GEMINIVIRIDAE

INTRODUCTION

Geminiviridae is a family of plant viruses. There are currently 485 species in this family, divided among 9 genera. Diseases associated with this family include: bright yellow mosaic, yellow mosaic, yellow mottle, leaf curling, stunting, streaks, and reduced yields. They have single-stranded circular DNA genomes encoding genes that diverge in both directions from a virion strand origin of replication (i.e. geminivirus genomes are ambisense). According to the Baltimore classification they are considered class II viruses. It is the largest known family of single stranded DNA viruses.

Higher classification: Virus Group II Rank: Family Order: Geplafuvirales Phylum: Cressdnaviricota Class: Repensiviricetes

GENERAL CHARACTERISTICS

 The worldwide expansion of agriculture has also resulted in the emergence and spread of numerous diseases and insect pests. Of particular importance are insect- transmitted viruses, especially in tropical and subtropical regions.  Geminiviruses are insect-transmitted viruses that have emerged, over the past 20 years, as the largest group of plant viruses (in terms of number of species) and one of the most economically important.  These viruses cause extremely damaging diseases in a wide range of crops throughout the world, including African cassava mosaic in Africa; bean golden mosaic (BGM) in the Americas; beet curly top in North America and the Middle East; cotton leaf curl in Asia; maize streak in Africa; and tomato yellow leaf curl in Africa, the Americas, Asia and Europe.  In Brazil, BGM and tomato diseases caused by a complex of geminiviruses are important diseases that lead to substantial yield losses in common beans and fresh market and processing tomato production.

STRUCTURE

Geminiviruses comprise a biologically and genetically diverse family (Geminiviridae) of viruses that share the following characteristics: a twinned quasi-icosahedral virus particle (virion) that measures ~18 X 30 nanometers and a small circular single-stranded DNA genome of ~2.9-5.2 kilobases (kb). The family name is derived from the distinctive twinned virions (the Latin word gemini means twin).

TRANMISSION

 Based upon genome structure, phylogenetic relationships, insect vector and host range, seven genera have been recognized: Begomovirus, Mastrevirus, Curtovirus, Topocuvirus,Becurtovirus, Turncurtovirus and Eragrovirus .  In nature, geminiviruses are transmitted by phloem-feeding insects, including various species of leafhoppers, a treehopper and whiteflies of the species Bemisia tabaci.  Gemini viruses are not transmitted through seeds, whereas many are graft- transmissible and some are mechanically (sap) transmissible.  Plants infected with geminiviruses show a wide range of symptoms including stunting; distorted growth; and leaf streaking and striations in monocotyledoenous plants and leaf crumpling, curling, distortion, golden-light green-yellow mosaic/mottle, interveinal yellowing, yellow spots, and vein swelling, purpling, and yellowing in dicotyledonous plants.