Coat protein-mediated resistance against an Indian isolate of the Cucumber mosaic virus subgroup IB in Nicotiana benthamiana

Coat protein (CP) -mediated resistance against an Indian isolate of the Cucumber mosaic virus (CMV) subgroup IB was demonstrated in transgenic lines of Nicotiana benthamiana through Agrobacterium tumefaciens-mediated transformation. Out of the fourteen independently transformed lines developed, two lines were tested for resistance against CMV by challenge inoculations. The transgenic lines exhibiting complete resistance remained symptomless throughout life and showed reduced or no virus accumulation in their systemic leaves after virus challenge. These lines also showed virus resistance against two closely related strains of CMV. This is the first report of CP-mediated transgenic resistance against a CMV subgroup IB member isolated from India.     

Alarming increase in the incidence of Cucumber mosaic virus in cowpea (Vigna unguiculata (L.) Walp.) in northern Nigeria

Cowpea plays a key nutritional role in the diet of the Nigerian people. Viral diseases are a major limitation to cowpea production worldwide, and thus, constant viral surveillance is crucial for monitoring and management purposes. In this study, cowpea leaf samples from fields in three northern Nigeria states, Kano, Kaduna and Niger, were tested to determine the status of six common viruses previously reported in these cowpea-producing states following the release of virus-resistant varieties. Cowpea aphid-borne mosaic virus (CABMV), Blackeye cowpea mosaic virus (BICMV), Cowpea mottle virus, Southern bean mosaic virus and Cucumber mosaic virus (CMV) were detected. Cowpea yellow mosaic virus, which was previously reported in all three states, was not detected in any of the samples tested, while CMV that was previously regarded as unimportant to cowpea production in Nigeria had the highest incidence in all three states, and the overall highest incidence of 58.8%, while CABMV had the lowest incidence (7.5%). CMV was also present in seven of the ten mixed infection combinations detected. Dual infection of CMV and BICMV, which often results in cowpea stunt, the most devastating cowpea disease in the USA, was the most frequently detected mixed infection (28.1%) and was detected in all three states. This observed elevation in CMV infection in cowpea must be closely monitored and swiftly managed to avert possible devastating crop yield losses.     

Analysis of the coat protein gene and untranslated region of RNA3 of Cucumber Mosaic Virus isolates infecting various Lilium species and hybrids: association of the isolate infecting asiatic hybrid lily with subgroup II

The variability in the coat protein gene of Cucumber mosaic virus (CMV) isolates from various Lilium species and hybrids namely L. longiflorum, L. tigrinum, Asiatic hybrid and Oriental hybrid lilies was studied by sequence comparison of ～900 bp regions spanning the entire coat protein, intercistronic regions and 3′-UTR. CMV isolate characterised from Asiatic hybrid lily showed the highest homology with subgroup II isolates (94 – 97%), whereas 73 – 76% homology was observed with those belonging to subgroup I. Similarly, another three isolates showed 91 – 98% amino acid sequence homology with subgroup I and 74 – 76% sequence homology with subgroup II. Based on the criteria for classification of CMV isolates all the Indian isolates fall in subgroup I, except the one characterized from Asiatic Hybrid lily which falls into subgroup II. Other lily isolates from world were placed in subgroup II. This is the first case of Asiatic hybrid lily CMV isolate belonging to subgroup II.     

Genetic variability of tobacco streak virus in South India based on the analysis of coat protein gene

Tobacco streak virus (TSV), a member of the genus Ilarvirus, family Bromoviridae is an important viral pathogen in peanut and other crops in South India. Fifteen TSV isolates naturally infecting groundnut, sunflower, onion, black gram, green gram, jute, tagetes, calotropis, pumpkin, watermelon and kenaf plants were collected from fields in different regions of Andhra Pradesh, Tamil Nadu and Karnataka. Virus was identified as TSV by direct antigen coating enzyme linked immunosorbent assay using TSV antiserum. The CP gene from each isolate was amplified using TSV coat protein specific primers. About 700 bp product was amplified, cloned, sequenced and determined its length as 717 nucleotides and codes for 239 amino acids. The sequence analysis revealed that the CP gene shared 91–100% and 91–99% sequence identity with TSV at nucleotide and amino acid level, respectively. The phylogenetic relationship based on the nucleotide sequence of these isolates from different geographical regions was also analysed in this study.     

