Potato protoplasts in crop improvement

Exploring the Significance of Somaclonal Variations in Horticultural Crops

Genetic and epigenetic variations produced via cell and tissue culture open up new sources of variability intra-species which can be used to improve crops. The use of in vitro generated somaclonal variations for selecting novel variants aids in the development of novel genotypes having desirable agronomic traits that can be released as varieties or utilized for breeding purposes. Horticultural crops give higher yield and productivity per unit area than other crops, as well as provide good economic returns which have led to an increase in their potential benefits throughout time. The last three to four decades have seen the selection and release of a number of valuable somaclonal variants, many of which possess remarkable features including disease resistance, high yield, improved nutritional quality and abiotic stress tolerance. Generating somaclonal variations has given breeders a novel alternative option for obtaining genetic diversity in horticultural crops and without advanced technologies. The variations introduced through tissue culture process, methods to determine and validate genetic changes in vitro regenerated plantlets, along with prospective application of such variations in horticultural crops' improvement are reviewed in the present work.

CRISPR/Cas9-Mediated Mutagenesis of the Granule-Bound Starch Synthase Gene in the Potato Variety Yukon Gold to Obtain Amylose-Free Starch in Tubers

Potato (Solanum tuberosum L.) is the third most important food crop after rice and wheat. Its tubers are a rich source of dietary carbohydrates in the form of starch, which has many industrial applications. Starch is composed of two polysaccharides, amylose and amylopectin, and their ratios determine different properties and functionalities. Potato varieties with higher amylopectin have many food processing and industrial applications. Using Agrobacterium-mediated transformation, we delivered Clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR/Cas9) reagents to potato (variety Yukon Gold) cells to disrupt the granule-bound starch synthase (gbssI) gene with the aim of eliminating the amylose component of starch. Lugol-Iodine staining of the tubers showed a reduction or complete elimination of amylose in some of the edited events. These results were further confirmed by the perchloric acid and enzymatic methods. One event (T2-7) showed mutations in all four gbss alleles and total elimination of amylose from the tubers. Viscosity profiles of the tuber starch from six different knockout events were determined using a Rapid Visco Analyzer (RVA), and the values reflected the amylopectin/amylose ratio. Follow-up studies will focus on eliminating the CRISPR components from the events and on evaluating the potential of clones with various amylose/amylopectin ratios for food processing and other industrial applications.

Genome editing in potato via CRISPR-Cas9 ribonucleoprotein delivery

Clustered regularly interspaced short palindromic repeats and CRISPR-associated protein-9 (CRISPR-Cas9) can be used as an efficient tool for genome editing in potato (Solanum tuberosum). From both a scientific and a regulatory perspective, it is beneficial if integration of DNA in the potato genome is avoided. We have implemented a DNA-free genome editing method, using delivery of CRISPR-Cas9 ribonucleoproteins (RNPs) to potato protoplasts, by targeting the gene encoding a granule bound starch synthase (GBSS, EC 2.4.1.242). The RNP method was directly implemented using previously developed protoplast isolation, transfection and regeneration protocols without further adjustments. Cas9 protein was preassembled with RNA produced either synthetically or by in vitro transcription. RNP with synthetically produced RNA (cr-RNP) induced mutations, i.e. indels, at a frequency of up to 9%, with all mutated lines being transgene-free. A mutagenesis frequency of 25% of all regenerated shoots was found when using RNP with in vitro transcriptionally produced RNA (IVT-RNP). However, more than 80% of the shoots with confirmed mutations had unintended inserts in the cut site, which was in the same range as when using DNA delivery. The inserts originated both from DNA template remnants from the in vitro transcription, and from chromosomal potato DNA. In 2-3% of the regenerated shoots from the RNP-experiments, mutations were induced in all four alleles resulting in a complete knockout of the GBSS enzyme function.

