Polymyxa Betae Research Articles

Bio-control of soil-borne virus infection by seed application of Glycyrrhiza glabra extract and the rhamnolipid Rhapynal

Main conclusionSeed-application of the natural products protects sugar beet and wheat plants against infection with plasmodiophorid-transmitted viruses and thus may represent an efficient, environmentally friendly, easy and cost effective biocontrol strategy.In times of intensive agriculture, resource shortening and climate change, alternative, more sustainable and eco-friendly plant protection strategies are required. Here, we tested the potential of the natural plant substances Glycyrrhiza glabra leaf extract (GE) and the rhamnolipid Rhapynal (Rha) applied to seeds to protect against infection of sugar beet and wheat with soil-borne plant viruses. The soil-borne Polymyxa betae- and Polymyxa graminis-transmitted viruses cause extensive crop losses in agriculture and efficient control strategies are missing. We show that GE and Rha both efficiently protect plants against infection with soil-borne viruses in sugar beet and wheat when applied to seeds. Moreover, the antiviral protection effect is independent of the cultivar used. No protection against Polymyxa sp. was observed after seed treatment with the bio-substances at our analysis time points. However, when we applied the bio-substances directly to soil a significant anti-Polymyxa graminis effect was obtained in roots of barley plants grown in the soil as well as in the treated soil. Despite germination can be affected by high concentrations of the substances, a range of antiviral protection conditions with no effect on germination were identified. Seed-treatment with the bio-substances did not negatively affect plant growth and development in virus-containing soil, but was rather beneficial for plant growth. We conclude that seed treatment with GE and Rha may represent an efficient, ecologically friendly, non-toxic, easy to apply and cost efficient biocontrol measure against soil-borne virus infection in plants.

Beet Soil-Borne Virus Is a Helper Virus for the Novel Beta vulgaris Satellite Virus 1A.

Sugar beet (Beta vulgaris) is grown in temperate regions around the world as a source of sucrose used for natural sweetening. Sugar beet is susceptible to a number of viral diseases, but identification of the causal agent(s) under field conditions is often difficult due to mixtures of viruses that may be responsible for disease symptoms. In this study, the application of RNAseq to RNA extracted from diseased sugar beet roots obtained from the field and from greenhouse-reared plants grown in soil infested with the virus disease rhizomania (causal agent beet necrotic yellow vein virus; BNYVV) yielded genome-length sequences from BNYVV, as well as beet soil-borne virus (BSBV). The nucleotide identities of the derived consensus sequence of BSBV RNAs ranged from 99.4 to 96.7% (RNA1), 99.3 to 95.3% (RNA2), and 98.3 to 95.9% (RNA3) compared with published BSBV sequences. Based on the BSBV genome consensus sequence, clones of the genomic RNAs 1, 2, and 3 were obtained to produce RNA copies of the genome through in vitro transcription. Capped RNA produced from the clones was infectious when inoculated into leaves of Chenopodium quinoa and B. vulgaris, and extracts from transcript-infected C. quinoa leaves could infect sugar beet seedling roots through a vortex inoculation method. Subsequent exposure of these infected sugar beet seedling roots to aviruliferous Polymyxa betae, the protist vector of both BNYVV and BSBV, confirmed that BSBV derived from the infectious clones could be transmitted by the vector. Co-inoculation of BSBV synthetic transcripts with transcripts of a cloned putative satellite virus designated Beta vulgaris satellite virus 1A (BvSat1A) resulted in the production of lesions on leaves of C. quinoa similar to those produced by inoculation with BSBV alone. Nevertheless, accumulation of genomic RNA and the encoded protein of the satellite virus in co-inoculated leaves was readily detected on Northern and Western blots, respectively, whereas no accumulation of satellite virus products occurred when satellite virus RNA was inoculated alone. The predicted sequence of the detected protein encoded by BvSat1A bears hallmarks of coat proteins of other satellite viruses, and virions of a size consistent with a satellite virus were observed in samples testing positive for the virus. The results demonstrate that BSBV is a helper virus for the novel satellite virus BvSat1A.

