Horsegram Yellow Mosaic Virus Research Articles

Exploring distribution and genomic diversity of begomoviruses associated with yellow mosaic disease of legume crops from India, highlighting the dominance of mungbean yellow mosaic India virus.

Yellow mosaic disease (YMD) caused by several begomoviruses is one of the major constraints of over a dozen leguminous crops worldwide, particularly in Asian and Southeast Asian countries. The present study aimed to investigate the distribution, diversity and prevalence of begomoviruses associated with YMD in leguminous hosts in five agro-climatic zones of India, to assess the extent of their geographical presence and develop location and crop-specific distribution maps. One hundred and seventy-four leguminous plant samples were tested from 32 locations in India to detect YMD-causing viruses. Additionally, publicly available data were incorporated into this study to provide a comprehensive overview of their distribution in India. This resulted in 581 reports on the DNA-A component representing 119 locations, which were also utilized to depict the distribution of YMD-causing viruses on a map of India. In this study, 117 full-length DNA-A and 103 DNA-B components were successfully characterized, representing the detected mungbean yellow mosaic India virus (MYMIV), mungbean yellow mosaic virus (MYMV), and horsegram yellow mosaic virus in the collected samples. Phylogenetic analysis of isolates of these species showed no differentiation based on location in India. Diversity indices revealed the abundance (55.9%) and dominance (0.56) of MYMIV across 119 locations. These findings hold significant implications for legume researchers, offering insights into disease prevalence and geographic distribution. Furthermore, the distribution of YMD-causing viruses in different agro-climatic zones will help researchers in developing zone-specific YMD-resistant cultivars of the legume crops and would facilitate effective disease management options.

Molecular characterization of virus species causing yellow mosaic disease of redgram in Andhra Pradesh

Redgram is animportant drought tolerant leguminous crop in the semi-arid subtropics. Many fungal, bacterialand viral diseases are major constraints for redgram production, apart from all these diseases, yellowmosaic disease (YMD) is observed in redgram crop in few localities of Chittoor district, Andhra Pradeshduring 2017. The present study was aimed to find out associated begomo virus species causing YMD inredgram.The total genomic DNA was isolated from YMV infected redgram leaves by modified CTAB method.The rolling circle amplification based full length clones were constructed in pUC18 vector. The two constructed clones (DNA-A and DNA-B) were confirmed by using gene specific primers and weresequenced.The coat protein gene andcomplete nucleotide sequence analysis was carried out with the knownbegomoviruses sequences obtained from Genbank database.The phylogenetic analysis of coat protein geneof YMV-AP-Red gram isolate shared 94.3-98.1% nucleotide identity with HgYMV isolates, followed byMYMV (81.2-85.2%), MYMIV (78.1-80.2%) and DoYMV(72.2-74%). Hence it was confirmed that viral speciescausing YMD in redgram from Tirupati, AndhraPradesh is a Horsegram yellow mosaic virus and it is avariant of HgYMV as it shared>94% similarity with other HgYMV isolates at nucleotide level.

Species diversity, phylogeny and evidence of recombination in begomoviruses associated with yellow mosaic disease of moth bean (Vigna aconitifolia) in South India

AbstractPolymerase chain reaction assays of eight yellow mosaic disease (YMD) affected moth bean samples using specific primers indicated the presence of Mungbean yellow mosaic virus (MYMV), Mungbean yellow mosaic India virus (MYMIV) and Horsegram yellow mosaic virus (HgYMV) in two samples (Mo1 and Mo5) and two of these three viruses in remaining six samples. Sequence data analysis of Mo1 and Mo2 revealed the involvement of multiple DNA‐A and DNA‐B molecules in both samples. Further analysis of DNA‐A and DNA‐B molecules confirmed the presence of three viruses viz., MYMIV, MYMV and HgYMV, in Mo1 and of two MYMV and HgYMV in Mo2 samples. Analysis of common region (CR) sequences of components (DNA‐A and DNA‐B) of each virus indicated >85% nucleotide identity confirming them to be cognate and species integrity. The recombination analysis revealed the presence of a total of six putative recombination events in the viruses under study. In a phylogenetic analysis of DNA‐A sequences of the viruses under study with bipartite legume‐infecting begomoviruses and some selected old and new world begomoviruses, MYMIV, MYMV and HgYMV grouped with respective virus species. Similar grouping and clustering were found in the DNA‐B sequences also. The present study reports infection by HgYMV in moth bean and the association of three viruses (MYMIV, MYMV and HgYMV) with moth bean yellow mosaic disease for the first time. The presence of mixed infection of begomoviruses provides opportunities for the exchange of DNA between the species which may lead to the development of new strain/virus species.

