Keywords

4.1 Introduction

Ornamental plants forms one of the major branches of horticulture and are grown for decoration of gardens and designing landscape for the purpose of enjoyment of gardeners, visitors, and the public (Mahesh et al. 2012). They are also used for beautification of homes (in house plants), as cut flowers and specimen display (Prajapat et al. 2012a; Marwal et al. 2013a). Majorly ornamental garden plants are grown for its aesthetic appearance such as flowers, scent, leaves, fruit, stem, bark, overall foliage texture, and aesthetic form and characteristics (Mahesh et al. 2012; Marwal et al. 2013b). Likewise certain trees may be called ornamental trees when they are used as part of landscape setting (Khan et al. 2005). The quality and quantity of ornamental plants are ascertained by biotic agents like plant viruses which are an important bottleneck in the production (Marwal et al. 2014). Among plant viruses, Geminiviridae is the largest family infecting a number of crops, weeds, and ornamental plants (Prajapat et al. 2011; Marwal et al. 2013c). They belong to class II of viruses and the largest single-stranded DNA viruses’ family. Members of this family infect both monocotyledonous and dicotyledonous plants. There are at present more than 300 species in this family which are divided among seven well-characterized genera (Mastrevirus, Begomovirus, Curtovirus, Topocuvirus, Eragrovirus, Becurtovirus, and Turncurtovirus) (Fauquet et al. 2011; Hernandez-Zepeda et al. 2013).

Disease symptoms caused by Geminiviruses are yellowing of leaf veins, bright yellow mosaic patterns, yellow mottle leaves, curling of leaves, stunted growth, leaf distortion, and leaf streaks (Rybicki and Hughes 1990; Konate et al. 1995; Prajapat et al. 2012b; Gilbertson et al. 1993; Thomas et al. 1986; Navot et al. 1991). These diseases are responsible for severe threat to the food production in the developing countries residing in the tropical and subtropical regions of the world (Moffat 1999) due to a number of reasons, such as recombination between Geminiviruses, transfer of diseased plant material to a new place, agriculture practices into new cultivated region, and migration of vectors that can spread the virus from one plant to another (Gilbertson et al. 1991; Marwal et al. 2012). Mastreviruses transmission is caused by the vector leafhoppers (Cicadulina mbila) (Muhire et al. 2013), Begomoviruses are transmitted by the vector whiteflies (Bemisia tabaci), Topocuviruses and Curtoviruses are transmitted by the vector treehoppers (Micrutalis malleifera), and Eragroviruses, Becurtoviruses, and Turncurtoviruses are transmitted by the vector leafhoppers (Circulifer haematoceps) (Varsani et al. 2014; Soto et al. 2005).

Mastreviruses comprises of a single genome component (ssDNA) which has the capability of infecting both monocotyledonous and dicotyledonous plants and prevails in the Old World. Curtoviruses and Topocuviruses also have one genomic DNA and infect only dicots in the New World (Hernandez-Zepeda et al. 2013; Briddon et al. 1996). Begomoviruses comprises the largest genera and are found in the Old and New World. Begomoviruses have either monopartite genomes or bipartite genomes known as DNA-A and DNA-B. Sometimes it has been found that a number of monopartite Begomoviruses are associated with satellite molecules (alphasatellites and betasatellites) (Hanley-Bowdoin et al. 2013). Eragroviruses and Becurtoviruses comprise of a single genome infecting only dicots in the Old World (Heydarnejad et al. 2007; Varsani et al. 2009a, b; Baliji et al. 2004). Ornamentals play an important role in persistence and spread of Geminiviruses which they serve as a potential alternative host of their primary inoculums. A scan through literature revealed that there is growing information on Geminiviruses infecting ornamental plants and investigations are therefore taken up with the aim of assessing the status of disease in India and at the global level for understanding the causal nature and severity of the vector pathogens. This chapter thus presents a tip of the iceberg of the diversity of Geminiviruses infecting ornamentals in India and across the globe.

4.1.1 Old World Echelon of Geminiviruses Infecting Ornamental Plants

Virus diseases of Geminiviruses are characterized with a number of visible symptoms. These diseases may lead to noteworthy yield losses to ornamental plants in field circumstances render them unfit for market use (Garcia-Arenal et al. 2001; Herrera-Vásquez et al. 2013). Detail on the distribution, incidence, and occurrence and of the Geminiviruses is necessitated in order to build up strategies for disease management. Similarly, one of the significant features in management of viral diseases is to investigate and comprehend of its survival in alternative hosts (Lapido 1988; Pruss et al. 1997; Weinberger and Msuya 2004). Geminiviruses in alternative hosts may serve as the source inoculum for fresh crops even when recognized by using virus-free seeds. Given below are the details of the diversity of various ornamental plants in the Old World serving as an alternate host of Geminiviruses.