Expression of coat protein gene of Cucumber mosaic virus (CMV-subgroup IA) Gladiolus isolate in Nicotiana tabacum

The coat protein (CP)-mediated resistance against Cucumber mosaic virus (CMV) subgroup IA was developed in transgenic lines of Nicotiana tabacum cv. Petit Havana using Agrobacterium tumefaciens-mediated transformation. Ten independently transformed lines have developed, four of which were tested for resistance against CMV using virus challenge inoculations. The transgenic lines exhibiting complete resistance remained healthy and symptomless in their life span and showed reduced or no virus accumulation in their systemic leaves after virus challenge inoculation. These transgenic lines also showed resistance against CMV strains which are not closely related to CMV-Gladiolus strains. This is the first report of CP-mediated transgenic resistance against a CMV subgroup IA member isolated from India showing resistance to all CMV strains occurring in the same vicinity.     

Characterization of cymbidium mosaic virus coat protein gene and its expression in transgenic tobacco plants

Cymbidium mosaic virus (CyMV) is the most prevalent virus infecting orchids. Here, we report the isolation of partial cDNA clones encoding the genomic RNA of CyMV. Like most of the polyadenylated monopartite positive-strand RNA viruses, the open reading frame (ORF) coding for the viral coat protein (CP) is located at the 3 end. The ORF predicts a polypeptide chain of 220 amino acids with a molecular weight of 23 600. Sequence comparison of this ORF to the CP sequences of potato virus X(PVX) and white clover mosaic virus (WCIMV) revealed a strong amino acid homology in the mid-portion of the CP, but the overall homology was low. The CyMV CP gene was placed downstream of a cauliflower mosaic virus 35S promoter and the chimaeric gene was transferred into Nicotiana benthamiana. Transgenic plants expressing the CyMV CP were protected against CyMV infection.     

Coat protein–mediated resistance to cucumber mosaic virus subgroup IB in black pepper (Piper nigrum L.)

In Vitro Cellular & Developmental Biology - Plant - Cucumber mosaic virus (CMV) infects a large number of plant species including Piper nigrum L. and related species. As natural resistance to...     

Satellite-RNA-mediated resistance to cucumber mosaic virus in transgenic plants of hot pepper (Capsicum annuum cv. Golden Tower)

We previously established a system of in vitro regeneration and Agrobacterium-mediated transformation for hot pepper plants. The level of protection against cucumber mosaic virus in the progeny of the transgenic hot pepper plants that express cucumber mosaic virus (CMV) satellite RNA was investigated. The transgenic hot pepper plants were self-fertilized, and their progeny were tested for stable inheritance and expression of the cDNA of CMV satellite RNA. Polymerase chain reaction and RNA gel blot analyses showed that the introduced gene was stably transmitted and expressed in the progeny. Symptom attenuation in the offspring was confirmed upon inoculation with CMV-Y or CMV-Korea (CMV-Kor) strains. Received: 30 September 1996 / Revision received: 5 May 1997 / Accepted: 22 May 1997     

Spectrum of resistance to root-knot nematodes and inheritance of heat-stable resistance in in pepper (Capsicum annuum L.)

