Molecular Characterization of Bean – Infecting Geminiviruses and Antiviral Strategies:

INTRODUCTION

            Bean golden mosaic of common bean (Phaseolus vulgaris) was first documented in 1961 as a minor disease in Brazil by A. Costa (Costa, 1965), who found that the causal agent was transmitted by the whitefly (Bemisia tabaci).  This disease was then reported in other bean production areas of Latin America (see Gálvez and Morales, 1989).  By the late 1970's and the early 1980's, this disease had caused major losses, and bean fields with 100% incidence were common (Goodman et al., 1977).  At an international workshop in Guatemala in 1992 (Morales, 1994), bean golden mosaic virus was listed as the major factor limiting bean production in many Latin American countries.  The most recent epidemic was in pole beans in Florida in 1993 (Blair et al., 1995).

            Characterization of the causal agent by Gálvez and Castaño (1976) and by Goodman et al. (1977) showed that a unique virus particle, the geminate virion, was associated with diseased beans.  Subsequently, using particles from bean golden mosaic-infected beans collected in Puerto Rico, Goodman (1977) was first to show that these geminate virions contained ssDNA.  Haber et al. (1981) then established that this virus had a genome divided between two ssDNA molecules, each about 2.6 kb, now designated DNA-A and DNA-B.  The first sequence for a whitefly-transmitted geminivirus, African cassava mosaic virus, was published in 1983 (Stanley and Gay, 1983), and then in 1985, Dr. Goodman's research group reported the sequence for the geminivirus causing golden mosaic symptoms on bean from Puerto Rico (Howarth et al., 1985).  In the mid-1980's all whitefly-transmitted geminiviruses causing golden mosaic symptoms were designated as bean golden mosaic virus.  Non-mosaic-causing whitefly-transmitted geminivirus (es) was (were) also present in Latin America but of minor importance except for Argentina (Gálvez and Morales, 1989).  A comprehensive review of the literature on bean-infecting geminiviruses is provided by Gálvez and Morales (1989).

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