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.     

Beet mild yellowing virus resistance derived from wild and cultivated Beta germplasm

Sugar beet (Beta vulgaris ssp. vulgaris L.) has a relatively narrow genetic base and several programmes have sought to evaluate the potential for introducing novel traits from wild and cultivated Beta germplasm into the crop. In particular, resistance to important sugar beet diseases has been identified within individual Beta accessions. We report here the successful transfer of resistance to Beet mild yellowing virus (BMYV) from garden beet, fodder beet and leaf beet accessions to progeny populations in initial crosses with sugar beet. Twelve plant populations derived from different Beta accessions were inoculated with viruliferous aphids carrying BMYV and the virus content of individual plants subsequently quantified by an ELISA test. Seven populations were significantly more resistant than a control sugar beet cultivar (P ≤ 0.05). BMYV resistance was successfully inherited in BC₁ and BC₂ generations, suggesting that resistance could potentially be introgressed from these sources into elite sugar beet lines.     

Overwintering of genetically modified sugar beet, Beta vulgaris L. subsp. vulgaris, as a source for dispersal of transgenic pollen

The potential impact of transgenic crops on community ecology will depend on the distribution and establishment of the new transgenic traits, on the sexual transfer of their new genes to the environment (Bartsch &; Pohl-Orf, 1996) and on the potential ecological impact of the transgenic trait. Flowering and pollen dispersal is important for outcrossing of the genetically engineered trait. For a biennial plant, like the cultivars of Beta vulgaris L., overwintering is normally necessary to become generative and to produce pollen and seeds (Abe et al., 1997), which usually does not happen with sugar beet as a field crop harvested in autumn (Longden 1989). The starting point for the project was a transgenic sugar beet, Beta vulgaris L. subsp. vulgaris (Lange et al., 1998), with rhizomania and herbicide ( Basta®, Liberty®) resistance. Cold tolerance is one of the most important factors for survival of sugar beet in Central- and North-Europe. Among other ways, spreading of transgenic traits into weed beet (Boudry et al., 1993) or wild beet can occur if genetically engineered – biennial – plants survive the winter, flower in spring and spread their pollen. Field experiments were performed with transgenic breeding lines and their hybrids, transgenic and non-transgenic hybrids with Swiss chard and three conventional beet cultivars to evaluate winter survival rates at seven different field sites. We could show that survival of sugar beet – transgenic as well as conventional ones – in Germany and at the Dutch border is possible. Survival rates were well correlated with temperature data and were unexpectedly high. Differences between sugar beet hybrids and breeding lines could be detected but not within different breeding lines or hybrids. There were no differences detectable between transgenic and non-transgenic plants. The data are crucial for the risk assessment of the release of transgenic sugar beet and are the basis for further experiments towards outcrossing and establishment.     

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.     

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.     

QTL for delayed bolting after winter detected in leaf beet (Beta vulgaris L.)

Growing sugar beet (Beta vulgaris L. ssp. vulgaris) as a winter crop in cool temperate climates is expected to increase yield potential. However, this requires bolting resistance after winter. One strategy to achieve complete bolting resistance is to accumulate genes for bolting delay from various genetic resources within the B. vulgaris gene pool. To identify such genes, a QTL mapping was performed in a segregating population derived from a biennial leaf beet with delayed bolting after winter. The population was tested for bolting delay after winter in two different experiments with natural or artificial vernalization. Three QTL for bolting delay were mapped on linkage groups 3, 5 and 9 affecting bolting time by up to 19 days. These QTL could be combined with recently reported bolting QTL to develop a winter sugar beet with complete bolting resistance.     

