Rina Kamenetsky

Floral development in bolting garlic

Abstract Garlic (Allium sativum L.) is a completely sterile plant, propagated only vegetatively. The aim of this research was to study the sequence of morphological processes occurring during floral initiation and development of a number of bolting garlic accessions from the Allium gene bank in Israel by using SEM. The garlic inflorescence is an umbel-like flower arrangement, the branches (flower clusters) of which arise from a common meristem. The numerous flowers have a distinct morphology typical of the genus Allium. Flower-stalk elongation precedes the swelling of the apical meristem and its subdivision into several centers of floral development. Within clusters, floral primordia develop unevenly. Differentiation of topsets begins after floral differentiation on the peripheral part of the apical surface, and their size, number and rate of development vary among genotypes. At least four morphological types differing in flower/topset ratio were distinguished among the 12 clones studied in this investigation. For further studies of flowering physiology and fertility restoration, only clones which can differentiate the greatest proportion of normal flowers and the least of topsets in the apical meristem should be selected.

Diversity in fertility potential and organo-sulphur compounds among garlics from Central Asia

Extending the collection of garlic (Allium sativum L.) accessions is an important means that is available for broadening the genetic variability of this cultivated plant, with regard to yield, quality, and tolerance to biotic and abiotic traits; it is also an important means for restoring fertility and flowering. In the framework of the EU project ‘Garlic and Health’, 120 garlic accessions were collected in Central Asia – the main centre of garlic diversity. Plants were documented and thereafter maintained in field collections in both Israel and The Netherlands. The collection was evaluated for biological and economic traits. Garlic clones vary in most vegetative characteristics (leaf number, bulb size and structure), as well as in floral scape elongation and inflorescence development. A clear distinction was made between incomplete bolting and bolting populations; most of the accessions in the latter populations produced flowers with fertile pollen and receptive stigma. Wide variations were recorded with regard to differentiation of topsets, their size, number and rapidity of development. Furthermore, significant variation in organo-sulphur compounds (alliin, isoalliin, allicin and related dipeptides) was found within garlic collections and between plants grown under differing environmental conditions. Genetic fingerprinting by means of AFLP markers revealed three distinct groups within this collection, differing also in flowering ability and organo-S content.

Life Cycle, Flower Initiation, and Propagation of the Desert Geophyte Allium rothii

Analyses of life cycle, morphogenesis of the monocarpic shoot, and propagation have been carried out on Allium rothii, a desert geophyte from the Western Irano-Turanian region. Plants from a natural population in the Negev Desert highlands were examined during a 2-yr study. The bulb of A. rothii is a temporary organ that is completely replaced by a renewal bulb within 2 yr. The ephemeroid root system is annual, superficial, and adapted for effective absorption during short periods of moist soil. Seeds germinate best in January and February at temperatures between 5⚬C and 15⚬C; germination is not affected by light. The germination process and stages of the life cycle are characterized. The synaptospermic mechanism assures protection of the mature seeds against insects and germination under more favorable conditions in depressions and near shrubs. Intrabulb development was studied by SEM. Five leaf primordia form in apical meristem in June-September; in October the apical meristem becomes reproductive. Anthers and perianth lobes appear in January, while the gynoecium is formed before flowering at the end of February.

Integrated transcriptome catalogue and organ-specific profiling of gene expression in fertile garlic ( Allium sativum L.).

