Wild Beet Research Articles

RAPD marker evaluation of phylogenetic relationships in species of genus Beta L.

RAPD markers are used for establishing phylogenetic relationships between and within various beet species. On the basis of the electrophoretic profiles obtained, phylogenetic trees are constructed by the unweighted pair group with arithmetic mean (UPGMA) method and relationships between wild and cultivated beet accessions stored in the world collection at the Vavilov Plant Industry Research Institute (VIR)are determined.

High Degree of Genetic Variation of Winter Hardiness in a Panel of Beta vulgaris L.

ABSTRACTGrowing sugar beet (Beta vulgaris L. subsp. vulgaris [sugar beet cultivar group]) as a winter crop requires the development of a winter sugar beet with controlled bolting and sufficient winter hardiness. To evaluate the genetic variation for winter hardiness in B. vulgaris L., we determined the survival rate (SR) in a panel of 396 accessions tested in eight overwintering field trials in Germany and Belarus. The panel included the cultivar groups sugar beet, fodder beet, garden beet, and leaf beet, as well as the wild beet B. vulgaris subsp. maritima (L.) Arcang. (BVM). Across all environments the effects of accession, environment, and accession × environment interaction were highly significant. Despite the complexity of the trait, the heritability for SR was estimated as h2 = 0.81, reflecting a large genetic variation in the panel. Environmental SRs ranged from 0.7 to 86.3% with a grand mean of 28.4%. In all environments at least one accession completely died while the maximum SR ranged from 39.9 to 100%. On average, sugar beet accessions performed best while accessions with the highest SR were among BVMs and leaf beets. The largest variation for SR was found in BVMs, followed by the leaf beets, whereas sugar beets showed the smallest variation. Our results suggest that winter hardiness in sugar beet is sufficient to survive mild winters but needs to be improved for continental climates with colder winters. Whether the limited variation in sugar beet is sufficient for this has to be further investigated.

Genetic identification of a novel bolting locus in Beta vulgaris which promotes annuality independently of the bolting gene B

Bolting tendency in the crop species Beta vulgaris, which includes sugar beet, is a complex trait governed by various environmental cues, including prolonged periods of cold temperatures over winter (vernalization) and photoperiod, and multiple genetic factors. Two loci which promote bolting in the absence of vernalization are known in beet, the major bolting locus B on chromosome II and the B2 locus on chromosome IX. Here, genetic linkage and quantitative trait locus analyses in two populations derived from a cross between a biennial genotype, which was identified in a phenotypic screen for EMS-induced bolting mutants and requires vernalization to bolt, and an annual wild beet accession revealed the presence of a novel major bolting locus B4 which is linked to the B locus but promotes annual bolting independently of B. The genetic distance between B and B4 on chromosome II is 11 cM. A sequence-based marker was identified which co-segregates with bolting behavior and co-localizes with the B4 locus.

Molecular basis of cytoplasmic male sterility in beets: an overview

Sugarbeet cultivars are almost exclusively hybrids, which are produced using the sole source of cytoplasmic male sterility (CMS), the so-called Owen CMS. Several alternative sources of CMS have been described. One of these, I-12CMS(3), was derived from wild beets collected in Pakistan, and another CMS source, GCMS, has a cytoplasmic origin in wild sea beets from France. During the past decade, male sterility-associated mitochondrial genes have been identified in these three CMS systems. Moreover, the recent development of a variety of DNA markers has permitted the genetic mapping of nuclear restorer-of-fertility genes for both Owen and GCMS. This review focuses on the mechanism of CMS in beets.

