Sports and hybrids of triploid Hosta ‘Sum and Substance’ reveal chromosome losses and gains in all three apical layers

Ploidy distributions in L1, L2, and L3 apical or meristematic layers of 56 different plants (79 accessions) from vegetative and sexual progeny of the triploid Hosta ‘Sum and Substance’ were determined. Nuclear DNA contents (2C) of each apical layer were measured by flow cytometry with propidium iodide, and inferred ploidies are calculated. During tissue culture, the triploid (L1–L2–L3?=?3–3–3) Hosta ‘Sum and Substance’ exhibited chromosome losses resulting in somaclonal variants such as DNA aneuploids (e.g., 2.7–2.7–2.7) and aneuploidy chimeras (e.g., 3–2.7–2.7). Most interestingly, some chimeras exhibited even an increase in genome size as in plants with 3.5–3–3 configuration. Hybrids of H. ‘Sum and Substance’ show only losses of nuclear DNA compared with the original triploid. This gives rise to fully aneuploid plants and no chimeras. The measurements of Hosta ‘Sum and Substance’ lineages of sports and hybrids indicate that chromosome losses or gains are an important source of new cultivars. The complexity of chromosomal distribution in derivatives from the triploid Hosta ‘Sum and Substance’ is discussed.     

PLANTLETS FROM PETAL SEGMENTS,PETAL EPIDERMIS,AND SHOOT TIPS OF THE PERICLINAL CHIMERA,CHRYSANTHEMUM MORIFOLIUM ‘INDIANAPOLIS'

Cultivated chrysanthemums, especially the greenhouse series of ‘Indianapolis’ cultivars, are probably periclinal chimeras for flower color. Therefore, in vitro propagation of chrysanthemum, which has recently been described, might produce plants not true to type. To test this, plantlets were generated from cultures of petal segments, petal epidermis, and shoot tips; these plantlets were grown to flowering to determine whether chrysanthemums with two genetically different chimeral layers in the petals are stable in tissue culture. Layer I displaced layer II in the formation of new meristematic areas in shoot tip and petal culture, showing that such chimeras are unstable in culture. Many more abnormal morphological types were exhibited by the plants which were regenerated from petal cultures rather than those from shoot tip cultures. Abnormalities included quilled and incised petal forms, as well as lack of anthocyanin pigmentation, characteristics which may not be attributable to the rearrangement of chimeral layers. Paramutation, true mutation, and environmenal effects are offered as possible explanations for this phenomenon.     

CAMELLIA + ‘DAISY EAGLESON,’ A GRAFT CHIMERA OF CAMELLIA SASANQUA AND C. JAPONICA

We have described a new, distinct camellia cultivar, Camellia + ‘Daisy Eagleson’ (Byrd ex Meyer), found on a rootstock of hexaploid C. sasanqua Thunb. ‘Maiden's Blush’ on which a scion of diploid C. japonica L. had been grafted. The new cultivar is a graft chimera with epidermal tissue from C. sasanqua and the internal tissue from C. japonica. Many characters expressed and measured at the cellular or tissue’ level showed complete independence in the chimera. These included chromsome number, anthocyanin synthesis, pH, cell size, and fragrance. Some characters expressed at the organ or whole plant level showed an interaction between the two components. These included floral morphology, leaf size, time of bloom, bud hardiness, and growth habit. One entirely new character we found was the presence of 6–8 styles in the chimeral flowers in contrast to the three styles typical of the component species. While the two components grew together in apparent harmonious and stable fashion, we have recovered each of the pure, homogeneous component cultivars a number of times from tissue replacement and displacement phenomena in the shoot and as adventitious shoots from roots. ‘Daisy Eagleson’ is only the third, fully-authenticated, woody graft chimera.     