4.1.2 Asia

In recent years the Geminiviridae family has received a great deal of attention, and it is one of the most important studied plant virus families. Several reviews on Geminiviruses covered different aspects of their serological properties, epidemiology, biology, and molecular biology (Polston and Anderson 1997; Hanley-Bowdoin et al. 1999; Morales and Anderson 2001). A new disease of Geminivirus Tobacco leaf curl Japan virus isolated from an ornamental plant Lonicera japonica (Honeysuckle) (Osaki and Inouye 1983) was reported in Japan exhibiting veinal chlorosis symptoms. The Tobacco leaf curl Japan virus genome showed a highest identity of 92.94% with previously reported Tobacco leaf curl Japan virus (Ali et al. 2014). Further in an another report from India, ornamental species of Jatropha, viz., J. integerrima, J. multifida, and J. podagrica, which are also used as biofuel (Speight and Singh 2014; Openshaw 2000) were found with a Geminivirus infection (mosaic symptoms) in CSIR-NBRI garden of Lucknow, India, characterized with molecular techniques. Based on the highest sequence identities of partial DNA-A genome (~1.2 kb) and close phylogenetic relationships, Tomato leaf curl Patna virus in J. multifida (HQ848381), Jatropha mosaic India virus in J. podagrica (HQ848382), and Papaya leaf curl virus in J. integerrima (JQ043440) were identified (Snehi et al. 2016).

Similarly Marwal et al. (2013a) identified a Begomovirus, which was found associated with its satellites molecules infecting a new host Tagetes patula in India. The identified virus reveals closeness with other same isolates of its family (Fig. 4.1). Further complete nucleotide was isolated from 15 samples having disease symptoms revealed positive hybridization results to a radioactively labeled probe of DNA-A of Tomato leaf curl New Delhi virus, confirming the prevalence of a Begomovirus in Clerodendron inerme (family Verbenaceae) (Chethana et al. 2013), a common ornamental plant, grown as a hedge in the gardens of India. Typical symptoms observed were bright yellow mosaic spots, small leaves, and stunted growth. Sequence analysis with sequences of other Begomoviruses showed the Geminivirus most similar to Cotton leaf curl Kokhran virus and Tomato leaf curl New Delhi virus (John et al. 2006). In an another incidence, Croton, also known as Codiaeum variegatum L., is cultivated as a famous ornamental plant (Mahesh et al. 2008) in the home gardens, as well garden of botanical importance and office gardens in and around Bengaluru, South India, which was observed with a leaf curl disease, severe inward curling, vein thickening, stunting, and reduction in leaf size. The phylogenetic analysis suggested that the identified Geminivirus was similar to many other Begomoviruses like Croton leaf curl virus and Ageratum yellow vein virus from the Indian subcontinent that infects tobacco, tomato, papaya, and cotton (Mahesh et al. 2010). Moreover in Lucknow, India, Solanum capsicastrum from the family Solanaceae also known as winter cherry grown in pots and beds in gardens for its ornamental value (Deepa and Jofeena 2015) was observed with a leaf curl disease accompanied by green blisters and distortions. Whiteflies transmission studies were positive on healthy plants producing symptoms similar to Geminivirus infection. Sequence analysis of the Begomovirus revealed 93% identity with Pepper leaf curl Lahore virus of Capsicum annuum from Pakistan (Srivastava et al. 2013). In an another report from Main Research Station (MRS), Raichur, Karnataka, Southern India sunflower plants were observed with a leaf curl disease and successfully transmitted by whiteflies. Symptoms like curling, malformation of leaves, leaf thickening, leaf enations, and severe stunting were observed on sunflower (Baldotto and Baldotto 2015) infected plants. Sequence analysis revealed of this Geminivirus with Begomoviruses clustered with Tomato leaf curl Karnataka virus (EU604297) (Govindappa et al. 2011).

Fig. 4.1
figure 1

The neighbor joining (NJ) phylogenetic tree based upon the alignments of the sequences of Ageratum enation virus with other geographical isolates of Ageratum enation virus

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In a remarkable report, first time a Begomovirus and associated betasatellite was found infecting Rosa indica plants in India. Its genome showed a greater diversity with other Begomoviruses reported from neighboring countries (Fig. 4.2) and poses a serious threat to other economically important crop species in India (Marwal et al. 2017; Sahu et al. 2014). Zinnia elegans an ornamental plant (Riaz et al. 2008) cultivated in India and during a survey were characterized with leaf curling, foliar deformation and distortion symptoms in Gorakhpur, and nearby locations of North Eastern Uttar Pradesh, India. Whiteflies were found in association with Zinnia elegans pointed the possible presence of Begomovirus in the field. Based on the highest nucleotide similarity of 97% and 99% at amino acid level, the closest relationship was showed with the isolates of Zinnia leaf curl virus (Pandey and Tiwari 2012). African daisy (Dimorphotheca sinuate) plant from the family Asteraceae, an ornamental plant (Uga 2005) used chiefly as a bedding plant in the garden area, was observed with yellow vein net symptoms in the year 2006 growing in the NBRI garden at Lucknow which showed nucleotide sequence of 98–97% identity with Tomato leaf curl virus (ToLCV) and 96% identity with Tobacco curly shoot virus (TobCSV) isolates (Raj et al. 2007). Similarly yellow vein net disease, shortening of leaves and stunting of plants, was observed in an ornamental from India plant belonging to family Asteraceae which is the Calendula officinalis (Kareem et al. 2014) in the gardens of Aligarh and Lucknow. The Geminivirus was successfully transmitted from naturally infected Calendula to healthy seedlings by whiteflies (Bemisia tabaci). Sequence analysis revealed the highest nucleotide sequence identities (95%, 94%, and 93%) of the virus infecting C. officinalis with Tobacco curly shoot virus (AF240675), Ageratum enation virus (AJ437618), and Tomato leaf curl Bangladesh virus (AF188481), respectively (Khan et al. 2005).

