Testing onions (Allium cepa L.) and otherAllium species for resistance toBotrytis allii Munn.

Summary While various methods of testing for neck rot resistance were compared, it was found thatBotrytis allii behaves as a wound parasite and that its pathogenicity is rather low. The degree of infection was strongly influenced by the amount of inoculum by the temperature at which the cultures were stored and by storage duration. Besides, infection appeared to be much influenced by pre-treating, the inoculated bulbs, the method of inoculation and finally the environmental conditions after inoculation.Three test methods were compared: inoculation of seedlings, of detached leaves and of bulbs. The bulb test seemed the most suitable because of its reliability and the possibility of carrying out the test at any desired period in autumn or winter. A drawback of the bulb test is that it is rather laborious.The results of the seedling test indicated that seedlings of the cultivated onion (Allium cepa) hardly ever showed any resistance. OtherAllium species proved highly resistant during the seedling stage. In an older stage however, the leaves of most of these species were found to be almost as susceptible as those of onion. The foliage of some ornamental onion species appeared to be very resistant.The test of about 20,000 bulbs of the cultivated onion yielded some strikingly resistant individuals.Samenvatting Het toetsen van uien (Allium cepa L.) en andere Allium soorten op resistentie tegen Botrytis allii Munn.Bij het vergelijken van verschillende methoden voor het toetsen op resistentie tegen koprot werd gevonden datB. allii zich gedraagt als een wondparasiet en dat de pathogeniteit van deze schimmel tamelijk gering is. De mate van infectie werd zeer beïnvloed door de hoeveelheid inoculum, door de temperatuur waarbij de sporen waren bewaard en door de tijdsduur van de bewaring. De infectie bleek ook sterk af te hangen van de voorbehandeling van de geï noculeerde bollen, de methode van inoculeren en tenslotte van de uitwendige omstandigheden na inoculatie.Er werden drie methoden onderling vergeleken: de toetsing van zaailingen, van afgeknipt blad en van bollen. Hiervan leek de bollentoets de geschiktste vanwege zijn betrouwbaarheid en de mogelijkheid de toets op elk gewenst moment in de herfst of de winter uit te voeren. Een nadeel is dat deze methode vrij veel arbeid vergt.De resultaten van de zaailingentoets toonden aan, dat zaailingen van de cultuur-ui nauwelijks enige resistentie bezitten.Als zaailing bleken andereAllium-soorten zeer resistent. In een later stadium bleken de bladeren van de meeste van deze soorten echter bijna even gevoelig te zijn als die van de ui.Enkele sieruiensoorten hadden zeer resistent blad.Het toetsen van ongeveer 20.000 bollen vanAllium cepa leverde enkele opvallend resistente exemplaren op.     

Breeding for resistance to neck rot (Botrytis allii) in onions (Allium cepa)

Summary For 10 years the method developed by Van der Meer et al, (1970) to test neck rot resistance in onions has been applied in a breeding programme. From experiments with market varieties, inbred lines and half-sib families it is concluded that neck rot resistance as determined by this method is a quantitative character, which shows continuous variation and is in part fixable by selection. The practical importance of this type of neck rot resistance is not yet clear.Report no. 68     

Methods to determine solidity and dry matter content of onions (Allium cepa L.)

Summary Different testing methods to measure solidity and dry matter content of onion bulbs were examined. The correlation coefficients between the characters determined were calculated. No strong correlations were found between the results of the different methods of measuring solidity. The refraction value of the press juice gives reliable information on the dry matter content of the onion bulb.     

Screening for resistance to anthracnose (Colletotrichum gloeosporioides Penz.) in Allium cepa and its wild relatives

Colletotrichum gloeosporioides is an airborne disease which causes significant yield losses in shallots (A. cepa var. ascalonicum) grown in the tropics. Breeding for resistance to this disease in shallots has been scarcely carried out and has been primarily focussed on Allium cepa material. Wild species related to shallot might provide sources of resistance and therefore a screening of this material was carried out. Three different isolates of C. gloeosporioides originating from Brazil, Nigeria and Indonesia, were used in the screening procedure. The accessions screened of A. cepa and A. oschaninii were most susceptible to the three isolates. Partial resistance was observed in accessions of A. altaicum, A. fistulosum, A. galanthum, A. pskemense and A. roylei. The highest level of resistance was found in accessions of A. galanthum and A. fistulosum. A. roylei was highly resistant to the Brazilian isolate but very susceptible to the Nigerian and Indonesian isolates. A genetic analysis of the resistance present in A. roylei to the Brazilian isolated revealed that it is dominantly inherited and most probably determined by more than one gene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inbreeding depression and single cross hybrids in leeks (Allium ampeloprasum ssp. porrum)