Transcriptome-based single nucleotide polymorphism markers for genome mapping in Japanese pear (Pyrus pyrifolia Nakai)

The development of single nucleotide polymorphism (SNP) markers in Japanese pear (Pyrus pyrifolia Nakai) offers the opportunity to use DNA markers for marker-assisted selection in breeding programs because of their high abundance, codominant inheritance, and potential for automated high-throughput analysis. We developed a 1,536-SNP bead array without a reference genome sequence from more than 44,000 base changes on the basis of a large-scale expressed sequence tag (EST) analysis combined with 454 genome sequencing data of Japanese pear ‘Housui’. Among the 1,536 SNPs on the array, 756 SNPs were genotyped, and 609 SNP loci were mapped to linkage groups on a genetic linkage map of ‘Housui’, based on progeny of an interspecific cross between European pear (Pyrus communis L.) ‘Bartlett’ and ‘Housui’. The newly constructed genetic linkage map consists of 951 loci, comprising 609 new SNPs, 110 pear genomic simple sequence repeats (SSRs), 25 pear EST–SSRs, 127 apple SSRs, 61 pear SNPs identified by the “potential intron polymorphism” method, and 19 other loci. The map covers 22 linkage groups spanning 1341.9 cM with an average distance of 1.41 cM between markers and is anchored to reference genetic linkage maps of European pears and apples. A total of 514 contigs containing mapped SNP loci showed significant similarity to known proteins by functional annotation analysis.     

Genetic analysis of Anatolian pear germplasm by simple sequence repeats

The pear (Pyrus communis L.) is a fruit species grown in many temperate regions of the world. Turkey harbours a rich and ancient pear germplasm adapted to diverse ecological regions of the country. The aim of this study was to genetically characterise locally grown Anatolian pear germplasm. We have analysed large numbers (228) of pear accessions originated from six eco‐geographically diverse regions using 18 simple sequence repeat (SSR) markers and identified 308 SSR alleles. Genetic similarities among the accessions examined were generally below 80%. The highest heterozygosity rate was obtained for the SSR locus ‘CH02D11’ derived from apples and ‘KA16’ and ‘NH0021a’ derived from pears. No identical or synonymous genotypes were found, while five homonymous genotypes were identified. Factorial correspondence analysis could not clearly separate different pear accession groups studied, suggesting that Anatolian pear accessions were intermixed possibly due to gene flow and/or germplasm movements between different eco‐geographical regions. However, most pear accessions were grouped according to their collection sites in structure analyses. The SSR data reported here for Anatolian pear accessions will be valuable for future germplasm management efforts as well as for comparative studies that investigate genetic relationships of pears from Anatolia and the surrounding regions.     

Methode zum Nachweis der Dauersporen des Kohlhernieerregers Plasmodiophora brassicae in gärtnerischen Kultursubstraten

Populations of pathogenic Pseudomonas syringae pv. syringae were monitored on apparently healthy leaves, blossoms, and fruit from two apple orchards with known histories of blister bark and a pear orchard with a known history of blossom blast. Populations on blossoms and fruits were higher on pears than on apples. Yellow-pigmented, non-pathogenic bacteria might have suppressed or masked the presence of P. syringae pv. syringae on apple trees. Populations of P. syringae pv. syringae on apple and pear leaves fluctuated sharply but higher levels generally occurred during the 1984/85 growing season than during the drier 1983/84 season. This investigation indicates that the resident phase of P. syringae pv. syringae is probably a major source of inoculum for apple blister bark and pear blossom blast in South Africa.     

Ultrastructural changes in the cell walls of ripening apple and pear fruit

Ultrastructural changes in the cell walls of “Calville de San Sauveur” apples (Malus sylvestris Mill) and “Spadona” pear (Pyrus communis L.) fruit were followed during ripening. In apple, structural alterations in cell walls became apparent at advanced stages of softening and showed predominantly dissolution of the middle lamella. In pears softening was also associated with the dissolution of the middle lamella, and in addition a gradual disintegration of fibrillar material throughout the cell wall. In fully ripe fruit almost all of the fibrillar arrangement in the cell wall was lost. Application of enzyme solutions containing polygalacturonase and cellulase to tissue discs from firm pear fruit led to ultrastructural changes observed in naturally ripening pears. In apple polygalacturonase alone was sufficient to dissolve the middle lamella region of the cell walls, as was also found to occur in naturally ripening fruit. In both apple and pear the cell wall areas containing plasmodesmata maintained their structural integrity throughout the ripening process. At advanced stages of ripening vesicles appeared in the vicinity of plasmodesmata.     