Fig. 4.2
figure 2

Phylogenetic tree of Rose leaf curl virus with other Begomoviruses showing more than 85% sequence similarities with our isolate. Here, KF584008, Rose leaf curl virus isolate sikar AS22; GQ478342, Rose leaf curl virus clone RoLCuV-[PK,Fai,06]; HM140368, Papaya leaf crumple virus-Nirulas [India:New Delhi:Papaya:2007]; LK028571, Hollyhock yellow vein mosaic Islamabad virus, isolate 3AK; LM645009, Hollyhock yellow vein mosaic Islamabad virus, clone 2YI; KR052159, Papaya leaf crumple virus isolate Mohali, clone Pap-Moh7; KX302711, Papaya leaf crumple virus isolate Kolkata clone B2_4N; LM645010, Cestrum yellow leaf curling virus, clone CN-146; DQ116884, Tomato leaf curl Pakistan virus isolate Rahim Yar Khan 1 clone PT7; FM164938, Tomato leaf curl Pakistan virus, clone MI38; KP698312. Papaya leaf crumple virus isolate C1; LN864816, Papaya leaf curl Faisalabad virus, isolate ZF-19; LK028574, Papaya leaf curl Faisalabad virus, isolate Pakistan, Faisalabad; KX168427, Pedilanthus leaf curl virus; KY978406, Pedilanthus leaf curl virus isolate 248ISBD; KT159766, Euphorbia yellow leaf curl virus isolate PK1A; JN807764, Pedilanthus leaf curl virus-[Crape Jasmine]; LN717037, Cestrum leaf curl Islamabad virus, isolate CS-152; KM978186, Euphorbia yellow leaf curl virus isolate PK1; FM877858, Chili leaf curl India virus; KT948069, Duranta leaf curl virus isolate 57SA; AM948961, Tomato leaf curl Pakistan virus; KP780424, Euphorbia yellow leaf curl virus isolate PK2; HF568781, Pedilanthus leaf curl virus, isolate Pakistan, Multan, clone SPA1; LN713272, Pedilanthus leaf curl virus, clone SAZ59; KC852148, Euphorbia leaf curl virus isolate Shandong; AJ558121, Euphorbia leaf curl virus-[G35], isolate G35; GU732204, Tomato leaf curl Pakistan virus isolate ToLCPKV [IN:Bih]; KM359408, Papaya leaf crumple virus isolate A-87; HE580234, Catharanthus yellow mosaic virus, clone KN4; LK028570, Catharanthus yellow mosaic virus, isolate DR-151

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In Guangdong, China, leaf curl disease symptoms were observed in Allamanda plants. Allamanda is an ornamental flowering plant (Chaveerach et al. 2014) also known as yellow bell, golden trumpet, or buttercup flower, and is a genus of tropical shrubs or vines belonging to the dogbane family (Apocynaceae). The Geminivirus DNA-A suggested the highest sequence identity (81.2%) to Tomato leaf curl Guangdong virus. The threshold value for demarcation of Begomovirus is less than 89%. Hence Allamanda leaf curl virus name was proposed for this new Geminivirus (He et al. 2009). Further in Jiangsu province of China, yellow mosaic symptoms were observed in Clerodendrum cyrtophyllum (Hamdy et al. 2007), and two Geminiviruses (YX2-I and YX2-II) were identified from the collected samples. Computational softwares suggested YX2-I to be a different species of Begomovirus named were given as Clerodendrum golden mosaic Jiangsu virus. Whereas YX2-II were an isolate of bipartite Begomovirus Clerodendrum golden mosaic China virus. In infectivity study, DNA-A of Clerodendrum golden mosaic China virus was capable of showing interaction with the betasatellite associated with Tobacco curly shoot virus producing symptoms in Nicotiana glutinosa and Nicotiana benthamiana plants. The Clerodendrum golden mosaic Jiangsu virus easily interacts with Tobacco curly shoot virus but negative with Clerodendrum golden mosaic China virus DNA-B in Nicotiana benthamiana host (Li and Zhou 2010). Similarly an ornamental plant Clerodendrum cyrtophyllum was established with a Geminivirus infection from Fujian (China) with symptoms of yellow mosaic patterns. Extracted DNA-A was mainly clade with Clerodendrum golden mosaic virus in the phylogenetic analyses having 78.9% nucleotide sequence identity. Accordingly DNA-B was also identified suggesting being the first report of a bipartite Begomovirus infecting Clerodendrum cyrtophyllum in China (Yang et al. 2009). A new incidence of Hibiscus rosa-sinensis, an ornamental plant (Pekamwar et al. 2013), was showing yellow and leaf curl symptoms in Guangzhou, Guangdong Province of China. Comparison showed that DNA-A had more than 89% sequence identify with all isolates of Cotton leaf curl Multan virus (CLCuMV). Satellite DNA molecule was also found to be associated with Hibiscus rosa-sinensis. Pairwise comparison indicated that DNAbeta had the highest sequence identities with CLCuMV DNAbeta (92.1%). It is concluded that the Begomovirus infecting Hibiscus rosa-sinensis is an isolate of CLCuMV (Mao et al. 2008).