Development and application of molecular and bioinformatic tools for the genetic monitoring of wild beets

AbstractCrop Wild Relatives (CWR) are an economically important plant genetic resource (PGR) for plant breeding. One strategy to conserve PGR in the natural habitat (in situ) is the genetic reserve technique. This approach protects the existing intraspecific diversity and allows, in contrast to the ex situ approaches, the emergence of new diversity.The genetic reserve conservation technique will be tested in practice with the Genus Beta within the framework of the EU Project “AEGRO”. Beta patula (Ait.) (BP) and Beta vulgaris (L.) maritima (Arcang.) (BVM) are used as models. Both species are important resources for sugar beet breeding. BP is a rare and endangered species with a very limited habitat. In contrast BVM is widespread along the shores of Western Europe. This subspecies is expected to migrate in a northward direction as a consequence of the global climate change. The impact of this migration on the genetic diversity will be examined in future analyses and will establish a basis for future research.A total of 557 plants from 14 sampling plots were analyzed using 25 SSR markers (Simple Sequence Repeat Marker). Additionally, a monitoring database for storing and post processing all laboratory and field data was developed.For the first time the geographic pattern of genetic diversity in the wild beet BP was described and decision criteria for the establishment of a genetic reserve for BP was postulated. The knowledge of geographic patterns of genetic diversity in the wild beet BVM was consolidated as a baseline for further investigations on the potential influence of climate changes and the corresponding geographic range shift on genetic diversity.

Development and application of molecular and bioinformatic tools for the genetic monitoring of wild beets

Crop Wild Relatives (CWR) are an economically important plant genetic resource (PGR) for plant breeding. One strategy to conserve PGR in the natural habitat (in situ) is the genetic reserve technique. This approach protects the existing intraspecific diversity and allows, in contrast to the ex situ approaches, the emergence of new diversity.The genetic reserve conservation technique will be tested in practice with the Genus Beta within the framework of the EU Project “AEGRO”. Beta patula (Ait.) (BP) and Beta vulgaris (L.) maritima (Arcang.) (BVM) are used as models. Both species are important resources for sugar beet breeding. BP is a rare and endangered species with a very limited habitat. In contrast BVM is widespread along the shores of Western Europe. This subspecies is expected to migrate in a northward direction as a consequence of the global climate change. The impact of this migration on the genetic diversity will be examined in future analyses and will establish a basis for future research.A total of 557 plants from 14 sampling plots were analyzed using 25 SSR markers (Simple Sequence Repeat Marker). Additionally, a monitoring database for storing and post processing all laboratory and field data was developed.For the first time the geographic pattern of genetic diversity in the wild beet BP was described and decision criteria for the establishment of a genetic reserve for BP was postulated. The knowledge of geographic patterns of genetic diversity in the wild beet BVM was consolidated as a baseline for further investigations on the potential influence of climate changes and the corresponding geographic range shift on genetic diversity.

Plant Nematode Control

The cyst nematode Heterodera schachtii belongs to the most important biotic stress factors in sugar beet cultivation. Nematodes can be controlled by crop rotation, by fumigation with nematicides or by growing resistant crops. However, nematicides are no longer admitted to be used because of their toxic environmental impacts, the crop rotation system is often agronomically impracticable and the genetic resistance is so far not available in sugar beet germplasms. Thus, alternative strategies for nematode control have been applied in the past years. For instance, genetic resistance from wild beet species were identified and transferred into the elite breeding materials. Today several nematode tolerant varieties of sugar beet are commercially available. In addition, different approaches based on genetic engineering have been developed to improve plant nematode resistance. Nevertheless, an effective control of nematodes in sugar beet cultivation still remains a great challenge.

Germination under aseptic conditions of different ecotypes of wild beet (Beta vulgaris L. ssp maritima)

The characterization of the wild beet relatives, as well as their use for the selection of useful traits, is limited by difficulties associated with the germination of these plants. Currently available germination protocols deliver low percentage, unsynchronised and lengthy germination. We tested several procedures likely to weaken the woody/ corky structure where the seeds are enclosed, the glomerule. Our results show that with an H2O2 treatment [30% (v/v) twice for one hour], followed by aseptic hand scarification and incubation in half-strength Murashige and Skoog it is possible, within days, to establish a synchronized culture due to successful germination, 40 to 90% depending on the ecotype.

