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Phytoplasmas are minute phytopathogenic bacteria that induce excessive vegetative growth, known as witches'-broom (WB), in many infected plant species during the later stages of infection. The WB structure is characterized by densely clustered little (small) leaves, which are frequently accompanied by chlorosis (yellowing). The mechanisms behind the formation of little leaves within WB structures (LL-WB) are poorly understood. To address this gap, the LL-WB formation was extensively studied using sweet cherry virescence (SCV) phytoplasma-infected sweet cherry plants. Based on morphological examinations, signs of premature leaf senescence were observed in LL-WB samples, including reduced leaf size, chlorosis, and alterations in shape. Subsequent physiological analyses indicated decreased sucrose and glucose levels and changes in hormone concentrations in LL-WB samples. Additionally, the transcriptomic analysis revealed impaired ribosome biogenesis and DNA replication. As an essential process in protein production, the compromised ribosome biogenesis and the inhibited DNA replication led to cell cycle arrest, thus affecting leaf morphogenesis and further plant development. Moreover, the expression of marker genes involved in premature leaf senescence was significantly altered. These results indicate a complicated interplay between the development of leaves, premature leaf senescence, and the pathogen-induced stress responses in SCV phytoplasma-infected sweet cherry trees. The results of this study provide insight into understanding the underlying molecular mechanisms driving the formation of little leaves and interactions between plants and pathogens. The findings might help control phytoplasma diseases in sweet cherry cultivation.

Background: Little leaf disease caused by phytoplasma infection is a significant threat to eggplant (also known as brinjal) cultivation in India. This study focused on the molecular characterisation of the phytoplasma strains and insect vectors responsible for its transmission and screening of brinjal germplasm for resistance to little leaf disease., Results: Surveys conducted across districts in the Tamil Nadu state of India during 2021-2022 showed a higher incidence of phytoplasma during the Zaid (March to June), followed by Kharif (June to November) and Rabi (November to March) seasons with mean incidence ranging from 22 to 27%. As the name indicates, phytoplasma infection results in little leaf (reduction in leaf size), excessive growth of axillary shoots, virescence, phyllody, stunted growth, leaf chlorosis and witches' broom symptoms. PCR amplification with phytoplasma-specific primers confirmed the presence of this pathogen in all symptomatic brinjal plants and in Hishimonus phycitis (leafhopper), providing valuable insights into the role of leafhoppers in disease transmission. BLAST search and phylogenetic analysis revealed the phytoplasma strain as "Candidatus Phytoplasma trifolii". Insect population and disease dynamics are highly influenced by environmental factors such as temperature, relative humidity and rainfall. Further, the evaluation of 22 eggplant accessions revealed immune to highly susceptible responses where over 50% of the entries were highly susceptible. Finally, additive main effect and multiplicative interaction (AMMI) and won-where biplot analyses identified G18 as a best-performing accession for little leaf resistance due to its consistent responses across multiple environments., Conclusions: This research contributes essential information on little leaf incidence, symptoms, transmission and resistance profiles of different brinjal genotypes, which together ensure effective and sustainable management of this important disease of eggplants., (© 2024. Crown.)

The typical phytoplasma symptoms of little leaf, yellowing, chlorosis, witches' broom, and stunting growth were observed on Acalypha indica plants during the field survey conducted at Lucknow and surrounding districts in year 2015-2016. To confirm the association and possibility of phytoplasma etiology, PCR assays were performed using universal primer pairs (P1/P6) and nested primer pairs (R16F2n/R2) in a total of five diseased samples along with control. A ~1.2 Kb amplicon was observed in nested PCR assay in diseased sample; however, no band was observed in control sample. The positive amplicons were sequenced for 16S rDNA and used for the virtual RFLP analysis and phylogenetic studies. BLASTn search showed 99-100% sequence identities with the 'Candidatus phytoplasma asteris' members (16SrI group) and phylogenetic analysis showed closest relationship with member of 16SrI group. The virtual RFLP assigned it as a member of 16SrI-B subgroup. This is the first record of phytoplasma association of 'Ca. P. asteris' subgroup B with A. indica in the world.

Porroca is a lethal disease of coconut (Cocos nucifera) emerging in Central America. Previously known only from Colombia, it has spread rapidly across the Isthmus of Panama in the last decade. Porroca is characterized by the production of stiff, dwarfed leaves, usually followed by the death of the palms within 2 years. We describe the long-distance spread of the disease as determined from regular censuses of more than 200,000 coconut palms in the indigenous Comarca of Kuna Yala and the Republic of Panama. Spread is temporally and spatially variable, with the disease moving across the landscape as much as 40 km per year. Porroca may represent a significant new threat to coconut production in the Caribbean Region.