Discovery of Methyl (5 Z)-[2-(2,4,5-Trioxopyrrolidin-3-ylidene)-4-oxo-1,3-thiazolidin-5-ylidene]acetates as Antifungal Agents against Potato Diseases

Synthesis, isomerism, and fungicidal activity against potato diseases of new (5 Z)-[2-(2,4,5-trioxopyrrolidin-3-ylidene)-4-oxo-1,3-thiazolidin-5-ylidene]acetate derivatives with 1,3-thiazolidine-4-one and pyrrolidine-2,3,5-trione moieties linked by an exocyclic C═C bond were described. Their structures were clearly confirmed by spectroscopic and spectrometric data (Fourier transform infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance, and mass spectrometry), elemental analysis, and X-ray diffraction crystallography. A bioassay for antifungal activity in vitro against Phytophthora infestans, Fusariun solani, Alternaria solani, Rhizoctonia solani, and Colletotrichum coccodes demonstrated that 2,4,5-trioxopyrrolidin-1,3-thiazolidine derivatives exhibited a relatively broad spectrum of antifungal activity. One of the compounds showed considerable activity against all of the strains; in the case of F. solani, P. infestans, and A. solani, it possesses comparable or better fungicidal efficacy than the positive control Consento. Consequently, this compound is a promising fungicidal candidate for plant protection.

Efficient targeted multiallelic mutagenesis in tetraploid potato (Solanum tuberosum) by transient CRISPR-Cas9 expression in protoplasts

Altered starch quality with full knockout of GBSS gene function in potato was achieved using CRISPR-Cas9 technology, through transient transfection and regeneration from isolated protoplasts. Site-directed mutagenesis (SDM) has shown great progress in introducing precisely targeted mutations. Engineered CRISPR-Cas9 has received increased focus compared to other SDM techniques, since the method is easily adapted to different targets. Here, we demonstrate that transient application of CRISPR-Cas9-mediated genome editing in protoplasts of tetraploid potato (Solanum tuberosum) yielded mutations in all four alleles in a single transfection, in up to 2 % of regenerated lines. Three different regions of the gene encoding granule-bound starch synthase (GBSS) were targeted under different experimental setups, resulting in mutations in at least one allele in 2-12 % of regenerated shoots, with multiple alleles mutated in up to 67 % of confirmed mutated lines. Most mutations resulted in small indels of 1-10 bp, but also vector DNA inserts of 34-236 bp were found in 10 % of analysed lines. No mutations were found in an allele diverging one bp from a used guide sequence, verifying similar results found in other plants that high homology between guide sequence and target region near the protospacer adjacent motif (PAM) site is essential. To meet the challenge of screening large numbers of lines, a PCR-based high-resolution fragment analysis method (HRFA) was used, enabling identification of multiple mutated alleles with a resolution limit of 1 bp. Full knockout of GBSS enzyme activity was confirmed in four-allele mutated lines by phenotypic studies of starch. One remaining wild-type (WT) allele was shown sufficient to maintain enough GBSS enzyme activity to produce significant amounts of amylose.

Genetic and epigenetic uniformity of polyembryony derived multiple seedlings of Hevea brasiliensis

Hevea brasiliensis Muell. Arg (Para rubber tree) is a tropical tree species of Amazonian origin widely cultivated in several parts of the world for natural rubber, a highly priced commodity inevitable for the world rubber industry. Large, tree to tree variation in growth and latex yield among individual plants of high yielding Hevea clones is a common phenomenon observed in mature rubber plantations. The genetic heterogeneity of the seedlings which are used as rootstocks for propagation through budgrafting is considered as a major factor responsible for this variation. In order to minimize this variation, attempts were made to develop highly uniform rootstock material via an in vitro technique by inducing zygotic polyembryony in Hevea. Immature open pollinated fruits of a high yielding clone RRII 105 were cultured by half ovulo embryo culture technique. Multiple embryos were induced from the 8-10-week-old zygote with a novel combination of gibberellic acid (GA3), kinetin, and zeatin. Plantlets were successfully generated from the multiple embryos and raised in the field post hardening. Screening using genetic and epigenetic molecular markers revealed that the multiple seedlings developed are highly uniform and are of single zygotic origin. Development of plants having genetic and epigenetic uniformity suggests that this technique is ideal for raising uniform rootstock material in Hevea which may significantly reduce intraclonal variations. Moreover, these plants could serve as ideal material for physiological and molecular investigations towards the understanding of stock-scion interaction process in rubber.