甜菜种质资源品质性状鉴定与评价

旨在更加科学真实地评价甜菜种质资源的品质性状,有针对性地对种质资源优异品质性状进一步挖掘利用。引用甜菜块根蔗糖可回收率、杂质指数、可回收蔗糖量3 个综合指标,排除甜菜块根中有害性非糖分钾、钠、α-氮的影响,对参试的162 份甜菜种质资源2 年试验鉴定结果的有关品质性状进行分析。结果表明：甜菜块根中影响蔗糖提取的有害性非糖分钾、钠、α-氮在不同的种质资源材料间差异较大,其中钠含量在参试种质资源材料中极差达到4.763 mmol/100 g,为平均数的1.84 倍,变异系数34.43%;α-氮含量和钾含量在不同参试种质资源材料间也表现出较大差异,变异系数分别为16.90%和19.03%。通过对参试种质资源材料的评价,筛选出蔗糖含量高、有害性非糖分含量低的高糖组种质资源材料10份、中高糖组48份材料,2组平均蔗糖可回收率分别为15.88%和14.95%;筛选出杂质指数低于4.0、块根产量在45.00 t/hm2以上的丰产型种质资源材料7份,杂质指数4.0~4.5、块根产量在45.00 t/hm2以上丰产性较好的种质资源材料14 份。甜菜块根中可回收蔗糖量指标综合了蔗糖可回收率和块根产量2个性状指标,利用该项指标评价种质资源材料,可以挖掘出丰产优质的种质资源。用可回收蔗糖量指标评价甜菜品种,筛选丰产、高工艺品质的品种,兼顾甜菜种植者和制糖企业双方利益,有利于甜菜制糖产业可持续发展。     

Root traits and yield in sugar beet: identification of AFLP markers associated with root elongation rate

Morpho-physiological and molecular analysis were conducted to identify useful root indexes of sugar beet nutrient uptake capacity and productivity. Root architectural parameters, root elongation rate, sulfate uptake rate and glucose and fructose content in the root apex, traits involved in the plant response to sulfate stress, were evaluated in 18 sugar beet genotypes characterized by different root yield. Morpho-physiological traits, determined on 11-day-old seedlings grown in hydroponics under sulfate deprivation, showed variations from 59 to 197% and were significantly correlated (P < 0.01) with root yield. Under field conditions, the highest root yield genotype (L18), which has the highest root phenotypic values following sulfate shortage, also showed the greatest root length density and leaf relative water content, with respect to the lowest root yield genotype (L01). Bulk segregant analysis based on AFLP analysis, done on a segregating progeny obtained from the cross between the two lines L01 × L18, allowed the identification of two AFLP markers associated to the root elongation rate parameter that showed the highest variation among all the analyzed root traits. The genetic diversity of root adaptive traits and the use of marker-assisted selection aimed at increasing sugar yield under water and nutrient stress in sugar beet breeding programmes are discussed.     

利用SRAP与SSR标记分析不同类型甜菜的遗传多样性

为选育优质甜菜新品种, 指导种质资源引进和利用, 为进行分子标记辅助选择育种提供科学依据, 采用SRAP和SSR两种分子标记方法相结合, 对甜菜单胚雄性不育系及保持系等49份材料进行遗传多样性分析。利用4个表型差异显著的甜菜品系对SRAP的64对引物组合及SSR的11对引物组合进行扩增, 分别筛选出有效引物组合11对和9对。SRAP的11对引物组合共产生199条扩增带, 其中有86条多态性带, 多态性带的比率平均为43.7%。SSR的9对引物共产生35条扩增带, 多态性比率为100%。全部材料的平均遗传距离为0.3860, 平均遗传相似系数为0.6795, 大约30%的材料遗传距离或遗传相似系数具显著或极显著差异。遗传相似系数平均值比较, 多胚四倍体品系0.7264＞单胚杂交组合0.7243＞国外品种0.7060＞多胚二倍体品系0.6908＞单胚品系0.6837。在遗传距离0.20处, 将49个甜菜材料划分为A、B、C、D 4个类群, D类群又分为4个亚类, 较好地显示了甜菜材料丰富的遗传多样性。表明不同甜菜品种具有相当高的异质性, 国外与国内材料的遗传基础存在一定差异, 但生产应用的甜菜品种间存在亲缘关系较近、遗传基础较窄的倾向。     

Assessing fitness parameters of hybrids between weed beets and transgenic sugar beets

