Genetic analysis of resistance in Brussels sprout to cauliflower mosaic and turnip mosaic viruses

A total of 28 inbred lines of Brussels sprout were assessed in the glasshouse for their reaction to inoculation with cauliflower mosaic (CaMV) or turnip mosaic (TuMV) virus. There was significant variation for resistance to both viruses. From the 28 inbred lines parents were chosen for two 9 × 9 diallel crossing programmes. The parents and their F₁ progeny were assessed for their reaction to CaMV or TuMV in the field. There was significant additive and non-additive (dominance) variation but no maternal effects. Resistance to both viruses was generally dominant but with some evidence of a recessive gene for resistance to CaMV. Resistance to TuMV and CaMV was apparently controlled by at least four genes and two genes respectively. The heritability of resistance to each virus was high. The implications for breeding F₁ hybrid Brussels sprout cultivars are discussed.     

Resistance of transformed and non-transformed oilseed rape cv. HM-81 to the infection with cauliflower mosaic,turnip yellow mosaic and turnip mosaic viruses

Resistance of transformed and non-transformed spring oilseed rape cv. HM-81 to the infection with cauliflower mosaic virus (CaMV), turnip yellow mosaic virus (TYMV) and turnip mosaic virus (TuMV) was studied, to determine the influence of transformation on susceptibility of plants to viruses. For experiments the non-segregating R 1 generation of primary transformant HM-81-JZ and control plants of cv. HM-81 were used. The primary transformant was obtained by inoculation of stems withAgrobacterium rhizogenes 15834. All transformed plants of R 1 generation had typically „transformed“ phenotype. No significant differences were revealed in the resistance of both transformed and non-transformed plants to each virus, as proved by qualitative and quantitative ELISA and visual evaluation of symptoms. Transformed plants infected with turnip yellow mosaic virus showed significantly lower reduction of green mass yield than non-transformed. In the case of CaMV and TuMV infection reduction of yield of transformed and non-transformed plants was almost the same.     

A tobamovirus infecting capsicum in Australia

A tobamovirus infection of Capsicum annuum is recorded for the first time in New South Wales, Australia. The causal virus is described and shown to differ from tobacco (TMV) and tomato (ToMV) mosaic viruses in its host reactions and serology. Seventeen capsicum cultivars were tested for reaction to the Australian isolate and ranked according to symptom severity. Field and glasshouse observations indicated that the virus causes a decrease in height and weight of plants, fruit malformation and leaf mosaic symptoms. It is proposed that the capsicum tobamovirus strains are sufficiently distinctive from TMV and ToMV to be grouped together and designated a separate virus: capsicum mosaic virus (CaMV).     

The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus-derived genes.     

Selection for immunity in swede (Brassica napus) to infection by turnip mosaic virus

Fully heritable immunity to turnip mosaic virus (TuMV) was found in swede (Brassica napus) cvs Ruta Otofte and Bangholm. Attempts to ‘break’ this immunity were unsuccessful. The reactions of two immune lines of cv. Ruta Otofte to cauliflower mosaic virus, clubroot (Plasmodiophora brassicae) and powdery mildew (Erysiphe cruciferarum) were unchanged compared with the unselected parent line. A symptomless response to TuMV inoculation (possibly immunity) was also found in cv. Acme but not in the clubroot resistant cv. Marian. The percentage of plants which gave a symptomless response to TuMV inoculation differed greatly between cultivars and some seed stocks.     

Viruses infecting winter oilseed rape (Brassica napus ssp. oleifera)

Turnip mosaic virus (TuMV) and cauliflower mosaic virus (CaMV) have been found infecting field crops of winter oilseed rape (Brassica napus ssp. oleifera) in South Warwickshire. Other viruses found include broccoli necrotic yellows virus (BNYV) and a member of the beet western yellows virus group. Systemic leaf symptoms caused by TuMV varied within and between cultivars; the three predominant reaction types were classified as necrotic, mosaic and immune. Some recently introduced cultivars of oilseed rape were more severely affected by TuMV infection than older cultivars. Reactions to CaMV were less varied and immunity was not found. The seed yield from TuMV and CaMV-infected plants was less than that of healthy control plants. This effect was due to infected plants producing either fewer seeds, smaller seeds or both. Germination of seeds from infected plants was unaffected if sown soon after harvest. After storage for one year the germination of seed from a virus infected plant was significantly less than that of seed from a virus-free plant. All commercial cultivars tested were experimentally susceptible to turnip yellow mosaic virus (TYMV) and some American strains of cucumber mosaic virus (CMV).     

