Influence of insect pollinators and harvesting time on the quality of Stevia rebaudiana (Bert.) Bertoni seeds

Stevia rebaudiana (Bert.) Bertoni has sporophytic self-incompatibility and this may lead to poor seed yield and quality, which are obstacles to large-scale crop establishment. This research investigated the influence of insect pollinators and the harvesting time on the qualitative and quantitative characteristics of the ripe seeds. A pot trial under open field conditions was established to evaluate the abundance of insect pollinators and three harvesting times on the production of ripe seeds, germination percentage, mean germination time and thousand seed weight (TSW) in 36 F1 open-pollinated genotypes. Large variability in the number of corymbs of capitula, flowering time, reproductive period and seed yield was observed among the genotypes. Genotypes with promising phenological and reproductive properties were identified. The worst germination percentage and TSW were recorded in the latest harvest. Significant linear regressions were found among the investigated parameters (insect number, germination percentage, TSW, seeds yield per plant and cycle length), confirming complex interactions on the yield and quality of stevia seeds. Results indicate that earlier flowering genotypes produced higher seed quantity, due to favourable weather conditions during the reproductive phase. Moreover, cross-pollination and the insect abundance, as Apidae and Syrphidae, play a crucial role for enhancing the stevia seed yield and quality.     

Bimodal changes in germinability of pea seeds under the influence of low doses of gamma-radiation

Pea seeds (cv. 'Nemchinovskii-85', harvest of 2002, 80%-germination percentage) were exposed to gamma-radiation with doses ranging from 19 cGy to 100 Gy. One week after the irradiation with doses of 19 cGy and 3 Gy. the germination percentage decreased to 58 and 45%, respectively; at doses of 7 and 10 Gy it was 73 and 70% respectively. At greater doses (25, 50, and 100 Gy), germination percentage decreased in proportion. Anomalous changes in seed germination percentage (as a function of irradiation dose) were caused by the redistribution of irradiated seeds between fractions I and II. The measurements of room temperature phosphorescence in air-dry seeds and the phosphorescence of endogenous porphyrines of imbibing seeds showen that the germination decrease after the irradiation with low doses (19 cGy and 3 Gy) was caused by the increase in the number of weak seeds of fraction II, which had high rates of water uptake and suffered from hypoxia under seed coat. Some of these seeds suffocated from hypoxia, and other seeds produced seedlings with morphological defects (such seeds were considered incapable of germination). During storage of seeds irradiated at doses 19 cGy-10 Gy, the recovery of germination percentage (after its initial decrease) was caused by the decrease in seed number in fraction II. The subsequent germination decrease was caused by seed death. The higher was the irradiation dose, the faster were changes in germination percentage during storage of irradiated seeds. Bimodal changes in pea seed germination with the increase of y-irradiation dose has apparently the same origin as the changes in seed germination during accelerated ageing.     

Stress integrated tests and cytological analyses reveal Brassica villosa subsp. drepanensis seed quality decrease upon long-term storage

Under stress integrated germination test (SIGT), seeds undergo osmo-saline stresses, which enable to detect differences in vigour of long-term stored seeds with high germination percentage (G%). The quality of Brassica villosa subsp. drepanensis seeds stored in a genebank (at ? 20°C for 16 years) was compared with seeds at harvest by standard germination tests (GT), SIGT and cytogenetic analysis. No differences were detected in G% and mean germination time under GT. Conversely, SIGT performed with NaCl ? 0.9 MPa osmotic potential did not influence G% at harvest but reduced that of stored seeds, SIGT at ? 1.4 MPa reduced G% of both. Cytogenetic analysis showed reduction of mitotic index, appearance of chromosomal aberrations and smaller nucleoli in stored seeds compared with harvest seeds germinated in water. SIGT at ? 0.9 MPa had no effect on mitotic index, but increased chromosome aberrations and nucleoli number. SIGT at ? 1.4 MPa inhibited G% of harvest and stored seeds, reduced mitoses in harvest and completely prevented it in stored seeds. The results indicate that GT does not faithfully reflect the quality of stored seeds, with misinterpretation of their vigour, whereas SIGT and cytogenetical parameters are sensitive, reliable and inexpensive methods for early prediction of genetic erosion in germplasm banks.     

