Detection of the luteoviruses, beet mild yellowing virus and beet western yellows virus, in aphids caught in sugar-beet and oilseed rape crops, 1990–1993

The incidence of beet mild yellowing luteovirus (BMYV) and non-beet-infecting strains of beet western yellows luteovirus (BWYV) in individual winged aphids, caught in yellow water-traps, in sugar beet during the spring and early summer, and in oilseed rape plots in the autumn, was monitored using monoclonal antibodies in ELISA tests from 1990 to 1993. Between 0% and 8% of the Myzus persicae trapped in sugar beet each year carried BMYV, whereas 0% to 4% caught in oilseed rape in the autumn contained this virus. In 1990, 6.5% of Macrosiphum euphorbiae trapped in sugar beet contained BMYV, but in subsequent years less than 1% were carrying virus. Much higher proportions (26–67%) of the M. persicae tested from sugar beet contained BWYV, and similar proportions tested from oilseed rape (24–45%) also carried this virus in the autumn. In contrast only 3–19% of the M. euphorbiae caught in sugar beet contained BWYV, and none in oilseed rape. In 1991 and 1992 large numbers of Breuicoryne brassicae were caught in the plot of oilseed rape, of which over 50% contained BWYV; none were carrying BMYV. In transmission studies between 1990 and 1992, 1% and 27% of M. persicae transmitted BMYV and BWYV respectively to indicator plants; subsequent ELISA tests on the same aphids showed that 3% and 33% respectively contained the two viruses. One percent of M. euphorbiae transmitted BMYV, but none were found to contain BMYV using ELISA; 15% transmitted BWYV whilst only 5% were found to carry the virus. In 1992 and 1993 the incidence of BMYV-infection in the sugar-beet fields in which aphids had been trapped ranged from 1.2%, in a field which had received granular pesticide (aldicarb) at drilling plus three foliar aphicidal sprays, to 39.5% in a field which had received only one foliar spray. In 1992 in a sugar-beet crop which had received no aphicidal treatments, and where 2.8% of immigrant M. persicae and 2.5% of M. euphorbiae contained BMYV, 11.6% of plants developed BMYV infection. Lowest levels of infection were associated with the use of granular pesticides at drilling. In 1990, 80% of oilseed rape plants in a field plot were infested with a mean of seven wingless M. persicae per plant by mid-December; 37% of these plants were infected with BWYV. The studies show that M. persicae is the principal vector of BWYV, and large proportions of winged M. persicae carry the virus, in contrast to BMYV, which is consistent with the common occurrence of BWYV in brassica crops such as oilseed rape.     

Studies on beet western yellows virus in oilseed rape (Brassica napus ssp. oleifera) and sugar beet (Beta vulgaris)

Oilseed rape (Brassica napus L. ssp. oleifera) was studied as a potential overwintering host for the sugar-beet yellowing viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMYV), and their principal vector, Myzus persicae. In spring 1982, plants infected with a virus which reacted positively in enzyme-linked immunosorbent assay (ELISA) with BMYV antibody globulin were found in oilseed-rape crops; none of the plants contained virus which reacted with BYV antibody globulin. This virus was subsequently identified as beet western yellows virus (BWYV). No leaf symptoms could be consistently associated with infection of oilseed rape, but the virus was reliably detected by sampling any leaf on an infected oilseed-rape plant. Some isolates from oilseed rape did infect sugar beet in glasshouse tests, but the proportions of inoculated plants which became infected were low. Apparently there is therefore little danger of much direct transmission of BWYV by M. persicae from oilseed rape to sugar beet in spring. BWYV was introduced to and spread within oilseed-rape crops in autumn by M. persicae, and autumn-sown oilseed rape proved to be a potentially important overwintering host for M. persicae. In a survey of 80 autumn-sown crops of oilseed rape in East Anglia, northern England and Scotland in spring 1983, 78 were shown to be extensively infected with BWYV. Experimental plots of oilseed rape with 100% BWYV-infection yielded approximately 13.4% less oil than plots with 18% virus infection, the result of a decrease in both seed yield and oil content.     