Summary All current commercial cultivars of leeks are open-pollinated and one of the major problems with the crop is poor uniformity with much of the variation being genetic in origin. Inbred lines and single cross hybrids were produced to try to reduce the genetic variation. Inbreds were generated by single seed descent from 5400 plants taken from six commercial cultivars and performance data for uniformity, yield and quality are presented for the S₁-S₃ generations. A few relatively vigorous inbred lines were obtained but overall, inbreeding depression was very severe with no compensating increase in uniformity as measured by coefficients of variation. In contrast, the experimental hybrids gave significant uniformity, yield and quality benefits compared to open-pollinated commercial cultivars and can be used as the basis for developing a range of commercial hybrid cultivars.Abbreviations SSD Single Seed Descent - HRI Horticulture Research International     

Pollen competition in onion (Allium cepa L.)

Summary Pollen mixtures with two components, one of which carried a dominant marker gene for red or white bulb skin colour, were used to pollinate flowers on onion umbels from several cultivars. Scoring progenies for the marker revealed that pollen components differed in their ability to effect fertilization, suggesting that gametophytic competition can occur in onions. In many cases, self-pollen appeared to have a competitive advantage over cross-pollen. Both of the male components and the female parent played a part in determining the final ratio obtained from a mixed pollination.Crossed seeds were slightly but significantly heavier than selfed seeds in nine out of ten umbels studied.     

Inheritance of Resistance to Downy Mildew (Peronospora destructor [Berk.] Casp.) from Allium roylei Stearn in the Backcross Allium cepa L. × (A. roylei ×A. cepa)

Allium roylei Stearn and both reciprocals of the interspecific hybrid between Allium cepa L. and A. roylei displayed no symptoms of Peronospora destructor (Berk.) Casp. after artificial or natural inoculations, whereas A. cepa was susceptible. In the offspring from the backcross A. cepa× (A. roylei ×A. cepa) resistant and susceptible plants segregated after artificial inoculations, fitting a 1: 1-ratio. This suggests that resistance is controlled by a single, dominantly-inherited locus (designated Pd₁) from the nuclear genome of A. roylei. During a severe epidemic in the field, plants from the same backcross segregated resistant and susceptible individuals in a 3: 1-ratio. Escapes may explain the deviation from the 1: 1-segregation, but the presence of a second resistance locus segregating independently from Pd₁ cannot be excluded, implicating possible differences in virulence between populations of P. destructor. The occurrence in the backcross offspring of plants having a morphology similar to A. cepa without showing symptoms of downy mildew opens perspectives for breeding P. destructor-resistant onion varieties.     

Screening immature bulbs of daffodil (Narcissus L.) crosses for resistance to basal rot disease caused by Fusarium oxysporum f. sp. narcissi

Summary Immature bulbs were used in two screening trials to identify daffodil genotypes resistant to basal rot disease caused by Fusarium oxysporum f. sp. narcissi. Progenies, having at least one parent with some resistance, were grown in compost infested with chlamydospores of the fungal pathogen, and survivors were recovered at final harvest. Survival rates were very low when one-year old bulbs were used; the greater survival of two-and three-year old bulbs indicates that resistance increased with bulb age. Selection pressure was influenced by inoculum concentration in the compost. Continuous variation of percentage bulb survival between progenies suggests a polygenic mode of inheritance; there was no evidence of maternal inheritance. Parental general combining ability (GCA) was highly significant and accounted for much of the difference in bulb survival between progenies, but non-additive parental effects were also apparent. GCA rankings in the two trials were similar and reflected the resistance of parental cultivars in the field. A three-dimensional graphing procedure was devised to depict goodness of fit of progeny data to the additive model.     

Introgression of leaf blight resistance from Allium roylei Stearn into onion (A. cepa L.)

Summary Segregation analysis in BC₁ and F₂ progenies from interspecific hybrids between Allium roylei and A. cepa demonstrated that leaf blight resistance is conditioned by one single dominant gene from A. roylei. This gene, designated Bs ₁ , was unlinked to the genes Pd ₁ and Pd ₂ determining downy mildew resistance. The prospects of exploiting A. roylei as a source for disease resistances in onion breeding are very promising.     

