Ex vitro elimination of seed dormancy and in vitro seedling performance of Cucumis africanus and Cucumis myriocarpus

Cucurbitacins from Cucumis africanus and Cucumis myriocarpus fruits are widely used in various industries. However, propagation of the two Cucumis species had been elusive due to seed dormancy, with seedlings performing poorly. The objective of this study was to determine the kind of seed dormancy under natural conditions and to eliminate the possibility of microbial degradation of inhibitory chemical compounds by germinating treated C. africanus and C. myriocarpus seeds under in vitro conditions. Forty seeds each, grouped as untreated, leached and leached-scarified (LS) batches, were arranged in a completely randomised design, with five replicates. Seeds in Murashige and Skoog medium were germinated under in vitro conditions for seven weeks at 25°C and 50–60% relative humidity. In both Cucumis species, untreated seeds did not germinate, whereas the LS seeds germinated in both species. In addition to the LS seeds, leached seeds in C. africanus germinated, but completely failed to germinate in C. myriocarpus. In all Cucumis species, seedlings from LS seeds outperformed those from leached seeds, suggesting that both chemical and physical dormancies were involved in seed dormancy and poor performance of seedlings in the two Cucumis species.     

Seed longevity in terrestrial orchids - Potential for persistent in situ seed banks

Terrestrial orchids typically produce numerous small seeds that contain very small nutrient reserves. The seeds are structurally adapted for wind dispersal but little is known about their fate after dispersal. Some studies of seed viability in situ indicate survival for up to two years in temperate orchid species. Seeds stored in the laboratory may last much longer. We investigated seed viability of seven North American orchid species with seed packets buried in a range of soil and wood substrates within their natural habitats. In Goodyera pubescens most seeds germinated within one year. Four other species continued to germinate sparsely during the observation period, but after almost seven years many seeds were still viable. In one species, Liparis liliifolia, seeds that had been in situ for four years had germination rates as high as 68% when sown in vitro with a compatible fungus. The remaining two species did not germinate during the observation period but the seeds were judged to be intact and tested positively for viability after four years in the ground. These observations are interpreted as different species-specific strategies for in situ germination and their seed bank potential is discussed.     

Conserving seeds of useful wild plants in Mexico: main issues and recommendations

The efficient storage and germination of seeds underpin the effective use of plants for livelihoods and sustainable development. A total of 204 wild species useful for local communities of the Tehuacán–Cuicatlán Valley were collected and stored in seed banks in country for long term conservation, and 66 % (i.e., 134) duplicated in the U.K., as an effective means of ex situ conservation. Of the 204 species, 147 (122 of which also duplicated in the U.K.) were previously listed as useful plants in the ethnofloristic inventory of the Valley. Based on literature surveys, we found that one of the major impediments to the use of stored seeds of wild species is the lack of knowledge of how to germinate the seed. In detailed studies, we found that seeds of 18 useful plant species from 10 different families germinated readily and could be propagated. In contrast, four species (Actinocheita filicina, Bursera submoniliformis, Karwinskia mollis and Lippia graveolens) produced dormant seeds and therefore further studies are needed before their use can be maximised in large scale propagation programmes in support of conservation and livelihoods. Overall, this large-scale study on useful wild plant species in Mexico confirms that conventional seed banking can effectively support sustainable development and livelihood programmes.     

Nodulation pattern and acetylene reduction (nitrogen fixation) activity of some highland and lowland Acacia species of Ethiopia

 Endosymbionts from the Ethiopian highland acacia species Acacia abyssinica, A. negrii and A. etbaica, and the lowland species A. nilotica, A. prasinata, A.senegal, A. seyal, A. tortilis and Faidherbia (Acacia) albida were isolated and characterized. Seven tree species were found to be nodulated by species of both Rhizobium and Bradyrhizobium. F. (Acacia) albida and A. senegal were nodulated by only Bradyrhizobium or Rhizobium, respectively. In A. abyssinica, both genera were isolated from the same nodule, whereas in A. nilotica and A. tortilis, both strains were isolated from different nodules of the same plant. The nitrogen fixation (acetylene reduction) activities varied considerably and showed no correlation with the nitrogen content of the plant. Highland species were as effective as lowland plants, thus demonstrating good potential for soil reclamation. The endosymbionts isolated proved rather promiscuous, efficiently nodulating other Acacia spp. and some tropical grain legumes, but did not nodulate temperate legumes. Received: 7 August 1997     