BackgroundGarlic is cultivated and consumed worldwide as a popular condiment and green vegetable with medicinal and neutraceutical properties. Garlic cultivars do not produce seeds, and therefore, this plant has not been the subject of either classical breeding or genetic studies. However, recent achievements in fertility restoration in a number of genotypes have led to flowering and seed production, thus enabling genetic studies and breeding in garlic.ResultsA transcriptome catalogue of fertile garlic was produced from multiplexed gene libraries, using RNA collected from various plant organs, including inflorescences and flowers. Over 32 million 250-bp paired-end reads were assembled into an extensive transcriptome of 240,000 contigs. An abundant transcriptome assembled separately from 102,000 highly expressed contigs was annotated and analyzed for gene ontology and metabolic pathways. Organ-specific analysis showed significant variation of gene expression between plant organs, with the highest number of specific reads in inflorescences and flowers. Analysis of the enriched biological processes and molecular functions revealed characteristic patterns for stress response, flower development and photosynthetic activity. Orthologues of key flowering genes were differentially expressed, not only in reproductive tissues, but also in leaves and bulbs, suggesting their role in flower-signal transduction and the bulbing process. More than 100 variants and isoforms of enzymes involved in organosulfur metabolism were differentially expressed and had organ-specific patterns. In addition to plant genes, viral RNA of at least four garlic viruses was detected, mostly in the roots and cloves, whereas only 1–4% of the reads were found in the foliage leaves.ConclusionsThe de novo transcriptome of fertile garlic represents a new resource for research and breeding of this important crop, as well as for the development of effective molecular markers for useful traits, including fertility and seed production, resistance to pests and neutraceutical characteristics.

Flower development in garlic: the ups and downs of gaLFY expression

The lack of sexual processes prohibits genetic studies and conventional breeding in commercial cultivars of garlic. Recent restoration of garlic flowering ability by environmental manipulations has opened new avenues for physiological and genetic studies. The LEAFY homologue gaLFY has been shown to be involved in the floral development, while two alternatively spliced gaLFY transcripts are expressed in flowering genotypes. In the present work, quantitative real-time PCR and two techniques of RNA in situ hybridization were employed to analyze spatiotemporal expression patterns of the gaLFY during consequent stages of the garlic reproductive process. Temporal accumulation of gaLFY is strongly associated with reproductive organs, significantly increased during florogenesis and gametogenesis, and is down-regulated in the vegetative meristems and topsets in the inflorescence. The two alternative transcripts of the gene show different expression patterns: a high level of the long gaLFY transcript coincided only with floral transition, while further up-regulation of this gene in the reproductive organs is associated mainly with the short gaLFY transcript. It is concluded that gaLFY is involved at different stages of the sexual reproduction of garlic. These new insights broaden our basic understanding of flower biology of garlic and help to establish conventional and molecular breeding systems for this important crop.

Male gametogenesis and sterility in garlic (Allium sativum L.): barriers on the way to fertilization and seed production

Commercial cultivars of garlic (Allium sativum) do not produce flowers and seed; hence, information on microgametogenesis and genetic knowledge of this important crop is unavailable. Recently, physiological studies enabled flowering and fertility restoration in garlic bolting genotypes by environmental manipulations, thus broadening of the genetic variation and facilitating genetic studies. The present report provides first detailed description of the development of male gametophytes in 11 garlic genotypes varying in their fertility traits. Morphological and anatomical studies revealed completely fertile genotypes, as well as variation in anther and pollen development and disruption of the male organs and gametes at different developmental stages. Three types of plant sterility were observed, including complete sterility, male sterility and environmentally induced male sterility. The ITS1 and ITS2 regions of rRNA of the studied genotypes proved to be strongly conservative and thus did not correspond with the phenotypic expression of fertility or sterility in garlic. On the other hand, two-dimensional protein separation maps revealed significant differences between fertile and sterile genotypes, as well as between developmental stages of microsporogenesis. Further research is needed to investigate the internal mechanisms and environmental component of garlic sterility, as well as the possible molecular markers of these traits.