In Pakistan Vinca minor L., an ornamental plant (Farahanikia et al. 2011) was monitored with geminiviral symptoms near the School of Biological Sciences, Lahore, Pakistan. Genome was characterized, and computational analysis like basic local alignment search tool analysis highlights 93% nucleotide sequence identity with Pedilanthus leaf curl virus originating from Pakistan (Haider et al. 2008). From Pakistan, another ornamental plant, Duranta erecta, also known as golden dewdrop, is cultivated as hedge in the gardens (Bruggeman 1964) belonging to the family Verbenaceae, indicated reduced leaf size, leaf curling, and chlorosis. The Geminivirus sequences isolate showed similarity with Croton yellow vein virus and Papaya leaf curl virus. These results proved that the Begomovirus residing in golden dewdrop is either a recombinant virus or a distinct Begomovirus. Duranta leaf curl virus was the name suggested for this Geminivirus (Iram et al. 2005). In a similar report from Pakistan, Duranta repens (pigeon berry) (Keong 1982) from the Verbenaceae family infected with Begomovirus showed the highest levels of DNA-A sequence identity to Croton yellow vein mosaic virus (91%), whereas DNA-B showed the highest level of identity with Tomato leaf curl New Delhi virus segment B (94%), suggesting a bipartite Geminivirus associated with the leaf curl disease of D. repens (Tahir et al. 2006). In Pakistan an ornamental shrub redbird flower, also known as Pedilanthus tithymaloides (Srivastava et al. 1985), observed with symptoms of leaf curl and enation. Complete Begomovirus and betasatellite genome was sequenced, revealing nucleotide sequence identity to a Pedilanthus leaf curl virus and Tobacco leaf curl betasatellite, respectively. This Geminivirus is one of an increasing number of monopartite Begomoviruses shown to be associated with a betasatellite (Tahir et al. 2009). In another incidence, an ornamental plant Catharanthus roseus (Nejat et al. 2015) known as Madagascar periwinkle, well known for its medicinal uses such as anti-cancerous properties of its alkaloids, was found infected with Geminiviruses in Pakistan. Complete genome of two Begomoviruses (clone KN4 and KN6) was determined. Clone KN4 showed nearly 87% DNA sequence identity with Chili leaf curl India virus (ChiLCIV), and ~85% identity to Papaya leaf curl virus (PaLCV) represents a new species, named as Catharanthus yellow mosaic virus (CYMV). The sequence of another Begomovirus (clone KN6) showed the highest level of sequence identity (~99–99%) to Papaya leaf crumple virus (PaLCrV) reported from India. Sequence analysis shows that KN4 and KN6 are recombinants of Pedilanthus leaf curl virus (PedLCV) and Croton yellow vein mosaic virus (CrYVMV) (Ilyas et al. 2013).

For the first time in Malaysia, a whitefly-transmitted Begomovirus was detected using serological and molecular techniques in Mimosa invisa (Srivastava et al. 2012). The observed symptoms in infected plants were yellowing and stunted growth. Sequence comparison showed that this Geminivirus has the greatest sequence similarity (92%) to Ageratum yellow vein China virus (Koravieh et al. 2008). Ha et al. (2008) identified two Begomovirus that infect ornamental plants in Vietnam. Sequence analysis of the complete genomes showed that they belong to novel species and was identified in Vietnam for the first time. This includes Clerodendrum golden mosaic virus (ClGMV), infecting glory bower (Clerodendrum philippinum) (Venkatanarasimman et al. 2012), and Mimosa yellow leaf curl virus (MiYLCV), infecting mimosa (Mimosa sp.). The DNA-1 molecule from mimosa formed a distinct branch between DNA-1 sequences originating from China. In July 2011, symptoms of mild yellowing and leaf curling were presented on an ornamental plant Zinnia elegans (Riaz et al. 2008) from Vietnam (Hue City). Zinnia leaf curl virus, Ageratum enation virus, Tobacco leaf curl virus, and Alternanthera yellow vein virus were found to be associated with leaf curl disease of Zinnia elegans. Therefore, this virus may pose a serious threat to many plants (Li et al. 2013). In an another report, complete nucleotide sequences of the Geminivirus DNA-A genome and its DNA β satellite of Honeysuckle yellow vein mosaic virus and Eupatorium yellow vein virus were identified in Honeysuckle sp. (Kitamura et al. 2004; Kemp et al. 1991) and ornamental plant Eupatorium sp. (Deepa and Jofeena 2015), respectively, in Japan. Genome pairwise comparison of DNA-A and its DNA β satellite showed that this Geminivirus had significance threshold of 84% identity. Furthermore, recombination analysis highlighted that members of this group had the genetic variation indicative of many recombination events (Ueda et al. 2008).