Germination ecology of <Emphasis Type="Italic">Scorpiurus subvillosus</Emphasis> L. seeds: the role of temperature and storage time

Scorpiurus subvillosus L., wide spread in pastures of Mediterranean basin, is disappearing in the native pastures of the Hyblean plateau (Sicily, southern Italy), because of overgrazing and intensive management techniques. Moreover, it exhibits seed coat dormancy, which delays and reduces germination preventing its diffusion. This paper represents a first attempt in order to investigate changing in germination determined by storage time and temperature on seeds of two populations of S. subvillosus. Germination of S.␣subvillosus seeds was tested in relation to four storage time (30, 130, 200 and 360 days after harvest (DAH)), eight constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40°C) and two populations of different provenience (30 and 600 m above mean sea level). The experiments were conducted either on scarified and unscarified seeds. In S. subvillosus the failure of germination under favourable conditions must be attributed␣only to seed coat, since seed scarification enhanced germination percentage with values up to 100% at almost all tested temperatures. In both treatments, but with a grater incidence in unscarified, seed germination increased gradually as temperature raised, peaking at 20–25°C, then declined with further increases of temperatures. At 40°C no germination occurred. Storage time induced a softening effect, which is somewhat limited by the natural ageing of seeds occurring from about 6 months after harvest.     

Effect of high temperature on moisture loss,imbibition and germination of seeds ofTrianthema Govindia Buch.-Ham. ex DC

Summary Seeds of erect and prostrate plants ofTrianthema govindia Buch. ham. ex DC., growing in shade and open respectively, differed significantly in seed weight and percentage germination. Effect of high temperature exposure to these seeds has been studied in view of water depletion, imbibition and seed germination. The seeds of both the types were subjected to temperatures of 40, 50, 60, and 70° C for 24, 48, 96, and 144 hours. The three factors viz., loss of water, water imbibition and germination of seeds were positively correlated to the duration of treatment at different temperatures. A highly significant positive correlation was also observed between moisture depletion and imbibition, and between imbibition and germination. The percentage germination was favoured at 40° C in both the types of seeds and was increased with the increase of treatment duration. However, at higher temperatures (50 and 60° C) the percentage declined while at 70° C the seeds lost their vitality.     

Are fungi important for breaking seed dormancy in desert species? Experimental evidence in Opuntia streptacantha (Cactaceae)

Seeds of Opuntia spp. have physiological dormancy; they need a period of after-ripening to break dormancy, and the embryos have low growth potential. We evaluated the combined effects of seed age and presence of fungi on the testa on germination of Opuntia streptacantha, an abundant species in the Chihuahuan Desert (Mexico), assuming that older seeds have broken seed dormancy and fungi can reduce mechanical resistance to germination. In a preliminary experiment, we found no germination of 9-year-old (1998) and freshly collected (2007) seeds. However, we obtained 67% and 27% germination from 9-year-old and fresh non-sterilized seeds, respectively, and found fungi growing on the testa of all germinated seeds. Two fungal strains were isolated and identified using ribosomal internal transcribed spacer (ITS) sequence analysis: Penicillium chrysogenum and Phoma sp. In a second experiment, we inoculated seeds with strains of P. chrysogenum and Phoma sp., as well as Trichoderma koningii and binucleate Rhizoctonia (Gto17S2), to evaluate their ability to break seed dormancy. Seeds inoculated with P. chrysogenum, Phoma sp. and T. koningii had higher germination than controls for both seed ages, but germination was higher in older seeds. Scanning electron microscopy showed that these fungi eroded the funiculus, reducing its resistance. Binucleate Rhizoctonia did not lead to germination and controls had almost no germination. Our results strongly indicate that fungi are involved in breaking seed dormancy of O. streptacantha, and that the effect of fungi on seeds is species-specific.     

