Phytoplasmal diseases

Abstract

Phytoplasmas are phloem-restricted phytopathogenic mollicutes transmitted by hemipteran insects. Phytoplasmas belonging to different 16S rDNA groups and Candidatus Phytoplasma species have been reported to be associated with coconut. Several economically important phytoplasmal diseases affecting coconut have been reported worldwide, which include the lethal yellowing disease in Caribbean and African regions as well as the non-lethal maladies like root (wilt) disease and Weligama leaf wilt in Asia. Application of molecular technologies has enabled the development of phytoplasmal diagnostic techniques. However, molecular detection of coconut phytoplasmas is many a time intriguing owing to its exclusive phloem confinement, non-uniform distribution and subminimal titres in palms. Palm-phytoplasmal interactions as well as transmission mechanism by insects are poorly understood. Since the phytoplasmal diseases cannot be cured, research on incursion management is currently based on strengthening quarantine and breeding for disease resistance. Management practices are also available to obtain satisfactory yield even from disease-affected palms in the case of non-lethal phytoplasmal diseases. Outbreak of phytoplasmal diseases as a victim of climate change is a reality in view of extensive migration and survival superiority of insect vectors even under climate extremities.