Sex allocation in an hermaphroditic plant: the case of gynodioecy in Thymus vulgaris L.

Resource allocation to male and female functions was investigated in Thymus vulgaris L. (thyme), a gynodioecious species, in which females produce twice as many seeds as hermaphrodites. Negative correlations were found between male and female fertility of hermaphrodites, providing evidence of a trade-off. There was a high variability in sexual investment, some of the hermaphrodites functioning almost as males, and others almost as females. Estimation of the relative cost of male and female gametes showed that the female advantage in seed production was mainly due to reallocation of the resources not allocated to male function into female function. The determination of sex allocation was shown to have a genetic component, and there were some evidence that an interaction between nuclear and cytoplasmic genomes was involved.     

Genetic control of oil content in oilseed rape (Brassica napus L.)

In oilseed rape (Brassica napus L.) like in most oleaginous crops, seed oil content is the main qualitative determinant that confers its economic value to the harvest. Increasing seed oil content is then still an important objective in oilseed rape breeding. In the objective to get better knowledge on the genetic determinism of seed oil content, a genetic study was undertaken in two genetic backgrounds. Two populations of 445 and a 242 doubled haploids (DH) derived from the crosses “Darmor-bzh” × “Yudal” (DY) and “Rapid” × “NSL96/25” (RNSL), respectively, were genotyped and evaluated for oil content in different trials. QTL mapping in the two populations indicate that additive effects are the main factors contributing to variation in oil content. A total of 14 and 10 genomic regions were involved in seed oil content in DY and RNSL populations, respectively, of which five and two were consistently revealed across the three trials performed for each population. Most of the QTL detected were not colocalised to QTL involved in flowering time. Few epistatic QTL involved regions that carry additive QTL in one or the other population. Only one QTL located on linkage group N3 was potentially common to the two populations. The comparisons of the QTL location in this study and in the literature showed that: (i) some of the QTL were more consistently revealed across different genetic backgrounds. The QTL on N3 was revealed in all the studies and the QTL on N1, N8 and N13 were revealed in three studies out of five, (ii) some of the QTL were specific to one genetic background with potentially some original alleles, (iii) some QTL were located in homeologous regions, and (iv) some of the regions carrying QTL for oil content in oilseed rape and in Arabidopsis could be collinear. These results show the possibility to combine favourable alleles at different QTL to increase seed oil content and to use Arabidopsis genomic data to derive markers for oilseed rape QTL and identify candidate genes, as well as the interest to combine information from different segregating populations in order to build a consolidated map of QTL involved in a specific trait.     

Natural selection and gynodioecy in Thymus vulgaris L.

Thymus vulgaris L. is a gynodioecious species with hermaphrodites (mF) and females (mS) widely distributed in southern France and in which reproduction of which is exclusively sexual. Numerous samples have been collected in the French Mediterranean region and the percentage of mS varies from 5 to 95% in different populations. By studying environmental conditions—the area covered at ground level by vegetation, stones and rocks—high percentages of mS are found to be related to a high vegetation cover and an absence or a scarcity of stones. Grasslands and old fields favour mS, while rocky sites favour mF. This relationship, which has been found both on the plains and on a mountain, is related to the most important reproductive characteristics of T. vulgaris —genetic control of male sterility, mode of pollination, percentage of selling and seed production. These relationships agree with the assumption that unstable environmental conditions such as grasslands or old fields in southern France favour maximum seed production and outcrossing. The greater stability of uncultivated areas such as rocky sites allows for the maintenance of autogamy. Consequently, it is natural selection which adjusts the percentage of male sterility in natural populations of Thymus vulgaris.     

Founder effects and sex ratio in the gynodioecious Thymus vulgaris L.