The performance of carrot seeds in relation to their viability

The germination and emergence characteristics, and early seedling growth, of carrot seeds cv. Chantenay red-cored from different sources with a range of germination from 54–94%, was compared. Seeds from protected crops (mean temperature of growth 21°C, r.h. 45–70%) gave higher percentage germination than those from crops grown outdoors (mean temperature 15°C, 70–100% r.h.). Germination was also higher from mature (seed moisture content at harvest 20% or lower) than immature seed (seed moisture content at harvest between 20 and 60%). High percentage germination (>90%) was associated with low mean germination times and low spreads of germination times whilst the reverse was true for low percentage germination. Similar relationships were found for seedling emergence characters in the field although a lower proportion of the viable seeds produced seedlings from slowly than rapidly germinating seed lots. In general, seed lots having a low percentage germination gave greater variability in plant weight than those of higher percentage germination. There was no effect of seed source on radicle or shoot relative growth rates or on post-emergence seedling growth rates.     

The Light-Sensitivity of Germination of Ficus benjamina var. nuda (Moraceae) Seeds and Its Ecological Significance

In this paper , Ficus benjamina L . var . nuda seeds were used as experimental materials, effects of temperature, light , phytohormone ( gibberellin , 6-benzyladenine and ethylene ) , nitrogenous compounds ( sodium nitroprusside,nitrate , and nitrite ) on seed germination were studied , and ecological significance of light in seed germination was discussed. Under alternating photoperiod (14 h light , 10 h dark , 12μmol m- 2 s - 1 ) , final germination percentage of seeds was 87. 5% , 100% , 100% , 100% , 98% , 89% and 100% , respectively, at 15℃ , 20℃ , 25℃ , 30℃ , 35℃ , 40℃ and 30℃􊄯20℃ , mean germination time of seeds was 34 . 7 d , 16 . 3 d , 5. 6 d , 4 .8 d , 6 . 4 d , 9 d and 6 .3 d , respectively. Germination percentage of seeds which were incubated for 35 d at 15℃ , 20℃ , 25℃ , 30℃ , 35℃ , 40℃ , 30℃􊄯20℃ and dark was zero , and these seeds rapidly germinated after addition of alternating photoperiod . Light intensity of 0 . 5 - 20μmol m- 2 s - 1 markedly increased final germination percentage of seeds . However , different light intensity influencedhardly final germination percentage of seeds, but altered germination rate of seeds . Under photoperiod of 24 h , final germination percentage of seeds notably increased with increasing length of light duration . The seeds treated for 24 h ,36 h , and 48 h by continuous light could germinate at subsequent dark. Different concentrations of exogenous gibberellin, 6-benzyladenine, ethylene, sodium nitroprusside , nitrate and nitrite could not replace light and not accelerate seed germination, and these seeds rapidly gained germinablity after addition of alternating photoperiod . Germination behavior of F. enjamina L . var . nuda seeds was closely related to long-term adaptation for tropical forest .     

Determination of anti-microbial properties of Ocimum viride concentrations on Rhizopus stolonifer infection and germination of soybean (Glycine max L. Merill)

Investigation was conducted to determine the anti-microbial properties of different concentrations of Ocimum viride and germination of soybean. Analysis of variance recorded a highly significant difference on the percentage occurrence of different fungal diseases at 5% probability level. Ocimum viride at 0.04 ppm had the highest mycelia growth inhibition 77.0%, while 0.00 ppm (control) recorded the lowest mycelia inhibition 1.00% of Rhizopus stolonifer. Investigation revealed that spot recorded the highest percentage occurrence 50%, scab 34%, mould 43% and blight 31.0% recording the lowest. Also the microorganisms isolated from diseased soybean were Rhizopus stolonifer, Fusarium oxysporum, Aspergillus species although the inhibition was very high on Rhizopus stolonifer, followed by Aspergillus sp, then mould when Fusarium sp was low. Also, Ocimun viride extract was observed to possess a high anti-microbial properties as it inhibited the growth of all the micro-organisms identified to be associated with the soybean sees. Result showed that seeds treated with crude extract of 0.04ppm had the highest percentage germination irrespective of the days of germination, followed by 0.03 ppm, then 0.02 ppm, when 0.00 ppm had the lowest. However, 0.01 and 0.02 ppm, respectively, recorded similar percentage germination 64%; 64% at 4 days after planting. Days of planting were highly significant on the percentage germination at 5% probability level, as germination of the soybean seeds increased with days of planting and highest percentage germination of 98% was recorded on the 6th day of planting while no germination was recorded from the 1st till the 4th day of planting.     