Flowering physiology and some vegetative traits of short-day shallot: A comparison with bulb onion

Summary The critical physiological age of shallot (Allium cepa var. aggregatum) grown from seed and sets, and the effect of temperature on stored bulbs and the flowering habit were studied in Israel. Three short-day genotypes were grown from seeds or sets. Prior to storage, bulbs were sorted according to size and incubated in low (5-10°C), intermediate(13-20°C) or high (30°C) temperatures for various periods. Plants were grown in the open fieldand inthe phytotron, and their vegetative and blooming development was investigated. Our findings show significant genotypic differences in flowering; cold treatment is essential for floral initiation; and the length of the juvenile phase is tightly dependent on the environment. In the field, early-sown shallots had a faster growth rate, accumulated more mass, and produced earlier and more auxillary buds and side shoots than those from the late sowing. Shallots can be induced to flower by cold treatment in storage, the optimum temperature being 5-10°C, whereas high and intermediate storage temperaturesdelay the development of the inflorescence. During growth, high temperatures may suppress already initiated nflorescences.Plants from larger sets flowered more readily than those from small ones, and genotypes varied significantly in their response to cold induction. The impact of genotype and environment on bulb and seed production as well as the similarities anddifferences in flowering habits between shallot and bulb onion are discussed.

Visualization of morphological structure and water status during storage of Allium aflatunense bulbs by NMR imaging

Abstract The effect of cold storage on the developmental morphology and water status in bulb tissues of Allium aflatunense B. Fedtsch. was studied using scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Morphological MR images were produced by a T1-weighted spin echo pulse sequence. Water status was assessed according to the ratio between two images acquired at two different echo times (4 and 25 ms) from which an apparent T2 value was calculated. A significant decrease in T2 in both vernalized and non-vernalized bulbs was observed after 4 months in storage. This effect may be associated with a reduction in water mobility in stored bulbs. At the end of the storage period, the apparent T2 values in the basal plate were significantly lower in vernalized than non-vernalized bulbs. Intrabulb floral development was similar in both vernalized and non-vernalized bulbs, but scape elongation and actual bloom occurred only in the vernalized plants. Changes in intrabulb development and water status during storage cannot by themselves provide a valid explanation for the significant differences between vernalized and non-vernalized bulbs during the growth stage. The possible role of the basal plate is discussed.

Lateral Development and Florogenesis of a Tropical Shallot: A Comparison with Bulb Onion

The developmental morphology of laterals and flowers was studied in shallot. Growth analyses and microscopic observations revealed strong similarities in organ development between shallots and bulb onions. However, some significant differences were observed, mainly with regard to the minimum physiological age for both laterals and floral differentiation and to the development of the inflorescence. When grown from seed, the initiation of laterals and the first signs of floral differentiation become evident already after the third and sixth true leaves, respectively, as compared to the bulb onion, which first produces 13 or 10-14 leaves, respectively. The shallot inflorescence can be described as an umbel-like flower arrangement, where branches (flower clusters) arise from a common meristem. Leaf formation continues at the axillary meristems in shallots simultaneously with floral development of the original apex. In blooming onion, however, the lateral meristem develops into an adventitious dormant bud. A detailed description of shallot florogenesis and the similarities and differences between blooming shallot and bulb onion are discussed.

Unlocking variability: inherent variation and developmental traits of garlic plants originated from sexual reproduction

Recent collections of fertile garlic (Allium sativum) accessions from Central Asia allow a detailed study of seedling developments and the evaluation of inherent variations. We hereby provide a comprehensive account of the ontogenesis of a population of garlic seedlings and their vegetative and reproductive traits. A nucleotide binding site profiling marker technology was applied to provide conclusive evidence for the cross-pollination nature of garlic, and to compare the levels of polymorphism between progeny derived from a single mother clone fertilized by several pollinators. The seedlings’ population demonstrates a large variation in vegetative and reproductive characters, including bulbing ability, bulb color and size, clove number, and response to environmental conditions, similar to that of the genepool of vegetatively propagated garlic clones. In addition, a large variation in flowering and seed production ability was recorded. The understanding of garlic physiology, the availability of the large variability unleashed by sexual reproduction, and the possible utilization of sexual hybridization opens the way for genetic studies and breeding work.