Evidence of local evolution of tomato-infecting begomovirus species in West Africa: characterization of tomato leaf curl Mali virus and tomato yellow leaf crumple virus from Mali |
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Authors: | Y-C Zhou M Noussourou T Kon M R Rojas H Jiang L-F Chen K Gamby R Foster R L Gilbertson |
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Institution: | (1) Department of Plant Pathology, University of California-Davis, Davis, CA 95616, USA;(2) Institute D’Economie Rurale, C.R.R.A. de Sotuba, BP: 262, Bamako, Mali;(3) Department of Entomology, Purdue University, West Lafayette, IN, USA |
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Abstract: | Tomato yellow leaf curl (TYLC) and tomato leaf curl (ToLC) diseases are serious constraints to tomato production in Mali and
other countries in West Africa. In 2003 and 2004, samples of tomato showing virus-like symptoms were collected during a survey
of tomato virus diseases in Mali. Three predominant symptom phenotypes were observed: (1) TYLC/ToLC (stunted upright growth
and upcurled leaves with interveinal yellowing and vein purpling), (2) yellow leaf crumple and (3) broccoli or bonsai (severe
stunting and distorted growth). Squash blot (SB) hybridization with a general begomovirus probe and/or SB/PCR analyses revealed
begomovirus infection in plants with each of these symptom phenotypes and no evidence of phytoplasma infection. Sequence analysis
of PCR-amplified begomovirus fragments revealed two putative new begomovirus species associated with the TYLC/ToLC and yellow
leaf crumple symptom phenotypes, respectively. Full-length clones of these begomoviruses were obtained using PCR and overlapping
primers. When introduced into N. benthamiana and tomato plants, these clones induced upward leaf curling and crumpling (the TYLC/ToLC-associated begomovirus) or downward
leaf curl/yellow mottle (yellow leaf crumple-associated begomovirus) symptoms. Thus, these begomoviruses were named tomato
leaf curl Mali virus (ToLCMLV) and tomato yellow leaf crumple virus (ToYLCrV). The genome organization of both viruses was
similar to those of other monopartite begomoviruses. ToLCMLV and ToYLCrV were most closely related to each other and to tobacco
leaf curl Zimbabwe virus (TbLCZV-ZW]) and tomato curly stunt virus from South Africa (ToCSV-ZA). Thus, these likely represent
tomato-infecting begomoviruses that evolved from indigenous begomoviruses on the African continent. Mixed infections of ToLCMLV
and ToYLCrV in N. benthamiana and tomato plants resulted in more severe symptoms than in plants infected with either virus alone, suggesting a synergistic
interaction. Agroinoculation experiments indicated that both viruses induced symptomatic infections in tomato and tobacco,
whereas neither virus induced disease symptoms in pepper, common bean, small sugar pumpkin, African eggplant, or Arabidopsis. Virus-specific PCR primers were developed for detection of ToLCMLV and ToYLCrV and will be used to further investigate the
distribution and host range of these viruses. |
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