SSRs isolated from apple can identify polymorphism and genetic diversity in pear

Apple simple sequence repeats (SSRs) were intergenerically applied to the characterization of 36 pear accessions, including 19 Japanese pears (Pyrus pyrifolia), 7 Chinese pears (P. bretschneideri, P. ussuriensis), 5 European pears (P. communis), 3 wild relatives (P. calleryana), and 2 hybrids between P. pyrifolia and P. communis. All of the tested SSR primers derived from apple produced discrete amplified fragments in all pear accessions. Nucleotide repeats were detected in the amplified bands by both Southern blot and sequencing analysis, and nucleotide sequences of pear were compared with those of apple. The differences in fragment size among pear or between pear and apple were, in many cases, due to the differences in repeat number. Interestingly, the DNA sequence of flanking regions in apple was highly conserved in pear. Hybrids from P. pyrifolia×P. communis showed one fragment inherited from each parent in all scorable cases, which suggested that each primer pair amplified fragments originating from the same locus. A total of 79 alleles were detected from seven SSR loci in pear, and all pear varieties except for the mutants could be differentiated. In conclusion, SSRs isolated from apple are highly conserved in pear and could be utilized as DNA markers in the latter genus. Received: 17 July 2000 / Accepted: 22 September 2000     

Nuclear DNA content as an indicator of inflorescence colour stability of in vitro propagated solid and chimera mutants of chrysanthemum

In chrysanthemum, breeders seek for desirable characteristics of the inflorescence, which can first be established once the plant is mature. The present study aims to determine whether measurement of DNA content can be useful in the detection of somaclonal variants and/or separation of chimera components in chrysanthemum at the early in vitro multiplication stage. Eleven Chrysanthemum?×?morifolium (Ramat.) Hemsl. cultivars of the Lady group (a mother cultivar and ten of its radiomutants obtained by X-ray- or γ-irradiation; solid and periclinal chimeras) were propagated in vitro. Single-node explants were cultured in Murashige and Skoog (MS) medium, either without plant growth regulators (PGRs) or supplemented with 6-benzyladenine (BA) and indole-3-acetic acid (IAA). The nuclear DNA content was measured by flow cytometry (FCM) in the shoots produced in vitro. After acclimatization and growth of the plants in a glasshouse, inflorescence colour was recorded. The addition of PGRs to the medium almost doubled the mean number of shoots produced in vitro per explant, but caused a change in inflorescence colour of all (‘Lady Apricot’; periclinal chimera) or part of the plants (‘Lady Amber’; solid mutant and ‘Lady Salmon’; periclinal chimera). All radiomutants contained less DNA than the mother cultivar ‘Richmond’. There were significant differences in DNA content between plants of the same cultivar grown in media with or without PGRs for ‘Lady Apricot’ and ‘Lady Salmon’, but no phenotype alternation occurred in chrysanthemums produced in PGR-free medium compared to the original cultivars. Conversely, in medium with PGRs, chimeras produced flowers different from the original colour. In all except one cultivar (‘Lady Amber’; solid mutant) a lack of differences in genome size between plants grown in either medium coincided with a stable inflorescence colour. The occurrence of some plants of ‘Lady Amber’ with different inflorescence colour may be due to small DNA changes, undetectable by FCM. It can be concluded that FCM analysis of DNA content in young plantlets can be indicative of the stability of inflorescence colour in chrysanthemum, especially chimeric cultivars, and for mutant detection.