Detection and Molecular Variability of Turnip mosaic virus (TuMV) in Shaanxi,China

Turnip mosaic virus (TuMV) is one of the most devastating threats to oilseed rape by causing serious crop losses. A total of 86 leaf samples of oilseed rape from eight different locations in Shaanxi, China, were tested by RT‐PCR for TuMV; the results revealed an infection level of 43% by TuMV. The complete coat protein (CP) gene of 32 TuMV isolates was cloned and sequenced. Analysis of the CP gene with sequences from the database allowed the genetic classification of 170 TuMV isolates or sequences. Four genetic clusters were obtained: MB (mostly Brassica isolates), MR (mostly Radish isolates), IBR (mostly Intermediate between Brassica and Radish clusters) and OBR (mostly outside Brassica and Radish clusters). All subgroups were slightly related to the hosts, but unrelated to geographical origins. Most of Shaanxi TuMV isolates were on separate branches, compared with the 138 known isolates originating from other parts of the world. Our results help provide a better understanding of the genetic diversity of TuMV isolates infecting oilseed rape in Shaanxi, China.     

Curly Top of Cultivated Plants and Weeds and Report of a Unique Curtovirus from Iran

The incidence of curly top disease on cultivated plants and weeds was investigated in Kerman Province (southeastern Iran) from October 2003 to November 2004. A total of 1186 samples were collected in fields of sugar beet and other crops as well as within commercial plastic houses. Curtovirus infection of four field crops, three vegetables and 11 weeds was verified by indirect enzyme‐linked immunosorbent assay (ELISA) using a polyclonal antibody. An undescribed curtovirus, tentatively designated Iranian beet curly top virus (IBCTV), was isolated from three symptomatic beet samples collected randomly in widely separated regions of south‐eastern, southern and central Iran and used for molecular studies. A 672 bp segment of the coat protein (CP) gene of each isolate was amplified by PCR and sequenced. The results showed that the three isolates shared 98.5–98.7% nucleotide homology with each other but only 72.1–76.5% with other members of the genus Curtovirus. IBCTV was also detected by PCR using specific primers in other samples of sugar beet, tomato, spinach, turnip and several weed species collected in different parts of Iran. These results indicated that IBCTV is the dominant curtovirus in Iran.     

Detection of BMYV and BWYV isolates using monoclonal antibodies and radioactive RNA probes, and relationships among luteoviruses

In order to discriminate between sugar beet infecting beet mild yellowing virus (BMYV) and other isolates of beet western yellows virus (BWYV), monoclonal antibodies (MAbs) and radioactive riboprobes were used. With MAbs prepared against BMYV or potato leafroll virus (PLRV) no distinction could be established between BMYV and BWYV. Seven probes were synthesised from a lettuce infecting BWYV isolate; their localisation in the genome is known and they cover almost its entire length. Probes from the '3 part of the genome hybridised with all BMYV and BWYV isolates whereas those from the '5 part did not recognise BMYV isolates, showing that a divergent '5 region exists in the genomes of BMYV and BWYV. Probes also readily detected the virus in single aphids. The relevance of this finding for epidemiological studies is discussed.
MAbs and riboprobes were also tested against other luteoviruses (PLRV; barley yellow dwarf virus (BYDV) MAV, PAV and RPV strains). The serological relationship between BMYV and PLRV was confirmed and an epitope common to PLRV and BYDV-RPV was found. Using probes, PLRV and BYDV-RPV were found to share domains of homology with BWYV. BYDV-PAV showed weak homology with BWYV, while BYDV-MAV showed none.     

Effects of beet cryptic virus infection on sugar beet in field trials

The effects of beet cryptic virus (BCV) infection on sugar beet crops were investigated in field trials in 1990. Two sugar beet breeding stock lines were screened for infection by BCV. Seed lots containing different proportions of seed infected with BCV1 & 2 were obtained by crossing the stock lines and used in field trials at five different sites. Five characteristics of the infected plants were assessed. BCV infection appeared to have no significant effects on the sugar beet crop at four locations which suffered from drought stress but significant effects were found at one site where the crop was grown on grade 1 land with good moisture retention properties. Root yield and sugar yield were reduced by up to 17% and 20%, respectively, by BCV infection.     