Herbicide resistance is a desired trait for sugar beet (Beta vulgaris L.) production because it is a low‐competitor crop that requires careful weed management. However, gene flow to weed beet (also B. vulgaris) could jeopardize the weed control strategy by causing the emergence of resistant weed beets; it could also lead to further adaptation of weed beet as a troublesome weed for other crops by selecting more competitive plants. To evaluate the hazard that such a selection process represents, apart the herbicide resistance, we investigated the morphology and reproduction of progeny of weed beets having inherited a herbicide resistance gene. First‐generation resistant weed beet exhibited traits likely counter‐selected. But such crop traits rapidly disappeared with backcrossing to weedy relatives: no biologically relevant difference was noted between resistant and susceptible near‐isogenic siblings in the various experiments. In the absence of resistance selection, our data indicate low chances for weed beet to evolve more competitive forms than present weed beet populations. However, they also suggest that there is no fitness cost limiting transgenes spread.     

Efficiency of some molecular markers linked to rhizomania resistance gene (Rz 1 ) for marker assisted selection in sugar beet

Sugar beet (Beta vulgaris L.) is one of the two major products supplying sugar (sucroses) in the world. Rhizomania is one of the most destructive diseases of sugar beet world-wide. Holly is the major source of resistance to rhizomania. The objectives of this study were to identify the dominant homozygous genotypes resistant to rhizomania using ZN1 molecular marker, to field evaluate S₁ progenies of plants already proved to be containing the marker and also to determine the relationship of this and other SCAR (sequence characterized amplified region) markers with SNP1 (single nucleotide polymorphism) marker associated with the Rz ₁ gene. Molecular analysis was carried out on 27 O-type populations (consisting of 13 susceptible and 6 resistant genotypes). Field evaluation and scoring of the phenotypic traits including greenness, growth, uniformity and disease score of 12 O-type populations were carried out on a rhizomania-infested field. The percent agreement of coupling marker ZN1 and repulsion marker ZN8 with disease score was 0.91 and 0.93, respectively. Although all O-types had the Rz ₁ resistance gene but the phenotypic differences were observed due to the effect of different genetic backgrounds and modifier genes. Overall, the results showed that the selected markers can be used for marker-assisted selection (MAS) to reduce the time and cost of breeding programs and increase the efficiency of selection.     

Sources of resistance to <Emphasis Type="Italic">Phytophthora</Emphasis> root rot within the genus <Emphasis Type="Italic">Beta</Emphasis>

Phytophthora root rot caused by Phytophthora drechsleri Tucker is one of the most devastating sugar beet diseases in tropical areas. To identify genetic resources resistant to this disease, an aggressive isolate of P. drechsleri was selected. Then, a screening method was optimized based on the standard scoring scales of 1–9 (1: no symptoms, 9: complete plant death). Finally, 19 sugar beet lines, three cultivars, and 14 accessions of the wild species Beta vulgaris subsp. maritima, B. macrocarpa, B. procumbens, and B. webbiana were evaluated for resistance to the most aggressive isolate of P. drechsleri by using the optimized method (inoculum included 20 g of rice seed together with superficial wound creation). The isolates of P. drechsleri had significant variation in aggressiveness, and Kv10 was the most aggressive isolate on the susceptible variety Rasoul. The lines O.T.201-15, SP85303-0 (resistant check), and S2-24.P.107 had the lowest disease index with scores of 3.09, 3.13, and 3.27 respectively; they were categorized into the resistant group. The interaction between isolates and genotypes was not significant, which indicated the same response of each genotype to different isolates. Investigating the resistance of different generations of sugar beet revealed that progeny selection would be an effective method for increasing the resistance level of breeding materials to P. drechsleri. Among the wild species, the accession 9402 belonging to B. macrocarpa and the accession 7234 of B. vulgaris subsp. maritima had the lowest disease index (2.29 and 2.60, respectively) and were categorized into the resistant group.     

Diversity in root architecture and response to P deficiency in seedlings of <Emphasis Type="Italic">Cucumis melo</Emphasis> L.

