Abstract Diagnostics has played an important role in our understanding of the evolution of viruse... more Abstract Diagnostics has played an important role in our understanding of the evolution of viruses and the emergence of viral diseases. We have come a long way from the era of filterable viruses to viromes. This chapter briefly traces the development of techniques and their application in the diagnosis of plant virus diseases. Since the demonstration of the utility of serology in plant virus diagnosis in the late 1920s, serodiagnosis has been extensively used for research, field diagnosis, seed and planting material certification programs, and plant quarantine. Introduction of the highly sensitive enzyme-linked immunosorbent assay (ELISA) in the late 1970s gave a big push to serodiagnosis of plant virus diseases. The ability of synthetically produced affirmer proteins to specifically react with homologous antigen in ELISA-based tests is going to further strengthen serodiagnostic systems in the coming years. Serology and electron microscopy remained the key diagnostic systems until the development of nucleodiagnosis in the mid-1980s. In recent years, multiplex polymerase chain reaction has emerged as the most preferred diagnostic system. Microarray and next-generation sequencing are the ultimate nucleodiagnostic systems to detect known and discover unknown viral infections, as well as generating information on viral sequences derived from metagenomics sequence data.
Fungicidal spray schedule was worked out based on the occurrence of key weather factors. Two spra... more Fungicidal spray schedule was worked out based on the occurrence of key weather factors. Two sprays with wettable sulphur WP @ 0.2%, dinocap EC @ 0.05%, carbendazim WP @ 0.1%, tridemorph EC @ 0.1% or thiophanate-methyl WP @ 0.1% at 15 days interval, after the occurrence of high humidity and low temperature for 4–5 days in disease prone areas could combat the disease very effectively. Cost-benefit ratio was higher in sulphur treatment followed by carbendazim.
Sponge gourd (Luffa cylindrica), an important cucurbitaceous vegetable in India, is affected by a... more Sponge gourd (Luffa cylindrica), an important cucurbitaceous vegetable in India, is affected by a disease (2) causing yellow spots on newly emerged leaves, mosaic, mild leaf curling and distortion, small leaves, and misshapen fruits. Nearly 100% of sponge gourd plants were symptomatic in Delhi. Geminivirus-like particles were observed with electron microscopy of uranyl acetate-stained leaf-dip preparations of the diseased plants collected from experimental fields at the Indian Agricultural Research Institute in New Delhi during May and June of 2002. The virus was transmitted by the whitefly (Bemisia tabaci) to sponge and ridge gourd (L. acutangula) after an acquisition and inoculation access period of 24 h each. Whitefly-inoculated plants produced typical yellow mosaic symptoms and contained geminate particles. Nucleic acid extracted from the field-infected and experimentally infected plants hybridized with 32P-labeled probe to DNA-A of Indian cassava mosaic virus, suggesting associ...
The complete nucleotide sequence of the blackgram isolate of mungbean yellow mosaic virus, IMYMV-... more The complete nucleotide sequence of the blackgram isolate of mungbean yellow mosaic virus, IMYMV-Bg, which infects legumes in India, was determined and compared at the amino acid level with those of other whitefly-transmitted geminiviruses. The genome organization of IMYMV-Bg was similar to that of the begomoviruses. A unique feature of the genome organization was the sequence divergence of the common region (CR) between DNA-A and DNA-B. In order to understand the mechanism of viral DNA replication, the replication initiator protein, Rep, of IMYMV-Bg was overexpressed in E. coli. The recombinant and refolded Rep bound to CR-sequences of IMYMV-Bg in a specific manner. In this study, evidence is presented for ATP-upregulated cleavage function and ATP-mediated conformational change of Rep. It is hypothesized that, although ATP is not required for cleavage, ATP-mediated conformational changes may result in better access of Rep to the DNA-cleavage site. Evidence is also presented for a s...