4.1.3 Africa

Eragrostis curvula is known as South African wild grass and also cultivated as an ornamental plant (Leigh 1961) that was found to be infected with a new highly divergent Geminivirus species Eragrostis curvula streak virus. Eragrostis curvula streak virus has features similar to other specific Geminivirus genera such as replication-associated protein (Rep) similar to those of Begomoviruses, Curtoviruses, Topocuviruses, and Mastreviruses. Likewise Eragrostis curvula streak virus has the same unusual TAAGATTCC virion strand replication origin nonanucleotide similar to Beet curly top Iran virus. The transcription and replication origin was found structurally more similar to those of Begomoviruses and Curtoviruses. Eragrostis curvula streak virus also had homologue of the Begomovirus transcription activator protein gene found in Begomoviruses, a Mastrevirus-like coat protein gene and two intergenic regions (Varsani et al. 2009a). Panicum streak virus a Mastrevirus represents a close relative of Maize streak virus. Both are transmitted by the same leafhopper vector species. Sixteen new Panicum streak virus full-genome sequences were determined across Africa. Analysis of both the Geminiviruses suggested that the progress of Maize streak virus strains in whole Africa is apparently less constrained than that of Panicum streak virus strains. It was concluded that increased mobility of Maize streak virus to other closely related species such as Panicum streak virus may have been an important evolutionary step in the eventual emergence of Maize streak virus as a serious agricultural pathogen (Varsani et al. 2009b). Maize streak virus of the genus Mastrevirus is responsible for maize streak diseases of Zea mays across Africa. Nigeria is one of the West African countries, where maize is not cultivated throughout the year, hence Maize streak virus resides in alternative hosts like ornamental crops and weed plants. Maize streak virus isolates were obtained from maize and Digitaria ciliaris grass (Cardina et al. 2011). Further a novel highly divergent mastrevirus from Axonopus compressus (Kamal-Uddin et al. 2009) was characterized. Axonopus compressus is a species of grass, used a ground cover in gardens, and was named as Axonopus compressus streak virus (ACSV) (Oluwafemi et al. 2014).

4.1.4 Europe

Ipomoea indica, also known as blue morning glory, belongs to Convolvulaceae family of plants which prevails along the coast of Greek. Ipomoea indica grow like weeds and also as cultivated ornamentals (Palanisamy and Arumugam 2014). During the summer of 2013, yellowing of leaf veins symptoms were observed in Ipomoea indica, collected from Mandriko, Kremasti, and Kolymbari regions of Greece. The Geminivirus isolated from Kolymbari were ~99% similar among themselves and showed ~98% DNA identity with a Sweet potato leaf curl virus isolate obtained from Ipomoea indica plant in Sicily (Italy). The Geminivirus reported from Kremasti revealed ~93% nucleotide similarity with Sweet potato leaf curl virus obtained from Ipomoea indica plant from southern Spain. All the identified Geminiviruses infecting Ipomoea indica in Greece are isolates of Sweet potato leaf curl virus (Fiallo-Olivé et al. 2013a). Using advance and molecular techniques, two new strains of Abutilon mosaic virus have been characterized from Paris (France) and Stuttgart (Germany). Their phylogenetic results suggested clustering with other Abutilon mosaic virus strains reported from Middle American, whereas Geminiviruses from South American infecting Abutilon or Sida micrantha (Gomaa et al. 2016) are less closely related. By comparing the coat protein (CP) genes of the Abutilon mosaic virus forms a clade with Middle and South American Begomoviruses suggesting non-synonymous nucleotide exchanges for certain amino acid positions in the Abutilon mosaic virus cluster (Fischer et al. 2014).