     

Genetic constitution of germ cells in intervarietal and interspecific chimeras of Brassica induced by in-vitro grafting

The characteristics of intervarietal and interspecific chimeras synthesized by the graft-culture method were determined by morphology, anthocyanin pigmentation pattern, and crossing. In an intervarietal chimera between YR-ranpou (green cabbage) and Ruby ball (red cabbage) in Brassica oleracea, a segregation phenomenon was noted in which seeds giving rise to purple and green plants were both produced in a single capsule in F₁ progeny from crosses of chimeras with YR ranpou, the anthocyanin-free graft partner type. The degrees of segregation varied, reflecting the structure of the chimeras. YR ranpou-dominant chimeras produced capsules in which seeds gave rise to green plants at a high frequency, while Ruby ball-dominant chimeras produced capsules in which seeds in one capsule gave rise to purple plants at a high frequency. Mixed chimeras produced capsules with green plants or purple plants more regularly than did other chimeral types. Furthermore, a chimeral type in which seeds gave rise to green and purple plants was found in 3.2% of the total crosses. Segregation patterns in the progenies corresponded with the chimeral types. Chlorophyll-deficient variation (resulting in variegation or the production of albino plants) was found at a frequency of 2.6%. These results show that chimeric tissues are actually in a mixed state and that either the ovary develops from more than two cells or else that variation occurs in the germ-cell layer. In interspecific chimeras between Ruby ball and Komatsuna (B. campestris) various types of chimeras generally showed low pollen fertility, few capsules, and low seed-setting. Progenies from selves (geitonogamy), open crosses and crosses with the two parental species produce a predominantly homogeneous genotype showing either the Ruby ball or the Komatsuna type. Only two crosses produced four interspecific hybrids which expressed variations in their morphological and isozymic characters.     

Effect of a plant growth regulator prohexadione-calcium on insect pests of apple and pear

The effect of prohexadione-calcium, a plant growth regulator that inhibits gibberellin metabolism, on Cacopsylla pyricoloa (Foerster) in pear trees, and Choristoneura rosaceana (Harris) and Aphis spireacola Patch, in apple trees was studied. C. pyricoloa and A. spireacola populations were significantly reduced in prohexadione-calcium-treated pear and apple, respectively. Insecticide control of both pests with imidacloprid was synergized in treatments with prohexadione-calcium. In apples treated with prohexadione-calcium, there was a significant reduction in the number of C. rosaceana shelters per tree and amount of fruit injury at harvest attributable to the C. rosaceana. There was an additive effect when tebufenozide was used to control C. rosaceana in trees treated with prohexadione-calcium. Prohexadione-calcium significantly reduced vegetative growth in both pears and apples. Synergistic and additive treatment effects of prohexadione-calcium and pesticides used in this study may be due to better penetration and coverage of pesticides due to reduced foliar growth or to changes in the nutritional quality of the host plants.     

A high-density genetic linkage map of bronze loquat based on SSR and RAPD markers

We constructed a high-density genetic linkage map of bronze loquat (Eriobotrya deflexa) by using a three-way cross of loquat (Eriobotrya japonica) × (loquat × bronze loquat) and simple sequence repeat (SSR) and random amplified polymorphic DNA (RAPD) markers. The positions of the SSR loci used in this study were previously identified on reference maps of pears (Pyrus spp.) and apples (Malus spp.). The map of bronze loquat (‘Taiwan loquat No. 1’) consisted of 308 loci including 167 SSRs (8 loquat, 57 pear, and 102 apple SSRs), 140 RAPDs, and the loquat canker resistance gene Pse-a on 19 linkage groups covering a genetic distance of 1036 cM. Almost all loquat linkage groups were aligned to the pear consensus map by using at least two pear or apple SSRs, suggesting that positions and linkages of SSR loci were well conserved between loquat and pear and between loquat and apple. The constructed map may be used to determine the location of genes and quantitative trait loci of interest and to analyze genome synteny in the tribe Pyreae, subfamily Spiraeoideae of the family Rosaceae.     

