Sources of resistance to diseases of sugar beet in related <Emphasis Type="Italic">Beta</Emphasis> germplasm: I. Foliar diseases

Resistance to four foliar diseases of sugar beet (Beta vulgaris ssp. vulgaris), virus yellows caused by Beet mild yellowing virus (BMYV) and Beet yellows virus (BYV), powdery mildew (Erysiphe betae) and Cercospora leaf spot (Cercospora beticola), was assessed in up to 600 accessions of closely related wild and cultivated Beta species. Most accessions were from the Section Beta, a taxon containing types most closely related to, and sexually compatible with, sugar beet and therefore most valuable for use in crop improvement. Between 1–12% of accessions were highly resistant (resistance scores of 2 on an international standardised resistance scale of 1–9) to these diseases. These levels, however, underestimate the potential number of resistant sources available from this section as some accessions with intermediate mean resistance scores contained a significant proportion of highly resistant plants within segregating populations. Variation in resistance to all diseases except BYV was observed within the Section Beta. Much higher levels of resistance were observed, and more frequently, in more distantly related sections of the genus Beta. Accessions of the Section Corollinae were highly resistant to both viruses (>62% of accessions tested), but less so to Cercospora (15%) and they were very susceptible to powdery mildew. Section Procumbentes accessions were highly resistant to BMYV and Cercospora (100%) but less so to powdery mildew (50%) and BYV (20%). However, sexual incompatibility between these sections and sugar beet make utilisation of these sources impractical using conventional breeding methods.     

Major genes for resistance to beet necrotic yellow vein virus (BNYVV) in Beta vulgaris

Summary Inheritance of resistance to beet necrotic yellow vein virus (BNYVV) was studied in segregating F2 and backcross families obtained from crosses between resistant plants of the sugar beet selection Holly-1-4 or the wild beet accession Beta vulgaris subsp. maritima WB42 and susceptible parents. Greenhouse tests were carried out, in which seedlings were grown in a mixture of sand and infested soil. Virus concentrations of BNYVV in the rootlets were estimated by ELISA. To discriminate resistant and susceptible plants, mixtures of normal distributions were fitted to log₁₀ virus concentrations, estimated for segregating F1, F2 and BC populations of both accessions. The hypothesis that Holly-1-4 contained one single dominant major gene was accepted. For WB42, results fitted with the hypotheses that resistance was based on either one (or more) dominant major gene(s) showing distorted segregation, or two complementary dominant genes, which are both required for resistance. Resistance from WB42 appeared to be more effective against BNYVV than resistance from Holly-1-4.This research was carried out as part of a PhD study at the Graduate School Experimental Plant Sciences (EPS), Department of Virology, Wageningen, The Netherlands     

Breeding for resistance to rhizomania in sugar beet: A review

Currently rhizomania is the most important disease in sugar beet worldwide, and attack can lead to serious yield losses. The disease is caused by beet necrotic yellow vein virus (BNYVV) that is transmitted by the soil-borne fungus Polymyxa betae. Breeding sugar beet cultivars with resistance to rhizomania is regarded as the most appropriate way to enable continued production of this crop in BNYVV-infested fields and also to slow the spread of the disease. Breeding for resistance started with selection by scoring disease symptoms in field experiments. The development of non-destructive greenhouse tests, with determination of the virus concentration in rootlets using ELISA, has greatly improved the efficiency of selection. In this paper the impact of scientific research on the progress in breeding cultivars with resistance to rhizomania is reviewed. This includes the distribution, composition, and pathogenicity of the virus, the sources of resistance to virus and vector, the genetics of virus resistance, progress with breeding methods, and the use of molecular markers and pathogen-derived resistance. The yields and quality characteristics of recently introduced resistant cultivars now equal those of the commercial susceptible cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multiplicative models for cultivar by location interaction in testing sugar beets for resistance to beet necrotic yellow vein virus