Applications of biotechnology and genomics in potato improvement

Potato is the third most important global food crop and the most widely grown noncereal crop. As a species highly amenable to cell culture, it has a long history of biotechnology applications for crop improvement. This review begins with a historical perspective on potato improvement using biotechnology encompassing pathogen elimination, wide hybridization, ploidy manipulation and applications of cell culture. We describe the past developments and new approaches for gene transfer to potato. Transformation is highly effective for adding single genes to existing elite potato clones with no, or minimal, disturbances to their genetic background and represents the only effective way to produce isogenic lines of specific genotypes/cultivars. This is virtually impossible via traditional breeding as, due to the high heterozygosity in the tetraploid potato genome, the genetic integrity of potato clones is lost upon sexual reproduction as a result of allele segregation. These genetic attributes have also provided challenges for the development of genetic maps and applications of molecular markers and genomics in potato breeding. Various molecular approaches used to characterize loci, (candidate) genes and alleles in potato, and associating phenotype with genotype are also described. The recent determination of the potato genome sequence has presented new opportunities for genomewide assays to provide tools for gene discovery and enabling the development of robustly unique marker haplotypes spanning QTL regions. The latter will be useful in introgression breeding and whole-genome approaches such as genomic selection to improve the efficiency of selecting elite clones and enhancing genetic gain over time.

Facilitating the recovery of phenotypically normal transgenic lines in clonal crops: a new strategy illustrated in potato

Transgenic plants frequently exhibit altered phenotypes, unrelated to transgene expression, which are attributed to tissue culture-induced variation and/or insertional mutagenesis. Distinguishing between these possibilities has been difficult in clonal crops such as potato, due to their highly heterozygous background and the resulting inherent phenotypic variability associated with segregation. This study reports the use of transgene integration as a molecular marker to trace the clonal origin of single cells in tissue culture. Following transformation, multiple shoots have been regenerated from cell colonies of potato (Solanum tuberosum L.) and Southern analysis used to confirm their derivation from a single transformed cell. Analysis of phenotypic variation in field trials has demonstrated marked differences between these multiple regeneration events, the origin of which must have occurred after T-DNA insertion, and consequently during the tissue culture phase. This result unequivocally demonstrates that somaclonal variation occurs during tissue culture and independent of transgene insertion. Furthermore, the first shoots recovered do not necessarily exhibit less somaclonal variation, since later regeneration events can give rise to plants that are more phenotypically normal. Therefore, when developing transgenic lines for genetic improvement of clonal crops, multiple shoots should be regenerated and evaluated from each transformation event to facilitate the recovery of phenotypically normal transgenic lines.

Genetic transfer in plants through interspecific protoplast fusion

Protoplasts of sexually incompatible species have been fused and in some combinations have given rise to somatic hybrid plants. Partial elimination of parental chromosomes from either species is common in such hybrids, but total chromosome loss has generally occurred only with phylogenetically unrelated pairings. Genetic function of one parent may be retained despite a complete loss of its chromosomes, suggesting that genetic introgression is possible in the absence of complete donor chromosomes. A model interspecific combination for such studies is the potato-tomato somatic hybrid for which numerous phenotypes and karyotypes are encountered at the outset, with a broader range observed in the second somatic generation.

A simple and general method for transferring genes into plants

Transformed petunia, tobacco, and tomato plants have been produced by means of a novel leaf disk transformation-regeneration method. Surface-sterilized leaf disks were inoculated with an Agrobacterium tumefaciens strain containing a modified tumor-inducing plasmid (in which the phytohormone biosynthetic genes from transferred DNA had been deleted and replaced with a chimeric gene for kanamycin resistance) and cultured for 2 days. The leaf disks were then transferred to selective medium containing kanamycin. Shoot regeneration occurred within 2 to 4 weeks, and transformants were confirmed by their ability to form roots in medium containing kanamycin. This method for producing transformed plants combines gene transfer, plant regeneration, and effective selection for transformants into a single process and should be applicable to plant species that can be infected by Agrobacterium and regenerated from leaf explants.