Geminiviruses cause devastating plant diseases, particularly in the tropics and semi-tropics. Som... more Geminiviruses cause devastating plant diseases, particularly in the tropics and semi-tropics. Some of these diseases have been adversely affecting crop production since the early 20th Century, but the present century faces severe disease epidemics caused by newly emerging and reemerging whitefly (Bemisia tabaci) transmitted geminiviruses (WTGs), which affect crops like cassava, cotton, cucurbits, grain, legumes, and tomato. The growers of these crops in various parts of the world suffer severe economic losses due to WTG infections.1 Despite management practices, menacing disease epidemics caused by WTGs are becoming frequent and are occurring even in new regions that were previously free from such diseases. The frequency with which WTGs are appearing shows that these viruses are still evolving. In recent years, some WTGs have also moved to temperate agriculture, causing concern in the production of vegetables in greenhouses. Geminiviruses have unique twin particle morphology, and th...
The effect of okra mosaic virus (OMV) on growth and yield of okra plants varied with the time of ... more The effect of okra mosaic virus (OMV) on growth and yield of okra plants varied with the time of inoculation with OMV during the early rains. Inoculation of plants with OMV 14 and 21 days after emergence (DAE) significantly reduced the average weight of fruits per plant compared with those inoculated 28 DAE and the uninoculated control. Since number of fruits was significantly positively correlated with weight of fruits in all treatments, a similar pattern was also noted for number of fruits per plant. There were no significant differences in heights of plants inoculated 14 and 21 DAE, although these both differed significantly from plants inoculated 28 DAE. The latter was not significantly different from the uninoculated control. The relevance of these findings to the control of OMV in rain-fed okra plantings is discussed.
The causal virus of yellow mosaic of pigeon pea (Cajanus cajan) was found to be an extended host ... more The causal virus of yellow mosaic of pigeon pea (Cajanus cajan) was found to be an extended host range phenotype of mungbean yellow mosaic geminivirus (MYMV). The pigeonpea isolate (MYMV-Pp) could be transmitted by whitefly (Bemisia tabaci) to mungbean (Vigna radiata), blackgram (Vigna mungo), Frenchbean (Phaseolus vulgaris), soybean (Glycine max), Iimabean (Phaseolus lunatus), horsegram (Macrotyloma unijlorum) and cowpea (Vigna unguiculata). Double stranded DNA forms (open circular, linear and supercoiled) from infected plants were purified and cloned in to pUC18 and pBluescript SK+ vectors; four full length clones were obtained. All the four clones obtained were found to be D A-B on the basis of hybridization with MYMV-Bg DNA-B. Restriction analysis of clone pMY-PB3 revealed that it had a pattern similar to that of MYMV-Bg (blackgram isolate) D A-B, suggesting that MYMV-Bg and MYMV-Ppl are closely related. D A-B of MYMV-Ppl, however, differed considerably in its restriction maps f...
Plant viruses are not only serious pests but also valuable genetic resource. They are a rich sour... more Plant viruses are not only serious pests but also valuable genetic resource. They are a rich source of promoters for the expression of genes in plants. The 35S promoter of cauliflower mosaic virus has become an integral part of plant transformation system. Easy transmissibility, wide host range, ability to cause systemic infection and multiply in large numbers are ideal characteristics for their use as vector for transient expression of foreign genes in plants. This property has shown great promise for molecular 'pharming' of pharmaceuticals and development of oral vaccines against dreaded human and animal diseases. Plant viruses are also an important source of genes for developing transgenic plants resistant to viruses. As more knowledge about viral genes and their functions is generated, plant viruses will become even a greater asset and genetic resource.
Sixteen potyvirus isolates from sugarcane, maize, sorghum and jowar plants showing typical mosaic... more Sixteen potyvirus isolates from sugarcane, maize, sorghum and jowar plants showing typical mosaic symptoms under natural field conditions in different locations of India were compared for biological and serological properties. Results based on different hosts reaction and serological assays (DAC-ELISA, ISEM and Western blotting tests) indicated that potyvirus isolates belonged to two distinct species, viz., sugarcane mosaic virus (SCMV) and maize dwarf mosaic virus (MDMV). SCMV was recorded on sugarcane, maize, sorghum and jowar, and MDMV was only on maize and sorghum.