Summary Sugar beet cultivars were evaluated for resistance to beet necrotic yellow vein virus (BNYVV) on various locations in two consecutive years. Resistance levels of cultivars were measured by virus assays of plants from the field and the greenhouse. Infection levels in the fields were characterised by sampling plants of a susceptible indicator cultivar. For each year, statistical analyses were performed on two-way tables of cultivar by location for yield and quality parameters. In analysis of variance (ANOVA) significant main effects and significant cultivar by location interaction were found for all parameters (P<0.05). Interactions were further investigated by multiplicative models. In the Additive Main effects and Multiplicative Interaction effects (AMMI) model, interaction was written as the product of a cultivar score and a location score. Cultivar interaction scores were highly correlated to virus concentrations of the cultivars, and location interaction scores to virus concentrations of the susceptible indicator cultivar. Main effects of cultivars and locations were less clearly related to virus concentrations than interaction effects. In general, virus concentrations of plants from a greenhouse test gave higher correlations than virus concentrations of plants from the field. In the factorial regression model, virus concentrations were incorporated in the model. The model can be understood as a two-way ANOVA, with greenhouse virus concentrations and virus concentration of the indicator cultivar as concomitant variables on the cultivar and location factor. Results of analyses with both multiplicative interaction models showed that interactions of all yield and quality parameters can be described in terms of virus concentrations. Therefore, the relative performance of susceptible and partially resistant cultivars in infested fields can be estimated by means of three independent parameters, (i) the level of resistance determined in a greenhouse experiment, (ii) the yield and quality in non-infested fields, and (iii) the level of infection in the field.Abbreviations AMMI model Additive Main effects and Multiplicative Interaction effects model - ANOVA analysis of variance - BNYVV beet necrotic yellow vein virus - ELISA enzyme-linked immunosorbent assay - -amino N -amino nitrogen - K Kalium (potassium) - Na Natrium (sodium)     

Natural variation within the genus Beta and its possible use for breeding sugar beet: A review

Summary Sugar beet is a relatively young crop, which supposedly has a narrow genetic base. Natural variation occurring in primitive beet varieties and in wild Beta species has been used for breeding sugar beet. This paper reviews information on desirable characteristics in Beta germplasm and the attempts made for the introgression of such characters into commercial breeding material. After an introduction on the availability of germplasm and the possibilities of hybridisation, attention is focussed on the mating system (especially male sterility), on morphological and physiological characteristics, including yield and sugar content, and on resistances to diseases and pests.     

Identification and mapping of random amplified polymorphic DNA markers linked to a rhizomania resistance gene in sugar beet (Beta vulgaris L.) by bulked segregant analysis

Bulked segregant analysis was employed to identify random amplified polymorphic DNA (RAPD) markers linked to a gene that confers rhizomania resistance to a sugar beet line created from a Holly Sugar Company breeding population (USA). Polymorphism revealed with 160 arbitrary 10-mer oligonucleotide primers was screened in two bulks produced by separately pooling the individual DNAs from the six most resistant and the six most susceptible plants of an F₂ population segregating for rhizomania resistance. A study of the F₂ individuals showed that 19 primers generated 44 polymorphic markers which were then grouped into nine linkage groups. By analysis of variance, 12 were shown to have a significant effect upon the level of resistance and were mapped on a segment 22.3 cM long. A quantitative trait locus (QTL) of resistance was identified and located in a 4.6cM interval between two markers. It accounted for 67.4% of the observed variation and almost all the genetic variation. These results suggest that the identified QTL corresponds to a unique major gene conditioning the Holly resistance studied, which we have named Rz-l.     

