Morphological and Biochemical Stresses Induced in Plants Due to Phytoplasma Association

To date, very limited attempts have been made to understand the morphological and biochemical stresses induced due to phytoplasma infection in various plant species worldwide. As we know, phytoplasmas are wall-less prokaryotes that have profound effects, and infected plants exhibit distinct symptoms, including witches’ broom, phyllody, stunting, yellowing of leaves, and abnormal floral structures. The infections also cause anatomical changes in the affected plants, affecting chloroplasts, vascular bundles, and sieve elements. Biochemically, phytoplasma infections disrupt photosynthesis, leading to decreased photosynthetic efficiency. The infections also disrupt nutrient transport through the phloem, resulting in carbohydrate accumulation in leaves. Reactive oxygen species (ROS) production increases in infected plants, leading to oxidative stress, which triggers the activation of ROS scavenging systems. Furthermore, phytoplasma infections alter overall primary and secondary metabolites and protein levels, reflecting the plants’ defence responses and affecting nutrient metabolism. This chapter provides an overview of several plant species that have been studied in relation to phytoplasma association, highlighting the diverse morphological and biochemical changes induced by these infections. The impacts of phytoplasma infections vary across plant species. While some plants suffer severe yield losses and growth abnormalities, others exhibit desired symptom expression, such as ornamental cacti and succulents.