Capsicum annuum L. has resistance to root-knot nematodes (RKN) (Meloidogyne spp.), severe polyphagous pests that occur world-wide. Several single dominant genes confer this resistance. Some are highly specific, whereas others are effective against a wide range of species. The spectrum of resistance to eight clonal RKN populations of the major Meloidogyne species, M. arenaria (2 populations), M. incognita (2 populations), M. javanica (1 population), and M. hapla (3 populations) was studied using eight lines of Capsicum annuum. Host susceptibility was determined by counting the egg masses (EM) on the roots. Plants were classified into resistant (R; EM ≤ 5) or susceptible (H; EM >5) classes. The french cultivar Doux Long des Landes was susceptible to all nematodes tested. The other seven pepper lines were highly resistant to M. arenaria, M. javanica and one population of M. hapla. Variability in resistance was observed for the other two populations of M. hapla. Only lines PM687, PM217, Criollo de Morelos 334 and Yolo NR were resistant to M. incognita. To investigate the genetic basis of resistance in the highly resistant line PM687, the resistance of two progenies was tested with the two populations of M. incognita: 118 doubled-haploid (DH) lines obtained by androgenesis from F₁ hybrids of the cross between PM687 and the susceptible cultivar Yolo Wonder, and 163 F₂ progenies. For both nematodes populations, the segregation patterns 69 R / 49 S for DH lines and 163 R / 45 S for F₂ progenies were obtained at 22°C and at high temperatures (32°C and 42°C). The presence of a single dominant gene that totally prevented multiplication of M. incognita was thus confirmed and its stability at high temperature was demonstrated. This study confirmed the value of C. annuum as a source of complete spectrum resistance to the major RKN. Received: 2 July 1998 / Accepted: 11 March 1999     

Four sequence positions of the movement protein of Cucumber mosaic virus determine the virulence against cmv1‐mediated resistance in melon

The resistance to a set of strains of Cucumber mosaic virus (CMV) in the melon accession PI 161375, cultivar ‘Songwhan Charmi’, is dependent on one recessive gene, cmv1, which confers total resistance, whereas a second set of strains is able to overcome it. We tested 11 strains of CMV subgroups I and II in the melon line SC12‐1‐99, which carries the gene cmv1, and showed that this gene confers resistance to strains of subgroup II only and that restriction is not related to either viral replication or cell‐to‐cell movement. This is the first time that a resistant trait has been correlated with CMV subgroups. Using infectious clones of the CMV strains LS (subgroup II) and FNY (subgroup I), we generated rearrangements and viral chimaeras between both strains and established that the determinant of virulence against the gene cmv1 resides in the first 209 amino acids of the movement protein, as this region from FNY is sufficient to confer virulence to the LS clone in the line SC12‐1‐99. A comparison of the sequences of the strains of both subgroups in this region shows that there are five main positions shared by all strains of subgroup II, which are different from those of subgroup I. Site‐directed mutagenesis of the CMV‐LS clone to substitute these residues for those of CMV‐FNY revealed that a combination of four of these changes [the group 64–68 (SNNLL to HGRIA), and the point mutations R81C, G171T and A195I] was required for a complete gain of function of the LS MP in the resistant melon plant.     

Combining a host gene and a tobacco vein mottling virus coat protein gene for broad and effective resistance to potyviruses in tobacco (Nicotiana tabacum L.)

Over 100 transgenic tobacco lines in five genetic backgrounds were transformed with the tobacco vein mottling virus (TVMV) coat protein (CP) gene. Transgenic lines were initially tested for their reaction to inoculation with a TVMV systemic strain (TVMV-S) and a potato virus Y common strain (PVY-O). Of the 104 TVMV CP lines 60% were classified as resistant to PVY-O, whereas only 30% of these same lines were resistant to TVMV-S. A subset of six PVY-O-resistant transgenic lines and four control lines were tested for their reaction to a local isolate of TVMV, tobacco etch virus (TEV) and five isolates of PVY. The same ten lines were also tested for responses to a serial dilution of inoculum for two PVY isolates, PVY-KY1 and PVY-NN. Transgenic lines carrying an endogenous resistance gene known as Virgin A mutant (VAM) had greater resistance and a broader spectrum of resistance than did transgenic lines without the VAM gene. This additive effect of the endogenous resistance gene and coat protein-mediated resistance (CPMR) was not overcome by the highest inoculum concentration. The results indicate that the additive effect of the VAM gene and CPMR could extend the effectiveness of CPMR in controlling potiviruses. These findings could have important implications for plant improvement programs using CPMR against potyvirus diseases.