Genetic basis of resistance to sugarcane mosaic virus in European maize germplasm

 Sugarcane mosaic virus (SCMV) causes considerable damage to maize (Zea mays L.) in Europe. The objective of the present study was to determine the genetic basis of resistance to SCMV in European maize germplasm and to compare it with that of U.S. inbred Pa405. Three resistant European inbreds D21, D32, and FAP1360A were crossed with four susceptible inbreds F7, KW1292, D408, and D145 to produce four F₂ populations and three backcrosses to the susceptible parent. Screening for SCMV resistance in parental inbreds and segregating generations was done in two field trials as well as under greenhouse conditions. RFLP markers umc85, bnl6.29, umc10, umc44, and SSR marker phi075 were used in F₂ populations or F₃ lines to locate the resistance gene(s) in the maize genome. Segregation in the F₂ and backcross generations fitted to different gene models depending on the environmental conditions and the genotype of the susceptible parent. In the field tests, resistance in the three resistant European inbreds seems to be controlled by two to three genes. Under greenhouse conditions, susceptibility to SCMV in D32 appears to be governed by one dominant and one recessive gene. Allelism tests indicated the presence of a common dominant gene (denoted as Scm1) in all three resistant European inbreds and Pa405. Marker analyses mapped two dominant genes: Scm1 on chromosome 6S and Scm2 on chromosome 3. Received: 17 November 1997 / Accepted: 25 November 1997     

The incidence of viruses in wild Brassica nigra in Dorset (UK)

Using enzyme‐linked immunosorbent assays, the frequency of occurrence of six viruses was determined in Brassica nigra collected from five coastal sites in Dorset, spanning approximately 24 km. During 1998–2000, the viruses detected were: Turnip mosaic virus (genus Potyvirus) (TuMV), Turnip yellow mosaic virus (genus Tymovirus) (TYMV), Turnip crinkle virus (genus Carmovirus) (TCV), Turnip rosette virus (genus Sobemovirus) (TRoV), Beet western yellows virus (genus Polerovirus) (BWYV) and Cauliflower mosaic virus (genus Caulimovirus) (CaMV). Multiple infections were detected in some individuals (48/447). TuMV was detected infrequently over the three‐year period (5/597). A representative isolate of each virus was tested for its effects on glasshouse‐grown individuals from different half‐sib families of B. nigra from four of the sites. Whether inoculated manually or via aphids (Myzus persicae), TuMV caused a rapid (within 10 days) lethal systemic necrosis in the B. nigra seedlings except when they were near flowering at the time of inoculation. Each of the other viruses invaded systemically but were not lethal. Indeed, BWYV systemically invaded 13/19 glasshouse‐grown B. nigra seedlings but did not produce any visible symptoms. Otherwise, the isolates tested differed in their pathogenicity and in the symptoms they produced in infected B. nigra. With TYMV or TCV viral antigen concentration was closely linked to pathogenicity; for TRoV or CaMV, there was little or no difference in virus concentration between plants with and without symptoms. Substantial and reproducible differences were observed in sensitivity/susceptibility among B. nigra genotypes from different sites in Dorset challenged with the same virus isolate.     

The reactions of swede (Brassica napus) to infection by turnip mosaic virus

Turnip mosiac virus (TuMV) and cucumber mosaic virus (CMV) were the only viruses commonly isolated from naturally diseased swedes (Brassica napus) showing leaf mosaic and leaf and root necrosis. Only TuMV caused these symptoms when re-inoculated to swede. TuMV-infected plants showed a severe loss in leaf (55%) and root (63%) fresh weight after 140 days. Systemic leaf symptoms in infected swede plants varied greatly, but were predominantly necrotic (N) or mosaic (M). Plants were classified into one of seven reaction classes ranging from slight or severe necrosis, and mosaics with and without slight veinal necrosis. Swede cultivars differed markedly in their reaction to TuMV and contained different proportions of N- or M-reacting plants. The reactions of progeny of four resistant cv. Bangholm plants were separately inherited; progeny of two plants reacting either symptomlessly or necrotically and those of the other two plants developing mosaic symptoms only. Five isolates of TuMV from swede crops in different regions caused similar reactions but differed in virulence in the progeny of a self-pollinated resistant swede plant.     