Identification and Revival of Low Viability Seed Samples

Seeds stored for a long time may be difficult to germinate under standard conditions and are thus considered not to be viable. By using conductivity test an accession of Brassica rapa L. ssp. rapa with viable seeds was identified among seed material previously declared dead based on traditional filter paper germination tests. The identified accession was germinated by means of long time germination on aseptic agar based growth medium. After transplanting, weaning and vernalisation 0.8% of the seeds could be grown to plants, which flowered and produced seeds.     

Viability of Oryza sativa L. seeds stored under genebank conditions for up to 30 years

Germination ability, equilibrium relative humidity (eRH), and moisture content of ‘control’ seed samples representing 183 rice accessions stored in the active (2–4 °C) and base (?10 °C until 1993, then ?20 °C) collections of the T. T. Chang Genetic Resources Center were determined after storage for 20.5–30.5 years. Germination of seeds that had been stored in the base collection was generally high (>70 %), whereas germination was more variable for seeds stored in the active collection. Samples with lower viability after storage in the active collection were likely to have lower viability after storage in the base collection. There were significant differences in the moisture content-eRH relationship of the seeds depending on whether the seeds had been stored in the active or base collection. Based on re-test data for regular seed samples regenerated in 1979–1980 and stored in the active collection for up to 31 years, estimates of the time for ability to germinate to fall to 50 % (p ₅₀) ranged from 54 to 997 years. For the same seed samples stored in the base collection for approximately 31 years, ability to germinate has been maintained and germination increased due to improved procedures. The ability to germinate of base collection samples was also generally higher than that of ‘safety duplicate’ samples of the same seed lots that had been sent to the National Center for Genetic Resources Preservation, USA in 1981 and stored at ?18 °C. This may have been due to uptake of moisture either during processing for dispatch or as a consequence of poor packaging material. The results are discussed in relation to long-term seed storage and genebank management.     

Optimizing seed quality during germplasm regeneration inpearl millet

The effect of water stress during flowering and grain filling on seed longevity was studied in three pearl millet genotypes,ICTP-8202, ICTP-8203 and MBH-110. The seeds were produced by three pollination methods; open pollination, selfing(individual panicles enclosed in paper bags), and cluster bagging (panicles from 3–4 adjacent plants enclosed in a paper bag), stored in air-tight plastic bottles underambient conditions (20–40°C,30–80%RH) and germination was tested at 12-month'sintervals. The seeds lost germination completely after six years ofstorage in all treatments. Analysis of variance of the estimates of potential seed longevity (i.e. the seed lot constantK _i of the seed viabilityequation) showed significant effects of water stress andpollination method (P < 0.01). The interaction between irrigation treatment and method of pollination control was also significant (P < 0.05). Averaged over genotypes and pollination methods,potential longevity was greatest(K _i = 2.8) in theirrigated control, and averaged over genotypes and irrigationtreatments, it was greatest (K _i= 3.1) in seeds produced by open pollination. Theimplications of these results were discussed in relation to germplasmseed production.     

Nodulation status of native woody legumes and phenotypic characteristics of associated rhizobia in soils of southern Ethiopia

The nodulation of provenances of Acacia seyal, Acacia tortilis and Faidherbia albida, and other indigenous multipurpose tree species were tested in 14 different soil samples collected from diverse agro-ecological zones in southern Ethiopia. Associated rhizobia were isolated from these and from excavated nodules of field standing mature trees, and phenotypically characterized. Indigenous rhizobia capable of eliciting nodules on at least one or more of the woody legume species tested were present in most of the soils. Tree species were markedly different in nodulation in the different site soils. Sesbania sesban and Acacia abyssinica showed higher nodulation ability across the different sites indicating widespread occurrence of compatible rhizobia in the soils. The nodulation patterns of the different provenances of Acacia spp. suggested the existence of intraspecific provenance variations in rhizobial affinity which can be exploited to improve N fixation through tree selection. Altogether, 241 isolates were recovered from the root nodules of trap host species and from excavated nodules. Isolates were differentiated by growth rate and colony morphology and there were very fast-, fast-, slow-, and very slow-growing rhizobia. The bulk of them (68.5%) were fast-growing acid-producing rhizobia while 25.3% were slow-growing alkali-producing types. Fast-growing alkali-producing (2.9%) and slow-growing acid-producing strains (3.3%) were isolated from trap host species and excavated nodules, respectively. All isolates fell into four colony types: watery translucent, white translucent, dull glistering and milky (curdled) type. The diversity of indigenous rhizobia in growth rate and colony morphology suggested that the collection probably includes several rhizobial genera.     

