ABSTRACT
Cassava mosaic disease (CMD) is caused by various begomoviruses of the family Geminiviridae leading to considerable crop losses in Africa and Asia. Recombination between their genomic components has generated new pathotypes with enhanced virulence in Africa. Here, we report about a survey on the biodiversity of begomoviruses in cassava from southern India (Tamil Nadu and Kerala states) performed in 2001 and 2002. Viral DNA A components from stem cuttings were analysed using polymerase chain reaction and restriction fragment length polymorphism. Eight representative examples were completely sequenced. The majority of DNA sequences (7 of 8) obtained were more closely related to that of Sri Lankan cassava mosaic virus (SLCMV) than of Indian cassava mosaic virus (ICMV). Only one sequence collected in Kerala was related to ICMV. The diversity of the SLCMV-like sequences was rather low compared to the variability of African viruses associated with cassava mosaic disease. Based on DNA A sequence data, all of these isolates should be classified as variants of SLCMV or ICMV. Phylogenetic analysis revealed mosaic structures within the DNA sequences which may indicate footprints of recombination events between ancestors of SLCMV and ICMV.
Subject(s)
DNA, Viral , Geminiviridae/genetics , Manihot/virology , Plant Diseases/virology , Biodiversity , Disease Progression , India , Phylogeny , Polymorphism, Restriction Fragment Length , Recombination, Genetic , Sequence Homology, Amino AcidABSTRACT
Cassava mosaic disease (CMD) is a major constraint to cassava production in Africa and Asia. Of the two begomoviruses associated with CMD on the Indian subcontinent, Indian cassava mosaic virus (ICMV) and Sri Lankan cassava mosaic virus, only the latter has been successfully reintroduced into cassava to resolve the aetiology of the disease. Here, we report the complete nucleotide sequence of an ICMV isolate from Maharashtra (ICMV-[Mah2]), central India. Biolistic inoculation of the cloned components produced a systemic infection and typical mosaic symptoms in cassava, thereby fulfilling Koch's postulates. The availability of infectious clones will provide a valuable tool to screen new cassava cultivars for disease resistance under defined conditions.