Thymus vulgaris is a gynodioecious species (in which females and hermaphrodites coexist) with a highly variable frequency of females among natural populations (5–95%) and a high average female frequency (60%). Sex determination involves both cytoplasmic genes responsible for male sterility, i.e. the female phenotype, and specific nuclear factors responsible for the restoration of male fertility, and thus a hermaphrodite phenotype. In this study, molecular markers of the mitochondrial genome have been used to quantify the cytoplasmic diversity in 11 clumps of individuals observed in four recently founded populations. The very low diversity within patches in conjunction with the strong diversity among patches strongly suggests that clumps of individuals are the result of single matrilinear families. In clumps that contain mainly females, all the analysed females showed the same cytoplasmic pattern. This pattern differed from that shown by neighbouring hermaphrodites, indicating that the determination of sex is locally cytoplasmic. A comparison of genetic diversity before and after fire in one population showed that disturbances may cause a reduction in genetic diversity and a concurrent induction of local cytoplasmic determination of sex. Such cytoplasmic determination of sex in colonizing populations, together with the greater seed set of females, may largely improve the colonizing ability of the species.     

Genetic control of morphological characters of the beet (Beta vulgaris L.)

A brief review of theoretical and practical results of investigation of genetical control of a number of traits of beet, including self-incompatibility, monogerm-multigerm, cytoplasmic male sterility and some others is presented. Data concerning linkage groups of individual genes, determining morphological and biochemical traits are demonstrated.     

The consequences of gynodioecy in natural populations of Thymus vulgaris L.

Summary Gene flow between the two sexual forms is asymmetrical in gynodioecious species: genes are transferred from male-fertile individuals (mF, hermaphrodites) to male-sterile individuals (mS, females) by pollen but from mS to MF individuals by diploid seeds. This situation is expected to cause differences in the genetic make up of mF and mS individuals. The expected differences were found in an experiment on a natural population of the gynodioecious species, Thymus vulgaris L. (thyme). The effectiveness of gynodioecy as a means of regulating heterozygosity and adaptability to various conditions of the environment is discussed.     

Antifungal activity of thyme (Thymus vulgaris L.) essential oil and thymol against moulds from damp dwellings

AIMS: To characterize antifungal activities of essential oil of thyme (Thymus vulgaris L.) and pure thymol, as comparative substance, on different mould species isolated from damp dwellings. METHODS AND RESULTS: Fifty samples of wall scrapes were collected from damp dwellings in Zagreb, the capital of Croatia. The members of the following mould genera were recovered from the samples: Aspergillus (44%), Penicillium (18%) Alternaria, Ulocladium, Absidia and Mucor (8%) Cladosporium, Trichoderma and Rhizopus (6%), and Chaetomium (2%). Two strains of Stachybotrys chartarum were isolated from damp dwellings in Slovakia. Antifungal activities of the thyme essential oil, which contains p-cymene (36.5%), thymol (33.0%) and 1,8-cineole (11.3%) as main components, and pure thymol were determined by the dilution method and exposure to vaporous phase of the oil. Minimum inhibitory concentrations (MIC) of both thymol and essential oil were bellow 20 microg ml(-1), except for Mucor spp. (50.20 microg ml(-1)). Thymol exhibited approximately three-times stronger inhibition than essential oil of thyme. The vaporous phase of the thyme essential oil (82 microg l(-1)) in glass chambers strongly suppressed the sporulation of moulds during 60 days of exposure. CONCLUSION: The thyme essential oil possesses a wide range spectrum of fungicidal activity. The vaporous phase of the oil exhibited long-lasting suppressive activity on moulds from damp dwellings. SIGNIFICANCE AND IMPACT OF THE STUDY: Essential oil of thyme and thymol could be used for disinfection of mouldy walls in the dwellings in low concentration.     

Reproductive capacities in the sexual forms of the gynodioecious species Thymus vulgaris L.

The reproductive capacities of the females (male-steriles or mS) of Thymus vulgaris L. have been investigated, in terms of size and weight of plants, seed production, germination ability and pollination. The data, collected during nine years under controlled conditions and in natural situations are discussed in comparison with the results known in the literature. It is suggested that the large diversity of characteristics promoting sexual polymorphism could justify the high and variable rates of mS met in natural conditions in T. vulgaris.     

