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The role and interactions of begomoviruses and satellite DNAs associated with okra leaf curl disease in Mali, West Africa

¹ University of California-Davis;
² AVRDC West Africa Office

³ E-mail: rlgilbertson{at}ucdavis.edu

Okra leaf curl disease (OLCD) is a major constraint on okra (Abelmoschus esculentus) production in West Africa. Two monopartite begomoviruses (okra virus-1 and okra virus-2), a betasatellite and a DNA1 satellite were associated with OLCD in Mali. Okra virus-1 was an isolate of Okra yellow crinkle virus (OYCrV), okra virus-2 was a recombinant isolate of Cotton leaf curl Gezira virus (CLCuGV), and the betasatellite was a variant of Cotton leaf curl Gezira betasatellite (CLCuGB). Cloned DNAs of OYCrV and CLCuGV were infectious and induced leaf curl symptoms in Nicotiana benthamiana plants, but did not induce OLCD in okra. However, when these clones were individually co-inoculated with the cloned CLCuGB DNA, symptom severity and viral DNA levels were increased in N. benthamiana plants, andtypical OLCD symptoms were induced okra. The CLCuGB also was replicated by, and increased symptom severity of, three monopartite tomato-infecting begomoviruses, including two from West Africa. The sequence of the DNA1 satellite was highly divergent, indicating it represents a distinct West African lineage. The DNA1 replicated autonomously, and replication required the DNA1-encoded Rep protein. Although DNA1 reduced helper begomovirus DNA levels, symptoms were not attenuated. In the presence of the CLCuGB, DNA levels of the helper begomoviruses and DNA1 were substantially increased. Together, these findings establish that OLCD in Mali is caused by a complex of monopartite begomoviruses and a promiscuous betasatellite, with an associated parasitic DNA1 satellite. These findings are discussed in terms of the etiology of OLCD and the evolution of new begomovirus/satellite DNA complexes.

Received 20 October 2008; accepted 15 December 2008.