The inheritance of resistance to beet necrotic yellow vein virus (BNYVV) in B. vulgaris subsp. maritima, accession WB42: Statistical comparisons with Holly-1-4

In this study, the inheritance of resistance to Beet necrotic yellow vein virus (BNYVV) in accessions Holly-1-4and WB42 was investigated. Crosses between both resistant sources and susceptible parents were carried out and F₁F₂ and BC₁ populations were obtained. Virus concentrations in WB42and its F₁ populations were lower than in Holly-1-4. Observed ratios of susceptible and resistant plants in segregating populations of Holly-1-4 as well as WB42 were in agreement with hypothesis of one dominant major gene. Segregation of plants in F₂ populations obtained from crosses betweenHolly-1-4 and WB42 revealed that the resistance genes in Holly-1-4 and WB42 were nonallelic and linked loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

The production of alien monosomic additions in Beta vulgaris as a source for the introgression of resistance to beet root nematode (Heterodera schachtii) from Beta species of the section Patellares

Summary Experiments were carried out for adding the chromosome carrying resistance to beet root nematode (Heterodera schachtii) from the wild Beta species of the section Patellares (B. procumbens, B. webbiana and B. patellaris) to the genome of B. vulgaris. Preliminary experiments indicated that crosses between the wild species and B. vulgaris cultivars of the mangold type yielded on average more viable F₁ hybrids than crosses with sugar and fodderbeet. However, crossability varied strongly between individual parental combinations. It was concluded that most types of B. vulgaris can be hybridized with the wild species of the section Patellares if a sufficient number of pair-crosses is made. Crosses between diploid cultivars or species of the section Vulgares and diploid wild species of the section Patellares yielded many hybrids which, however, were highly sterile. From crosses between tetraploid B. vulgaris and the wild species a great number of viable allotriploid and allotetraploid hybrids was obtained. In the backcross progenies of allotriploid hybrids 26% alien monosomic additions occurred, of which 4.1% carried the resistance bearing chromosome of B. procumbens or B. patellaris. The programme will be continued by sereening progenies of the resistant monosomic addition plants for the occurrence of resistant disomic introgression products.     

Sugar beets homozygous for resistance to beet cyst nematode (Heterodera schachtii Schm.), developed from monosomic additions of Beta procumbens to B. vulgaris

Summary Monosomic additions of Beta vulgaris x B. procumbens with resistance to beet cyst nematode (Heterodera schachtii Schm.) were used for the production of resistant diploids through incorporation of the B. procumbens chromosome fragment bearing the resistance gene(s) into one of the sugar beet chromosomes. The heterozygotes obtained accordingly were selfed for producing homozygotes. These homozygotes differed morphologically from commercial sugar beet varieties, but produced reasonable amounts of pollen. Female transmission of resistance was 100%, whereas male transmission, apart from some exceptions, was more than 90%. The number of hypersensitivity reactions to penetrated larvae was related to the degree of susceptibility. Larval development was severely retarded in the resistant plants, preventing most of them to produce cysts. If cysts were formed, their content was considerably less as compared to those in the susceptible plants.     

Peroxidase activity as a possible test for distinguishing s-plasm from n-plasm in sugar beet (Beta vulgaris L.)

Summary The O-type lines (N-plasm) of sugar beet (Beta vulgaris L.) proved to have a consistently lower peroxidase activity (49.2–62.7%) than their male sterile (MS) equivalents (S-plasm).Similar differences in peroxidase activity (45.4–56.3%) were found when O-type lines were compared with unrelated MS lines. They were also observed in different parts of the plant (cotyledons, hypocotyl + radicle, true leaves) and were reproducible.The fertile lines could be grouped by their level of peroxidase activity in categories of either S-plasm or N-plasm.The peroxidase activity test could be used for selection of N-plasm lines from fertile sugar beet populations and for selection of MS and O-type lines of higher stability.     

Assessment of the degree of genetic variation in beet based on RFLP analysis and the taxonomy of Beta

Summary Clones derived from Beta vulgaris and Beta maritima were assayed for their ability to detect restriction fragment length polymorphisms (RFLPs) in different beet accessions. The clones able to detect polymorphism were used as genetic markers to assess the degree of genetic variation existing between and within different species of the genus Beta. The data support the current taxonomy of the Beta vulgaris section, while the great genetic similarity found between Beta webbiana and Beta procumbens indicates that they could belong to the same species.Enough variation was found between Beta vulgaris cultivars, allowing the isolation of a sufficient number of genetic markers for the construction of detailed genetic maps.     