Genetic control of immunity to turnip mosaic virus in winter oilseed rape (Brassica napus ssp. oleifera) and the effect of foreign isolates of the virus

Immunity to a UK isolate (UK 1) of turnip mosaic virus (TuMV) was studied in eight lines of oilseed rape selected from cv Rafal. Six of these lines were uniformly immune and two segregated. Segregation ratios in the F₂ generation of reciprocal crosses between two uniformly immune lines and two uniformly susceptible cultivars (Mikado and Yeoman) showed that immunity was controlled by a dominant nuclear allele. The immunity was confirmed by the inability to detect virus particles in mechanically inoculated plants by back inoculations, ELISA and ISEM tests. Plants were immune to repeated inoculations and aphid transmissions. The immunity was effective against one other UK isolate and two German isolates of TuMV. Another UK isolate (UK 3) and a Greek isolate partially overcame the immunity causing local infection and a Canadian and a Danish isolate overcame it completely causing systemic mosaic-type symptoms. When these immunity-breaking strains were tested against swede line 165 which is also immune to UK 1 TuMV, the Canadian isolate overcame the immunity whereas the Danish isolate did not. Using this swede line, one susceptible and one immune line of oilseed rape as differentials, four distinct groups of TuMV isolates could be identified. Selections of oilseed rape immune to UK TuMV isolates were more severely affected by the Canadian TuMV than UK TuMV susceptible selections. The gene determining immunity to TuMV had no pleiotropic effect on susceptibility to cauliflower mosaic virus. The implications on these findings in relation to breeding for virus resistance are discussed.     

Effects of turnip mosaic virus and turnip yellow mosaic virus on the survival, growth and reproduction of wild cabbage (Brassica oleracea)

Wild plants of Brassica oleracea (wild cabbage) are commonly infected with turnip mosaic poty virus (TuMV), turnip yellow mosaic tymovirus (TYMV) and several other viruses. A field experiment in which plants were inoculated either with TuMV or TYMV showed that virus infection significantly reduced survival, growth and reproduction. Relative to water inoculated-controls, plants infected with TYMV had greater mortality, were shorter, had a smaller leaf area and number, showed a greater amount of damage from herbivory and chlorosis, were less likely to flower and produced fewer pods and lower total seed output. Plants infected with TuMV did not appear to be adversely affected at first; however, mortality after 18 months was higher than control plants. Although TuMV infection had no effect on the number of plants flowering, the infected plants did produce fewer pods and a lower total seed output. We conclude that both viruses can significantly affect vegetative and reproductive performance of wild cabbage and hence that introgression of virus resistance (particularly when conferred by a major gene or a transgene) from a crop might increase plant fitness in natural populations of this species. Ecological risk assessments of virus resistance transgenes must do more than survey adult plants in natural populations for the presence of the target virus. Failure to detect the virus could be due to high mortality on infection with the virus.     

Interspecific hybrids between kenaf ( Hibiscus cannabinus ) and roselle ( H. sabdariffa )

The successful interspecific cross is reported for the first time between kenaf (Hibiscus cannabinus L.), a diploid species (2n=36) and roselle (Hibiscus sabdariffa L.), a tetraploid species (2n=72). Kenaf, grown for its bast fiber and also under investigation as a source of paper pulp, is fast-growing and well adapted to mechanical harvesting, but susceptible to root-knot nematodes. Roselle, also grown for its bast fiber, is slower growing, not well adapted to mechanical harvesting, but certain varieties are resistant to root-knot nematodes. Five hybrid plants were produced from the pollination of 4,445 flowers of kenaf with pollen from roselle; no hybrid plants were produced from 2,655 pollinations made in the reciprocal direction. One line of roselle was the parent of 3 of the 5 hybrids; one line of kenaf was the parent of 2 of these 3. The F₁ hybrids were triploid, and varied in vigor, growth habit and vegetative morphology, but had similar flowers. Two of the F₁ hybrids showed high pollen fertility, apparently as a result of restitution at first meiotic division leading to unreduced spores. These two hybrids each produced a small amount of seed, which gave rise to an F₂ population of 22 plants. The F₂ plants vary in vigor but are morphologically uniform, have thick leaves with mosaic sectors, and are presumably spontaneous allohexaploids. The theoretical possibilities of increasing the percentage of recovery of the F₁ interspecific hybrids and of developing a synthesized hybrid variety useful for bast fiber and paper pulp are discussed. Research done cooperatively by Crops Research Division and Agricultural Engineering Research Division, Agricultural Research Service, U.S. Department of Agriculture (USDA), and the University of Florida Agricultural Experiment Station. Cytological investigations were carried out at the Department of Biological Sciences, Florida State University. Thanks are extended to the many individuals and organizations who supplied material for this study, and to M. Griffin Bell and E. Otho Richey, Agricultural Research Technicians, for their enthusiastic assistance.     