​RCA-based Detection of Begomoviruses in Weed Genera Associated with Legumes in Southern Karnataka

Background: Yellow mosaic disease (YMD) caused by begomoviruses transmitted through the insect vector Bemisia tabaci poses a serious threat to the production of legume crops. Methods: Season-long surveys were carried out for YMD occurrence in six different legume crops and associated natural weeds both symptomatic and asymptomatic across the districts of southern Karnataka, India. The samples were analyzed through RCA PCR using specific primer pairs. Result: Up to 94.1 per cent YMD incidence was recorded and nine weed species were commonly found associated with legume crops. The weeds viz., Ageratum conyzoides, Alternanthera sessilis, Commelina benghalensis and Euphorbia geniculata were abundantly found in the surveyed regions. The weeds were both symptomatic and asymptomatic. Rolling circle amplification coupled polymerase chain reaction method was employed to detect yellow mosaic virus in asymptomatic weeds. Phylogenetic analysis based on the sequences of PCR amplified products of weeds and symptomatic legumes revealed a close clustering of the weed samples with horsegram yellow mosaic virus, legume yellow mosaic virus and mungbean yellow mosaic virus. Overall, our data suggests the role of weed species associated with legume crops as alternative/collateral hosts of begomoviruses and their role in the epidemiology of yellow mosaic disease.

​RCA-based Detection of Begomoviruses in Weed Genera Associated with Legumes in Southern Karnataka

Background: Yellow mosaic disease (YMD) caused by begomoviruses transmitted through the insect vector Bemisia tabaci poses a serious threat to the production of legume crops. Methods: Season-long surveys were carried out for YMD occurrence in six different legume crops and associated natural weeds both symptomatic and asymptomatic across the districts of southern Karnataka, India. The samples were analyzed through RCA PCR using specific primer pairs. Result: Up to 94.1 per cent YMD incidence was recorded and nine weed species were commonly found associated with legume crops. The weeds viz., Ageratum conyzoides, Alternanthera sessilis, Commelina benghalensis and Euphorbia geniculata were abundantly found in the surveyed regions. The weeds were both symptomatic and asymptomatic. Rolling circle amplification coupled polymerase chain reaction method was employed to detect yellow mosaic virus in asymptomatic weeds. Phylogenetic analysis based on the sequences of PCR amplified products of weeds and symptomatic legumes revealed a close clustering of the weed samples with horsegram yellow mosaic virus, legume yellow mosaic virus and mungbean yellow mosaic virus. Overall, our data suggests the role of weed species associated with legume crops as alternative/collateral hosts of begomoviruses and their role in the epidemiology of yellow mosaic disease.

Identification and Molecular Characterization of Mung Bean Yellow Mosaic Virus in French Bean through Coat Protein Gene

Background: French bean (Phaseolus vulgaris L.), is one of the important legume vegetables grown in India. The disease mung bean yellow mosaic virus (MYMV) limits successful production of beans. MYMV has become an epidemic in bean growing regions, particularly in the tropical and subtropical countries. In summer, the disease is more serious and widely distributed and reported in various countries. The current study is aimed at identification of MYMV and molecular characterization of mung bean yellow mosaic virus in French bean. This study will be helpful for early detection of the virus, so that better preventive measures can be taken to control MYMV.Methods: The investigations were conducted during 2016-2017, all the agro climatic zones of Karnataka province were surveyed. The coat protein (CP) gene of MYMV was amplified using gene specific primer with DNA isolated from MYMV infected leaves samples in french bean. Polymerase chain reaction products were Sequenced and analysed using a bioinformatic tool. Result: The CP gene decrypt sequences analysis revealed that the identity and similarity in global alignment for all the obtained sequences ranging from 80.8 to 95.3% with reference to MYMV, whereas for horse gram yellow mosaic virus (HYMV) it ranges from 90.4 to 99.1%. Two distinct yellow mosaic viruses infecting french bean (MYMV and HYMV) were identified and it was observed that there exists considerable genetic variation among these species. Present work showed that the CP region is efficient enough to provide a simple, rapid and reliable method for early detection of MYMV infections in french bean, which would help to develop proper management strategies to control these viruses.