Stable and extreme resistance to common scab of potato obtained through somatic cell selection

Somatic cell selection with thaxtomin A as a positive selection agent was used to isolate variants of potato cv. Russet Burbank with strong to extreme resistance to common scab. Glasshouse and field trials identified 51 variants with significantly reduced disease incidence (frequency of infected tubers) and severity (tuber lesion coverage) compared with the parent cultivar. The most promising variants exhibited extreme disease resistance, rarely showing lesions, which were invariably superficial and shallower than those on the parent. Resistance traits were consistently expressed both in 10 glasshouse and two field trials at different locations, with varied inoculum and disease pressure. Disease-resistant variants differed in their response to thaxtomin A in tuber slice bioassays. Of 23 variants tested, 10 showed reduced thaxtomin A susceptibility, with the remaining 13 responding similar to that of the parent. Thus, toxin tolerance was not the only factor responsible for observed disease resistance; however, four of the five most disease-resistant variants had enhanced thaxtomin A tolerance, suggesting that this factor is important in the expression of strong disease resistance. Pathogenicity and toxin tolerance remained stable over a 6-year period, demonstrating that selected phenotypes were robust and genetic changes stable. The majority of disease-resistant variants had tuber yields equivalent to the parent cultivar in glasshouse trials. This suggests that selection for disease resistance was not associated with negative tuber attributes and that certain variants may have commercial merit, worthy of further agronomic testing.

Breeding virus resistant potatoes (Solanum tuberosum): a review of traditional and molecular approaches

Tetraploid cultivated potato (Solanum tuberosum) is the World's fourth most important crop and has been subjected to much breeding effort, including the incorporation of resistance to viruses. Several new approaches, ideas and technologies have emerged recently that could affect the future direction of virus resistance breeding. Thus, there are new opportunities to harness molecular techniques in the form of linked molecular markers to speed up and simplify selection of host resistance genes. The practical application of pathogen-derived transgenic resistance has arrived with the first release of GM potatoes engineered for virus resistance in the USA. Recently, a cloned host virus resistance gene from potato has been shown to be effective when inserted into a potato cultivar lacking the gene. These and other developments offer great opportunities for improving virus resistance, and it is timely to consider these advances and consider the future direction of resistance breeding in potato. We review the sources of available resistance, conventional breeding methods, marker-assisted selection, somaclonal variation, pathogen-derived and other transgenic resistance, and transformation with cloned host genes. The relative merits of the different methods are discussed, and the likely direction of future developments is considered.

Characteristics of genetic variation in the progenies of protoplast-derived plants of rice, Oryza sativa cv Nipponbare

Genetic variation in protoplast-derived rice (Oryza sativa L.) plants was characterized using first and second generation selfed progenies. A total of 133 regenerated plants were obtained from ten protoplasts of the japonica rice cultivar Nipponbare. Sixty two regenerated plants which set enough seeds for the subsequent field tests at the next generation and were derived from five protoplasts were selected, and their selfed seeds were used as the first selfed-seed progeny (Pt(1) generation). Fifteen plants were selected from each of the 15 Pt(1) lines, and their selfed seeds were used for tests at the Pt(2) generation. Thirty seven Pt(1) lines (60%) segregated plants with detrimental mutant characters of yellowgreen phenotype, dwarf stature, dense and short panicle, or low seed fertility. According to the segregation patterns in the lines having mutated plants among those originated from the same protoplasts, the stages of mutation induction were estimated. Additionally, five quantitative traits were changed in almost all Pt(1) and Pt(2) lines. Varied quantitative traits of heading date, number of spikelets per panicle, and seed fertility, were in a heterozygous state. However, culm and panicle lengths showed high uniformity, whereas reduced culm and panicle lengths were caused by mutational changes in polygenes and/or multiple genes.

Multiplication of tobacco mosaic virus in tobacco callus tissues and in vitro selection for viral disease resistance

Tobacco mosaic virus-resistant tobacco was selected in vitro using callus tissues induced from axillary buds of systemically infected tobacco plants. Callus lines in which the virus was continuously multiplying were first isolated and redifferentiated into shoots. By the procedure, non-diseased, healthy shoots were successfully isolated from diseased shoots, which showed typical mosaic symptoms of the virus, and regenerated into intact plants.These regenerated plants showed resistance to virus inoculation, and selfed progeny of virus-resistant regenerants segregated the resistance and susceptibility according to the Mendelian system.