Light and Temperature Requirements during Germination of Potential Perennial Grasses for Rehabilitation of Degraded Sandy Arabian Deserts

Few plants can tolerate the loose sandy‐soils of the arid deserts. Selection of native plants that could be used in rehabilitation of degraded deserts necessitates information about their seed dormancy and germination requirements. This study assessed the effects of light and temperature requirements during germination for eight common perennial grasses that have the potential to rehabilitate the arid Arabian deserts. The selected grasses vary considerably in seed mass. Germination of clonally propagated grasses (six species) was significantly greater, but slower, than that of two non‐clonal grasses. Four of these six species (Lasiurus scindicus , Panicum turgidum , Aeluropus lagopoides and Halopyrum mucronatum ) produce larger seeds and attained greater germination in both light and darkness at a wide range of temperatures. However, the other two (Centropodia forsskaolii and Coelachyrum piercei ) produce medium‐sized seeds with higher dormancy. Smaller seeds of Sporobolus arabicus were positively photoblastic at all temperatures, but those of Sporobolus spicatus were neutrally photoblastic at lower temperatures and positively photoblastic at higher temperatures. There was a significant negative relationship between seed mass and relative light germination, indicating that small seeds require more light during germination. It is recommended to use seeds of the six clonal grasses for restoration of degraded arid deserts. The ability of these grasses to germinate in different light and temperature regimes indicates their ability to germinate at any time of the year, even when seeds are buried. The light and temperature requirements of the different grasses are explained in the light of their adaptation and distribution in natural habitats. Copyright © 2017 John Wiley & Sons, Ltd.     

Differentiation between two sub-species of <Emphasis Type="Italic">Acacia senegal</Emphasis> complex: <Emphasis Type="Italic">Acacia senegal</Emphasis> (L.) Willd. and <Emphasis Type="Italic">Acacia dudgeoni</Emphasis> Craib ex Holland using morphological traits and molecular markers

The Acacia senegal complex is formed by closely related species of Acacia senegal (L.) Willd. These species share several botanical characters, so from a morphological point of view, there is no clear discontinuity between some of them. A. dudgeoni Craib ex Holland is one species of the A. senegal complex that was formerly described as A. senegal ssp. senegalensis var. samoryana (A. Chev.) Rob. In order to differentiate Acacia senegal from A. dudgeoni, we analyzed a range of morphological traits such as tree height and diameter in natural stands, and, at the nursery stage, seedling height, number of branches, main root depth, biomass dry weight and leaf characteristics. Within addition, molecular polymorphism analyses were conducted using 11 microsatellite markers. Leaf characteristics and molecular markers appear to be the most effective tools to distinguish A. senegal from A. dudgeoni. These tools can improve our understanding of the relationship between two species belonging to the same species complex.     

Impact of Acacia auriculiformis on the chemical fertility of sandy soils on the Batéké plateau,D.R. Congo

A 17‐year chronosequence of Acacia auriculiformis fallows on Arenosols of the Batéké Plateau (D.R. Congo) was surveyed and compared with virgin savannah soils to assess chemical soil fertility changes induced by these N‐fixing trees. Significant increases in organic carbon content, total nitrogen content, cation exchange capacity and sum of base cations were found after relatively short fallow periods of only 4 years and did not only affect the forest floor, but extended to at least 50 cm depth. The Acacia act as a major source of organic matter (OM), hence increasing organic carbon and nitrogen content and decreasing the C/N ratio. The increased OM content suggests that humification processes are the main cause of the significant decrease in pH. Total exchangeable cations initially increased slowly but doubled (topsoil 0–25 cm) and tripled (subsoil 25–50 cm) after 10 years. The point of zero net proton charge was systematically lower than soil pH and decreased with increasing OM content, thereby increasing the cation exchange capacity, although concurrent acidification retarded a significant beneficial impact at field pH on Acacia fallows of 10 years and older. Although the chemical soil fertility improves steadily with time, after 8 years of Acacia fallow the absolute amounts of available nutrients are still small and slash and burn practices are required to liberate the nutrients stored in the remaining biomass and litter before each new cropping period.     