Transmission and host range of Horsegram yellow mosaic virus (HgYMV) causing common bean (Phaseolus vulgaris L.) yellowing disease in Sri Lanka

The common bean (Phaseolus vulgaris L.) yellowing disease (BYD) is caused by the Horsegram yellow mosaic virus (HgYMV), which is a begomovirus transmitted by whiteflies (Bemisia tabaci Genn.). It is a serious threat to the common bean cultivation in Sri Lanka. Despite the fact that the disease has been affecting bean production for a long time, its etiology and virus vector relationships are not understood well. Therefore, the present work was carried out to identify major aspects of the etiology of the virus. Initially a survey was conducted to determine the prevalence of the virus in representative bean growing locations in Sri Lanka, followed by a host range study using 54 plant species. Characteristics of virus-vector relationships were determined by conducting a series of virus transmission tests under glass-house conditions. The survey results revealed the incidence of BYD at some time or the other in most of the sampled localities, which are scattered around all four major districts where the common bean is grown. Through the host range study, it was demonstrated that Ageratum sp., Glycine max Merrill., Macrotyloma uniflorum (Lam.) Verdc., and Phaseolus lunatus L. are susceptible to HgYMV, indicating a narrow host range. In addition to the symptomatology, the successful entry of the virus following inoculation was confirmed through PCR using degenerate primers. Relative transmission efficiency was found to be 96.7 %, which corresponds to 0.24 of the estimated probability of transmission through a single whitefly (p*). The virus could be transmitted through probing by a single viruliferous whitefly with an incidence of 36.7 % (p* = 0.37). The minimum acquisition access period and inoculation access period were 20 min in each case and the respective disease incidence values were 30.0 % (p* = 0.04) and 36.7 % (p* = 0.05). The whiteflies could retain the virus in an active state for up to 9 days.

Breeding for Enhancing Legumovirus Resistance in Mungbean: Current Understanding and Future Directions

Yellow mosaic disease (YMD) affects several types of leguminous crops, including the Vigna species, which comprises a number of commercially important pulse crops. YMD is characterized by the formation of a bright yellow mosaic pattern on the leaves; in severe forms, this pattern can also be seen on stems and pods. This disease leads to tremendous yield losses, even up to 100%, in addition to deterioration in seed quality. Symptoms of this disease are similar among affected plants; YMD is not limited to mungbean (Vigna radiata L. Wilczek) and also affects other collateral and alternate hosts. In the last decade, rapid advancements in molecular detection techniques have been made, leading to an improved understanding of YMD-causing viruses. Three distinct bipartite begomoviruses, namely, Mungbean Yellow Mosaic India Virus (MYMIV), Mungbean Yellow Mosaic Virus (MYMV), and Horsegram Yellow Mosaic Virus (HgYMV), are known to cause YMD in Vigna spp. Vigna crops serve as an excellent protein source for vegetarians worldwide; moreover, they aid in improving soil health by fixing atmospheric nitrogen through a symbiotic association with Rhizobium bacteria. The loss in the yield of these short-duration crops due to YMD, thus, needs to be checked. This review highlights the discoveries that have been made regarding various aspects of YMD affecting mungbean, including the determination of YMD-causing viruses and strategies used to develop high-yielding YMD-resistant mungbean varieties that harness the potential of related Vigna species through the use of different omics approaches.

Molecular detection and characterisation of Horsegram Yellow Mosaic Virus (HgYMV) infecting Lima bean (Phaseolus lunatus) in India