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.     

Failure of British isolates of beet western yellows virus to infect potato

Potato cultivars were tested for susceptibility to two British isolates of beet western yellows virus originally obtained from sugar beet and oil seed rape. Neither isolate was transmitted by Myzus persicae to virus-free potato plants, either by itself or in association with potato leafroll virus.     

The case for headland set-aside: consideration of whole-farm gross margins and grain production on two farms with contrasting rotations

Spreadsheet calculations were used to compare headland set-aside with rotational set-aside in terms of gross margin and grain production on two farms with contrasting rotations. At Broom's Barn, Suffolk there was a five course rotation consisting of sugar beet and four cereals, while at Bunny Park, Nottinghamshire oilseed rape was the break crop, followed by three cereals. For both farms a sensitivity analysis was used to investigate the effect of the proportion of the farm required to be set aside, the extent of headland yield reduction and the cereal price on the outcome of the spreadsheet calculations. In general headland set-aside out-performed rotational set-aside. Yields on headlands were always less than the main body of the field, but it was on the turning headlands where yield was particularly depressed. Thus the advantage, in terms of gross margin, of setting aside the headlands was greatest when the requirement could be fulfilled by fallowing most turning headlands, but no non-turning headlands. Generally, rotational set-aside reduced grain production more than headland set-aside, but when the spreadsheet models were adjusted to maintain the area of sugar beet, the situation was reversed. In this case headland set-aside produced a larger gross margin and had the greatest impact on grain production. An extension of the analysis is to ask the question: even if set aside is not an option, is it worthwhile to crop rather than fallow headlands? For cereals and oilseed rape the answer is in the affirmative; the gross margin for headlands remains positive, even when prices are much reduced, because the arable area payment more than offsets the variable costs. This does not hold for crops such as sugar beet that are not eligible for arable area payments. An additional benefit from headland set-aside is its potential to enhance the environment through increased habitat diversity and the provision of ‘buffer zones’ to prevent agrochemicals from drifting into hedges and watercourses.     

The use of monoclonal antibodies to detect beet mild yellowing virus and beet western yellows virus in aphids

Information on infectivity of the aphids which invade sugar beet root crops each Spring is required for forecasting incidence and providing advice on control of virus yellows. Monoclonal antibodies, produced in the USA to barley yellow dwarf virus (BYDV) and in Canada to beet western yellows virus (BWYV), were used to distinguish between sugar-beet-infecting strains of the luteovirus beet mild yellowing virus (BMYV), and the non-beet-infecting strains of the closely-related BWYV in plant and aphid tissue. Totals of 773 immigrant winged Myzuspersicae and 124 Macrosiphum euphorbiae were caught in water traps in a crop of sugar beet between 25 April and 5 August 1990. Using the monoclonal antibodies and an amplified ELISA, 67%M. persicae and 19%M. euphorbiae were shown to contain BWYV; 8%M. persicae and 7%M. euphorbiae contained BMYV. In studies with live winged aphids collected from the same sugar beet field during May, 25 of 60 M. persicae and two of 13 M. euphorbiae transmitted BWYV to the indicator host plant Montia perfoliata; two M. persicae and two M. euphorbiae transmitted BMYV. In another study three of 65 M. persicae and one of three M. euphorbiae in which only BWYV was detected, transmitted this virus to sugar beet.     