Medium-term seed storage of 50 genera of forage legumes and evidence-based genebank monitoring intervals

Genebanks maintaining seeds for long-term genetic resources conservation monitor seed lots to detect early loss in viability. Monitoring is costly and depletes valuable seed. Three decades of genebank seed germination test results of diverse forage species from 50 legume genera in the International Livestock Research Institute’s medium-term store (circa 8 °C with 5% moisture content) were analysed to determine whether advice on seed monitoring intervals could be derived. Cumulative normal distributions were fitted by probit analysis for each seed lot and compared within each genus. Six patterns of within-genus variation were identified: no detectable trend in germination test results during storage (4 genera); detectable trends, but variable (positive to negative) amongst lots (5); consistent slope of loss in viability amongst lots (17); consistent slope of increase in ability to germinate amongst lots (21); common loss in viability amongst lots (2); common increase in ability to germinate amongst lots (1). Seed lot monitoring intervals for the medium-term store were derived for each of 19 genera with consistent loss in viability across seed lots: three genera provided comparatively rapid deterioration, five met the general expectations for a medium-term store (2–10 years’ maintenance of high viability), whilst 11 provided much better survival. Moreover, 26 further genera provided no evidence as yet of seed deterioration; of these, 22 improved in ability to germinate during storage indicating confounding of hardseededness with viability in germination tests.     

Diversity analysis of <Emphasis Type="Italic">Acacia tortilis</Emphasis> (Forsk.) Hayne ssp. <Emphasis Type="Italic">raddiana</Emphasis> (Savi) Brenan (Mimosaceae) using phenotypic traits,chromosome counting and DNA content approaches

Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan (Family Fabaceae; subfamily Mimosoideae) is a pioneer tree of dry areas. In spite of its several uses, there are no any published studies which deal with genetic diversity of Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan in Tunisia. For this reason, here we study its genetic diversity with morphometric (only in Tunisian populations), chromosome counting, and cytometric (in Tunisian and Ziambabwean populations) approaches. Morphological field studies of four Tunisian populations (Bouhedma, Haddej, Hajeb and Gtar, respectively, designated as A, B, C, D) of A. tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan using a general linear model (ANOVA) revealed statistically highly-significant differences between populations for all examined characters (P < 0.0001). Significant differences were found also between genotypes for the majority of morphological traits (P < 0.0001) except the width of 10 pods (laP), weight of 10 pods (Wt) and seed number of 10 pods (Sn) (P ≥ 0.110). The variability in the tree, pod and seed characters can be exploited for agro-industrial purposes. The DNA amount and chromosome numbers of populations Umguza and Gwaii River from Ziambabwe and of Tunisian populations A, B, C and D were determined. Tunisian populations had 2C nuclear DNA contents of 2.95–3.03 pg, and were shown to be tetraploid (2n = 4x = 52), whilst the two Ziambabwean populations had 1.39–1.40 pg and were diploid (2n = 2x = 26). It is suggested that the Tunisian populations are paleotetraploids, adapted to the more-arid local conditions.     

ODAP levels in some <Emphasis Type="Italic">Lathyrus</Emphasis> species distributed on Burdur-Isparta provinces in Turkey

Lathyrus species are distributed in natural areas of Turkey and are cultivated for use in human and animal food. Plants and seeds of Lathyrus species contain a neurotoxic substance called \upbeta\upbeta-N-oxalyl-L- \upalpha\upalpha, \upbeta\upbeta–diamino propanoic acid (ODAP). When consumed in large quantities, ODAP may cause a kind of paralysis known as lathyrism. In this note, ODAP levels were determined in Lathyrus species collected in the Burdur-Isparta provinces. The leaves and seeds of plant samples were analysed using High Performance Liquid Chromatography (HPLC). ODAP was not detected in L. aphaca L. var. pseudoaphaca (Boiss.) Davis, L. sphaericus Retz., or L. aureus (Stev.) Brandza; the seed samples of L. cicera L. and L. clymenum L. contained 0.053 and 0.171% ODAP, respectively. Leaf samples of L. cicera L. contained 0.018% ODAP. This preliminary note seems to point to a secondary gene pool that may serve as a valuable source of genetic material for grass pea improvement.     