The use of in vitro-grown microtuber discs inAgrobacterium-mediated transformation of Russet Burbank and Lemhi Russet potatoes

We have usedin vitro-grown microtuber discs in the transformation of Russet Burbank and Lemhi Russet potato (Solanum tuberosum L.) cultivars byAgrobacterium-mediated gene transfer. Transformed plants were selected by their resistance to kanamycin and identified by β-glucuronidase activity. Northern blot analysis confirmed the presence of the corresponding messenger RNA. The ability to transform these two cultivars promises significant improvements to agronomically important varieties.

Somaclonal variation--genetic basis and breeding applications

Somaclonal variation, the recovery of genetic changes in plants regenerated from tissue culture, offers an opportunity to uncover natural variability and to use this variability for the development of new varieties. This review focuses on the unique variation generated by this technique and the current use of somaclonal variation to develop new plant varieties.

Field assessment of dihaploid Solatium tuberosum and S. brevidens somatic hybrids

Following both chemical and electrical fusion of protoplasts of a dihaploid line of potato (Solanum tuberosum), (PDH40), with those of the wild species, Solanum brevidens, 11 and 40 somatic hybrid plants, respectively were obtained. Fifteen of these somatic hybrid genotypes and the two parents were studied further in a small field trial to assess field performance and phenotypic variability. In the UK, somatic hybrid plants are classified as genetically engineered organisms, and the UK Advisory Committee on Genetic Manipulation have imposed various restrictions on field experiments. Examination of the somatic hybrids in the field showed extensive phenotypic variability, and no two genotypes were identical. Some of the variation reflected changes in chromosome numbers, but other factors were also involved. Half the somatic hybrid genotypes produced tubers in the field, although the tubers were smaller and differed morphologically from those of PDH40. The results of the study suggest that the extent of somaclonal variation manifested in somatic hybrids is greater than that found in protoplast-derived plants of potato. The implications of this observation and the current regulations concerning field experiments of somatic hybrid plants in the UK are discussed.

Regeneration of amphidiploid plants from tissue cultures of Allium wakegi

Callus was induced from the bulb of Allium wakegi Araki on MS semisolid medium supplemented with several growth regulating substances. The calli were subcultured every 40 days. At the time of every subculture the callus was subdivided to be used for chromosome studies, plant regeneration, or continuous callus multiplication. The chromosome constitution of cells in callus and regenerated plants varied over the culture period, and at the 3rd subculture amphidiploid plants were obtained. They appeared even more frequently than amphihaploid plants in the 4th subculture. Hypoamphihaploid regenerants appeared as stumpy shoots but none of these shoots proceeded further to form a normal plant. By Giemsa C-banded karyotype, the chromosome constitution of amphidiploid plants was found to result from exact doubling of the chromosome sets of amphihaploid common species. Amphidiploid plants show better viability and growth than common plants. The possibility and the expectation of new crop plants to be developed from amphidiploid plants will be discussed.

A rapid transformation method for Solanum tuberosum using binary Agrobacterium tumefaciens vectors

A tuber disc transformation and regeneration system was devised for potato (Solanum tuberosum). Tuber discs were found to be the most morphogenetic organ on a medium previously optimised for tomato regeneration. Shoot regeneration from tuber discs was rapid and transformed as shown by nopaline assays and Southern blot analysis. The ease and speed of the tuber disc method will allow for the increased use of this commercially important plant in transformation studies.

In vitro selection of alfalfa plants resistant to Fusarium oxysporum f. sp. medicaginis

From two lines of Medicago sativa characterized by a high regeneration capability, calli resistant to culture filtrate of Fusarium oxysporum f. sp. medicaginis have been selected. In these calli regeneration capability was greatly reduced and only one plant per callus was recovered. Regenerated plants have been evaluated for resistance to culture filtrate and for in vivo resistance to the pathogen. Three plants out of eight were resistant to the fungus and a high correlation between resistance to culture filtrate and in vivo resistance was observed.