Selective allele loss and interference between cauliflower mosaic virus DNAs

Summary Some cauliflower mosaic virus (CaMV) alleles are selectively lost during growth of the virus in mixedly infected turnip plants. Viral DNA from plants co-inoculated with DNA of the cabbage S isolate and infectious cabbage S DNA with an extra EcoRI restriciion site lacked the extra site. The EcoRI allele was also lost in most plants co-inoculated with a non-infectious mutant of cabbage S DNA while little selective allele loss was observed with two other non-infectious mutant DNAs. Plants co-inoculated with DNAs of closely-related isolates (CM4-184 and W) contained both parental viral DNAs and some DNAs with characteristics of both parents. Interference, scored as a reduced frequency of infection or a delay in symptom appearance relative to plants inoculated with wild-type DNA, occurred when plants were inoculated with wild-type and mutant DNAs covalently attached to one another in partial dimer plasmid DNAs. Similarities in the conditions leading to selective allele loss and those leading to interference suggest that both may have been due to active gene conversion between CaMV DNA molecules.     

Cytology of inbreds and f 1 hybrids of pearl millet

Summary The meiotic behaviour of chromosomes was studied in four inbred lines and their F ₁ hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F ₁ hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F ₁'s had mean chiasma frequencies higher than the means of the respective participating parents. The F ₁'s, however, differed in the degree of heterosis exhibited. In the F ₁ hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F ₁ hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F ₁'s did not show any significant differences between the two seasons. The F ₁'s exhibited less variation in mean chiasma frequency than the inbred lines, showing that F ₁'s were developmentally more stable. The F ₁'s did not show any meiotic abnormalities in either season.     

Consequences of interspecific hybridization and virus infection on the growth and fecundity of three threatened coastal Lepidium (Brassicaceae) species from New Zealand

Lepidium castellanum, L. juvencum and L. oleraceum are threatened coastal cresses endemic to New Zealand. These three species were selfed and interspecific hybrids generated for examination of hybrid fitness and inbreeding depression. In controlled glasshouse experiments, the interspecific hybrids and selfed progeny were inoculated with a strain of the introduced Turnip mosaic virus (TuMV) previously isolated from wild populations of L. aegrum. Experiments tested the hypothesis that heterosis in the interspecific hybrids provides a gain in TuMV resistance in comparison to selfed plants. We show that interspecific hybrids of three genetically distinct species of Lepidium increased plant performance and reduced susceptibility to the effects of the TuMV. We suggest that interspecific hybridization could be implemented as a conservation management strategy and that a broader outlook may be required to mitigate the negative impacts of introduced pathogens on threatened species.     

Integrated transcript and metabolite profiling reveals coordination between biomass size and nitrogen metabolism in Arabidopsis F1 hybrids

Heterosis refers to the improved agronomic performance of F₁ hybrids relative to their parents. Although this phenomenon is widely employed to increase biomass, yield, and stress tolerance of plants, the underlying molecular mechanisms remain unclear. To dissect the metabolic fluctuations derived from genomic and/or environmental differences contributing to the improved biomass of F₁ hybrids relative to their parents, we optimized the growth condition for Arabidopsis thaliana F₁ hybrids and their parents. Modest but statistically significant increase in the biomass of F₁ hybrids was observed. Plant samples grown under the optimized condition were also utilized for integrated omics analysis to capture specific changes in the F₁ hybrids. Metabolite profiling of F₁ hybrids and parent plants was performed using gas chromatography-mass spectrometry. Among the detected 237 metabolites, 2-oxoglutarate (2-OG) and malate levels were lower and the level of aspartate was higher in the F₁ hybrids than in each parent. In addition, microarray analysis revealed that there were 44 up-regulated and 12 down-regulated genes with more than 1.5-fold changes in expression levels in the F₁ hybrid compared to each parent. Gene ontology (GO) analyses indicated that genes up-regulated in the F₁ hybrids were largely related to organic nitrogen (N) process. Quantitative PCR verified that glutamine synthetase 2 (AtGLN2) was upregulated in the F₁ hybrids, while other genes encoding enzymes in the GS-GOGAT cycle showed no significant differences between the hybrid and parent lines. These results suggested the existence of metabolic regulation that coordinates biomass and N metabolism involving AtGLN2 in F₁ hybrids.     