Ipomoea indica, a vegetatively propagated ornamental plant, was found exhibiting yellow vein disease symptoms in Norwich, Spain. A Geminivirus (AJ132548) was identified using molecular techniques, which showed low sequence similarity with Ageratum yellow vein virus (AYVV), Tomato leaf curl virus from southern India, and other Begomoviruses. DNA-B was absent when characterized with degenerate DNA-B primers. This virus was named as Ipomoea yellow vein virus (IYVV). Whiteflies transmission studies were carried out on healthy I. indica plants using biotypes S, Q (from Spain), and B (from Israel) that showed non-transmissible nature of Ipomoea yellow vein virus to healthy Ipomoea indica, Lycopersicum esculentum, Nicotiana tabacum, or nightshade. The loss of vector transmissibility of this Geminivirus was due to many years of vegetative propagation of the host plant as an ornamental, as occurred in Honeysuckle yellow vein mosaic virus (HYVMV) and Abutilon mosaic virus (AbMV) (Banks et al. 1999). Sweet potato (Ipomoea batatas) is cultivated in a number of places globally and houses Geminiviruses in this vegetatively propagated cash crop (Milind and Monika 2015) causing a hinder to its production around 90% yield loss. A survey was conducted in Spain to identify Geminiviruses infecting sweet potato and Ipomoea indica. A total of 15 isolates were sequenced, and results showed the presence of Sweet potato leaf curl virus (SPLCV), Ipomoea yellowing vein virus, three new species of Begomovirus, and a novel strain of SPLCV. The analysis confirmed that a number of recombination events have transformed Ipomoea infecting Begomoviruses in Spain (Lozano et al. 2009).

4.1.5 Australia

Mastreviruses infects a wide range of monocotyledonous plants in the Old World. Mastreviruses showed maximum diversity in African subcontinent. A research was carried out in Australia for the better understanding of mastrevirus diversity in Australia. For the same 41 Mastreviruses were found naturally in native grasses in Australia. Out of them four new Mastrevirus were found in addition to the four previously characterized species. Two highly divergent Mastrevirus recovered from a single Sporobolus plant (used in garden) were most closely related to African streak viruses showed inter- and intraspecies recombination (Kraberger et al. 2012).

4.1.6 New World Echelon of Geminiviruses Infecting Ornamental Plants

The ornamentals are unquestionably among the crops whose gardening consequences into generation of jobs and cohort of income. Geminiviruses are known to cause massive crop yield losses across the globe (Rojas et al. 2005; Rybicki 1994). The harm caused by Geminiviruses affects both the quality and quantity of the preferred parts of the crops. Moreover, they were found to be widely distributed in surveyed locations (Seal 2006; Stanley et al. 2005; Hanley-Bowdoin et al. 2000; Padidam et al. 1999). As the battle to eradicate Geminivirus diseases continues, the virologists and plant breeders are hereby urged not to neglect the damages on ornamentals that are caused by the viruses reported below from the New World.

4.1.7 North America

With the help of molecular techniques like rolling circle amplification, two viral genomes were amplified from salvia (Salvia splendens) cv. “Dancing Flame” (Błażewicz-Woźniak et al. 2012) exhibited variegated foliage resembling Geminivirus symptoms in the United States. Bioinformatic analysis suggested the positiveness of Begomovirus Clerodendron golden mosaic China virus. The virus was detected in all symptomatic salvia plants but absent in non-variegated plants. Further study was done on graft transmission of virus to healthy Salvia splendens which reproduced the original symptoms. Even attempts were made to transmit the virus with the help of whitefly, Bemisia tabaci biotype B, but were negative (Valverde et al. 2012). For the first time a Topocuvirus, i.e., Tomato pseudo curly top virus (TPCTV), has been recorded in Florida whose genome was cloned and sequenced. Topocuvirus is the only Geminivirus transmitted by treehopper vector. Infectivity assay was carried out via Agrobacterium-mediated inoculation of several host species. Descendants of the Topocuvirus were transmissible by the treehopper vector in Micrutalis malleifera (Fowler). The genome and coat protein of Tomato pseudo curly top virus show features distinct from all previously characterized Geminiviruses, revealing close relationship to Beet curly top virus (Briddon et al. 1996). In Ohio State of the United States, an ornamental plant “Gold Veined Oxalis” (Oxalis debilis) (Junejo et al. 2016) displays eye-catching yellow vein foliage which was used for graft transmission to other Oxalis debilis plants. DNA was isolated and subjected to polymerase chain reaction; amplified sequence revealed that a Geminivirus was responsible for yellow vein symptoms with Bemisia tabaci the carrier vector. The Begomovirus was suggested the name Oxalis yellow vein virus (OxYVV) which showed 87%, 85%, and 83% DNA sequence identities with Sida mottle virus, Okra mottle virus, and with Tomato yellow spot virus, respectively, confirming another instance of a Geminivirus that augments the aesthetic beauty of ornamental plants (Herrera et al. 2015).