The present study developed a PCR protocol using designed sequence virus-specific sets of primers (HYMV-A1500F & HYMV-A1500R and D-HYMV-B2200F & D-HYMV-B2200R) for the amplification of the complete DNA-A and DNA-B components of lima bean isolate of Horsegram yellow mosaic virus (HgYMV-Lb). The PCR products were cloned and sequenced. The nucleotide sequences of HgYMV-Lb was determined and compared with those of other whitefly-transmitted geminiviruses. The length of the single-stranded DNA-A and DNA-B components of HgYMV-Lb were 2735 and 2670 nucleotide, respectively. The DNA-A sequences were found most similar to the corresponding sequences of begomovirus species infecting legumes by up to 97% nucleotide identity. The DNA-B sequences were most similar to isolates of both Mungbean yellow mosaic virus and Mungbean yellow mosaic India virus at approximately 70% nucleotide identity. The genome organisation of HgYMV-Lb was also similar to that of a typical begomovirus bipartite genome. The DNA-A component has six Open Reading Frames (AV1/CP, AV2, AC1/REP, AC2/TrAP, AC3/REn, and AC4) and DNA-B has two (BC1 and BV2). The number, size and arrangement of the Open Reading Frames in the genome were similar to the Old world begomoviruses. In addition, phylogenetic analysis of DNA-A sequence clustered HgYMV-Lb into a group of legume-infecting begomoviruses from the Indian sub-continent, particularly with Mungbean yellow mosaic virus. Based on DNA-B sequences, HgYMV-Lb was clustered into the group with Mungbean yellow mosaic virus infecting soybean in Madurai (MYMV-Sb:Mad) and Mungbean yellow mosaic India virus in Bangladesh (MYMIV-BD:Yb). Thus, based on the PCR and sequence analysis, the association of a bipartite begomovirus with lima bean showing symptoms yellow mosaic disease in India was confirmed. Also, it was identified that the begomovirus was a novel isolate of previously described Horsegram yellow mosaic virus . Keywords : Horsegram, Lima bean, Yellow mosaic virus , Begomovirus

Molecular detection and characterisation of Horsegram Yellow Mosaic Virus (HgYMV) infecting Lima bean (Phaseolus lunatus) in India

The present study developed a PCR protocol using designed sequence virus-specific sets of primers (HYMV-A1500F & HYMV-A1500R and D-HYMV-B2200F & D-HYMV-B2200R) for the amplification of the complete DNA-A and DNA-B components of lima bean isolate of Horsegram yellow mosaic virus (HgYMV-Lb). The PCR products were cloned and sequenced. The nucleotide sequences of HgYMV-Lb was determined and compared with those of other whitefly-transmitted geminiviruses. The length of the single-stranded DNA-A and DNA-B components of HgYMV-Lb were 2735 and 2670 nucleotide, respectively. The DNA-A sequences were found most similar to the corresponding sequences of begomovirus species infecting legumes by up to 97% nucleotide identity. The DNA-B sequences were most similar to isolates of both Mungbean yellow mosaic virus and Mungbean yellow mosaic India virus at approximately 70% nucleotide identity. The genome organisation of HgYMV-Lb was also similar to that of a typical begomovirus bipartite genome. The DNA-A component has six Open Reading Frames (AV1/CP, AV2, AC1/REP, AC2/TrAP, AC3/REn, and AC4) and DNA-B has two (BC1 and BV2). The number, size and arrangement of the Open Reading Frames in the genome were similar to the Old world begomoviruses. In addition, phylogenetic analysis of DNA-A sequence clustered HgYMV-Lb into a group of legume-infecting begomoviruses from the Indian sub-continent, particularly with Mungbean yellow mosaic virus. Based on DNA-B sequences, HgYMV-Lb was clustered into the group with Mungbean yellow mosaic virus infecting soybean in Madurai (MYMV-Sb:Mad) and Mungbean yellow mosaic India virus in Bangladesh (MYMIV-BD:Yb). Thus, based on the PCR and sequence analysis, the association of a bipartite begomovirus with lima bean showing symptoms yellow mosaic disease in India was confirmed. Also, it was identified that the begomovirus was a novel isolate of previously described Horsegram yellow mosaic virus.Keywords: Horsegram, Lima bean, Yellow mosaic virus, Begomovirus

Molecular characterization and infectivity of Mungbean Yellow Mosaic India virus associated with yellow mosaic disease of cowpea and mungbean

Grain legumes are an important source of dietary protein across Southeast Asia, but they suffer severe losses due to Yellow mosaic diseases (YMD), caused by members of the genus Begomovirus (family Geminiviridae). Cowpea is an annual tropical grain legume extensively cultivated in sub-Saharan Africa, Southeast Asia and South America. More than 20 viruses are reported in cowpea around the world. Despite its economic importance, little attention has been paid to the viruses infecting cowpea in India. We conducted an elaborate survey and characterization of begomoviruses infecting cowpea in the central and northeast region of India. We report complete sequences of 13 components (6 DNA-A, 6 DNA-B, and 1 complete genome) belonging to four strains of MYMIV, each of CGMV and FbSLCV. Nucleotide sequence comparison analysis showed the cowpea isolates MYMIV DNA-A [KY556679] having highest similarity (98%) with reported soybean isolate of MYMIV segment DNA-A [AY049772] and lowest similarity (77%) with lima bean isolate of horsegram yellow mosaic virus (HYMV) [AM932429] whereas cowpea isolates MYMIV DNA-B [KY556680] showed highest identity (98%) with MYMIV Brebs3 segment [JN368446] and lowest identity (94%) with MYMV LBG623 segment [KF928962]. Our survey revealed maximum incidence of MYMIV infection in cowpea in the central and northeast India. We therefore characterized the MYMIV infection in cowpea as well as its natural host, mungbean through agroinoculation of dimeric infectious clones and confirmed the pathogenicity of MYMIV. This is the first report of cowpea isolate of MYMIV infecting mungbean with YMD symptoms which is experimentally demonstrated through Koch's postulate.

