Cotton crop has been severely affected by multiple begomoviruses in Pakistan and India. In our previous study, we found okra enation leaf curl virus (OELCuV), cotton leaf curl Multan betasatellite (CLCuMuB) and cotton leaf curl Multan alphasatellite (CLCuMuA) infecting cotton in Pakistan. The current study was designed to investigate the infectivity of OELCuV and its ability to trans-replicate non-cognate CLCuMuB. Agro-infectious clones containing the partial tandem repeats of OELCuV and CLCuMuB were constructed and the infectivity assays were carried out through Agrobacterium mediated transformation in the model host species Nicotiana benthamiana under controlled conditions. The results showed that in the inoculated plants OELCuV alone can cause downward curling and yellowing of leaves with thickened veins. However, when co-inoculated with the non-cognate CLCuMuB it could functionally trans-replicate CLCuMuB resulting in a more severe phenotype. The expression of Pre-coat/V2 protein in the N. benthamiana plants through the potato virus X (PVX) system caused localized cell death after severe leaf curling in the infiltrated leaves. The tissue tropism of the virus was associated with the systemic development of a hypersensitive response (HR), which ultimately lead to the plant death. The results indicated the involvement of V2 protein in the pathogenicity of OELCuV and its ability to trigger the host defense machinery. This study also demonstrated the ability of OELCuV to trans-replicate CLCuMuB resulting in typical leaf curl disease symptoms in N. benthamiana.

Coat protein (CP) of geminivirus is not requisite for replication of viral DNA yet it is multifunctional and have crucial role in virus transmission by insect vector, systemic infection and virion development. Although in geminivirus, systemic infection rely both on function of CP and specific host-geminivirus-vector interaction but in bipartite begomoviruses CP is dispensable for systemic infection and progression of symptoms. Nevertheless its role in spreading systemic infection cannot be neglected in monopartite viruses' viz. mastrevirus, begomoviruses and curtoviruses, therefore any alteration in CP gene upshot in a new epidemiological adaptation hence worth to study. So the study was designed to present a better picture to view regarding coinfection within different Geminiviruses belonging to mastrevirus and begomovirus particularly due to vector inspecificity consequently resulted in revolutionary recombination events, which ultimately yield new viruses, have more drastic affects on crops. Moreover, co-evolution of both genera may open new horizons in understanding the complexity of cotton leaf curl disease and then to chalk out strategies to counter this emerging threat in Pakistan.

Tomato leaf curl new Delhi virus, a geminivirus with a wide host range is a contagious pathogen of tomato, which also infects many other crops and weeds. Whitefly (Bemisia tabaci Gennadius), a polyphagous vector, is the agent responsible for its spread on a large scale. The pathogen is responsible for a major reduction in the yield of tomato. Ten commercial cultivars of tomato plant were selected to evaluate the effect of virus titer on crop yield. The yield potential along with other traits of these cultivars was assessed on the basis of symptom development, and virus DNA accumulation. The relationship between the virus titer, symptom severity, and agro-economic traits were established. The present results explain that the high level of virus accumulation in plant tissue results in the development of severe symptoms and leads to a major reduction in yield in case of susceptible cultivars, but this is not true for the cultivars showing intermediate resistance. The virus DNA remains low and approximately constant in resistant cultivars and has minimal effect on the yield and health of tomato.

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