Opportunities for synthetic plant chimeral breeding: Past and future

Many plant periclinal chimeras are selected by horticulturalists due to their distinctive, valuable phenotypes, and because they are relatively stable. Most of these have arisen by induced or spontaneous mutation. Interspecific chimeras have been accidentally produced from graft unions of plants from a wide range of families. Early last century Winkler developed a technique to produce interspecific chimeras from graft unions (graft chimeras). More recently in vitro techniques have been developed to synthesize interspecific and intervarietal chimeras. However, these techniques have only been successful for species in the families Solanaceae and Cruciferae, and rarely assessed on plants in other families. Research is required to improve these techniques or develop new approaches so that the efficiency of chimeral shoot production is improved and the techniques are applicable to plants in a wide range of families. The unique characteristics of interspecific or intervarietal chimeras show the potential of chimeral breeding to produce new cultivars. If chimeral breeding techniques were improved, they could become a standard breeding approach for some horticultural crops.     

Treatment with chlorous acid to inhibit spores of Alicyclobacillus acidoterrestris in aqueous suspension and on apples

Aim: To test the efficacy of a chemical (chlorous acid) for reducing the numbers of viable Alicyclobacillus acidoterrestris spores in laboratory media and on apples. Methods and Results: Alicyclobacillus acidoterrestris spores in aqueous suspension and on apple surfaces of four different cultivars were treated with 268 ppm chlorous acid. Treatment with 268 ppm chlorous acid sharply reduced the numbers of spores of A. acidoterrestris in laboratory media by 1·6, 4·3, and 7·0 log₁₀ reductions for 5, 10, and 15 min treatments, respectively. Chlorous acid also effectively reduced the spore load on apple surfaces. Alicyclobacillus acidoterrestris spore counts were significantly reduced by about 5 log₁₀ after 10 min treatment on four different apple cultivars (‘Red Delicious’, ‘Golden Delicious’,’ Gala’, and ‘Fuji’). There was no synergistic effect on spore reduction when chlorous acid treatment was combined with heat. Conclusions: These results show that chlorous acid is highly efficacious against A. acidoterrestris spores on apple surfaces. Significance and Impact of the Study: Chlorous acid can be used as an alternative sanitizer of chlorine to control a major A. acidoterrestris contamination source in juice processing plants.     

Oviposition preference of Anthocoris nemorum and A. nemoralis for apple and pear

Anthocoris nemorum L. and Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) are important predators of insect pests in pome fruit. Females insert their eggs in leaf tissue. The females’ choice of oviposition site is important for the subsequent distribution of nymphs on host plants. Oviposition preference for apple and pear leaves was tested in the laboratory in four experiments (experiments 1–4). In three experiments it was tested whether simulated insect damage to leaves (experiments 5 and 6) or the presence of prey (experiment 7) influenced oviposition preference. The effect of the presence of prey was only tested for A. nemorum on apple leaves. There was a highly significant anthocorid species × plant interaction for the number of eggs laid on apple and pear leaves. Anthocoris nemorum laid more eggs on apple than on pear leaves, while A. nemoralis preferred pear. Anthocoris nemorum's preference for apple increased over the 6‐week period in which experiments 1–4 were performed, from 66% to 91% eggs laid on apple leaves. No change over time in preference was found for A. nemoralis. Across experiments 1–4, the majority of A. nemorum eggs were laid near leaf margins, whereas eggs of A. nemoralis were more commonly found in the leaf centre, 5 mm or more from the margin, with a highly significant leaf region × species interaction. There was no significant difference in preference for leaf side between A. nemorum and A. nemoralis, but there was a highly significant plant × leaf side × experiment interaction. Thus, more eggs were laid on the ventral than on the dorsal side of pear leaves in experiment 4, while significantly more eggs were laid on the dorsal side of apple leaves in experiments 3 and 4. Choice tests between damaged and healthy leaves showed that A. nemorum laid significantly more eggs on the damaged leaves, while A. nemoralis preferred healthy leaves. Anthocoris nemorum showed a near‐significant preference for ovipositing on leaves with eggs of Operophtera brumata (Lepidoptera: Geometridae). The oviposition preferences found correspond to the natural distribution of these predators in apple and pear orchards. The preference of A. nemorum for leaf margins, and of A. nemoralis for the leaf centre as an oviposition site, supports earlier observations. A preference for leaf side for oviposition site has not been reported earlier. Preference for damaged leaves could help A. nemorum to locate prey in a field situation.     