The male-sterility polymorphism of Silene vulgaris: analysis of genetic dat from two populations and comparison with Thymus vulgaris.

Results are given of genetic studies of male sterility using plants from two natural populations from Sussex, England. Both populations have substantial frequencies of females, approximately 0.25 in population 1 and 0.60 in population 3. As in the few other gynodioecious populations studied in detail, many genetic factors are present. In population 1, there are at least two, and more likely three, different cytoplasmic types, one of which appears to produce male sterility in progeny from any hermaphrodite pollen donor; in other words restorer alleles for this cytoplasm are rare or absent from the population. The other two populations can be carried in hermaphrodites that have the dominant restorers. In population 1, there are also probably three restorer loci with complementary recessive male-sterility alleles, as well as a locus with duplicate action, which cannot produce male sterility unless the plant is also homozygous for the recessive allele at another locus. The results from population 3 are quite similar, though there was no evidence in this population for an unrestored sterility cytoplasm. A similar joint nucleocytoplasmic model with multiple restorers fits data from Thymus vulgaris.     

Evaluation of the preservative properties of Thymus vulgaris essential oil in topically applied formulations under a challenge test

The preservative properties of thyme essential oil (3%) with a known composition were evaluated in two types of final formulations, suitable for use as pharmaceutical or cosmetic vehicles, by means of a standard challenge test proposed by the latest European Pharmacopoeia. The required preservation efficacy criteria were satisfied against the bacterial strains, against the yeast in one of the formulations, but not against the mould strain involved in this study. Interactions between the essential oil compounds and other factors present in the final formulation might have influenced the activity of this essential oil, leading to an incomplete satisfaction of the criteria.     

Complex determination of male sterility in Thymus vulgaris L.: genetic and molecular analysis

Summary Nucleocytoplasmic determination of male sterility in Thymus vulgaris L. has been assumed in all papers attempting to explain the remarkably high frequencies of male steriles found in natural populations of this species. This paper provides strong evidence that both nuclear and cytoplasmic genes are involved in the determination of male sterility of this species, giving a complex inheritance. Interpopulation and intrapopulation crosses have shown that the ratio of females versus hermaphrodites among offsprings varied widely from 10 to 11. Furthermore, interpopulation crosses consistently yielded a higher frequency of females than intrapopulation crosses. Nucleocytoplasmic inheritance was demonstrated by an absence of male fertiles in backcrosses and asymmetrical segregation in reciprocal crosses. Molecular analysis of the mitochondrial DNA of some of the parents used in crosses suggested the involvement of different cytoplasms in the inheritance of male steriliy.     

Essential oil polymorphism of Thymus praecox subsp. arcticus on the British Isles

The essential oils of 732 individual plants of Thymus praecox Opiz subsp. arcticus (E. Durand) Jalas (syn. T. drucei Ronn.) collected in Scotland, Ireland, and in the south of England have been analysed by gas chromatography (GC) and mass spectrometry (GC–MS) in order to elucidate the chemical character of this subspecies on the British Isles. In total, 69 components were identified, most of them monoterpenoids and sesquiterpenoids with hedycaryol, linalyl acetate, linalool, the germacradienols, trans-nerolidol, T-cadinol, and β-caryophyllene being the most important compounds. The analysis of the quantitative essential oil data by means of neural networks revealed that T. praecox subsp. arcticus growing in Britain is highly polymorphous. There were 17 chemotypes with the hedycaryol chemotype as the most frequent (24% of the plants), followed by the linalool/linalyl acetate chemotype (22% of the plants) and germacra-1(10),4-dien-6-ol chemotype (18% of the plants). It seems that each part of the British Isles has its special chemotype pattern with 13 chemotypes in Scotland, 11 in Ireland, and 17 in the south of England. An overview of the North Atlantic region of Europe revealed that the polymorphism of T. praecox subsp. arcticus in the essential oil is more distinctive in the southern than in the northern regions, with only 2, 5, and 1 chemotypes in Greenland, Iceland, and Norway, respectively.     