Coat protein and movement protein based characterization of Lima bean yellow mosaic virus disease in Karnataka (India)

Yellow mosaic disease caused by a Begomovirus has become an important production constraint in lima bean cultivation in Karnataka. The begomovirus causes Lima bean Yellow Mosaic Virus (LYMV), was characterized by sequencing the CP and MP genes. Distinct viral gene specific PCR product corresponding to CP and MP gene ~1000 bp and ~900 bp was obtained. The PCR product were sequenced and compared with the reference Begomoviruses sequences from the NCBI blast database. LYMV (GKVK isolate) shared highest nucleotide identity (98%) with Horsegram yellow mosaic virus (HgYMV) of French bean isolate (Accession No. AM932425.1). Phylogenetic analysis of CP and MP gene sequences of LYMV-GKVK isolate showed that LYMV-GKVK clustered with isolates of HgYMV Horsegram and French bean isolates of Tamil Nadu, Srilanka, Karnataka. Based on Nucleotide Identity begomovirus infecting lima bean at Bangalore is to be considered as strain of HgYMV. The disease was also successfully transmitted to French bean and Horsegram when experimentally transmitted using whitefly vector. Therefore, the begomovirus causing yellow mosaic disease of lima bean is considered as strain of HgYMV. Lima bean is infected by Mungbean Yellow Mosaic India Virus (MYMIV) according to earlier reports whereas our study the reports the infection of HgYMV on Lima bean from Karnataka. Thus it is concluded that Lima bean is infected by both MYMIV and HgYMV in different geographical locations.

Characterisation of full genome ofDolichos yellow mosaic virusbased on sequence comparison, genetic recombination and phylogenetic relationship

Yellow mosaic disease (YMD) is one of the most important diseases affecting different leguminous crops and causes significant yield losses in Indian sub-continent. Eight different bipartite begomovirus species are known to cause YMD in more than 10 leguminous crops. These species are collectively known as legume yellow mosaic viruses (LYMVs), and their full genomes have been characterised except for Dolichos yellow mosaic virus (DoYMV). In this study, full genome of DoYMV isolate (KJ481204 and KJ481205) infecting dolichos has been characterised. The DNA-A of DoYMV consists of 2761 nucleotides and DNA-B of 2733 nucleotides with a genome organisation typical of Old World bipartite begomoviruses. Nucleotide identity of DNA-B (KJ481205) of DoYMV with DNA-B of other legumoviruses was 57.5–61.0%. Both components contain a nonanucleotide and conserved inverted repeat sequences with the potential to form a stem-loop. Nucleotide identity of common region of DoYMV was 90.3%, above the threshold nucleotide identity (>85%) for considering a DNA-B molecule as cognate of DNA-A of a begomovirus. Four recombination events in DNA-A and two in DNA-B of DoYMV isolate were detected. Mungbean yellow mosaic virus, Rhynchosia yellow mosaic virus and Horsegram yellow mosaic virus were identified as probable parents.

Velvet bean severe mosaic virus: a distinct begomovirus species causing severe mosaic in Mucuna pruriens (L.) DC