Genetic transformation in two potato cultivars with T-DNA from disarmed Agrobacterium

Derivatives of potato (Solanum tuberosum cv.'s 'Maris Bard' and 'Desiree') transformed with disarmed T-DNA from genetically engineered Agrobacterium tumefaciens strains were isolated. The transformed plants were recovered from shoot-forming tumours induced by infection of wounds with mixedcultures of shoot-inducing A. tumefaciens strains T37 and either Agrobacterium strain LBA1834(pRAL1834), (Hille et al. 1983) or LBA4404(pBIN6; pRAL4404), (Bevan 1984). Two small-scale feasibility experiments gave at least four 'Maris Bard' plants transformed with pRAL1834 T-DNA and two 'Desiree' plants with pBIN6 T-DNA. The transformed 'Maris Bard' plants were morphologically abnormal and highly aneuploid. This was probably an unfortunate side-effect of a tissue culture-step introduced to promote the efficiency of shoot regeneration. The transformed 'Desiree' plants, in contrast, were isolated without promoting additional shoot-growth. They were morphologically normal, contained 47 and the euploid 48 chromosomes per cell respectively and had improved growth on media containing kanamycin.

Field performance and cytology of protoplast-derived rice (Oryza sativa): high yield and low degree of variation of four japonica cultivars

Protoplast-derived rice plants of four Japanese cultivars, Nipponbare, Fujisaka 5, Norin 14 and Iwaimochi were individually cultivated in a submerged paddy field. They exhibited more stems, which resulted in more panicles than respective control plants. Other characteristics of protoplast-derived plants were (compared with controls): a slightly shorter or similar culm length, fewer spikelets per panicle, slightly lower seed fertility and similar or lighter 1,000 kernel weight. Grain yield of protoplast-derived plants was more than that of respective control plants in four cultivars. The cause of the higher yield of protoplast-derived plants seems to be mainly due to increased panicle number. Among 126 protoplast-derived plants, 1 triploid, 10 tetraploids and 1 aneuploid were found. Furthermore, 11 variants with low seed fertility showing no gross chromosomal anomalies and one plant with abnormal panicles were found. In total, about 80% of protoplastderived plants showed normal characters. The present results are encouraging for the possibility of rice breeding using protoplasts.

Plant regeneration from leaf protoplasts of Solanum torvum

A protocol to obtain regenerated plants from protoplasts of Solanum torvum Sw a wild species of eggplant resistant to Verticillium wilt is reported. Leaf protoplasts were enzymatically isolated from six-week old seedlings grown in a controlled environment chamber. Protoplasts were plated on modified KM medium (0.4 M glucose)+(mg/l): 1.0 p-chlorophenoxyacetic acid (CPA)+1.0 naphthaleneacetic acid (NAA)+0.5 6-benzylaminopurine (BAP) and 0.02 abscisic acid (ABA). The protoplast density was 5×10(4) per ml with 5 ml placed in each of two quadrants in X-dishes (100×15 mm). The reservoir medium was modified KM+(mg/l): 0.1 NAA+0.5 BAP+0.1 M sucrose+0.1 M mannitol+0.6% washed agar+1% activated charcoal. Dishes were initially placed in the dark at 27°C. Protoplast division was initiated in 1-2 weeks and 4 weeks later p-calli were 1-3 mm. Plating efficiency was 11% when measured at 3 weeks. Six-week old p-calli were transferred individually onto Whatman No. 1 filter paper layered on modified KM (0.15 M sucrose)+mg/l: 2.0 indoleacetic acid (IAA)+2.0 zeatin+0.5% washed agar for 2 weeks. Subsequently, shoots occurred within 4 weeks at 70% efficiency on MS+30 g/l sucrose+2 mg/l zeatin. Shoots were rooted on half strength MS+10 g/l sucrose.

Uniformity of plants regenerated from orange (Citrus sinensis Osb.) protoplasts

Using 25 plants (protoclones) regenerated from orange (Citrus sinensis Osb.) protoplasts, several characters, including leaf and flower morphology, leaf oil, isozyme patterns and chromosome number, were examined. No significant variations in each character were recorded among the protoclones. Uniformity observed among protoclones was identical to that of nucellar seedlings.