Breeding for more phosphorus (P)-efficient crops is one strategy to reduce the use of P fertilizers, thus mitigating the environmental and economic impacts of agriculture. Variation in root architecture and the response to P deficiency were studied in C. melo. Forty accessions representing genetic diversity within the species were screened for their root systems in normal and deficient P conditions at the seedling stage. Various parameters of P-uptake and P-use were analyzed in a subset of accessions at 40 days. Significant differences in root architecture were observed, with the taproot systems prevailing among the wild and exotic accessions, and more branched root systems in cultivated stocks. Moreover, differences in the plastic response of roots to P starvation were observed. Variation in different P-use and -uptake traits correlated with the root architecture. Within ssp. melo, the inodorus and flexuosus landraces had larger and more branched roots and more efficient P-uptake, thereby providing a close genepool for breeding. Within ssp. agrestis, conomon and momordica accessions can be sources of interest for the enhancement of variation in root architecture and P-use efficiency into cultivated melons. Therefore, the diversity observed within C. melo species could be useful in breeding P-efficient melon cultivars.     

An assessment of the genetic relationship between sweet and grain sorghums, within Sorghum bicolor ssp. bicolor (L.) Moench, using AFLP markers

Compared to grain sorghums, sweet sorghums typically have lower grain yield and thick, tall stalks which accumulate high levels of sugar (sucrose, fructose and glucose). Unlike commercial grain sorghum (S. bicolor ssp. bicolor) cultivars, which are usually F₁ hybrids, commercial sweet sorghums were selected as wild accessions or have undergone limited plant breeding. Although all sweet sorghums are classified within S. bicolor ssp. bicolor, their genetic relationship with grain sorghums is yet to be investigated. Ninety-five genotypes, including 31 sweet sorghums and 64 grain sorghums, representing all five races within the subspecies bicolor, were screened with 277 polymorphic amplified fragment length polymorphism (AFLP) markers. Cluster analysis separated older sweet sorghum accessions (collected in mid 1800s) from those developed and released during the early to mid 1900s. These groups were emphasised in a principle component analysis of the results such that sweet sorghum lines were largely distinguished from the others, particularly by a group of markers located on sorghum chromosomes SBI-08 and SBI-10. Other studies have shown that QTL and ESTs for sugar-related traits, as well as for height and anthesis, map to SBI-10. Although the clusters obtained did not group clearly on the basis of racial classification, the sweet sorghum lines often cluster with grain sorghums of similar racial origin thus suggesting that sweet sorghum is of polyphyletic origin within S. bicolor ssp. bicolor     

The Diploidised Meiosis of Tetraploid Beta macrocarpa and its Possible Application in Breeding Sugar Beet

Accessions of Beta macrocarpa Guss., collected on the Canary Islands, were tetraploid (2n = 36). Three of these accessions were studied in detail. The plants were rather uniform in their morphological appearance, both within and between accessions, and were annual and fully self-compatible. Meiosis was completely diploidised, suggesting an alloploid nature of the tetraploid species. Crosses with diploid B. vulgaris yielded triploid hybrids which were sterile or nearly so; a few descendants of such hybrids were highly aneuploid. Crosses between tetraploid B. macrocarpa and autotetraploid cytotypes of B. vulgaris showed variable results, only part of these crosses yielded tetraploid hybrids. The tetraploid hybrids exhibited somewhat higher fertility than the triploids. An F₂ generation showed partial hybrid dwarfness, partial fertility and segregation for carliness and coloration of the hypocotyl. All hybrids had multivalents at meiosis (averages: 2.5—5.4 multivalents per pollen mother cell), indicating suppression of the diploidised meiosis. The possibilities of application of the diploidised meiosis in breeding sugar beet are discussed.     

