Differential symptomology, susceptibility, and titer dynamics manifested by phytoplasma-infected periwinkle and tomato plants

Authors: IVANAUSKAS, ALGIRDAS - Nature Research Centre; Inaba, Junichi; Zhao, Yan; Bottner, Kristi; Wei, Wei

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2024
Publication Date: 3/10/2024
Citation: Ivanauskas, A., Inaba, J., Zhao, Y., Bottner-Parker, K.D., Wei, W. 2024. Differential symptomology, susceptibility, and titer dynamics manifested by phytoplasma-infected periwinkle and tomato plants. Plants. 13:787. https://doi.org/10.3390/plants13060787.
DOI: https://doi.org/10.3390/plants13060787

Interpretive Summary: Phytoplasmas are pathogenic bacteria that can infect various plant species, leading to significant global economic losses. Understanding the relationship between symptom severity, disease progression, and phytoplasma concentration is crucial for effective agricultural disease management. By employing a small seedling grafting approach, ARS scientists in Beltsville, Maryland, conducted a study to examine the dynamics of phytoplasma infection in periwinkle and tomato, both infected with the same phytoplasma strain. The study revealed that within both plant hosts, the higher phytoplasma concentration occurred during the early infection stage, characterized by abnormal reproductive growth, rather than in the later stage, marked by excessive vegetative growth. These findings challenge previous assumptions about the timing of peak phytoplasma concentrations during infection. Furthermore, periwinkles exhibited significantly higher phytoplasma levels compared to tomatoes, highlighting the distinct responses of periwinkle and tomato plants to phytoplasma infection. This study has the potential to improve agricultural disease management strategies and contribute to our understanding of plant-pathogen interactions, making it valuable for researchers in plant pathology, plant physiology, and horticulture.

Technical Abstract: Phytoplasmas are intracellular pathogenic bacteria that infect a wide range of plant species, including agriculturally important crops and ornamental trees. However, our understanding of the relationship between symptom severity, disease progression, and phytoplasma concentration remains limited due to the inability to inoculate phytoplasmas mechanically into new plant hosts. The present study investigated phytoplasma titer dynamics and symptom development in periwinkle and tomato, both infected with the same potato purple top (PPT) phytoplasma strain using a small seedling grafting approach. Virescence (VIR), phyllody (PHY), and witches’-broom (WB) symptoms sequentially developed in periwinkle, while in tomato plants, big bud (BB, a form of phyllody), cauliflower-like inflorescence (CLI), and WB appeared in order. Results from quantitative polymerase chain reaction (qPCR) targeting the PPT phytoplasma's 16S rRNA gene revealed that in both host species, phytoplasma titers differed significantly at different infection stages. Notably, the highest phytoplasma concentration in periwinkles was observed in samples displaying phyllody symptoms, whereas in tomatoes, the titer peaked at the BB stage. Western blot analysis, utilizing an antibody specific to PPT phytoplasma, confirmed substantial phytoplasma presence in samples displaying phyllody and BB symptoms, consistent with the qPCR results. These findings challenge the conventional understanding that phytoplasma infection dynamics result in a higher titer at later stages, such as WB (excessive vegetative growth), rather than in the early stage, such as phyllody (abnormal reproductive growth). Furthermore, the PPT phytoplasma titer was markedly higher in periwinkles than in tomato plants, indicating differing susceptibilities between the hosts. This study reveals distinct host responses to PPT phytoplasma infection, providing valuable insights into phytoplasma titer dynamics and symptom development, with implications for the future management of agricultural disease.