Populations of weedy crop–wild hybrid beets show contrasting variation in mating system and population genetic structure

Reproductive traits are key parameters for the evolution of invasiveness in weedy crop–wild hybrids. In Beta vulgaris, cultivated beets hybridize with their wild relatives in the seed production areas, giving rise to crop–wild hybrid weed beets. We investigated the genetic structure, the variation in first-year flowering and the variation in mating system among weed beet populations occurring within sugar beet production fields. No spatial genetic structure was found for first-year populations composed of F1 crop–wild hybrid beets. In contrast, populations composed of backcrossed weed beets emerging from the seed bank showed a strong isolation-by-distance pattern. Whereas gametophytic self-incompatibility prevents selfing in wild beet populations, all studied weed beet populations had a mixed-mating system, plausibly because of the introgression of the crop-derived Sf gene that disrupts self-incompatibility. No significant relationship between outcrossing rate and local weed beet density was found, suggesting no trends for a shift in the mating system because of environmental effects. We further reveal that increased invasiveness of weed beets may stem from positive selection on first-year flowering induction depending on the B gene inherited from the wild. Finally, we discuss the practical and applied consequences of our findings for crop-weed management.

A new source of cytoplasmic male sterility found in wild beet and its relationship to other CMS types

We found a number of male-sterile plants in a wild beet (Beta vulgaris L. subsp. maritima) accession line, FR4-31. The inheritance study of the male sterility indicated the trait to be of the cytoplasmic type. The mitochondrial genome of FR4-31 proved to lack the male-sterility-associated genes preSatp6 and orf129, which are characteristic of the Owen CMS and I-12CMS(3) cytoplasms of beets, respectively. Instead, the truncated cox2 gene involved in G CMS originating from wild beets was present in the FR4-31 mitochondrial genome. In Southern hybridization using four mitochondrial gene probes, the FR4-31 cytoplasm showed patterns similar to those typical of the G cytoplasm. It is thus likely that the FR4-31 cytoplasm has a different CMS mechanism from both Owen CMS and I-12CMS(3), and that the FR4-31 and G cytoplasms resemble each other closely. A restriction map of the FR4-31 mitochondrial DNA was generated and aligned with those published for the Owen and normal fertile cytoplasms. The FR4-31 mitochondrial genome was revealed to differ extensively in arrangement from the Owen and normal genomes, and the male-sterile Owen and FR4-31 genomes seem to be derived independently from an ancestral genome.

Haploids and homozygous diploids, triploids and tetraploids in sugar beet

Attempts to induce haploid parthenogenesis in sugar beet by pollination with wild beet pollen and irradiated sugar beet pollen resulted in five haploid plants. Seven additional haploids were found among inbred lines, and still another in the C1 generation after colchicine treatment of an inbred line. The frequency of haploids in different kinds of sugar beet seed, also studied, was higher in offspring from diploids pollinated by tetraploids (about 0.2%) than in diploid crosses. The haploids and homozygous diploid and tetraploid lines synthesized from three of the haploids are briefly described. In a greenhouse experiment with diploids, triploids and tetraploids, which originated from one and the same haploid, the diploids and the euploid triploids did not differ in root weight, while euploid tetraploids weighed on an average 7 per cent less than the diploids. At both the triploid and tetraploid levels, aneuploidy had a much greater negative influence on root development than the physiological imbalance caused by the increase in genome number. Contrary to the root weight, the weight of the leaves increased with the increase in genome number, even when including the aneuploids. These results are discussed in relation to the influence of heterozygosity on the performance of autotetraploids and the present situation in polyploid breeding in sugar beet.