Photosynthetic responses of radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> var. <Emphasis Type="Italic">longipinnatus</Emphasis>) plants to infection by turnip mosaic virus

Plant growth, chlorophyll (Chl) content, photosynthetic gas exchange, ribulose-1,5-bisphosphate carboxylase (RuBPCO) enzyme activity, and Chl fluorescence in radish (Raphanus sativus var. longipinnatus) plants were examined after turnip mosaic virus (TuMV) infection. Plant fresh mass, dry mass, Chl content, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and RuBPCO activity were significantly lower in infected plants after 5 weeks of virus infection as compared to healthy plants. The 5-week virus infection did not induce significant differences in intercellular CO₂ concentration (C _i, photochemical efficiency of photosystem 2, PS2 (F_v/F_m), excitation capture efficiency of open PS2 reaction centres (F_v'/F_m'), effective quantum efficiency of photosystem 2 (ΔF/F_m'), and photochemical quenching (q_P), but non-photochemical quenching (q_N) and alternative electron sink (AES) were significantly enhanced. Thus the decreased plant biomass of TuMV-infected plants might be associated with the decreased photosynthetic activity mainly due to reduced RuBPCO activity.     

Effect of plant growth conditions, plating density, and genotype on the anther culture response of soft white spring wheat hybrids

Ten soft white spring wheat (Triticum aestivum L.) F₁ hybrids were grown under three temperature regimes, and anthers were cultured at two plating densities to investigate the effect of plant growth conditions, plating density, and genotype on embryo induction and plant regeneration. Anthers from plants grown at high temperature (25 °/18 °C) or from plants transferred from low (15 °/12 °C) to high temperature generally produced more embryos and green shoots, with a lower frequency of albinos, than did anthers from plants grown at low temperature. However, plating densities of 10 versus 20 anthers per milliliter, had little effect on anther response. Four of the five hybrids with `Fielder' as the female parent produced more embryos and green shoots than did hybrids with `AC Reed' as the female parent. Received: 12 July 1996 / Revision received: 1 April 1997 / Accepted: 30 April 1997     

The restoration of male fertility in F1 wheat hybrids

The yield of F₁ wheat hybrids is often limited by reduced male fertility. Improvement depends upon selecting male and female parents capable of allowing good fertility ‘restoration’ in the F₁ hybrids. Assessment of restoring potential in growth rooms was difficult because fertility was much lower than in field grown plants. In the field, two experiments showed differences between parent lines but also that the fertilities of the F₁ hybrids were site-specific, and that this factor might be considered during further selection. Variation between reciprocal crosses, possibly due to cytoplasmic differences, rendered a proposed test for the early assessment of fertility restoration capacity amongst potential male-sterile lines to be of doubtful value with present stocks.     

Light quantity and photosystem function mediate host susceptibility to Turnip mosaic virus via a salicylic acid-independent mechanism

Evidence going as far back as the early part of the 20th century suggests that both light and chloroplast function may play key roles in host susceptibility to viruses. Despite the long history of such work, confirmation of these phenomena and a determination of the underlying mechanisms remain elusive. Here, we revisited these questions using modern imaging technologies to study the susceptibility of Nicotiana benthamiana to Turnip mosaic virus (TuMV). We found that both light deficiency and photosystem impairment increased the susceptibility of N. benthamiana to TuMV infection. Time-lapse photography studies indicated that, under these conditions, rub-inoculated plants exhibited greater numbers of infection foci and more rapid foci development. The rate of systemic movement was also accelerated though cell-to-cell movement appeared unchanged. Inhibition of salicylic acid (SA)-mediated defense responses is not likely responsible for changes in susceptibility because SA and pathogen response-1 gene induction were not affected by light deficiency or chloroplast impairment and treatment of plants with SA had no measureable impact on TuMV infection. Taken together, these data suggest that both light and optimal chloroplast function influence virus infection either by limiting the cellular resources needed by TuMV to establish replication complexes or the host's ability to activate SA-independent defenses.