A review of sources of resistance to turnip yellows virus (TuYV) in Brassica species

Turnip yellows virus (TuYV; previously known as beet western yellows virus) causes major diseases of Brassica species worldwide resulting in severe yield-losses in arable and vegetable crops. It has also been shown to reduce the quality of vegetables, particularly cabbage where it causes tip burn. Incidences of 100% have been recorded in commercial crops of winter oilseed rape (Brassica napus) and vegetable crops (particularly Brassica oleracea) in Europe. This review summarises the known sources of resistance to TuYV in B. napus (AACC genome), Brassica rapa (AA genome) and B. oleracea (CC genome). It also proposes names for the quantitative trait loci (QTLs) responsible for the resistances, Tu rnip Y ellows virus R esistance (TuYR), that have been mapped to at least the chromosome level in the different Brassica species. There is currently only one known source of resistance deployed commercially (TuYR1). This resistance is said to have originated in B. rapa and was introgressed into the A genome of oilseed rape via hybridisation with B. oleracea to produce allotetraploid (AACC) plants that were then backcrossed into oilseed rape. It has been utilised in the majority of known TuYV-resistant oilseed rape varieties. This has placed significant selection pressure for resistance-breaking mutations arising in TuYV. Further QTLs for resistance to TuYV (TuYR2-TuYR9) have been mapped in the genomes of B. napus, B. rapa and B. oleracea and are described here. QTLs from the latter two species have been introgressed into allotetraploid plants, providing for the first time, combined resistance from both the A and the C genomes for deployment in oilseed rape. Introgression of these new resistances into commercial oilseed rape and vegetable brassicas can be accelerated using the molecular markers that have been developed. The deployment of these resistances should lessen selection pressure for resistance-breaking isolates of TuYV and thereby prolong the effectiveness of each other and extant resistance.     

Rhizoctonia solani AG 11 isolated for the first time from sugar beet in Poland

Two isolates of Rhizoctonia solani AG11 were isolated from sugar beet seedlings from South-west Poland. Both isolates gave C2 reactions in anastomose pairings with the tester isolates of AG11. The membership of both isolates to AG11 was confirmed by analysis of pectic isozyme profiles, and by verification that the internal transcribed spacer sequences of both isolates matched the references in the GenBank database. Both AG11 isolates formed white-beige to creamy-colored mycelium with wide concentric zonation. One of them formed light-colored sclerotia. The average daily rate of hyphal growth at 21 °C was 22.8 mm and 22.6 mm on PDA. They were mildly pathogenic to sugar beet seedlings due to the mycelial and secondary metabolites’ activity. The sensitivity to fungicides typically used in sugar beet protection was different for each isolate; one of them (isolate ID11) was less sensitive to thiram than the other (isolate ID3). This article discusses the worldwide occurrence of R. solani AG11, expands the currently known host range, shows its broad world distribution in regions of moderate climate, and confirms the isolates’ low frequency.     

Crop management and agronomic context of the Farm Scale Evaluations of genetically modified herbicide-tolerant crops

The Farm Scale Evaluations of genetically modified herbicide-tolerant crops (GMHT) were conducted in the UK from 2000 to 2002 on beet (sugar and fodder), spring oilseed rape and forage maize. The management of the crops studied is described and compared with current conventional commercial practice. The distribution of field sites adequately represented the areas currently growing these crops, and the sample contained sites operated at a range of management intensities, including low intensity. Herbicide inputs were audited, and the active ingredients used and the rates and the timings of applications compared well with current practice for both GMHT and conventional crops. Inputs on sugar beet were lower than, and inputs on spring oilseed rape and forage maize were consistent with, national averages. Regression analysis of herbicide-application strategies and weed emergence showed that inputs applied by farmers increased with weed densities in beet and forage maize. GMHT crops generally received only one herbicide active ingredient per crop, later and fewer herbicide sprays and less active ingredient (for beet and maize) than the conventional treatments. The audit of inputs found no evidence of bias.     

Survey of two beet viruses in South Kazakhstan and Central Asia

During two surveys of beet root crops in South Kazakhstan and Central Asia conducted in 1988 and 1989, 465 of 990 samples were found to contain beet mosaic virus (BMV) by double-antibody sandwich (DAS) ELISA. BMV infection was widely scattered in the area surveyed, and its incidence varied considerably, reaching 100% in some fields adjacent to beet seed crops. BMV isolates from Kazakhstan, Kirgizia, Uzbekistan and Ukraine were found to be serologically closely related in DAS-ELISA test. Beet yellows virus (BYV) was not detected in any location surveyed in South Kazakhstan and Central Asia. BYV spread into the area is probably prevented by its geographical isolation.     