Phenotypic and genomic characterization of vine cactus collection (Cactaceae)

Hylocereus (Berger) Britton et Rose, Selenicereus (Berger) Britton et Rose and Epiphyllum Haw. species have commercial potential as exotic fruit crops in semi-arid and arid lands. The high genetic variability among these species offers an opportunity for commercial cultivation. Toward this end we investigated genomic and morphological characteristics including: nuclear DNA content (2C-values), stomatal length and density, potential yield and reproductive parameters in 64 Hylocereus, Selenicereus and Epiphyllum accessions. Nuclear DNA content ranged from 3.21 pg for S. grandiflorus (L.) Britton et Rose spp. grandiflorus to 8.77 pg for H. megalanthus (Vaup.) Bauer. All species were diploid except the tetraploids H. megalanthus and S. vagans (Bgek.) Britton et Rose. Stomatal length and density, fruit weight, potential yields, number of viable seeds per fruit and fruit maturation times were highly variable among accessions. No significant correlations were found between stomatal length, density, and nuclear DNA content, nor between fruit weight and seed number. The high genetic variability found between the accessions here provides further support for the excellent prospects of conserving and domesticating these exotic species.     

Measurement of nuclear DNA content of the genus <Emphasis Type="Italic">Trifolium</Emphasis> L. as a measure of genebank accession identity

The collection, identification and maintenance of genebank accessions of the genus Trifolium is a major task because of the large number of genera and their occasional morphological similarity. We investigated whether the measurement of nuclear DNA content can serve as an additional criterion for identification of mislabeled accessions. Relative nuclear DNA content was determined by flow cytometry measurements for a total of 151 genebank accessions of 23 Trifolium species with notable agronomical value. Among 23 species analyzed, 15 were found to possess a uniform relative nuclear DNA content, with intraspecific variability of the majority of analyzed species lower than 5%. Within six Trifolium species, 1–2 atypical accessions with outstanding differences in relative DNA content, chromosome number and morphological features were found. In T. hybridum and partially in T. ambiguum these outstanding differences could be ascribed to variations in accession ploidy level. For the remaining atypical accessions, the determined nuclear DNA content, chromosome number and morphological features were not related to those characteristic of the species. Additionally taxonomic identity of atypical accessions was determined using ITS region sequencing and morphological observations. We propose flow cytometric measurements of nuclear DNA content as simple and reliable technique which can be used at seedling stage to verify identity and genetic stability of Trifolium genebank accessions.     

Phylogenetic relationships between <Emphasis Type="Italic">Ensete</Emphasis> and <Emphasis Type="Italic">Musa</Emphasis> species as revealed by the <Emphasis Type="Italic">trnT trnF</Emphasis> region of cpDNA

Complete sequences of transcribed spacers and introns from the trnT trnF region of chloroplast DNA (cp DNA) were generated from Musaceae species to establish the phylogenetic relationships among 3 species of Ensete including the economically important Ensete ventricosum (Welw.) Cheesman and 13 species of Musa. Parsimony analysis and pair wise distance data produced a single tree, with Ensete and Musa as clearly distinguished clades. Six Musa and three Ensete clades were generated. The topology of these clades did not change when the data were split into spacers and introns, although the split resulted in poor bootstrap support. Removing a hotspot from the entire data set improved clade support. The clades produced are discussed with reference to existing taxonomic and phylogenetic treatments. In contrast to previous suggestions, most of the Rhodochlamys species that we investigated clustered together with strong support establishing their distinctiveness from the Musa species studied. Ensete glaucum (Roxb.) Cheesman and Musa beccartii Simmonds appear to represent ancestral forms of Ensete and Musa, respectively for the presently studied species, and both genera have a common ancestor that is yet to be established. Our data also show that E. ventricosum cannot be reduced to E. glaucum, nor can E. gilleti (De Wild.) Cheesman be reduced to E. ventricosum, as some authorities have suggested. Ensete gilleti or a species very close to it appears to be the ancestral species of E. ventricosum.     

