Molecular Characterization of Bean – Infecting Geminiviruses and Antiviral Strategies:

MOLECULAR DETECTION METHODS

            Three molecular methods for the detection of bean-infecting geminiviruses have been evaluated: serology (Cancino et al., 1995), polymerase chain reaction (PCR, Rojas et al., 1993; Wyatt and Brown, 1996) and DNA:DNA hybridization (Gilbertson et al., 1991b).  Monoclonal antibodies prepared against BGMV isolate Brazil and BGYMV isolate Guatemala were evaluated by Cancino et al. (1995).  General PCR primer pairs are available for detection of DNA-A (Rojas et al., 1993, Wyatt and Brown, 1996) and DNA-B (Rojas et al., 1993).  These primers for DNA-A have been used effectively in many different laboratories throughout the world.  The rep/cp gene primer pair (PAL1v1978/PAR1c715, Rojas et al., 1993) offers the advantage over the cp gene primer pair (Wyatt and Brown, 1996) in that the rep/cp gene primer pair amplifies a fragment, which has more useful sequence information for determining the taxonomic relationships among geminiviruses.  This is because the cp primers amplify the most conserved part of the cp gene, and there is no relationship between this cp gene region and the replication of the virus.  DNA:DNA hybridization methods with specific and general probes have been reported for bean-infecting geminiviruses (Gilbertson et al., 1991b).  These hybridization methods have worked most effectively with radioisotopes, which is a limitation for their use in many countries.  More recently, a general probe of the most conserved 500-bp region in the cp gene of the Western Hemisphere geminiviruses was developed (Nakhla and Maxwell, unpublished data). 

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