Emerging geminivirus problems: A serious threat to crop production

Abstract

Geminiviruses form the second largest family of plant viruses, the Geminiviridae, represented by four genera: Mastrevirus, Curtovirus, Topocuvirus and Begomovirus. During the last two decades these viruses have emerged as devastating pathogens, particularly in the tropics and subtropics, causing huge economic losses and threatening crop production. Epidemics caused by re-emerging and newly emerging geminiviruses are becoming frequent even in regions that were earlier free from these viruses. Compared to mastreviruses and curtoviruses, begomoviruses have emerged as more serious problems in a variety of crops, for example, cassava, cotton, grain legumes and vegetables. Major contributory factors for the emergence and spread of new geminivirus diseases are the evolution of variants of the viruses, the appearance of the whitefly 'B' biotype and the increase in the vector population. Variability in geminiviruses has arisen through mutations, recombination and pseudorecombination. Genomic recombination in geminiviruses, not only between the variants of the same virus but also between species and even between genera, has resulted in rapid diversification. From the disease point of view, most virulent variants have developed through recombination of viral genomes such as those associated with cassava mosaic, cotton leaf curl, and tomato leaf curl diseases. Heterologous recombinants containing parts of the host genome and/or sequences from satellite-like molecules associated with monopartite begomoviruses provide unlimited evolutionary opportunities. Human activity has also played an important role in the emergence of serious geminivirus diseases across the globe, like the changes in cropping systems, the introduction of new crops, the movement of infected planting materials and the introduction of host susceptibility genes through the exchange of germplasm.

Chlorotic Curly Stunt: A Severe Begomovirus Disease of Bottle Gourd in Northern India

“…Begomoviruses are major threat in numerous crops in India due to favorable environmental conditions and abundance of vector, B. tabaci [35]. Leaf curl of tomato was known to occur in India for nearly 60 years [37], but whitefly transmitted diseases of cucurbits were not serious concern until 1980s [34].…”

“…Several viruses, like Cucumber mosaic virus [36] Cucumber green mottle mosaic virus [23] Papaya ring spot virus-W [19], Watermelon mosaic virus [1] and Zucchini yellow mosaic virus [38] are known to affect bottle gourd cultivation in India. During the last two decades, begomoviruses have emerged as a severe constraint in cultivation of cucurbits in India [35]. In the early sixties, yellow vein mosaic (YVM) disease of pumpkin (Cucurbita moschata) caused by a whitefly transmitted virus (apparently a begomovirus) was reported from central-western India.…”

Microsatellites reveal extensive geographical, ecological and genetic contacts between invasive and indigenous whitefly biotypes in an insular environment

“…In the past two decades, B. tabaci has become a major problem both as a pest and as vector of plant viruses, especially begomoviruses Jones, 2003;Varma & Malathi, 2003). However, it has been well known since the 1950s that this species covers several distinct entities named ' biotypes' (Bird & Maramorosch, 1978).…”

gb4gv: A genome browser for geminivirus

“…India lost an estimated $300 million for infection in grain legumes in 1992, and Florida lost 48 approximately $140 million for infection in tomato in 1999 (Varma & Malathi 2003). 49 The spread of Geminiviruses and the severity of their infections have been 50 increasingly climbing due to their virulence to infect multiple hosts through their insect 51…”