Velvet bean [Mucuna pruriens (L.) DC] is one of the most important medicinal plants. It is used to treat many ailments, but is widely used for the treatment especially for Parkinson's disease because of the presence of 3,4-dihydroxyphenylalanine (L-dopa) in it. It was noticed in last 5 years that the plants in the field showed severe mosaic, downward curling of the leaves, stunting, etc. This is consistently observed over the years in India. The disease was transmitted by whiteflies and by grafting and the causal agent was found to be a bipartite begomovirus. The whole genome was amplified by rolling circle amplification (RCA) using ϕ-29 DNA polymerase and characterized. DNA-A and DNA-B shared a 124-nucleotide (nt) long highly conserved (98%) common region (CR). Comparisons with other begomovirus showed that DNA-A sequence has highest identity (76%) with an isolate of Mungbean yellow mosaic India virus (MYMIV; AY937195) reported from India. This data suggested that the present isolate is a new species of genus Begomovirus for which the name "Velvet bean severe mosaic virus" (VbSMV) is proposed. DNA-B has a maximum sequence identity of 49% with an isolate of Horsegram yellow mosaic virus (HgYMV; AM932426) reported from India. Infectious clones consisting of a 1.7 mer partial tandem repeat of DNA-A and a dimer of DNB-B were constructed and agro-inoculated to Macuna pruriens (L.) DC plants, which showed field observed symptoms 24 days post-infiltration (dpi). In phylogenetic analysis, DNA-A and DNA-B of the present isolate grouped with DNA-A of different begomoviruses reported from fabaceous crops. The study presents first ever molecular evidence of any disease in velvet bean and whole genome analysis of the causative virus which is a distinct bipartite species of Begomovirus.

First report of Horsegram yellow mosaic virus infecting Phaseolus vulgaris in Sri Lanka

Bean ( Phaseolus vulgaris ) is one of the most important vegetables in Sri Lanka. In 1999, a new bean disease was reported from the town of Balangoda, Sri Lanka. Symptoms included a bright yellow mosaic pattern on the leaves, rugosity,…

Characterization of a begomovirus causing horsegram yellow mosaic disease in India

The virus causing horsegram (Macrotyloma uniflorum) yellow mosaic disease has been shown to be a typical Old World bipartite begomovirus. The viral origin of the disease has been established through agroinoculation of horsegram using partial tandem repeat clones of both DNA-A and DNA-B. The DNA-A genome shows less than 89% identity with the corresponding sequences of all the begomoviruses in the databases earlier to this sequence submission (AJ627904). Therefore Horsegram yellow mosaic virus (HgYMV-[IN:Coi]) can be considered to be a new species of the genus Begomovirus (family Geminiviridae). Phylogenetic analysis shows that this virus is part of the cluster of mungbean yellow mosaic viruses of legumes from South and South East Asia.

Legume yellow mosaic viruses: genetically isolated begomoviruses

The yellow mosaic diseases of a number of legumes across Southern Asia are caused by four species of whitefly-transmitted geminiviruses (genus Begomovirus, family Geminiviridae): Mungbean yellow mosaic virus, Mungbean yellow mosaic India virus, Dolichos yellow mosaic virus and Horsegram yellow mosaic virus. They cause losses to a number of important pulse crops, a major source of dietary protein in the region. The viruses have host ranges limited to plants of the family Fabaceae and efforts to limit losses are hampered by limited availability of conventional resistance sources and/or the lack of durability of the resistance that has been identified. There is ample evidence for genetic interaction between these begomoviruses within the legumes, in the form of both classical recombination and component exchange, but little evidence for interaction with viruses that infect other plants. This is indicative of genetic isolation, the viruses in legumes evolving independently of the begomoviruses in plant species of other families. This has implications for the development of engineered resistance in legumes, which holds the promise of durability but has yet to be transferred to the field. The viruses causing yellow mosaic diseases of legumes across southern Asia, four of which have been identified so far, are bipartite begomoviruses (genus Begomovirus, family Geminiviridae): Mungbean yellow mosaic virus, Mungbean yellow mosaic India virus, Horsegram yellow mosaic virus and Dolichos yellow mosaic virus. Physical properties: The legume yellow mosaic viruses (LYMVs), like all members of the Geminiviridae, have geminate (twinned) particles, 18-20 nm in diameter, 30 nm long, apparently consisting of two incomplete T = 1 icosahedra joined together in a structure with 22 pentameric capsomers and 110 identical protein subunits. Symptoms caused by LYMVs are largely dependent on host species and susceptibility. Initially symptoms appear as small yellow specks along the veins and then spread over the leaf. In severe infections the entire leaf may become chlorotic. In blackgram the chlorotic areas sometimes turn necrotic. Infections of French bean usually do not produce a mosaic but instead induce a downward leaf curling. Control is based mainly on preventing the establishment of the whitefly vector, Bemisia tabaci, in the crop by application of insecticides. Changes in agricultural practices, such as moving the cropping period out of periods of high vector incidence (the wet period in late summer) to times of low vector incidence (dry season in early summer) have met with some, albeit short-term, benefits. The use of natural, host plant resistance is efficacious, although the available sources of resistance in most legume crops are limited. In mungbean the resistance is attributed to two recessive genes which are used effectively to control the disease. http://www.danforthcentre.org/iltab/geminiviridae/, http://www.iwglvv.org/