Decontamination of grains and legumes infected with Aspergillus spp. and Penicillum spp. by cold plasma treatment

The objective of this study was to determine the efficacy of a self-designed low pressure cold plasma (LPCP) system using air gases or SF6. For the inactivation and/or elimination of two pathogenic fungi, Aspergillus spp. and Penicillum spp. artificially contaminated on seed surface. The plasma decontamination process was performed by batch process in vacuum chamber, using gas injection followed by plasma discharge for the duration of 5-20 min. The plasma treatment reduced the fungal attachment to seeds below 1% of initial load depending on the initial contamination level, while preserving germination quality of the seed. A significant reduction of 3-log for both species was achieved within 15 min of SF6 plasma treatment time. Air gases plasma and SF6 plasma in particular provides an interesting surface decontamination alternative for seeds.     

Micropropagation ofDendrobium fimbriatum Hook. by green pod culture

Present studies have demonstrated that immature seeds obtained from green pod ofDendrobium fimbriatum Hook., an endangered epiphytic forest orchid having horticultural importance, can be germinated asymbioticallyin vitro for rapid micropropagation. Vacin and Went medium containing 0.1 mg L^-1 NAA and 15% coconut water was found most effective for high percentage (80-90%) seed germination and seedling development. This method can be exploited for their rapid micropropagation and conservation.     

Seed Germination and Radicle Growth of a Halophyte, Kalidium caspicum(Chenopodiaceae)

Effects of temperature, light, NaCl and polyethylene glycol(PEG)-6000 on seed germination and radicle growth in a halophyticshrub, Kalidium caspicum(L.) Ung.-Sternb. were investigated.When seeds were incubated in deionized water at constant temperaturesbetween 10 and 30°C, the percentage germination in the darkexceeded 75%; light suppressed seed germination at alternatingtemperatures. Incubating seeds with a hypersaline solution ofNaCl for 30 d had no adverse effect on their germinability.The percentage germination of seeds incubated with a –0.8MPa NaCl solution was 73, 80 and 54% at 10, 20 and 30°C,respectively, but all radicles died before their length exceeded5 mm. In contrast, when seeds were incubated with a –0.8MPa PEG solution at 20°C, 68% of seeds germinated, and 95%of the emerging radicles survived beyond 5 mm. The high sensitivityof small radicles of this species to salinity indicated thatsalt must be removed from the soil surface for seedling establishment.Copyright2000 Annals of Botany Company Chinese desert, radicle growth, germination, halophyte, Kalidium caspicum, salinity     

Germination responses to GA3 and stratification of threatened Festuca L. species from Eastern Mediterranean

The seed germination characteristics of three threatened Festuca sp. [F. punctoria Sm., F. cyllenica Boiss. et Heldr. subsp. uluana Markgr.-Dannenb., F. paphlagonica (St.-Yves) Markgr.-Dannenb. subsp. paphlagonica] were investigated. These species are endemic and spread on alpine belt. The study was carried out with wet-cold and dry-cold stratification throughout 15 days, different doses of GA3 (50, 100 and 150 ppm) and hormone-stratification combined treatments, and non-treatment series. We found that the germination rates of three fescue seeds for various treatment series were different. The mean germination percentage of F. cyllenica was higher (80%) than that of F. punctoria and F. paphlagonica which were fairly low (50-60%). Germination rates increased by wet-stratification treatment in F. punctoria and also increased with 100 ppm GA3 application to the seeds of F. paphlagonica. When taken into consideration the germination percentages of all fescue species, the seeds of F. punctoria and F. paphlagonica can be dormant, but the seeds of F. cyllenica are non-dormant.     