Abstract Diagnostics has played an important role in our understanding of the evolution of viruse... more Abstract Diagnostics has played an important role in our understanding of the evolution of viruses and the emergence of viral diseases. We have come a long way from the era of filterable viruses to viromes. This chapter briefly traces the development of techniques and their application in the diagnosis of plant virus diseases. Since the demonstration of the utility of serology in plant virus diagnosis in the late 1920s, serodiagnosis has been extensively used for research, field diagnosis, seed and planting material certification programs, and plant quarantine. Introduction of the highly sensitive enzyme-linked immunosorbent assay (ELISA) in the late 1970s gave a big push to serodiagnosis of plant virus diseases. The ability of synthetically produced affirmer proteins to specifically react with homologous antigen in ELISA-based tests is going to further strengthen serodiagnostic systems in the coming years. Serology and electron microscopy remained the key diagnostic systems until the development of nucleodiagnosis in the mid-1980s. In recent years, multiplex polymerase chain reaction has emerged as the most preferred diagnostic system. Microarray and next-generation sequencing are the ultimate nucleodiagnostic systems to detect known and discover unknown viral infections, as well as generating information on viral sequences derived from metagenomics sequence data.
Fungicidal spray schedule was worked out based on the occurrence of key weather factors. Two spra... more Fungicidal spray schedule was worked out based on the occurrence of key weather factors. Two sprays with wettable sulphur WP @ 0.2%, dinocap EC @ 0.05%, carbendazim WP @ 0.1%, tridemorph EC @ 0.1% or thiophanate-methyl WP @ 0.1% at 15 days interval, after the occurrence of high humidity and low temperature for 4–5 days in disease prone areas could combat the disease very effectively. Cost-benefit ratio was higher in sulphur treatment followed by carbendazim.
Sponge gourd (Luffa cylindrica), an important cucurbitaceous vegetable in India, is affected by a... more Sponge gourd (Luffa cylindrica), an important cucurbitaceous vegetable in India, is affected by a disease (2) causing yellow spots on newly emerged leaves, mosaic, mild leaf curling and distortion, small leaves, and misshapen fruits. Nearly 100% of sponge gourd plants were symptomatic in Delhi. Geminivirus-like particles were observed with electron microscopy of uranyl acetate-stained leaf-dip preparations of the diseased plants collected from experimental fields at the Indian Agricultural Research Institute in New Delhi during May and June of 2002. The virus was transmitted by the whitefly (Bemisia tabaci) to sponge and ridge gourd (L. acutangula) after an acquisition and inoculation access period of 24 h each. Whitefly-inoculated plants produced typical yellow mosaic symptoms and contained geminate particles. Nucleic acid extracted from the field-infected and experimentally infected plants hybridized with 32P-labeled probe to DNA-A of Indian cassava mosaic virus, suggesting associ...
The complete nucleotide sequence of the blackgram isolate of mungbean yellow mosaic virus, IMYMV-... more The complete nucleotide sequence of the blackgram isolate of mungbean yellow mosaic virus, IMYMV-Bg, which infects legumes in India, was determined and compared at the amino acid level with those of other whitefly-transmitted geminiviruses. The genome organization of IMYMV-Bg was similar to that of the begomoviruses. A unique feature of the genome organization was the sequence divergence of the common region (CR) between DNA-A and DNA-B. In order to understand the mechanism of viral DNA replication, the replication initiator protein, Rep, of IMYMV-Bg was overexpressed in E. coli. The recombinant and refolded Rep bound to CR-sequences of IMYMV-Bg in a specific manner. In this study, evidence is presented for ATP-upregulated cleavage function and ATP-mediated conformational change of Rep. It is hypothesized that, although ATP is not required for cleavage, ATP-mediated conformational changes may result in better access of Rep to the DNA-cleavage site. Evidence is also presented for a s...
