Two bipartite begomoviruses, Indian cassava mosaic virus (ICMV) and Sri Lankan cassava mosaic virus (SLCMV), have been isolated from mosaic-diseased cassava originating from central India and Sri Lanka, respectively. ICMV was transmitted with low efficiency from cassava to Nicotiana benthamiana by sap inoculation to give leaf curl symptoms. SLCMV was much more virulent in this host, producing severe stunting, leaf curl, and chlorosis. These symptoms were reproduced when their cloned genomic components (DNAs A and B) were introduced into N. benthamiana by either mechanical or Agrobacterium-mediated inoculation (agroinoculation). SLCMV is more closely related to ICMV (DNA A, 84%; DNA B, 94% nucleotide identity) than African cassava mosaic virus (ACMV) (DNA A, 74%; DNA B, 47% nucleotide identity). Sequence comparisons suggest that SLCMV DNA B originated from ICMV DNA B by a recombination event involving the SLCMV DNA A intergenic region. Pseudorecombinants produced by reassortment of the cloned components of ICMV and ACMV were not infectious in N. benthamiana, emphasising their status as distinct virus species. In contrast, a pseudorecombinant between ACMV DNA A and SLCMV DNA B was infectious. Consistent with these observations, iteron motifs located within the intergenic region that may be involved in the initiation of viral DNA replication are conserved between SLCMV and ACMV but not ICMV. When introduced into N. benthamiana by agroinoculation, SLCMV DNA A alone produced a severe upward leaf roll symptom, reminiscent of the phenotype associated with some monopartite begomoviruses. Furthermore, coinoculation of SLCMV DNA A and the satellite DNA beta associated with ageratum yellow vein virus (AYVV) produced severe downward leaf curl in N. glutinosa and yellow vein symptoms in Ageratum conyzoides, resembling the phenotypes associated with AYVV DNA A and DNA beta infection in these hosts. Thus, SLCMV DNA A has biological characteristics of a monopartite begomovirus, and the virus probably evolved by acquisition of a DNA B component from ICMV.

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Serodiagnosis of symptomatic samples of sugarcane collected from number of sugarcane growing localities in Marathwada (Maharashtra), Andhra Pradesh (AP) and Tamil Nadu (TN) indicated that the sugarcane was predominantly infected by sorghum mosaic potyvirus-an immunity breaking strain (SrMV-IBS) in 39 localities out of 41 (95%) whereas mixed infections of sugarcane with SrMV-H was evident only in 5 localities (12%). Moreover, mixed infections of sugarcane with sugarcane mosaic potyvirus strains including SCMV-A (7%), SCMV-B (22%), SCMV-SC (7%) and with maize dwarf mosaic potyvirus-strain A (MDMV-A: 17%) were also evident in some localities. Infections of sugarcane by MDMV-A was detected only in Marathwada but not in AP and TN whereas infections of sugarcane by SrMV-H, S CMV-A, SCMV-B and SCMV-SC besides SrMV-IBS were found in Marathwada, AP and TN by SCMV-D, SCMV-E, infections of sugarcane varieties grown in Marathwada, AP and TN by SCMV-D, SCMV-E, SCMV-MDB and johnsongrass mosaic potyvirus (JGMV) were found to be totally absent in all the surveyed localities. Of these potyviruses detected in sugarcane, only three, SrMV-IBS (100%), SrMV-H (71%) and SCMV-B (14%) were mechanically transmitted from field infected sugarcane to glasshouse grown CK-6OAt CS-3541 and Maldandi (M-35-1) sorghum genotypes.