Ca. P. solani’. A stamp gene phylogenetic analysis allowed us to distinguish between the new genotype infections in the grapevines and the ‘weeds’ Convolvulus arvensis and Erigeron bonariensis in Iranian vineyards, highlighting the close genetic relatedness of the strains of ‘Ca. P. solani’ found in Iran and Azerbaijan. The most common genotype in the grapevines was tuf b/V24/stamp III, which was associated with C. arvensis. This information contributes toward the identification of further routes of introduction of ‘Ca. P. solani’ in Iran to sustain the control measures for the management of BN.
Florida citrus production has declined 75% due to Huanglongbing (HLB), a disease caused by the pathogenic bacterium Candidatus Liberibacter asiaticus (CLas). Methods to combat CLas are costly and only partially effective. The cross-compatible species Poncirus trifoliata and some of its hybrids are known to be highly tolerant to CLas, and thus can potentially serve as an alternative feedstock for many citrus products. To further investigate the commercial potential of citrus hybrids, three citrus hybrids, US-802, US-897, and US-942, were studied for their potential as feedstocks for citrus co-products using steam explosion (STEX) followed by water extraction. Up to 93% of sugars were recovered. US-897 and US-942 have similar volatile profiles to that of the commercial citrus fruit types and as much as 85% of these volatiles could be recovered. Approximately 80% of the pectic hydrocolloids present in all three hybrids could be obtained in water washes of STEX material. Of the phenolics identified, the flavanone glycosides, i.e., naringin, neohesperidin, and poncirin were the most abundant quantitatively in these hybrids. The ability to extract a large percentage of these compounds, along with their inherent values, make US-802, US-897, and US-942 potentially viable feedstock sources for citrus co-products in the current HLB-blighted environment.