An evaluation of single plant randomised field trials of sugar beet (Beta vulgaris L.)

Summary Diploid, monogerm families of sugar beet were grown in transplanted field trials randomised on a single-plant basis. Individual roots were weighed and a range of chemical characters were assessed. There was no significant difference in performance between plants that had members of their own family as nearest neighbours within the row and plants that had randomly assigned neighbours. Good correlations were found between the performance of families in single-plant trials and their performance in conventional plot trials. We conclude that single-plant randomisation could prove useful for genetical studies and for breeding trials particularly when seed or facilities are limited.     

Variation in some agronomically important characters in a germplasm collection of beet (Beta vulgaris L.)

Summary A geographically representative selection of germplasm of Beta vulgaris, section Beta has been assessed for characteristics important in sugarbeet breeding, including downy mildew resistance, resistance to aphid colonisation and infection by the beet virus yellow complex. The occurrence of maintainer lines for cytoplasmic male-steriles was also investigated. Desirable qualities were found in some accessions, including nothern European wild vulgaris ssp. maritima and some old multigerm cultivars of fodder beets.     

Correlation between polyovules and number of pistil lobes (stigmatic rays) in sugar beet (Beta vulgaris L.)

The polyovules phenomenon in sugar beet has the same importance for breeding as multigermity, because only mono-ovulic monogerm plants can be used for mechanized cultivation. The polyovules trait was investigated in two Japanese lines, mono-ovulic line NK-219-O and polyovulic line NK-183-cms. Plants of the former had three pistil lobes (stigmatic rays) in each flower, a single ovule per ovary, a single seed in the mature fruit and a single seedling germinated in subsequent tests. Plants of the latter had 5–6 pistil lobes in each flower, 2–3 ovules per ovary, double-seeds and double-seedlings. The correlations between a Pistil Lobes Index (PLI) and thenumber of ovules per ovary, percentage of double-seeds inan X-ray test, and percentage of double-seedlings in germination tests were 0.885, 0.838, and 0.749, respectivelyindicating close associations. These results are important both in sugar beet breeding for indirect selection to eliminate the undesirable polyovules trait and for botanicalinvestigations of the relationship among different parts of the gynoecium.     

Evaluation of globe artichoke and related germplasm for resistance to artichoke latent virus

Summary A total of 280 globe artichoke (Cynara scolymus L.) clones were assessed for reaction to naturally occurring artichoke latent virus (ALV) in field trials. Also, the reaction of 17 seed progenies of crosses which produced ALV-resistant clones in the field, 20 self progenies of parental genotypes common to these crosses, self progenies of 17 artichoke cultivars, and 7 accessions ofC. cardunculus andC. syriaca were evaluated in the glasshouse following mechanical inoculation with ALV. The local and systemic presence of ALV, and the relative virus content in infected plants were determined by ELISA.All cultivars and most of the otherC. scolymus material tested (clones and seed progenies) proved to be highly susceptible to ALV. Ten progenies were less susceptible to mechanical inoculation as shown by the moment the virus could be detected, and a slow rate of accumulation of viral antigen. Some plants in two seed progenies possessed apparently a high resistance as could be concluded from the failure of ALV to spread or to multiply in plant.Accessions ofC. cardunculus andC. syriaca were also highly susceptible to ALV. However, an interspecific hybridC. cardunculus x C. syriaca presented the highest level of resistance, the plants remained free of local and systemic infection. Ratios of resistant to susceptible plants in self progenies of resistant plants suggested that this resistance was dominant.     