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).     

Selection of natural isolates of Trichoderma spp. for biocontrol of Polymyxa betae as a vector of virus causing rhizomania in sugar beet

The soil fungus Polymyxa betae, Keskin, besides being a root parasite, plays a role of a vector in dissemination of Beet necrotic yellow vein virus (BNYVV) causing rhizomania in sugar beet. An alternative to its chemical control is the application of antagonistic microorganisms suppressing proliferation of the fungal vector. In the present work, 66 Trichoderma isolates have been obtained from sugar beet plantations from diverse locations in Slovakia. The ability of the selected isolates to grow at low temperature (10 °C) and to suppress the colonization of roots with P. betae and the multiplication of BNYVV in roots under glasshouse conditions were tested. The roots of sugar beet seedlings growing in the BNYVV-infested soil were analyzed by serological ELISA test using monoclonal and polyclonal antibodies for the presence of BNYVV and checked microscopically for the occurrence of cystosori of P. betae. The efficacy of the selected strains to suppress the proliferation of BNYVV varied on the average between 21 and 68%. On the basis of these tests, candidate strains for practical application in biocontrol of sugar beet rhizomania were selected.     

The effects of yellowing viruses on yield of sugar beet in field trials, 1985 and 1987

The separate effects of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) on yield of sugar-beet cultivars inoculated at different growth stages were assessed in field trials in 1985 and 1987. Early or mid-season inoculation decreased sugar yield by up to 47% for BYV, and up to 29% for BMYV. Infections after the end of July had no significant effect on yield. Both viruses caused significant increases in the juice impurities sodium, potassium and amino-nitrogen after infecting plants early in the season. Yield losses associated with infection were determined by the causative virus, the time of infection, and susceptibility of the sugar-beet cultivars.     

Weeds in fields with contrasting conventional and genetically modified herbicide-tolerant crops. II. Effects on individual species

We compared the effects of the management of genetically modified herbicide-tolerant (GMHT) and conventional beet, maize and spring oilseed rape on 12 weed species. We sampled the seedbank before and after cropping. During the season we counted plants and measured seed rain and biomass. Ratios of densities were used to calculate emergence, survival, reproduction and seedbank change. Treatments significantly affected the biomass of six species in beet, eight in maize and five in spring oilseed rape. The effects were generally consistent, with biomass lower in GMHT beet and spring oilseed rape and higher in GMHT maize. With few exceptions, emergence was higher in GMHT crops. Subsequent survival was significantly lowered for eight species in beet and six in spring oilseed rape in the GMHT treatments. It was increased for five species in maize and one in spring oilseed rape. Significant effects on seedbank change were found for four species. However, for many species in beet and spring oilseed rape (19 out of 24 cases), seed densities were lower in the seedbank after GMHT cropping. These differences compounded over time would result in large decreases in population densities of arable weeds. In maize, populations may increase.     

Characterization of Iranian Pectobacterium carotovorum Strains from Sugar Beet by Phenotypic Tests and Whole-cell Proteins Profile

Thirty isolates of Pectobacterium carotovorum from soft rot‐affected sugar beet plants in the Fars province of Iran were characterized phenotypically and by analysis of whole‐cell protein electrophoresis patterns. The isolates were found to be heterogeneous based on the results of physiological and biochemical tests and protein profiles. The results of numerical analysis of phenotypic characteristics and protein patterns showed that only 27% of the collected isolates (phenon 4) could be identified as P. betavasculorum when compared with reference strains. Strains of the first, second, third and fifth phenon shared similar characters with those of P. carotovorum subsp. carotovorum, P. betavasculorum and P. carotovorum subsp. odoriferum, but were distinct from these subspecies. Inoculation of phenon 4 isolates into wounded sugar beet petioles led to black streaking, root rot and vascular necrosis. Other isolates were incapable of causing systemic symptoms in inoculated plants.