Fitoplasmas asociados a rnfermedades en cultivos de frutales tropicales y subtropicales/Phytoplasmas associated to diseases in tropical and subtropical fruit crops

The discovery, just fifty year ago, of a new group of plant pathogens related to bacteria led to the finding of polymorphic prokaryotes, located in the phloem of many plant species affected by yellows-type diseases believed to be caused by viruses, considering their infectious nature and transmission by insects. Phytoplasmas lack relevant bacterial features such as cell wall, mobility, key enzymes and pathways nevertheless they have tricky metabolisms allowing them to a trans kingdom life of interaction between plant and insects therefore the tropical and subtropical environments are those providing major survival and evolution possibility for them. In the last years molecular data have provided considerable insights into phytoplasma molecular diversity, and genetic interrelationships; significant taxonomic progress has been achieved by the study of the 16S ribosomal gene and other conserved genes allowing designation of 33 ribosomal groups and 41 ‘Candidatus Phytoplasma’ species. However while a restricted number of such pathogens appears to be associated with phytoplasma diseases in fruit crops in temperate areas, an increasing number of phytoplasma strains are detected and associated, alone or in association with other pathogens in tropical and subtropical fruit crops. Severe phytoplasma-associated epidemic were reported in citrus, coconut, papaya, litchi and longan, and phytoplasma presence was occasionally detected in mango, banana, pineapple, macadamia and passion fruit. In some of these species such as coconut in America and Africa the presence of specific phytoplasmas belonging to groups 16SrIV and 16SrXXII was reported. However other ribosomal groups / ’Candidatus Phytoplasma’ species were detected in this and the other species (16rI, 16SrII, 16SrV, 16SrIX, and 16SrXII). The recent progress made in phytoplasma identification and molecular characterization together with the implementation of their growth in artificial media will help in devising management strategies aimed to reduce environmental impact of phytoplasma disease containment measures also trough international projects targeting tropical and subtropical areas such as the EU financed TROPICSAFE.