Genetic study of a new color of the beet Beta vulgaris L

A new genetic character of the beet Beta vulgaris L., named stem color, was described and studied genetically. This character was shown to be dominant trait and monogenically inherited. The first-year beet plants with the genotype Stc/_have red leafstalks, weakly colored central rib, and colored storage root; however, the root itself is not colored. The second-year plants have a red-colored low third of the floral shoot. The plants with the genotype stc/stc are uncolored. The Stc gene was localized to the first linkage group at a distance of 17.5 +/- 2.1 crossing over units from the gene B (Bolting), which controls the annual-perennial habit of beet.     

Intra-population terpene polymorphism of Thymus pulegioides L.: Evidence for seven chemotypes in a German limestone grassland

For Thymus pulegioides L. (Lamiaceae), occurring in almost entire Europe, about 20 different essential oil chemotypes are described in approximately 25 studies. However, only few studies mention chemotype diversity on population level, describing up to five chemotypes growing together. The aim of the study was to investigate the chemotype diversity within one T. pulegioides population of a limestone grassland in Germany. Essential oil compounds from samples of 93 thyme cushions were extracted with solid phase extraction (SPE) and analysed by GC-MS. Cluster analysis and nonmetric multi-dimensional scaling (NMDS) of the samples’ essential oil composition revealed the existence of seven different chemotypes: linalyl acetate-chemotype (56 individuals), geraniol-citral-linalyl acetate-chemotype (5), geraniol-citral-chemotype (7), thymol-chemotype (8), carvacrol-chemotype (2), linalool-chemotype (1), and β-caryophyllene-germacrene D-β-bisabolene-chemotype (14). The pattern of major monoterpenes from all chemotypes could be explained by the inhibition of specific steps in monoterpene biosynthesis. The sesquiterpene-dominant chemotype might be caused by a block in a very early step of monoterpene production or a regulatory/channeling mechanism. While the geraniol-citral-linalyl acetate-chemotype has been found for the first time, the other chemotypes have been found in other regions and the β-caryophyllene-germacrene D-β-bisabolene-type is similar to other sesquiterpene chemotypes rarely found in other areas. The large intra-population chemical polymorphism in this study raises questions about the chemotype diversity of thyme in other regions of Germany and potential correlations between essential oil composition and abiotic factors or biotic interactions.     

New monoterpene glucoside from the aerial parts of thyme (Thymus vulgaris L.)

A new monoterpene glucoside (1) was isolated from a methanol extract of the dried aerial parts of thyme (Thymus vulgaris L.), together with known 2- and 5-beta-D-glucopyranosylthymoquinols (2 and 3, respectively), and (-)-angelicoidenol-beta-D-glucopyranoside (4). The structure of 1 was elucidated to be (R)-p-cymen-9-yl beta-D-glucopyranoside by spectral evidence and enantioselective synthesis from (R)- and (S)-p-cymen-9-ol derived from p-cymen-8-ol.     

Spatial structure of nuclear factors involved in sex determination in the gynodioecious Thymus vulgaris L.