Variation of gynogenesis ability in onion (Allium cepa L.)

Onion varieties from Northern-Europe, Eastern-Europe, Southern-Europe and the U.S. including populations, inbreds, synthetics and clones were tested for their gynogenesis ability for three years: 1993-1995. Embryos were induced in Petri dishes using in vitro culture of flower buds. Embryo rate, regeneration rate, survival rate, embryo quality and ploidy level of regenerants are described. Important genotype and variety effects are pointed out; embryo production and plant regeneration ranged from 0 to 17% and from 0 to 11% of inoculated flowers, respectively. Highest results were obtained with inbreds and synthetics for embryo production as well as for plant regeneration. Populations expressed various responses which were generally low. Geographic origin and year effects were covered by the effects of genetic structure of varieties and specific genotype of donor plant. Among regenerants, 80% were haploid and 13% were spontaneous diploid. No relation has been found between general quality and ploidy level of regenerants. The choice of plant material for successful gynogenesis in onion is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation in pollen viability in the onion (Allium cepa L.)

Summary The pollen viability of onions in a glasshouse was recorded from May to October 1975, using the fluorescein test. The average viability was 60–95% for most of this period but fell to less than 1% during the last two weeks of August. There was great variation in pollen viability between anthers within a flower and between flowers within a head. Attempts to induce pollen inviability by low temperature treatments at various stages of inflorescence development were unsuccessful. Low levels of pollen inviability appear to be a characteristic feature of onions, but the high level of inviability which was found both in this and in a previous season was associated particularly with the August period.     

洋葱种质资源遗传多样性的ISSR分析

应用ISSR标记对32份洋葱种质资源的遗传多样性进行了分析。从31个ISSR引物中筛选出4条扩增产物条带清晰、多态性高的引物,在32份资源样品中共扩增出39条带,其中31条带为多态性位点,平均每个引物扩增的多态带数为7.75条,多态性条带比率（PPB）为79.48%。资源间的遗传相似系数在0.552~0.960之间,具有较为丰富的遗传多样性。ISSR聚类分析表明,在L取值为D=0.68时,可将32份洋葱资源分成5类：第一类包括18份种质资源,主要以Yellow Sweet Spanish系统为主;第二类包括1份种质资源,为Bejo Daytona;第三类包括3份种质资源,为Yellow Globe系统;第四类包括9份种质资源,为Yellow globe danvers系统;第五类包括1份种质资源,为Yellow Danvers system系统。较好地揭示了洋葱种质资源间的遗传多样性与亲缘关系,可为洋葱遗传育种和杂交亲本选择提供科学依据。     

Biochemical characterization of white onion landraces (Allium cepa L.) through HPLC analysis of endosperm seed proteins

Water-, salt-, alcohol- and alkali-soluble seed storage proteins, extracted from 21 cipolla bianca di Pompei landraces (Allium cepa L.), were analyzed by anionic exchange-high performance liquid chromatography (AE-HPLC). Chromatographic elution profiles (time range 0–40 min) at 280 nm of water-soluble seed proteins evidenced the presence of 21 peaks, which allowed all the landraces studied to be distinguished from each other. The differences detected were both qualitative (presence/absence of one or more peaks) and quantitative; the water-soluble proteins were useful in differentiating landraces and cultivars while the other seed protein fractions only showed a weak polymorphism. The cluster analysis, based on HPLC data, showed that the landraces clustered with a genetic similarity degree ranging between 69% and 94%. The possibility of discriminating among closely related onion landraces during the course of breeding programmes could allow the identification of biochemical markers linked to useful agronomical traits. As observed by chromatographic analysis, the globulin composition of onion water-soluble seed protein appears to be independent of environmental growth conditions. The biochemical characterization of the available typical onion germplasm may contribute to obtain a community recognition and denomination, such as Denomination of Protected Origin (D.O.P.), Indication of Protected Origin (I.G.P.) or Specificity Attestation (A.S.). The biochemical method here developed resulted of high resolution, cost-effective and time-saving for characterization and genetic purity assessment of the landraces studied.     