Comparative epitope profiles of the particle proteins of whitefly‐transmitted geminiviruses from nine crop legumes in India

SummaryGeminiviruses associated with yellow or golden mosaic diseases of legume crops in two regions of India were compared by testing their reactivity with 27 monoclonal antibodies (MAbs) prepared to the particles of African cassava mosaic (ACMV) or Indian cassava mosaic (ICMV) viruses. The viruses fell into two main groups. Group 1 comprised isolates of dolichos yellow mosaic virus; these reacted with three or four ACMV MAbs and four ICMV MAbs. Group 2 comprised isolates of horsegram yellow mosaic virus, together with isolates from blackgram, cowpea, French bean, pigeonpea, soybean, Indigofera hirsuta and probably also isolates from mungbean. These reacted with three or four ACMV MAbs but with few or no ICMV MAbs. Isolates within each group differed slightly in epitope profile, depending on the source species (Group 2) or geographical origin (Groups 1 and 2). Isolates from lima bean resembled those in Group 2 but had some antigenic differences, and their status is uncertain. The poor detectability of geminivirus isolates in mungbean may reflect a low virus concentration in this species.

Recognition and differentiation of seven whitefly‐transmitted geminiviruses from India, and their relationships to African cassava mosaic and Thailand mung bean yellow mosaic viruses

SUMMARYParticles resembling those of geminiviruses were found by immunosorbent electron microscopy in extracts of plants infected in India with bhendi yellow vein mosaic, croton yellow vein mosaic, dolichos yellow mosaic, horsegram yellow mosaic, Indian cassava mosaic and tomato leaf curl viruses. All these viruses were transmitted by Bemisia tabaci whiteflies, all reacted with at least one out of ten monoclonal antibodies to African cassava mosaic virus (ACMV), and all reacted with a probe for ACMV DNA‐1, but scarcely or not at all with a full‐length probe for ACMV DNA‐2. Most of the viruses were distinguished by their host ranges when transmitted by whiteflies, and the rest could be distinguished by their pattern of reactions with the panel of monoclonal antibodies. Horsegram yellow mosaic virus was distinguished from Thailand mung bean yellow mosaic virus by its lack of sap transmissibility, ability to infect Arachis hypogaea, failure to react strongly with the probe for ACMV DNA‐2 and its pattern of reactions with the monoclonal antibodies.Structures resembling a ‘string of pearls’, but not geminate particles, were found in leaf extracts containing malvastrum yellow vein mosaic virus. Such extracts reacted with two of the monoclonal antibodies, suggesting that this whitefly‐transmitted virus too is a geminivirus. All seven viruses from India can therefore be considered whitefly‐transmitted geminiviruses.

Isolation and Characterization of a Geminivirus Causing Yellow Mosaic Disease of Horsegram (Macrotyloma uniflorum [Lam.] Verdc.) in India*

AbstractHorsegram yellow mosaic disease was shown to be caused by a geminivirus; horsegram yellow mosaic virus (HYMV). The virus could not be transmitted by mechanical sap inoculation. Leaf dip and purified virus preparations showed geminate virus particles, measuring 15‐18 * 30 nm. An antiserum for HYMV was produced and in enzyme‐linked immunosorbent assay (ELISA) and immunosorbent electron microscopy (ISEM) tests HYMV was detected in leaf extracts of fieldinfected bambara groundnut, french bean, groundnut, limabean, mungbean, pigeonpea and soybean showing yellow mosaic symptoms. Bemisia tabaci fed on purified HYMV through a parafilm membrane transmitted the virus to all the hosts listed above but not to Ageratum conyzoides, okra, cassava, cowpea, Croton bonplandianus, Lab‐lab purpureus, Malvastrum coromandalianum and tomato. No reaction was obtained in ELISA and ISEM tests between HYMV antibodies and extracts of plants diseased by whitefly‐transmitted agents in India such as A. conyzoides yellow mosaic, okra yellow vein mosaic, C. bonplandianus, yellow vein mosaic, M. coromandalianum yellow vein mosaic, tomato leaf curl and cassava mosaic. HYMV was also not found to be related serologically to bean golden mosaic, virus.