Mexico has been a house of number of local and cultivated eudicots (Worberg et al. 2007) in its Yucatan Peninsula and was found with Geminivirus symptoms. Thirteen different Geminiviruses were identified mainly Begomoviruses. Out of all, five were new Begomovirus species named as Boerhavia yellow spot virus (BoYSV), Anoda golden mosaic virus (AnGMV), Desmodium leaf distortion virus (DeLDV), Hibiscus variegation virus (HiVV), and Papaya golden mosaic virus (PaGMV). Already identified species of Begomoviruses were Sida golden mosaic virus (SiGMV), Melon chlorotic leaf curl virus (MCLCuV), Euphorbia mosaic virus (EuMV), Tobacco apical stunt virus (TbASV), and Okra yellow mosaic Mexico virus (OkYMMV) which were found for the first time. Finally viruses earlier reported in Yucatan Peninsula were Tomato mottle virus (ToMoV), Pepper golden mosaic virus (PepGMV), and Bean golden yellow mosaic virus (BGYMV) which were recognized in eudicots plants. Their phylogenetic analysis grouped all Begomoviruses in Western Hemisphere clade (Hernández-Zepeda et al. 2007).

4.1.8 South America

The major destructive group of viruses infecting cultivated crops across the globe is Geminiviruses. In a study in Boqueirão which is place in Paraíba state of Brazil, leaf samples were sampled from Sida spp. (Gomaa et al. 2016) and tomato crops. Geminiviruses were isolated, and 30 DNA-A were identified. Computational analysis reveals only two Begomovirus, Sida mottle Alagoas virus (SiMoAV) infecting Sida spp. and Tomato mottle leaf curl virus (ToMoLCV) obtained from tomato crops. Rep gene of ToMoLCV showed the highest variability and recombination events in comparison to SiMoAV. This study highlights ToMoLCV as the chief Begomovirus harboring tomatoes in northeastern side of Brazil (Ferro et al. 2016). Moreover there are also reports of Geminiviruses that are responsible for variegation in flower that comprises beautiful mosaic patterns caused by Abutilon mosaic virus mainly on the leaves of flowering maple (Abutilon pictum; Malvaceae) (Święczkowska and Kowalkowska 2015). This plant is also known as parlor maple or Indian mallow and used as an ornamental plant in America. “Gold Dust” and “Thompsonii” are the cultivar used for parlor maple. Initially parlor maple belongs to Brazil and now prevails across the South and Central America and has been growing for ornamental purpose since the 1800s (Keur 1934). Even Morren in 1869 was successfully transmitted the variegation caused by Geminiviruses through graft inoculations. Even in recent years, there have been other reports of plant viruses associated with unique phenotypes of ornamental plants, and some of them are being marketed as novel plant cultivars (Valverde et al. 2011). Whiteflies transmitted Geminiviruses are responsible for serious infections in crops and are frequently also coupled with non-cultivated plants. Two new Geminiviruses were identified in Pavonia sp. (da Silva et al. 2016) belonging to Malvaceae family in Brazil. When their sequence comparisons were carried out and further phylogenetic analysis was done, it was revealed that these novel Geminiviruses correspond to the New World Begomoviruses. The DNA sequences of the DNA-A of the two viruses revealed the highest similarity to Abutilon mosaic Bolivia virus (AbMBoV). Based on the symptoms identified in the field and taking into account the host plant, the names Pavonia mosaic virus (PavMV) and Pavonia yellow mosaic virus (PavYMV) were proposed for these two new Geminiviruses (Pinto et al. 2015).

Geminiviruses plays a crucial role in the crop production worldwide; hence it’s a necessity to detect the viral pathogen at an early stage of plant infection. Abutilon mosaic virus (AbMV) is a Begomovirus species and belongs to Geminiviridae family of plant viruses, which known to infect ornamental plants across the globe. In the garden area of Tumbaco (Equador) Abutilon hybridum plants (Holser and Bost 2004) were observed with mosaic patterns bright yellow in color as a sign of infection symptoms. The Geminivirus was identified (KP877621) by the help of degenerate primers against Begomovirus in polymerase chain reaction showing 68 to cent percent nucleotide identity with other Begomoviruses. A novel method using Raman spectroscopy was performed acting as a diagnostic tool for AbMV infection by recording the spectrum from leaves of both healthy and symptomatic samples. In leaves carotenoids form the basis for Geminivirus identification by showing a sharp decline in the intensity of the bands. The change in the intensity of the bands, especially at 1526 cm−1, was designated as the basis for earlier detection of Geminiviral infection in plants (Yeturu et al. 2016). Even the complete sequences of new bipartite Geminivirus infecting Datura stramonium in Venezuela were also obtained. The name proposed for this new Begomovirus were Datura leaf distortion virus (DLDV) which were obtained from Datura stramonium L. plant belonging to Solanaceae family (Hansen and Clerc 2002). The dendrogram revealed that Datura leaf distortion virus separates out in two divergent clades of New World Begomoviruses (Khurana and Marwal 2016; Fiallo-Olivé et al. 2013b).