Morphological and Molecular Detection of Spongospora subterranea on Plant Harvest in Infected Powder Scab Plots in Antioquia

Potato powdery scab is a disease that negatively affects both roots, causing gall formation, and tubers, resulting in brown pustules. Additionally, it leads to the development of resistance structures that can persist in the soil for several years. Globally, it is one of the most limiting diseases for potato cultivation. This study aimed to identify the species present in areas with a historical occurrence of powdery scab and to evaluate their role as alternative hosts for the pathogen. Samples were collected in the municipalities of Santa Rosa de Osos and La Unión (Ant- Col). The presence of structures (plasmodia and cystosori) associated with the pathogen in the roots was determined using trypan blue staining followed by optical microscopy analysis. Morphological identification revealed twenty-six families with pathogen structures, including Acmella mutisii, Amaranthus dubius, Bidens pilosa, Galinsoga quadriradiata, Holcus lanatus, Hypochaeris radicata, Juncus microcephalus, Oxalis corniculata, Pennisetum clandestinum, Phytolacca bogotensis, Poa annua, Polygonum nepalense, Raphanus raphanistrum, Rumex crispus, Sonchus oleraceus, Trifolium repens, Verbena litoralis, along with Fragaria x ananassa, Solanum tuberosum, and Zea mays. Molecular analysis using RT-PCR for the detection of Plasmodiophoromycetes revealed the presence of Spongospora subterranea in Solanum tuberosum; Polymyxa betae in S. tuberosum, O. corniculata, and T. repens; and Polymyxa graminis in Z. mays. This comprehensive study highlights the importance of crop rotation and weed control to disrupt the pathogen’s lifecycle as effective strategies to mitigate the impact of the disease. It emphasizes the role of alternative hosts and their substantial contribution to elevated inoculum levels.

Rhizomania: Hide and Seek of Polymyxa betae and the Beet Necrotic Yellow Vein Virus with Beta vulgaris.

The molecular interactions between Polymyxa betae, the protist vector of sugar beet viruses, beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and Beta vulgaris have not been extensively studied. Here, the transmission of BNYVV to sugar beet by P. betae zoospores was optimized using genetically characterized organisms. Molecular interactions of aviruliferous and viruliferous protist infection on sugar beet were highlighted by transcriptomic analysis. P.betae alone induced limited gene expression changes in sugar beet, as a biotrophic asymptomatic parasite. Most differentially expressed plant genes were down-regulated and included resistance gene analogs and cell wall peroxidases. Several enzymes involved in stress regulation, such as the glutathione-S-transferases, were significantly induced. With BNYVV, the first stages of the P. betae life cycle on sugar beet were accelerated with a faster increase of relative protist DNA level and an earlier appearance of sporangia and sporosori in plants roots. A clear activation of plant defenses and the modulation of genes involved in plant cell wall metabolism were observed. The P. betae transcriptome in the presence of BNYVV revealed induction of genes possibly involved in the switch to the survival stage. The interactions were different depending on the presence or absence of the virus. P. betae alone alleviates plant defense response, playing hide-and-seek with sugar beet and allowing for their mutual development. Conversely, BNYVV manipulates plant defense and promotes the rapid invasion of plant roots by P. betae. This accelerated colonization is accompanied by the development of thick-walled resting spores, supporting the virus survival. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Türkiye’de şeker pancarı üretim alanlarında enfeksiyon oluşturan Beet necrotic yellow vein virus izolatlarının p31 geninin moleküler karakterizasyonu

Beet necrotic yellow vein virus (BNYVV), which is known as "the agent of rhizomania disease" and transmitted by Polymyxa betae, is the most destructive and prevalent virus species in sugar beet fields in Turkey and in the world. In this study, seventeen BNYVV-infested soil samples were selected according to their geographic locations. Firstly, BNYVV was propogated as bait plant technique. 
 P31 protein encoded by BNYVV RNA-4 is associated with efficient vector transmission and virulence. In this study, nucleotide sequences of p31 coding region of 12 different isolates were obtained. The BLAST and phylogenetic analysis divided BNYVV isolates into two different p31 groups as Group II and Group III. The Group II consisted of IGR-6, IGR-9 and ERC-52 isolates and found to have high nucleotide identity with Kas2 isolate (99.76%-99.88%). Also, GZP-27, ELZ-44, SMS-61, EDR-125, BRS-148, CNK-150, KAS-281, KYS-524 and ANK-617 which were divided into Group III had the highest similarity (99.88%-100%) with IV isolate (Italy).