Geminiviruses cause devastating plant diseases, particularly in the tropics and semi-tropics. Som... more Geminiviruses cause devastating plant diseases, particularly in the tropics and semi-tropics. Some of these diseases have been adversely affecting crop production since the early 20th Century, but the present century faces severe disease epidemics caused by newly emerging and reemerging whitefly (Bemisia tabaci) transmitted geminiviruses (WTGs), which affect crops like cassava, cotton, cucurbits, grain, legumes, and tomato. The growers of these crops in various parts of the world suffer severe economic losses due to WTG infections.1 Despite management practices, menacing disease epidemics caused by WTGs are becoming frequent and are occurring even in new regions that were previously free from such diseases. The frequency with which WTGs are appearing shows that these viruses are still evolving. In recent years, some WTGs have also moved to temperate agriculture, causing concern in the production of vegetables in greenhouses. Geminiviruses have unique twin particle morphology, and th...
The effect of okra mosaic virus (OMV) on growth and yield of okra plants varied with the time of ... more The effect of okra mosaic virus (OMV) on growth and yield of okra plants varied with the time of inoculation with OMV during the early rains. Inoculation of plants with OMV 14 and 21 days after emergence (DAE) significantly reduced the average weight of fruits per plant compared with those inoculated 28 DAE and the uninoculated control. Since number of fruits was significantly positively correlated with weight of fruits in all treatments, a similar pattern was also noted for number of fruits per plant. There were no significant differences in heights of plants inoculated 14 and 21 DAE, although these both differed significantly from plants inoculated 28 DAE. The latter was not significantly different from the uninoculated control. The relevance of these findings to the control of OMV in rain-fed okra plantings is discussed.
The causal virus of yellow mosaic of pigeon pea (Cajanus cajan) was found to be an extended host ... more The causal virus of yellow mosaic of pigeon pea (Cajanus cajan) was found to be an extended host range phenotype of mungbean yellow mosaic geminivirus (MYMV). The pigeonpea isolate (MYMV-Pp) could be transmitted by whitefly (Bemisia tabaci) to mungbean (Vigna radiata), blackgram (Vigna mungo), Frenchbean (Phaseolus vulgaris), soybean (Glycine max), Iimabean (Phaseolus lunatus), horsegram (Macrotyloma unijlorum) and cowpea (Vigna unguiculata). Double stranded DNA forms (open circular, linear and supercoiled) from infected plants were purified and cloned in to pUC18 and pBluescript SK+ vectors; four full length clones were obtained. All the four clones obtained were found to be D A-B on the basis of hybridization with MYMV-Bg DNA-B. Restriction analysis of clone pMY-PB3 revealed that it had a pattern similar to that of MYMV-Bg (blackgram isolate) D A-B, suggesting that MYMV-Bg and MYMV-Ppl are closely related. D A-B of MYMV-Ppl, however, differed considerably in its restriction maps f...
Plant viruses are not only serious pests but also valuable genetic resource. They are a rich sour... more Plant viruses are not only serious pests but also valuable genetic resource. They are a rich source of promoters for the expression of genes in plants. The 35S promoter of cauliflower mosaic virus has become an integral part of plant transformation system. Easy transmissibility, wide host range, ability to cause systemic infection and multiply in large numbers are ideal characteristics for their use as vector for transient expression of foreign genes in plants. This property has shown great promise for molecular 'pharming' of pharmaceuticals and development of oral vaccines against dreaded human and animal diseases. Plant viruses are also an important source of genes for developing transgenic plants resistant to viruses. As more knowledge about viral genes and their functions is generated, plant viruses will become even a greater asset and genetic resource.
Sixteen potyvirus isolates from sugarcane, maize, sorghum and jowar plants showing typical mosaic... more Sixteen potyvirus isolates from sugarcane, maize, sorghum and jowar plants showing typical mosaic symptoms under natural field conditions in different locations of India were compared for biological and serological properties. Results based on different hosts reaction and serological assays (DAC-ELISA, ISEM and Western blotting tests) indicated that potyvirus isolates belonged to two distinct species, viz., sugarcane mosaic virus (SCMV) and maize dwarf mosaic virus (MDMV). SCMV was recorded on sugarcane, maize, sorghum and jowar, and MDMV was only on maize and sorghum.
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