Fine‐scale geographical structure of genetic diversity in inland wild beet populations

Introgression arising from crop-to-wild gene flow provides novel sources of genetic variation in plant species complexes. Hybridization within the Beta vulgaris species complex is of immediate concern; crop lineages (B. vulgaris ssp. vulgaris) hybridize easily with their wild relatives (B. vulgaris ssp. maritima) thereby threatening wild beet gene diversity with genetic swamping. Hybridization 'hotspots' occur in European seed production areas because inland ruderal wild beets occur and reproduce in sympatry with cultivated beets. We studied gene flow occurring between seed-producing cultivars and ruderal wild B. vulgaris in southwestern France to determine whether feral beets, arising from unharvested cultivated seed, represent an opportunity for crop-to-wild gene flow. We surveyed 42 inland ruderal beet populations located near seed production fields for nucleo-cytoplasmic variation and used a cytoplasmic marker diagnostic of cultivated lines. Occurrence of cultivated-type cytoplasm within ruderal populations clearly reflected events of crop seed escape. However, we found no genetic signatures of nuclear cultivated gene introgression, which suggests past introgression of cultivated cytoplasm into a wild nuclear background through seed escape rather than recent direct pollen flow. Overall, patterns of genetic structure suggested that inland ruderal wild beet populations act as a metapopulation, with founding events involving a few sib groups, followed by low rates of seed or pollen gene flow after populations are established. Altogether, our results indicate that a long-lived seed bank plays a key role in maintaining cultivated-type cytoplasm in the wild and highlight the need for careful management of seed production areas where wild and cultivated relatives co-occur.

Nested Ty3-gypsy retrotransposons of a single Beta procumbens centromere contain a putative chromodomain

LTR retrotransposons belong to a major group of DNA sequences that are often localized in plant centromeres. Using BAC inserts originating from the centromere of a monosomic wild beet (Beta procumbens) chromosome fragment in Beta vulgaris, two complete LTR retrotransposons were identified. Both elements, designated Beetle1 and Beetle2, possess a coding region with genes in the order characteristic for Ty3-gypsy retrotransposons. Beetle1 and Beetle2 have a chromodomain in the C-terminus of the integrase gene and are highly similar to the centromeric retrotransposons (CRs) of rice, maize, and barley. Both retroelements were localized in the centromeric region of B. procumbens chromosomes by fluorescence in-situ hybridization. They can therefore be classified as centromere-specific chromoviruses. PCR analysis using RNA as template indicated that Beetle1 and Beetle2 are transcriptionally active. On the basis of the sequence diversity between the LTR sequences, it was estimated that Beetle1 and Beetle2 transposed within the last 60,000 years and 130,000 years, respectively. The centromeric localization of Beetle1 and Beetle2 and their transcriptional activity combined with high sequence conservation within each family play an important structural role in the centromeres of B. procumbens chromosomes.

Pollen dispersal in sugar beet production fields

Pollen-mediated gene flow has important implications for biodiversity conservation and for breeders and farmers' activities. In sugar beet production fields, a few sugar beet bolters can produce pollen as well as be fertilized by wild and weed beet. Since the crop, the wild beets, and the weed beets are the same species and intercross freely, the question of pollen flow is an important issue to determine the potential dispersal of transgenes from field to field and to wild habitats. We report here an experiment to describe pollen dispersal from a small herbicide-resistant sugar beet source towards male sterile target plants located along radiating lines up to 1,200 m away. Individual dispersal functions were inferred from statistical analyses and compared. Pollen limitation, as expected in root-production fields, was confirmed at all the distances from the pollen source. The number of resistant seeds produced by bait plants best fitted a fat-tailed probability distribution curve of pollen grains (power-law) dependent on the distance from the pollen source. A literature survey confirmed that power-law function could fit in most cases. The b coefficient was lower than 2. The number of fertilized flowers by background (herbicide-susceptible) pollen grains was uniform across the whole field. Airborne pollen had a fertilization impact equivalent to that of one adjacent bolter. The individual dispersal function from different pollen sources can be integrated to provide the pollen cloud composition for a given target plant, thus allowing modeling of gene flow in a field, inter-fields in a small region, and also in seed-production area. Long-distance pollen flow is not negligible and could play an important role in rapid transgene dispersal from crop to wild and weed beets in the landscape. The removing of any bolting, herbicide-resistant sugar beet should be compulsory to prevent the occurrence of herbicide-resistant weed beet, thus preventing gene flow to wild populations and preserving the sustainable utility of the resistant varieties. Whether such a goal is attainable remains an open question and certainly would be worth a large scale experimental study.