Reduced titer of BNYVV in transgenic sugar beets expressing the BNYVV coat protein

Summary Rhizomania is a disease of sugar beet caused by the furovirus beet necrotic yellow vein virus (BNYVV). Coat protein mediated resistance has been reported for a number of viral diseases. This approach to virus resistance was therefore attempted for control of rhizomania. Two constructs of the coat protein gene of BNYVV were introduced into sugar beet by Agrobacterium-mediated transformation. The mRNA level was estimated to be 0.01% of the poly A⁺ RNA. Expression of the coat protein gene was under the detection limit of our western blotting protocol i.e. below 0.01 g/50 g (0.02% of the total soluble protein). One transformation event per construct was tested in a greenhouse assay and in rhizomania infested soil in a field trial. In the greenhouse assay, transgenic plants showed a strong reduction of virus multiplication when compared to non-transgenic plants. This result was confirmed in the field trial, where a significant difference in virus multiplication was shown between plants with and without the coat protein gene.     

Chromosome localisation of genes for resistance to Heterodera schachtii, Cercospora beticola and Polymyxa betae using sets of Beta procumbens and B. patellaris derived monosomic additions in B. vulgaris

Beet cyst nematodes (BCN, Heterodera schachtii), Cercospora beticola, and rhizomania, caused by the beet necrotic yellow vein virus (BNYVV) and vectored by the soil-borne fungus Polymyxa betae, are the most serious diseases of sugar beet ( Beta vulgaris subsp. vulgaris). The wild Beta species of section Procumbentes are known to be completely resistant to H. schachtii, C. beticola and P. betae. Alien monosomic additions (2n=19), plants of cultivated beet (2n=18) carrying different individual chromosomes of B. procumbens (2n=18) or B. patellaris (2n=36), were tested in greenhouse experiments for resistance to these pathogens. Gene(s) conferring full resistance to the beet cyst nematode in B. patellaris are located on chromosome 1.1, and the other tested chromosomes of B. patellaris are not involved in the expression of resistance. Artificial inoculation under greenhouse conditions, with in vitro produced inoculum of C. beticola and spot-percentage rating of the disease intensity, showed that the high level of resistance that was observed in the wild species B. procumbens and B. patellaris was not found in any of the monosomic additions tested. It was suggested that genes on various chromosomes of the wild species are needed to express full resistance, and that the chromosomes of group 7 of B. patellaris and chromosome 7 of B. procumbens have the largest effect. The greenhouse tests for resistance to P. betae in B. patellaris derived monosomic additions showed that the addition families of group 4.1 have a strong partial resistance, while the addition families of group 8.1 appeared to be completely resistant to the pathogen. Resistance to P. betae in the two wild species as well as in the two resistant addition types did not exclude infection with BNYVV, but resulted in a considerable reduction of the virus concentration. It was concluded that resistance to the vector would complement virus resistance, and may provide a more effective and durable control of rhizomania. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sources of resistance to Pyrenophora tritici-repentis in bread wheats

Summary No complete resistance to Pyrenophora tritici-repentis has been located in more than 1400 bread wheats examined. Incomplete resistance, however, occurs at different levels in many spring and winter types and data are presented for the strongest sources of resistance detected. In particular, there is a high frequency of Brazilian spring wheats with appreciable levels of resistance to this pathogen. Recent international nurseries from CIMMYT, Mexico, also contain numerous potentially valuable sources of resistance and these wheats may be shorter and higher yielding in Australia than the Brazilian wheats. The resistances in many Brazilian cultivars may be largely common because the cultivars are often strongly interrelated. Some of the Brazilian wheats resistant to P. tritici-repentis are also resistant to one or more of the septoria diseases and/or possess tolerance to aluminium toxicity.     

Partial resistance of sugarbeet to beet cyst eelworm (Heterodera schachtii Schm.)

Summary Within Beta vulgaris and B. maritima origins some partial resistance to beet cyst eelworm was found which could be raised to a very limited extent by selection. However after the second backcross to commercial sugar beet varieties and successive selection of the inbreds this resistance was lost. It was demonstrated that in the rootsystem of resistant plants as much nematodes penetrate and develop as in susceptible ones but the ratio between males and females is different. It was therefore quite probable that this resistance is polyfactorial and merely recessive.