Metagenomics approach for Polymyxa betae genome assembly enables comparative analysis towards deciphering the intracellular parasitic lifestyle of the plasmodiophorids

Genomic knowledge of the tree of life is biased to specific groups of organisms. For example, only six full genomes are currently available in the rhizaria clade. Here, we have applied metagenomic techniques enabling the assembly of the genome of Polymyxa betae (Rhizaria, Plasmodiophorida) RES F41 isolate from unpurified zoospore holobiont and comparison with the A26–41 isolate. Furthermore, the first P. betae mitochondrial genome was assembled. The two P. betae nuclear genomes were highly similar, each with just ~10.2 k predicted protein coding genes, ~3% of which were unique to each isolate. Extending genomic comparisons revealed a greater overlap with Spongospora subterranea than with Plasmodiophora brassicae, including orthologs of the mammalian cation channel sperm-associated proteins, raising some intriguing questions about zoospore physiology. This work validates our metagenomics pipeline for eukaryote genome assembly from unpurified samples and enriches plasmodiophorid genomics; providing the first full annotation of the P. betae genome.

Quantification of rhizomania virus by automated RNA isolation and PCR based methods in sugar beet.

Rhizomania is a grave disease affecting sugar beet (Beta vulgaris L.). It is caused by the Beet Necrotic Yellow Vein Virus (BNYVV), an RNA virus transmitted by the plasmodiophorid vector Polymyxa betae. Genetic resistance to the virus has been accomplished mostly using phenotype-genotype association studies. As yet, the most convenient method to ascertain plant resistance has been the quantification of viral titer in roots through the ELISA test. This method is particularly time-consuming and clashes with the necessities of modern plant breeding. Here, we propose an alternative and successful phenotyping method based on the automatic extraction of the viral RNA from sugar beet roots and its relative and absolute quantification by quantitative real-time PCR (qRT-PCR) and digital PCR (dPCR), respectively. Such a method enables an improved standardization of the study, as well as an accurate quantification of the virus also in those samples presenting low virus titer, with respect to the ELISA test.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13337-021-00674-7.

Pest categorisation of beet necrotic yellow vein virus.

Following a request from the EU Commission, the Panel on Plant Health performed a categorisation of beet necrotic yellow vein virus (BNYVV), the causal agent of the sugar beet rhizomania disease. The virus is currently listed in Annex III as a protected zone (PZ) quarantine pest of the Commission Implementing Regulation (EU) 2019/2072. The identity of the BNYVV is well established. BNYVV is a soil‐borne virus transmitted by the obligate root plasmodiophorid endoparasite Polymyxa betae. BNYVV is widely distributed in the EU, but is not reported in the following EU PZs: Ireland, France (Brittany), Portugal (Azores), Finland and Northern Ireland. The virus may enter, become established and spread in the PZs via P. betae resting spores with soil and growing media as such or attached to machinery and with roots and tubercles of species other than B. vulgaris and with plants for planting. Introduction of BNYVV would have a negative impact on sugar beet and other beet crops in PZs, because of yield and sugar content reduction. Phytosanitary measures are available to reduce the likelihood of entry and spread in the PZs. Once the virus and its plasmodiophorid vector have entered a PZ, their eradication would be difficult due to the persistence of viruliferous resting spores in the soil. The main knowledge gaps or uncertainties identified concerning the presence of BNYVV in the PZs and the incidence and distribution of BNYVV in Switzerland, a country to which a range of specific requirements do not apply. BNYVV meets all the criteria that are within the remit of EFSA to qualify as a potential protected zone union quarantine pest. Plants for planting are not considered as a main means of spread, and therefore BNYVV does not satisfy all the criteria evaluated by EFSA to qualify as potential Union regulated non‐quarantine pest.

RNA silencing machinery contributes to inability of BSBV to establish infection in Nicotiana benthamiana: evidence from characterization of agroinfectious clones of Beet soil-borne virus.

Beet soil-borne virus (BSBV) is a sugar beet pomovirus frequently associated with Beet necrotic yellow veins virus, the causal agent of the rhizomania disease. BSBV has been detected in most of the major beet-growing regions worldwide, yet its impact on this crop remains unclear. With the aim to understand the life cycle of this virus and clarify its putative pathogenicity, agroinfectious clones have been engineered for each segment of its tripartite genome. The biological properties of these clones were then studied on different plant species. Local infection was obtained on agroinfiltrated leaves of Beta macrocarpa. On leaves of Nicotiana benthamiana, similar results were obtained, but only when heterologous viral suppressors of RNA silencing were co-expressed or in a transgenic line down regulated for both dicer-like protein 2 and 4. On sugar beet, local infection following agroinoculation was obtained on cotyledons, but not on other tested plant parts. Nevertheless, leaf symptoms were observed on this host via sap inoculation. Likewise, roots were efficiently mechanically infected, highlighting low frequency of root necrosis and constriction, and enabling the demonstration of transmission by the vector Polymyxa betae. Altogether, the entire viral cycle was reproduced, validating the constructed agroclones as efficient inoculation tools, paving the way for further studies on BSBV and its related pathosystem.