Molecular and morpho-physiological characterization of sea, ruderal and cultivated beets

Beta vulgaris genetic resources are essential for broadening genetic base of sugar beet and developing cultivars adapted to adverse environmental conditions. Wild beets (sea beets, B. vulgaris spp. maritima and their naturalized introgressions with cultivated beets known as ruderal beets) harbor substantial genetic diversity that could be useful for beet improvement. Here, we compared molecular and morpho-physiological traits of wild beets collected on the Adriatic coast of Italy with sugar beet using eight primer-pairs amplifying 194 polymorphic fragments and four root traits (glucose and fructose content in the root tip, root elongation rate, number of the of root tips, total root length and its distribution among diameters ranges). Genetic diversity was higher in the sea beet accession, which may be due to the highly variable selection pressures that occur in heterogeneous ecological niches, compared with the ruderal and cultivated beets. Sea and sugar beet accessions showed contrasting root patterns in response to sulfate deprivation: sugar beet showed an increase of reducing sugars in the root tips and higher root elongation rate, and the sea beet accession showed an increase in root tip number, total root length and fine root length (average diameter < 0.5 mm). The ruderal beet showed intermediary responses to sea and sugar beet accessions. AFLP and morpho-physiological cluster analyzes showed sea, ruderal and cultivated beets to be genetically distinct groups. The results of this study indicate variability in response to sulfate deprivation is present in undomesticated beets that could be deployed for sugar beet improvement.

Molecular Cytogenetic Mapping of Chromosomal Fragments and Immunostaining of Kinetochore Proteins in Beta

By comparative multicolor FISH, we have physically mapped small chromosome fragments in the sugar beet addition lines PRO1 and PAT2 and analyzed the distribution of repetitive DNA families in species of the section Procumbentes of the genus Beta. Six repetitive probes were applied, including genotype-specific probes—satellites pTS4.1, pTS5, and pRp34 and a dispersed repeat pAp4, the telomere (TTTAGGG)n, and the conserved 18S-5.8S-25S rRNA genes. Pachytene-FISH analysis of the native centromere organization allowed proposing the origin of PRO1 and PAT2 fragments. Comparative analysis of the repetitive DNA distribution and organization in the wild beet and in the addition lines allowed the development of a physical model of the chromosomal fragments. Immunostaining revealed that the PRO1 chromosome fragment binds α-tubulin and the serine 10-phosphorylated histone H3 specific for the active centromere. This is the first experimental detection of the kinetochore proteins in Beta showing their active involvement in chromosome segregation in mitosis.

DIAPAUSE AND PARASITISM OF THE SUGAR BEET LEAFMINER, PEGOMYA MIXTA VILLENEUVE (DIPTERA: ANTHOMYIIDAE), PUPAE REARED FROM CERTAIN CHENOPODIACEOUS HOST PLANTS AT GIZA