Heritable somaclonal variation in wild barley (Hordeum spontaneum)

Progenies of H. spontaneum plants regenerated from immature embryo derived calli were analysed for somaclonal variation on the following traits: (1) organization of the intergenic spacer of the rRNA genes; (2) B and C hordein pattern on SDS-PAGE; (3) genomic organization of the B and C hordein coding sequences; (4) mitochondrial DNA organization assayed by hybridization of Southern blots of total DNA with mitochondrial coding genes; (5) cytology. One out of twelve progeny plants was characterized as variant for two traits: (a) a loss of 1.8 and 2.5 kb Taq I intergenic rDNA spacer fragments and (b) a variant pattern of hordeins on 1-D SDS-PAGE. No numerical or structural chromosome variation was detected among the control plants therefore it is assumed that the variation was caused by the in vitro culture and transmitted, through sexual reproduction, to the analysed progeny.

Somaclonal variation in some agronomic and quality characters in wheat

A total of 256 selected lines derived from tissue culture of three hexaploid wheat cultivars were grown in a replicated hill plot experiment to examine somaclonal variation in agronomic characters. The lines were derived by single plant selection for various characters from a total of 100 regenerants, and were either SC3 or SC4 generation in the test. Significant variation was found in all the characters measured: height, grain number per spike, kernel weight, yield, total dry weight and harvest index. In most cases, variation could be identified which was both less than and greater than the parental controls. However, there was also an apparent effect of the parent cultivar on the total amount and direction of the variation. For two cultivars, lines could be traced back through the culture phase to individual explant embryos. Many of the original embryos contributed significant variation, and most characters showed significant variation arising from more than one embryo. In the following year, 32 lines selected from the hill plot experiment were grown in larger replicated plots and yield, harvest index and a number of grain and baking quality characters were measured. No lines selected for high yield or harvest index maintained significant improvements over their parental controls. However, significant variation was displayed for many of the quality characters examined. Significant increases in kernel weight, hardness and protein content, and a significant reduction in yellow pigmentation represented potentially useful improvements. Only unfavourable variation was seen in flour yield and in mixograph height, time and breakdown.

Plant regeneration from cultured cell-derived protoplasts of Pelargonium aridum, P. x hortorum and P. peltatum

Cultured protoplasts from cell suspensions of Pelargonium aridum, P.x hortorum and P. peltatum divided and formed callus. On agar-solidified regenerative medium, such protoplast-derived calli (p-calli) underwent plant regeneration at frequencies approaching 100% for P. aridum and 10% for P.x hortorum. Under similar conditions shoot primordia arose in 5% of P. peltatum p-calli, but these never developed into normal shoots. However, following a liquid-shake culture regime, whole plants were induced in 20% of P. peltatum p-calli. This approach also improved regeneration of P.x hortorum to 60%.

A comparison of somatic chromosomal instability in tissue culture regenerants from Medicago media Pers

Two cultivars (Heinrichs, Reaver) and two breeding lines (Br1, Le1) from Medicago media were cultured in a media protocol consisting of a high concentration 2,4-D induction step. Regenerants were produced from all four stocks. Representative samples from each regenerant population along with the corresponding control population were cytologically analyzed for chromosomal and pollen abnormalities. While numerical changes in chromosome numbers were found in all regenerant populations, there was considerable variation between the four stock groups. Heteroploidy was observed for both hypo and hyper aneuploid regenerants, but there were no differences in pollen stainability between hypo and hyper aneuploid regenerants and 'euploid' regenerants. Tissue culture regenerants generally produced a lower pollen stainability percent as compared to control populations grown from seeds. Gross and cryptic changes in chromosomes, or hormonal carry over effects or both were considered causes for poor pollen stainability in tissue culture regenerants. Cytological analyses indicate that the cultivar might play an important role in the cytological stability or instability of regenerant populations. Exploitation of this naturally existing situation to produce 'euploid' regenerants for field experiments and to obtain gross cytological stability in somaclones is discussed.