Studies on seed-borne fungi of wheat in seed health testing programme

Seed mycoflora associated with wheat was studied on different media with a particular reference to Blotter and potato dextrose agar (PDA) procedures of ISTA. Seed-borne fungi, viz. Fusarium moniliforme, Rhizopus spp., Mucor spp., Alternaria alternata, Aspergillus niger, Aspergillus flavus, Curvularia lunata, Drechslera spp, Alternaria spp. and Penicillium spp., were isolated from the variety HD264. Blotter method was found to be the best media for the isolation of mycoflora whether borne externally or internally. Total number and frequency of occurrence of fungi were recorded. The effect of seed treatment with different chemicals and eco-friendly botanicals was analysed on germination, and growth, better percentage of seed germination and reduction in fungal pathogen were due to biochemical seed treatment.     

Thiamine binding and metabolism in germinating seeds of selected cereals and legumes.

The basic characteristics of thiamine metabolism in germinating seeds of maize (Zea mays), oat (Avena sativa), faba bean (Vicia faba) and garden pea (Pisum sativum) are presented with a special emphasis of a possible thiamine storage function of seed thiamine-binding proteins (TBPs). Seeds were germinated for 6 d in the dark. Thiamine-binding activity in seeds decreased during germination by 50% in cereals and by 30% in legumes. The degradation of TBPs was also detected by polyacrylamide gel electrophoresis. The total thiamine content decreased rapidly to 20-40% of the initial value in cereal seeds during first 3 d of germination while in legume seeds thiamine content started changing from the fourth day and dropped by 50% at the sixth day. A composite pattern was found for the changes in thiamine pyrophosphate (TPP) contribution to total thiamine during seed germination. A peak of the coenzyme percentage was usually detected at the second day of germination. Another gain of TPP was often seen toward the sixth day of germination. The activity of thiamine pyrophosphokinase (EC 2.7.6.2) was high in resting legume seeds and did not significantly change during germination. In contrast, the low activity of this thiamine-activating enzyme in cereal seeds progressively increased during germination. Thiamine phosphate synthase (EC 2.5.1.3) was also detected in seeds and was shown to contribute significantly to the balance of thiamine compounds during seed germination.     

Antagonistic potentiality of Trichoderma harzianum towards seed-borne fungal pathogens of winter wheat cv. Protiva in vitro and in vivo

The antagonistic effect of Trichoderma harzianum on a range of seed-borne fungal pathogens of wheat (viz. Fusarium graminearum, Bipolaris sorokiniana, Aspergillus spp., and Penicillium spp.) was assessed. The potential of T. harzianum as a biocontrol agent was tested in vitro and under field conditions. Coculture of the pathogens and Trichoderma under laboratory conditions clearly showed dominance of T. harzianum. Under natural conditions, biocontrol effects were also obtained against the test fungi. One month after sowing, field emergence (plant stand) was increased by 15.93% over that obtained with the control treatment, and seedling infection was reduced significantly. Leaf blight severity was decreased from 22 to 11 at the heading stage, 35 to 31 at the flowering stage, and 86 to 74 at the grain filling stage. At harvest, the number of tillers per plant was increased by 50%, the yield was increased by 31.58%, and the 1,000-seed weight was increased by 21%.     

Enhanced symbiotic seed germination of Cypripedium macranthos var. rebunense following inoculation after cold treatment

Cypripedium macranthos var. rebunense is a well-known wild orchid in Japan, and is considered to be a symbol for rare plant conservation. A fungus isolated from roots of C. macranthos var. rebunense induced symbiotic germination of the species in vitro. Cold treatment of the seeds at 4°C prior to fungal inoculation was required for the symbiotic germination. Changing the timing of inoculation of the fungus to the seeds greatly improved germination frequency. Maximum germination was attained after seeds were inoculated just after the cold treatment for 12 weeks, and approximately 20% of the seeds developed into protocorms more than 1 mm long. These results suggest that fungal inoculation takes place at the beginning of spring in nature, and the tough impervious seed coat may preserve the seed from the infection during autumn and winter seasons. The lengthy culture period of more than 16 weeks at 20°C on the same medium with the fungus caused gradual browning and rot of the protocorms. By elimination of the fungus with a fungicide and by transfer to a nutrient rich medium, approximately 20% of the protocorms developed into healthy plantlets. The methods obtained here appear to be applicable to symbiotic germination of many other threatened Cypripedium spp.     