Leaves infested by the sugar beet learminer, Pegomya mkta Villeneuve (Diptera: Anthomyiidae) were collected from untreated sugar beet, Beta vuVaris L, spinach, Spinacia oletacea L., goosefoot, Chenopodium morale L and wild beet Beta vu/pans var. petennis during the period from November, 2004 to April, 2005 and with Chard, Beta vu&atis var. tide L. and mangold, Beta vuglatis var. niOtis during the same period in 2005 and 2006 in the farm of the Agric. Exp. Sta., at Giza. Rate and Incidence of diapause and parasitism and emergence of flies and parasitoids were determined. The overall mean of diapause was higher 49.3% (2004-2005) opposed to 38.5% (2005- 2006). Parasitism followed the same trend with 45.6% versus to 42.1% in the same seasons. Rate and incidence of dlapause and parasitism were highly variable among puparia reared from the different chenopothaceous host plants. The prevalence of higher general rates of diapause ( 67, 39.6 and 29.3%) and parasitism (77.3, 41.1 and 40.3%) were recorded on puparia reared from wild beet, goosefoot and sugar beet, whereas 55.1% (diapause) and 34.5% (parasitism) were attained on spinach puparia. Rate of diapause ranged between (0- 36.9%) and (10.6- 42.5%) on pupae developed from infested leaves of sugar beet and goosefoot in 2004- 2005 and 2005- 2006, but decreased from 64.6 to 45.7% and from 67.6 to 64.7% for those reared from spinadi and wild beet In the same period. However, parasitism ranged between (31.9- 37.2%), (38.7- 64.9%) and (52.9‌83.1%) on parasitized puparia collected from spinach, goosefoot and wild beet in 2005- 2006 and 2004- 2005, but increased from 39.1% to 40.6% on sugar beet puparia from the first to the second season one. In both seasons, puparia went into aestivation (summer diapause) during February- April, but 1.3% entered hibernation (overwinter diapause) during November-January in 2005- 2006. Aestivated puparia started at rates of 21.9 and 41.8% in February, increased to 27.6% and slightly decreased to 37.5% in March and reached the highest rates 84.8 and 70.7% in April of 2005 and 2006, respectively. Synchronization was found between the timing of the highest percentages of emerged flies about (92 and 91%) and parasitoids (91 and 79%) In November of 2005 and 2006. The huge numbers of emerged parasitoids occurred with the high rates of parasitism 78.9 and 62.8% In November, 2004 and 2005. Such synchronization was found In 2004- 2005 active season, but was lost in the second one. In April of 2005, the highest percentages of emerged parasitoids and flies were 70.8 and 43.2%, but were 34.2 and 49.4% in January and April in 2006. To prevent and promote parasitoids, insecticides must be entirely avoided, agricultural practices i. e. deeply plowing, destruction alternative host weeds, hand pick and destroying infested mined leaves weekly before the larvae drop to the soil and dropping kerosene into water irrigation in a rate of 30 liter / feddan (4200 m2) reduce the population size of P. mixta and largely solving the likelihood and severity of leafminers problems in sugar beets.

HOST PREFERENCES OF THE HAWAIIAN BEET WEBWORM, HYMENIA RECURVALIS( FAB.) (LEPIDOPTERA: PYRALIDAE)

The present work was carried out at Faculty of agriculture, Fayoum Univ. under laboratory conditions (25*2°C and 68 ± 5% R.H.). The obtained results are summarized as follow: Third instar larvae of Hymenia recurva/is (Fab.) prefered 6•hosts namly, nettle leaf,wild beet, table beet, spinach, sugarbeet and pigweed. Percentages of attracted larvae on these hosts showed 24.3, 18.5, 17.7, 15.0, 13.7 and 10.5%, respectively. The respective attraction on hosts for egg laying were on table beet, spinach, sugarbeet, wild beet, nettle leaf and pigweed. Hawaiian beet webworm, H. recurvallscomplete its life cycle on all hosts with significant differences in parameters especially pre-oviposition period and rate of egg deposition /9. Lowest period and highest rate were recorded on nettle leaf.