4.1.9 Management Strategies Against Geminiviruses

Conventional strategies can fail to control rapidly evolving and emerging plant viruses. Genome engineering strategies have recently emerged as promising tools to introduce desirable traits in many eukaryotic species, including plants (Zaidi et al. 2016). Transgene-induced silencing in plants is usually associated with methylation of nuclear DNA corresponding to the transcribed region of the target RNA despite transcription levels of the transgene remain unaffected (Saunders et al. 2004). RNAi technology when used against a Geminivirus (African cassava mosaic virus (ACMV)) showed 99% decrease of Rep transcripts and 66% reduction in viral DNA (Sanjaya et al. 2005). Targeting Rep and AV2 gene by antisense technology is found to be quite successful (Dasgupta et al. 2003). To make PTGS an effective method, both sense and antisense RNAs are a prerequisite, and a transgenic tobacco (Nicotiana benthamiana) using RNAi was developed (Singh et al. 2007). Sense and antisense constructs that were made of the movement protein genes (BC1 and BV1) of tomato mottle Geminivirus (TMoV) were transformed by Agrobacterium-mediated transformation in tobacco explants. Geminivirus was detected in inoculated leaves but was not readily detected in leaves beyond the inoculation sites in the highly resistant plants (Duan et al. 1997). A mastrevirus Maize streak Reunion virus (MSRV) collected in Yunnan Province, China, was identified by small RNA deep sequencing. This vsiRNAs profile derived from MSRV-YN was characterized, which might contribute to get an insight into the host RNA-silencing defense induced by MSRV-YN and provide guidelines on designing antiviral strategies using RNAi against MSRV-YN (Marwal and Gaur 2017; Chen et al. 2015).

Level of disease control obtained using traditional measures led to the search for other control measures that go beyond traditional host genetic resistance, chemical controls, and cultural practices. Recently, the CRISPR/Cas technology has emerged as potent genome editing tool, with remarkable applications in various organisms, including several plant species. The CRISPR/Cas system originates from prokaryotic organisms and acts as an adaptive immune system to protect them against invading foreign DNA, such as phages, by cleaving the nucleic acid by an RNA-guided DNA nuclease in a sequence-specific manner (Chaparro-Garcia et al. 2015). A virus-based guide RNA (gRNA) delivery system for CRISPR/Cas9-mediated plant genome editing (VIGE) that causes mutations in target genome locations has been reported. VIGE was executed by using a modified Cabbage leaf curl virus (CaLCuV) vector to express gRNAs in stable transgenic plants expressing Cas9 (Yin et al. 2015). CRISPR–Cas is an adaptive immune system in many archaea and bacteria that cleave foreign DNA on the basis of sequence complementarity. Geminiviruses causes great crop losses worldwide. In order to tackle such problem, a study was carried out by Baltes et al. (2015) in bean yellow dwarf virus (BeYDV) genome which was targeted for destruction with the CRISPR–Cas system. By using BeYDV-based replicons, transient assays were done disclosing that CRISPR–Cas reagents introduced mutations within the viral genome and thus reduced virus copy number. Transgenic plants infected with BeYDV showed less virus load and symptoms by expressing CRISPR–Cas reagents. This novel strategy demonstrates a perfect engineering resistance to Geminiviruses (Baltes et al. 2015). Similarly, using the Geminivirus, Beet severe curly top virus (BSCTV), transient assays performed in Nicotiana benthamiana which demonstrate that the sgRNA–Cas9 constructs inhibit virus accumulation and introduce mutations at the target sequences. Further, transgenic Arabidopsis and N. benthamiana plants overexpressing sgRNA–Cas9 are highly resistant to virus infection (Ji et al. 2015).

4.2 Conclusion

Throughout life, we are encircled by an indistinguishable stratum of atmosphere. We know that the atmosphere contains copious microscopic particles such as pollens, allergens, dust particles, and species of microorganisms ranging from bacteria to fungi and viruses. And the viruses are considered the foremost environmental danger to humans, animals, and plants. Several viruses affect the crop plants, but the major contribution is from the viruses belonging to the Geminiviridae family (Gaur et al. 2011). In recent years the Geminiviruses has received a great deal of attention, and it is one of the most important studied plant viruses. Several reviews on Geminiviruses covered different aspects of their biology, epidemiology, serological properties, and molecular biology (Prajapat et al. 2014). Tropical and subtropical regions are the most favorable regions for emerging of newly Geminiviruses which cause severe disease epidemics. Ornamentals can retain these Geminiviruses that can be transmitted by the insect vector back to crop plants causing yield loss of the crops. Once present in the new host, these viruses would have rapidly evolved giving rise to new devastating species. Ornamental plants forming one of the major branches of horticulture plays a huge role by supplementing the income of the rural people. The production of these plants becomes key drivers of economic development in many parts of the world. These ornamental plants serve as an alternative host for the viruses in gardens, and they may facilitate Geminivirus transmission to crop plants, thus enhancing the host range of this virus in different regions of the world (Marwal et al. 2016). Current trends for extensive and intensive agriculture, open international agricultural trade, food security, and sustained economy have brought new challenges in the fight against Geminivirus diseases. For this reason, this chapter focused on and presents the scenario of various reports of characterization and identification of different Geminiviruses infecting in ornamental plants worldwide.