Field evaluation for rhizomania resistance of transgenic sugar beet events based on gene silencing

Rhizomania is one of the most damaging and widespread diseases in the major sugar beet (Beta vulgaris L. subsp. vulgaris) growing regions worldwide. The causal agent, Beet necrotic yellow vein virus, is transmitted by a plasmodiophorid vector, Polymyxa betae Keskin. In this study, the inhibition of BNYVV multiplication was evaluated, under field conditions, in six sugar beet transgenic events generated based on gene silencing of the major coat protein gene (CP21). Phenotypic criteria, including scoring for disease symptoms and an immunoassay for viral accumulation, indicated that the transgenic events were less susceptible to rhizomania and had lower virus titre rates than non-transgenic plants of the susceptible cultivar ‘9597’. Disease severity and virus titres were comparable to the resistant cultivar ‘Dorothea’, which carries the Rz1-resistance gene and was bred through traditional means. This study provides a proof of concept for the effectiveness of the gene-silencing mechanism for introducing rhizomania resistance in sugar beet at the field level.

RNAseq Analysis of Rhizomania-Infected Sugar Beet Provides the First Genome Sequence of Beet Necrotic Yellow Vein Virus from the USA and Identifies a Novel Alphanecrovirus and Putative Satellite Viruses.

“Rhizomania” of sugar beet is a soilborne disease complex comprised of beet necrotic yellow vein virus (BNYVV) and its plasmodiophorid vector, Polymyxa betae. Although BNYVV is considered the causal agent of rhizomania, additional viruses frequently accompany BNYVV in diseased roots. In an effort to better understand the virus cohort present in sugar beet roots exhibiting rhizomania disease symptoms, five independent RNA samples prepared from diseased beet seedlings reared in a greenhouse or from field-grown adult sugar beet plants and enriched for virus particles were subjected to RNAseq. In all but a healthy control sample, the technique was successful at identifying BNYVV and provided sequence reads of sufficient quantity and overlap to assemble > 98% of the published genome of the virus. Utilizing the derived consensus sequence of BNYVV, infectious RNA was produced from cDNA clones of RNAs 1 and 2. The approach also enabled the detection of beet soilborne mosaic virus (BSBMV), beet soilborne virus (BSBV), beet black scorch virus (BBSV), and beet virus Q (BVQ), with near-complete genome assembly afforded to BSBMV and BBSV. In one field sample, a novel virus sequence of 3682 nt was assembled with significant sequence similarity and open reading frame (ORF) organization to members within the subgenus Alphanecrovirus (genus Necrovirus; family Tombusviridae). Construction of a DNA clone based on this sequence led to the production of the novel RNA genome in vitro that was capable of inducing local lesion formation on leaves of Chenopodium quinoa. Additionally, two previously unreported satellite viruses were revealed in the study; one possessing weak similarity to satellite maize white line mosaic virus and a second possessing moderate similarity to satellite tobacco necrosis virus C. Taken together, the approach provides an efficient pipeline to characterize variation in the BNYVV genome and to document the presence of other viruses potentially associated with disease severity or the ability to overcome resistance genes used for sugar beet rhizomania disease management.

Sojevi virusa nekrotičnog žutila nerava šećerne repe, prouzrokovača rizomanije

Rhizomania is the most important disease of sugar beet worldwide, caused by beet necrotic yellow veinvirus (BNYVV). This virus is transmitted by the zoospores of Polymyxa betae, which is widespread soil-borne pathogen. Severe sugar beet infections, with this virus, reduce root yield by 50% or more, resulting in sugar content and product quality reduction. Research on the genetic variability of BNYVV provides information that can elucidate its evolutionary and geographical origins, changes in virulence (breakthrough resistance to RBs), and the development of new epidemics. Beet necrotic yellow vein virus (BNYVV) has a worldwide distribution. Four major types of this virus have been detected: type A, B, P and J.