Growth Analysis of Onion (Allium cepa L.) in Relation to Irrigation and Nitrogen Fertilization

Studies were carried out at the Indian Institute of Horticultural Research, Bangalore during winter seasons of 1982—83 and 1983—84 to analyse the growth rhythm of onion in relation to irrigation and N fertilization. It was observed that irrigation at 0.45 to 0.65 bar soil water potential recorded higher dry matter accumulation and distribution, leaf area index (LAI), leaf area duration (LAD), leaf area ratio (LAR) and crop growth rate (CGR) during most of the stages, while net assimilation rate (NAR) and relative growth rate (RGR) were not markedly affected. Highest harvest index was noticed with irrigation at 0.65 bar.
Nitrogen fertilization significantly increased dry matter accumulation and distribution into different parts, LAI, LAD, LAR, CGR and harvest index. Although NAR and RGR showed an increasing trend with N fertilization, the effect was not significant during most of the stages. There was no significant interaction between soil water potential and N fertilization on any of the growth parameters.     

韭葱愈伤组织和不定芽诱导研究

以韭葱假茎和葱薹为外植体,进行离体培养。结果表明,在MS附加不同浓度的NAA和6-BA培养基上,韭葱假茎和葱薹均能诱导形成愈伤组织,但二者出愈率差异极显著。在MS+NAA1.0mg/L+6-BA2.0mg/L培养基上,韭葱假茎愈伤组织出愈率仅为27.09%,在MS+NAA2.0mg/L+6-BA1.0mg/L培养基上,韭葱葱薹愈伤组织出愈率高达77.09%。愈伤组织继代培养后,葱薹形成的愈伤组织不能分化形成芽,而假茎形成的愈伤组织可以诱导产生不定芽,在MS+NAA1.0mg/L+6-BA2.0mg/L培养基上,假茎芽的诱导率为20.83%,且假茎靠近茎基部处诱导产生的愈伤组织分化芽的能力最强。     

Gibberellic acid as a gametocide for the common onion (Allium cepa L.)

Summary A high concentration of gibberellic acid (GA₃, 2%) was found to act as a gametocide for the common onion, Allium cepa L., when sprayed in the beginning of the bolting process.This technique is suggested as a possible substitute for hand emasculation, since it would greatly facilitate interspecific and intervarietal crosses, recurrent backcrosses and the selection of good B lines.     

Genotypic variation of resistance to southern stem rot of Jerusalem artichoke caused by Sclerotium rolfsii

Southern stem rot caused by Sclerotium rolfsii is a significant problem of Jerusalem artichoke (Helianthus tuberosus L.) production in Thailand. Resistant varieties are not available. The objective of this study was to investigate genetic variability of Jerusalem artichoke genotypes for resistance to stem rot caused by S. rolfsii. Ninety-one Jerusalem artichoke genotypes were evaluated under greenhouse conditions. Traits evaluated included disease score, lesion length, days to permanent wilting, plant height, shoot dry weight, and root dry weight index. Number of days from inoculation until permanent wilting was the only trait with statistically significant differences among genotypes. Based on this trait, genotypes were categorized into two distinct groups: resistant and susceptible. Genotypes that consistently expressed relative resistance to S. rolfsii included HEL 280, HEL 278, HEL 293 and JA 98. These genotypes may be useful to plant breeders as sources of germplasm for incorporating resistance to S. rolfsii into Jerusalem artichoke.     

Chromosome and cytoplasm analyses of somatic hybrids between onion (Allium cepa L.) and garlic (A. sativum L.)

Chromosomes and cytoplasms were analyzed in two lines of a somatic hybrid between onion (Allium cepa L.) and garlic (A. sativum L.). One line of the somatic hybrid had 40 chromosomes and the other 41chromosomes. Genomic in situhybridization successfully revealed the chromosome constitution of the two lines. One line had 20 chromosomes from onion and17 chromosomes from garlic, and the other had 21 chromosomes from onion and 17chromosomes from garlic. Interestingly, both lines had three chimeric chromosomes. PCR-RFLP analyses of chloroplast and mitochondrial DNAs of both lines showed that these were identical to the onion parent. This revised version was published online in July 2006 with corrections to the Cover Date.     

An interspecific cross between Allium roylei Stearn and Allium cepa L., and its backcross to A. cepa

Summary Alloplasmic lines of B. napus with the cytoplasm of B. campestris, B. juncea, B. carinata and B. oleracea var. alboglabra were developed with the backcross substitution method. Cytoplasmic influence for different morphological and physiological attributes were absent. This suggests a common origin of the Brassica species concerned.