The sea beet source of resistance to multiple species of root-knot nematode

Development of commercially available host-plant resistance to Meloidogyne spp. is essential to sugarbeet (Beta vulgaris L.) root-knot nematode resistance breeding. Reactions of seedlings from resistant crosses and hybrid derivatives were evaluated against juvenile (J2) inoculations in the greenhouse. The noncultivated sea beet [B. vulgaris ssp. maritime (L.) Arcang] source of resistance is effective against the four economically important root-knot nematodes, i.e., M. incognita Races 1, 2 and 4 (Race 3 not tested), M. Javanica, M. arenaria Races 1 and 2, and M. hapla. In monoxenic culture, M. arenaria inoculations resulted in the most galling, and M. hapla, the least. Species combinations induced higher rates of infection. Different races of the same Meloidogyne species caused similar galling. Preliminary inoculation studies indicated that resistance was also effective to M. Chitwoodi and M. fallax. The trait of resistance to multiple Meloidogyne species may be valuable in developing sugarbeet, and possibly transgenic lines of other crops, resistant to root-knot nematode. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ecological aspects of transgenic sugar beet: transfer and expression of herbicide resistance in hybrids with wild beets

Summary An increasing number of genetically engineered cultivars of several crops is being experimentally released into the environment. In future, crops with new transgenic traits will probably play an important role in agricultural practice. The long-term effect of transgenes on community ecology will depend on the distribution and establishment of transgenic plants in the wild, on the sexual transfer of their new genes to the environment and on the potential ecological impact of the transgenic trait. The starting point was the use of transgenic sugar beet lines, Beta vulgaris subspec. vulgaris var. altissima DÖLL (Helm 1957), with transgenes coding for rhizomania and herbicide (BASTA^®) resistance. The first two questions to answer were: Can the transgenes be transferred via pollen to wild beets, Beta vulgaris subspec. maritima (L.) ARCANG. or cultivated relatives such as red beet or spinach beet and are they expressed in the hybrids? Can transgenes be monitored in young Beta vulgaris-hybrids? The experimental transfer of transgenes was conducted in 1993 at a field location in northern Germany. The beets were hand-pollinated with transgenic pollen. In a non destructive biotest, the hybrid seedlings were tested for herbicide resistance. Transgenic plants showed no noxious phenotypic effects whereas control plants developed leaf necroses. All herbicide resistant hybrids within the biotest were assumed to be transgenic.     

Observations on different mildew sources used in apple breeding at Ahrensburg

Fifty-six populations of common bean (Phaseolus vulgaris L.) were grown in Pontevedra (Northwestern Spain) in four different environments in order to study their genetic diversity in 18 agronomical traits. All characters showed significant differences among populations, and most of them had significant genotype-environment interactions. Broad-sense heritability for this pool of characters ranged from 0.87 (seed length) to 0.12 (seed yield). Sixteen populations which deserve special attention because of their breeding value for earliness, yield, pod and seed size have been identified.     

Assessing genetic diversity in the cassava (Manihot esculenta Crantz) germplasm collection in Brazil using PCR-based markers

Knowledge of the origin, organization and nature of the cassava (Manihot esculenta Crantz) germplasm collection in Brazil is incomplete due to lack of critical information on several aspects of the collection. This study verifies the utility of SSR-primed PCR markers for germplasm assessment and then utilizes these markers as well as RAPD's to characterize the Brazilian collection. We specifically address the following questions: 1)what is the relationship of morphologically closely related species to cultivated cassava? 2) What is the genetic diversity of cultivars within and between different habitats in Brazil? 3) Do agronomic traits and molecular markers reveal the same relationship among cassava accessions? 4) How complete is the Brazilian cassava collection and how well is it represented in the Word Core Collection of cassava, maintained by CIAT? Results of the interspecific studies of cassava and its wild relatives confirms the close relationship of cassava, Manihot esculenta ssp. esculenta to Manihot esculenta ssp. flabellifolia as well identifying several other closely related wild species. Next, PCR-based markers indicate a strong grouping of varieties related to the region of cultivation in Brazil. Moreover, important regions such as Cerrados and Amazon are relatively poorly represented in germplasm collections. Interestingly, the relationships of accessions based on agronomic traits are not fully congruent with relationships revealed with RAPD markers. Finally, the genetic diversity of the Brazilian cassava collection is not fully represented in the Core of the Word Core Collection of CIAT.