Improving in vitro mineral nutrition for diverse pear germplasm

Mineral nutrition in the media used for growth of in vitro plants is often difficult to optimize due to complex chemical interactions of required nutrients. The response of plant tissue to standard growth media varies widely due to the genetic diversity of the plant species studied. This study was designed as the initial step in determining the optimal mineral nutrient requirements for micropropagation of shoot tips from a collection of genetically diverse pear germplasm. Five mineral nutrient factors were defined from Murashige and Skoog salts: NH₄NO₃, KNO₃, mesos (CaCl₂·2H₂0–KH₂PO₄–MgSO₄), micronutrients (B, Cu, Co, I, Mn, Mo, and Zn), and Fe-EDTA. Each factor was varied over a range of concentrations. Treatment combinations were selected using response surface methods. Five pears in three species (Pyrus communis ‘Horner 51,’ ‘Old Home?×?Farmingdale 87,’ ‘Winter Nelis,’ Pyrus dimorphophylla, and Pyrus ussuriensis ‘Hang Pa Li’) were grown on each treatment combination, responses were measured, and each response was analyzed by analysis of variance. The analyses resulted in the identification of the following factors with the single largest effects on plant response: shoot quality (mesos), leaf spotting/necrosis (mesos), leaf size (mesos), leaf color (mesos, NH₄NO₃, and KNO₃), shoot number (NH₄NO₃ and Fe), nodes (NH₄NO₃ and KNO₃), and shoot length (mesos and Fe). Factors with the largest effects (mesos and Fe) were similar among the genotypes. This approach was very successful for defining the appropriate types and concentrations of mineral nutrients for micropropagation of diverse pear genotypes.     

STABILITY OF LEAF VARIEGATION IN SAINTPAULIA IONANTHA DURING IN VITRO PROPAGATION AND DURING CHIMERAL SEPARATION OF A PINWHEEL FLOWERING FORM

Plants of the foliarly variegated cultivar Saintpaulia ionantha Tommie Lou and the florally variegated cultivar Candy Lou were regenerated through tissue culture from leaf sections, petal sections, and subepidermal tissue. This provided explants with derivatives of all histogen layers of the shoot apex, layers I and II only, and layers II and III only. Over 1,000 plants of Tommie Lou and Candy Lou were grown to flowering. A low level of phenotypic variation was observed, but in no case could this be attributed to the separation of genotypically distinct cell lines. The foliar variegation pattern of both cultivars was stable through in vitro propagation. In contrast, the chimeral components of the flower color pattern in Candy Lou separated during regeneration. These data demonstrate that Tommie Lou-type foliar variegation is not caused by periclinal chimerism and that all leaf cell layers possess the genetic information necessary to produce variegated foliage. The production of all green and all white plants from a radiation-induced periclinal chimera demonstrated that the system used could detect chimeral separation. These results support the contention that adventitious shoots in Saintpaulia almost always differentiate in vitro from a derivative(s) of a single histogen layer, and this layer is usually the LI.     

Phacidiopycnis washingtonensis,Cause of a New Storage Rot of Apples in Northern Europe

Phacidiopycnis washingtonensis was identified by morphology and ITS sequence analysis as the cause of rubbery rot, a new storage disease of apples in northern Germany. Infected fruits had an unusually firm texture and pale appearance after storage in ultra‐low oxygen conditions, but turned dark brown to black in ambient atmosphere. Ultimately, the surface of rotted fruits became covered by black pycnidia producing cream‐coloured conidial exudates. Rubbery rot affected several apple varieties, including the commercially important ‘Jonagold’ and ‘Elstar’. Losses during storage were commonly below 1% but reached 5–10% in a few cases. Fruits of ‘Golden Hornet’ crab apple trees planted as pollinators in commercial orchards became heavily infected by P. washingtonensis in October. Conidia were released throughout the following season from infected fruit mummies, which remained attached to the crab apple tree.