Effect of rhizomania on red table-beet biomass production and molecular characterization of an isolate of Beet necrotic yellow vein virus from Brazil

In Brazil, Beet necrotic yellow vein virus (BNYVV), which causes rhizomania in red table-beet (Beta vulgaris subsp. vulgaris), was first reported in 2015. This study evaluated the pathogenic effects of the disease on biomass production of red table-beet plants under field conditions. The effect of rhizomania infection depended on the season when the experiment was conducted. BNYVV infection had no effect on dry weight of aerial parts of plants growing in autumn, and a marginal effect on storage roots, reducing the weight by 27.5%. In spring, rhizomania significantly reduced the dry weight of aerial parts by 48% and the storage-root weight by 64.6%. The presence of the possible vector Polymyxa betae was confirmed by PCR and subsequent nucleotide sequencing. The near-complete genome of a BNYVV isolate from Brazil was determined using high-throughput sequencing; the homologous sequence of the RNA-5 genome segment was not identified. The BNYVV genome of the Brazilian isolate was very similar to the type BNYVV-S isolate.

Resistance in Beta vulgaris L. subsp. maritima (L.) Thell. to the Rz1-breaking strain of rhizomania

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV) and transmitted by Polymyxa betae, is considered the most important disease of sugar beet and has spread to almost all production areas of the world. The most efficient way to control this soil-borne disease is through the cultivation of rhizomania-resistant varieties, which has proven successful since the 1980s. In the 2002–2003 season, sugar beet fields in the Imperial Valley, California, planted with a resistant commercial variety were observed with severe rhizomania symptoms suggesting resistance conferred by the most widely deployed gene, Rz1, was compromised. BNYVV isolates were identified to which all resistant check varieties became infected and tested positive for the virus (RB-BNYVV, Rz1-resistance breaking strain of Beet necrotic yellow vein virus). For continuing development of BNYVV and RB-BNYVV resistant germplasm, a highly important reservoir of resistance factors is the Beta vulgaris subsp. maritima (BVM) accession collection. We evaluated 404 BVM accessions under BNYVV and RB-BNYVV field and greenhouse conditions to identify and select rhizomania resistant accessions useful for sugar beet germplasm improvement. Accessions from Denmark, Ireland, and Portugal showed the highest level of rhizomania resistance as characterized by foliar yellowing due to rhizomania, rhizomania disease index, and percent resistant beets. The low bolting tendency of Denmark and Ireland accessions suggest these for pre-breeding donor material.

First Draft Genome Sequence of a Polymyxa Genus Member, Polymyxa betae, the Protist Vector of Rhizomania.

Polymyxa betae belongs to the Plasmodiophorida (Phytomyxea, Rhizaria). Here, we report the first draft genome sequence of a member of the Polymyxa genus, which includes two obligate root endoparasite species, vectors of important soilborne plant viruses. The genome assembly was represented by 1,001 contigs, with a cumulated length of 27,085,946 bp.

Ability of Non-Pathogenic Fusarium oxysporum Strain Fo47 to Suppress Rhizomania Disease of Sugar Beets in Morocco

Rhizomania is one of the most devastating diseases of sugar beet worldwide. The disease poses a serious threat to Moroccan production and it is capable of significantly decreasing quality and yield of sugar beet plantations. The long-term survival of its fungal vector (Polymyxa betae) in soil makes it a very difficult disease to manage. Therefore, this study investigated the potential of a non-pathogenic fungal Fusarium oxysporum strain Fo47 to control Polymyxa betae. This biocontrol agent was applied as soil treatment, seed treatment, or a combination of the both treatments. A bio-test was performed on treated soil. After four weeks of culture, the roots of sugar beet seedlings were retrieved and analyzed by the DAS-ELISA test. Results indicated that F. oxysporium Fo47 reduced the activity and survival of P. betae when compared to a reference biocontrol agent Trichoderma harzianum, which only revealed significant in reducing the viral load of Beet Necrotic Yellow Vein Virus (BNYVV) as seed treatment. The non-pathogenic Fusarium oxysporum Fo47 was more effective as soil treatment and allowed almost the same reduction of BNYVV virus concentration as T. harzianum 908. Therefore, our findings emphasizes that the performance of the biocontrol agent depends on the method of application.

Biological properties of Beet soil-borne mosaic virus and Beet necrotic yellow vein virus cDNA clones produced by isothermal in vitro recombination: Insights for reassortant appearance

Two members of the Benyviridae family and genus Benyvirus, Beet soil-borne mosaic virus (BSBMV) and Beet necrotic yellow vein virus (BNYVV), possess identical genome organization, host range and high sequence similarity; they infect Beta vulgaris with variable symptom expression. In the US, mixed infections are described with limited information about viral interactions. Vectors suitable for agroinoculation of all genome components of both viruses were constructed by isothermal in vitro recombination. All 35S promoter-driven cDNA clones allowed production of recombinant viruses competent for Nicotiana benthamiana and Beta macrocarpa systemic infection and Polymyxa betae transmission and were compared to available BNYVV B-type clone. BNYVV and BSBMV RNA1 + 2 reassortants were viable and spread long-distance in N. benthamiana with symptoms dependent on the BNYVV type. Small genomic RNAs were exchangeable and systemically infected B. macrocarpa. These infectious clones represent a powerful tool for the identification of specific molecular host-pathogen determinants.

