NATURAL GENOMIC AND ANTIGENIC VARIATION IN WHITEFLY-TRANSMITTED GEMINIVIRUSES (BEGOMOVIRUSES)

Abstract

Begomoviruses have circular single-stranded DNA genomes, cause many diseases of dicotyledons in areas with warm climates and are transmitted by whiteflies of the Bemisia tabaci complex. Their genomic and antigenic variation represents geography-related lineages that have little relation to host range. Genomic variation resulting from mutation is amplified by acquisition of extra DNA components, pseudo-recombination and recombination, both intraspecific and interspecific. Recombination, especially interspecific recombination, seems the key mechanism for generating novel virus forms, for enhancing biological fitness of pseudo-recombinants derived from closely related species and for maintaining the flow of genetic material among different geminiviruses occurring in the same geographical region. Recent begomovirus epidemics reflect favorable conjunctions of plant, vector, and viral (e.g. emergence of a novel recombinant virus) factors. Such epidemics typically result in co-infection of plants with different begomoviruses, leading to the appearance of further variants, especially recombinants. In their patterns of variation and evolution, begomoviruses differ greatly from plant viruses with RNA genomes.

Emerging threats of begomoviruses to the cultivation of medicinal and aromatic crops and their management strategies

“…[16,77,86,116]. Recombination has played a major role in evolution and emergence of new one among species/strains [58]. Earlier it was believed that DNA viruses are less prone to recombination but certain studies found that begomoviruses are highly prone to recombination [49,82,105,149].…”

“…This recombination leads to the formation of virulent strain than parent virus [149] and RNAi suppression of plant defence by begomoviruses is the key factor responsible for the disease development and transmission of virus [155]. In the early 1990s, geminiviruses caused up to 95% yield losses of tomatoes in the Dominican Republic, and inflicted over US$2 billion/year yield losses in cassava in Africa [58]. In Brazil, during the last four years, more than 11,000 jobs have been lost in the tomato industry because of whitefly-transmitted geminiviruses and other factors.…”

“…In recent years begomoviruses have been more interestingly researched as the diseases caused have reached epidemic status and poses a severe threat to global food security. Geminiviruses have been so long significant plant pathogens in Africa, Australia, Southeast Asia, Latin America and the Caribbean, Southern Europe and southwest United States with heavy loss in world economy and food security enormously [25,26,36,43,58,89,110,111,126,148,152,153]. Latin America has been reported most affected region by begomovirus, with 5 million hectares of agricultural land in more than 20 countries being affected by more than 30 distinct begomoviruses [24,25,61,89,110,148].…”

Fusion coat protein of pumpkin yellow vein mosaic virus with maltose binding protein: Applications in immunodiagnosis of begomoviruses

“…Both, immune-and nucleo-based techniques have been employed for the detection of begomoviruses [5]. Begomoviruses are phloem limiting, generally not sap transmissible and many of them do not have suitable propagative hosts.…”

“…To identify the optimum dilution of infected leaf sap, two fold dilutions of the infected leaf extracts [1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:128 and 1:256] were evaluated by ELISA. In order to determine the minimum quantity of viral antigen required for ELISA detection, purified recombinant CP at different concentrations [5,10,25, 50, 100, 500 and 1,000 ng] were tested. The antiserum showed titer of 1:250, when tested repeatedly with infected crude extract as antigen.…”