Assessing limitations on population growth in two critically endangered Acacia taxa

Flowering phenology, soil seedbank and the impact of fire, weeds and grazing were investigated in two rare Acacia taxa restricted to the agricultural district north of Perth Western Australia. Acacia aprica is known from six extant populations and one extinct population. Five of the extant populations are restricted to linear road reserves with the sixth population located in a small native vegetation remnant. Acacia cochlocarpa ssp. cochlocarpa is known from a single population also situated on a road verge. Size class structure, levels of canopy death and an absence of juveniles indicated that all populations are in decline. Flowering intensity and success varied between populations and years in A. aprica and between years in A. cochlocarpa ssp. cochlocarpa. Seed bank analysis indicated that seeds were patchily distributed while experimental fires demonstrated that such events could break seed dormancy and promote germination. Both taxa have similar germination physiologies and showed increased germination after seeds were exposed to heat. Following emergence, however, competition with annual weeds had a negative impact on seedling growth and survival in both taxa. While vertebrate grazing had some influence, weeds were the major inhibitory influence on recruitment. Reduced fire frequencies since fragmentation may be responsible for population decline in both taxa but other site specific factors such as weeds and grazing may affect the establishment of seedlings following fire.     

AFLP similarities among historic Danish cultivars of fodder beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L. subsp. <Emphasis Type="Italic">vulgaris</Emphasis>var. <Emphasis Type="Italic">rapacea</Emphasis> Koch)

Dead seeds of a fodder beet cultivar ‘Elvetham’ stored under ambient conditions since 1880 were compared to a homonymous sample preserved in an on-farm situation in Denmark. DNA was isolated from single seeds and successfully applied to Amplified Fragment Length Polymorphism (AFLP) analysis of the accessions. Six primer pairs were used to determine the similarity between the two accessions based on 112 polymorphic bands. Furthermore, similarity among seven cultivars of fodder beets representing the main types used in Scandinavia at the end of the 19th century was determined. This analysis was based on 152 polymorphic bands. Differentiation among the seven cultivars was determined to a mean G _ST value of 0.438, while G _ST between the two ‘Elvetham’ accessions was 0.266. A principal coordinate analysis based on jaccards similarity index illustrates that the two ‘Elvetham’ accessions are different from each other. The differentiation is higher than the value found between two separate ‘Eckerndorfer’ accessions. The results indicate that the cultivated accession has changed. Additionally, the value of applying old dead seed material for documentation in gene banks is demonstrated. During the analysis it was found that DNA isolated from seeds and leaves behaved differently in the AFLP process, however, the two fractions assigned to their common accession.     

MICRONUTRIENT COMPOSITION OF PAPAVER SOMNIFERUM L. GROWN UNDER LOW CADMIUM STRESS CONDITION

Micronutrient uptake and distribution within poppy plants (Papaver somniferum L.) were studied in two pot experiments using a loamy garden soil as substrate. In the first experiment a supplement of increasing cadmium (Cd) concentrations to the substrate and in the second the influence of cultivars and harvest time were studied. At the stage of seed ripening the taproots were already decaying, and the Cd concentration in the shoot reflected the Cd supply in the substrate. In the shoot the highest Cd concentrations were found in seeds. With 24 mg Cd per pot (6 mg kg^?1), Cd concentration reached 1.7 mg kg^?1.

The four poppy varieties (Edel-Weiss, Marianne, Soma, White Poppy) differed clearly in seed production but reached comparable Cd concentrations of about 1.3 mg kg^?1 in the seeds at the second harvest. Seeds made up 2.5 to 12.9% of shoot biomass, but stored 15 to 42% of total Cd in the shoot, which indicates a preferential translocation of Cd into seeds in this plant species.

In addition, Cd supply had a marginal effect on the concentration of micronutrients in seeds and stems + leaves. At the highest Cd supply of 6 mg Cd kg^?1 soil a growth reduction of about 25% could be observed.