Phylogenetic relationships of genus Beta species based on the chloroplast trnK (matK) gene intron sequence information

This was the first work to study the primary structure of the chloroplast lysine tRNA gene ( matK ) intron in beet species belonging to sections Beta and Procumbentes. It is demonstrated that this genome region is identical in all studied members of Beta section. Interspecies polymorphism was not found either in the species belonging to Procumbentes section. However, a comparison of sequences characterizing sections Beta and Procumbentes revealed distinctions between them in the studied fragment of the chloroplast genome. The history of beet studying began in 1753, when Carl Linnaeus described the cultivated beet under the name of Beta vulgaris L. By the end of XIX century, all wild beet forms have been already described. However, samples that were similar in certain morphological traits were named differently by different researchers [1]. In 1927, soviet botanist Transhel’ on the basis of analysis of herbarium samples and descriptions made by other researchers divided all species of the Beta genus into three sections: Patellares m., Vulgares m., and Corolliae m. [1]. Later, numerous attempts were made to supplement and improve this classification [2, 3]. This applied primarily to species of the Vulgares section, because sugar beet, which is of great agricultural importance as a source of sugar, belongs to this section. Study of morphological and biochemical markers made it possible to create a generally accepted system of classification of the Beta genus [4], according to which the Beta genus is divided into four sections: Beta (synonym Vulgares ), Corollinae, Nanae , and Procumbentes (synonym Patellares ). The Beta section includes three species, two of which are wild-growing ( B. macrocarpa Guss and B. patula Ait.). The third species of this section, B. vulgaris L., includes three subspecies, two of which are wild-growing (ssp. maritima (L.) Arcang and ssp. adanensis (Pamuk.) Ford-Lloyd and Will) and one cultivated (ssp. vulgaris ). The latter subspecies (cultivated beet) is divided into leaf, red, and sugar beet and mangel-wurzel. The development of molecular methods allowed data obtained by these techniques to be used for comparing different species of the Beta genus. For instance, a study of chloroplast and nuclear genes of the order Caryophyllales, to which the Beta genus belongs, showed that the matK gene is optimal for studying phylogenetic relationships within this order. Analysis based on the use of this gene made it possible to reveal more distinctions between Beta species than in the case of other chloroplast and nuclear genes [5]. In view of this, in studying the phylogeny of species of the Beta genus, we used a fragment of chloroplast lysine tRNA gene intron that contained the open reading frame (the matK gene) encoding the protein exhibiting maturase activity. The goal of this study was to determine the phylogenetic relationships between the members of the Beta genus (primarily the Beta section) on the basis of studying the nucleotide sequence of the intron fragment of the lysine tRNA gene ( trnK / matK ) of the chloroplast genome.

Identification of amino acids of the beet necrotic yellow vein virus p25 protein required for induction of the resistance response in leaves of Beta vulgaris plants

The RNA3-encoded p25 protein of beet necrotic yellow vein virus (BNYVV) is responsible for the production of rhizomania symptoms of sugar beet roots (Beta vulgaris subsp. vulgaris). Here, it was found that the presence of the p25 protein is also associated with the resistance response in rub-inoculated leaves of sugar beet and wild beet (Beta vulgaris subsp. maritima) plants. The resistance phenotype displayed a range of symptoms from no visible lesions to necrotic or greyish lesions at the inoculation site, and only very low levels of virus and viral RNA accumulated. The susceptible phenotype showed large, bright yellow lesions and developed high levels of virus accumulation. In roots after Polymyxa betae vector inoculation, however, no drastic differences in virus and viral RNA accumulation levels were found between plants with susceptible and resistant phenotypes, except at an early stage of infection. There was a genotype-specific interaction between BNYVV strains and two selected wild beet lines (MR1 and MR2) and sugar beet cultivars. Sequence analysis of natural BNYVV isolates and site-directed mutagenesis of the p25 protein revealed that 3 aa residues at positions 68, 70 and 179 are important in determining the resistance phenotype, and that host-genotype specificity is controlled by single amino acid changes at position 68. The mechanism of the occurrence of resistance-breaking BNYVV strains is discussed.