The effects of ripening and drying of carrot seed (Daucus carota) crops on germination

Carrot seeds taken from the parent plant were capable of germinating before the stage when maximum seed dry weight was reached but even after this stage, when the seed moisture content had fallen below 20%, improvement in seed germination characteristics continued. In the latter stages of seed growth losses by shedding were 12–20 kg/ha/day. For low density crops (10 plants/m²) the yield of viable seed was at a maximum in crops whose seed was harvested with a moisture content of between 20 and 40% but no consistent relationship could be established for high density crops (80 plants/m²). There were no effects of umbel order or plant density on mean germination time or spread of germination. At any early harvest, percentage germination was highest for primary-umbel-seeds and seeds from low density crops but the differences between the seed origins diminished with later harvests. Drying the seeds on the umbels improved the percentage germination, reduced the mean germination time and the spread of germination particularly at the early harvests compared with seeds removed from the umbels and germinated immediately without drying.     

Seed treatment with lactic acid bacteria against seed-borne pathogens of spring wheat

Antifungal potential of lactic acid bacteria (LAB) such as Lactobacillus sakei KTU05-6, Pediococcus acidilactici KTU05-7 and Pediococcus pentosaceus KTU05-8, KTU05-9 and KTU05-10 was tested on naturally contaminated wheat seeds. LAB influence on fungal growth on kernels, seedling diseases and seed germination was examined by laboratory and field experiments. KTU05-10 was selected and later used for seed treatment as solitary strain and in two- or three-component mixtures with KTU05-7 and KTU05-6. The occurrence of Fusarium spp. on wheat kernels in agar plate assays was decreased by seed treatment with all LAB cultures, and the efficacy of each strain depended on incubation temperature. Inoculation of wheat kernels with strains of solitary KTU05-10 and in mixtures with KTU05-7 and KTU05-6 significantly reduced the incidence of Fusarium spp., Bipolaris sorokiniana and Alternaria spp. LAB influence on seed germination and seedling diseases was observed in laboratory and field experiments, but in most cases, this influence was insignificant.     

豚草种带内生真菌及其对种子发芽和幼苗生长的影响

内生真菌是一类共生于植物体内,能够不同程度影响宿主植物生态适应性和竞争能力的微生物。分析内生真菌在豚草种子中的分布、种群结构,以及内生真菌发酵液对种子发芽和幼苗生长的作用。结果显示:发生于6个地区的豚草种子均能分离获得内生真菌,分离率在19%—92.63%之间,不同地区之间差异极显著(P0.01)。内生真菌主要存在于种子的总苞部位,分离率达到65.52%。发生于福建省长乐市松下镇的豚草种带内生真菌种群包含5个属,以链格孢属(Alternaria)真菌为优势菌群,占82.26%;其次为镰孢属(Fusarium)真菌,占9.68%;其它3个属的真菌发生较少,均低于5%。内生真菌主要以水平传播方式在豚草不同世代之间传播。供试的7个内生真菌菌株的发酵液均不同程度地抑制豚草种子发芽,降低幼苗地上部高度、根长度、根数量和总生物量,但不同菌株发酵液之间抑制程度差异明显,显示不同菌株对豚草种子发芽和幼苗生长产生不同的影响。内生真菌发酵液处理后的种子仍然保持较高程度的活力;不同内生真菌发酵液处理后,有活力的种子维持在50%—87.5%之间,均高于(或等于)清水处理的种子,说明内生真菌代谢产物只是抑制种子的发芽,但并不导致种子的腐烂和死亡。这些研究结果初步显示种子携带的内生真菌可能在豚草入侵生物学中发挥重要的作用。