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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 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., Competing Interests: The author(s) declare no conflict of interest.

Porocca is a lethal disease of coconut (Cocos nucifera) emerging in Central America. Previously known only from Colombia, it has spread 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. [ABSTRACT FROM AUTHOR]