Theoretical models have shown that the maintenance of high frequencies of females in gynodioecious species can be explained by the spatial structure of cytoplasmic and nuclear genes involved in sex determination. Whereas spatial structure of cytoplasmic factors which cause male-sterility has been studied in several taxa, that of nuclear factors that restore male-fertility (restoration factors) has received little attention. In this paper, we estimate spatial variation in the frequency of restoration factors associated with different cytoplasmic male-sterilities in the gynodioecious Thymus vulgaris. Clonal replicates of five female plants bearing at least four different male-sterilities and originating from five different populations (i.e., five cytogenotypes), were reciprocally transplanted into the original populations. Following open pollination at each site, seeds were harvested, germinated and grown to flowering. The frequency of hermaphrodites in each progeny was used to estimate the frequency of restoration factors in each population. For all cytogenotypes, there was marked variation in the rate of restoration among populations, indicating that spatial structure in nuclear restoration factors may influence the variation in female frequency in T. vulgaris. For three out of the five cytogenotypes, higher restoration rates were obtained for females introduced into their original population, which agrees with the theoretical prediction, under some hypotheses, that restoration factors are selected for in populations that contain the associated male-sterility (Gouyon and Couvet, 1985). The very low restoration rate in the progeny of one female clone in three populations indicates that stochastic events, such as founder effects, could lead to a local absence of restoration factors and thus the high female frequency (up to 90%) observed in some populations. Differences among cytogenotypes suggest that some male-sterilities are associated with rarer restoration factors and are thus more likely to cause patches of females to develop in young populations.     

Development, oil storage and dehiscence of peltate trichomes in Thymus vulgaris (Lamiaceae)

The development, oil storage and dehiscence mechanism of the peltate oil–producing trichome in Thymus vulgaris L. was studied by conventional, fluorescence and electron scanning microscopy. A single epidermal initial forms the glandular trichome whose primordium becomes distinguishable from non–glandular trichomes at its 3–celled stage. The further divisions determine the formation of three functional compartments, (a) a basal reservoir cell, (b) an "endodermal" cell, and (c) a group of secretory head cells. At first, the gland head shows a bowl–like shape with a folded cuticular covering that raises successively assuming a dome–like form. During the differentiation of the gland cells, histochemical tests reveal the occurrence of a precise sequence of metabolic events: synthesis of RNA, proteins, glycoproteins, polysaccharides and, finally osmiophilic substances. At maturity, the cuticular sheath is formed by a non–cellulosic polysaccharide framework on which the cuticle is deposed. Proceeding towards the senescence, the polysaccharide framework disappears and a large crescent shaped pore forms, whereby essential oils are released. Collected results are discussed in order to interpret gland function and essential oil production.     

Genetic control of high stearic acid content in seed oil of two soybean mutants

 Stearic acid is one of the two saturated fatty acids found in soybean [Glycine max (L.) Merr.] oil, with its content in the seed oil of commercial cultivars averaging 4.0%. Two mutants, KK-2 and M25 with two- and six-fold higher stearic acid contents in the seed oil than cv ‘Bay’, were identified after X-ray seed irradiation. Our objective was to determine the genetic control of high stearic acid content in these mutants. Reciprocal crosses were made between each mutant and ‘Bay’, and between the two mutants. No maternal effect for stearic acid content was observed from the analysis of F₁ seeds in any of the crosses. Low stearic acid content in ‘Bay’ was partially dominant to high stearic acid content in KK-2 and M25, and high stearic acid content in KK-2 was partially dominant to high stearic acid content in M25. Cytoplasmic effects were not observed, as demonstrated by the lack of reciprocal cross differences for stearic acid content in our analysis of F₂ seeds from F₁ plants. The stearic acid content in F₂ seeds of KK-2בBay’ and M25בBay’ crosses segregated into three phenotypic classes which satisfactorily fit a 1:2:1 ratio, indicating that high stearic acid content in KK-2 and M25 was controlled by recessive alleles at a single locus. The data for stearic acid content in F₂ seeds of the KK-2×M25 cross satisfactorily fit a 3:9:1:3 phenotypic ratio. The F₂ segregation ratio and the segregation of F₃ seeds from individual F₂ plants indicated that KK-2 and M25 have different alleles at different loci for stearic acid content. The alleles in KK-2 and M25 have been designated as st ₁ and st ₂, respectively. The stearic acid content (>30.0%) found in the st ₁ st ₁ st ₂ st ₂ genotype is the highest known to date in soybean, but it was not possible to develop the line with this genotype because the irregular seeds failed to grow into plants after germination. Therefore, tissue culture methods must be developed to perpetuate this genotype. Received: 28 March 1997 / Accepted: 18 April 1997