A SNP mutation affects rhizomania-virus content of sugar beets grown on resistance-breaking soils

Rhizomania is one of the most devastating biotic stresses affecting sugar beet (Beta vulgaris L.). It is caused by Beet necrotic yellow vein virus (BNYVV) vectored by the plasmodiophorid Polymyxa betae K. The only means available to control the disease is the use of genetically resistant varieties. “Rizor” or “Holly” (Rz1) and WB42 (Rz2) have been the most widely used resistance sources in the commercial varieties. Recently, naturally occurring resistance-breaking (RB) rhizomania strains have been identified causing major concerns. The aim of this study was to identify SNP mutations that show associations with resistance to rhizomania in sugar beet plants grown under resistance-breaking (RB)-BNYVV soils. Rhizomania virus content was evaluated by indirect triple-antibody sandwich-ELISA within two F 2 segregating populations respectively grown on an AYPR and IV-BNYVV strain infected soils. Bulked segregant analysis (BSA) was performed. The resistant and susceptible plants were genotyped with a 384-SNPs panel. Of the 384 SNPs, SNP249 was found to associate with the resistance both to the AYPR strain (R 2 = 0.37; P = 0.0004) and to the IV-BNYVV (R 2 = 0.09; P = 0.0074). Our results suggested that the SNP249 could be readily applicable for marker-assisted breeding of resistance to AYPR strain of rhizomania.

P25 pathogenicity factor deletion mutants of beet necrotic yellow vein virus occurring in sugar beet fields in Turkey

Beet necrotic yellow vein virus (BNYVV) causes rhizomania which is one of the most devastating diseases in sugar beet fields worldwide. BNYVV symptoms were observed in Rz1-resistant sugar beet plants in a number of fields in Aksaray and Konya Provinces during surveys in 2011. Seven soil samples, taken from problematic areas in these provinces and known to be infested with populations of Polymyxa betae Keskin carrying BNYVV, were used in bait plant and molecular studies. Initially, the presence of other soil-borne viruses was investigated by using ELISA and RT-PCR. It was determined that BNYVV was in co-infections with pomoviruses, namely beet soil-borne virus and/or beet virus Q. The partial RNA-3 segment of BNYVV was amplified by RT-PCR, and the nucleotide sequences involving the p25 coding region were obtained. The deduced amino acid (aa) sequences of the p25 protein indicated that four BNYVV populations had ‘ACHG’ or ‘VHHG’ residues at positions 67–70. In addition, three populations containing three nucleotide deletions, not shifting the reading frame but affecting the aa at position 67 (-DHG) or 68 (D-HG), were identified. A deleted form of the p25 was identified in both the A- and J-type BNYVV populations. The pathogenicities of these BNYVV populations in the sugar beet genotypes rz1 and Rz1 were investigated under controlled conditions. All seven BNYVV isolates were capable of overcoming Rz1 resistance. These results seem to indicate that mutants of BNYVV with a deletion are aggressive, as are the isolates without deletion. Resistant beet cultivars will most likely be more productive in the future if these isolates become widespread in Turkey.

Composting to sanitize plant‐based waste infected with organisms of plant health importance

The potential for using the composting process to sanitize plant waste infected with one of three plant pathogens was investigated using bench‐scale composting equipment. Two of these pathogens, the potato wart disease fungus Synchytrium endobioticum and Potato spindle tuber viroid (PSTVd) are currently subject to European quarantine regulations. The third, Polymyxa betae, a parasite of sugar beet, is regulated in some European countries when in association with Beet necrotic yellow vein virus (BNYVV), the causal organism of rhizomania disease of sugar beet. Survival of test organisms following various combinations of compost temperature, exposure time and moisture was determined using RNA‐based detection methodology and/or plant‐based bioassays. Mathematically definable relationships between compost treatment (temperature/time) and organism viability were identified for P. betae and S. endobioticum; these give some indication of the practicality of using composting for dealing with infected wastes. However, for PSTVd, the considerable variability in measured susceptibility of the viroid to the composting process meant that no such definable relationship could be determined and further work would be needed to extrapolate to practical situations.