Studies of halo-blight seed infection and disease transmission in dwarf beans

The transmission of Pseudomonas phaseolicola from plant to seed was mainly by the penetration of bacteria from external pod lesions to the underlying seeds. There was no evidence for translocation of bacteria from other parts of the plant to the seed, and symptomless pods contained only healthy seeds. Although a small proportion of infected seeds showed obvious symptoms of infection, the majority showed either slight symptoms, which could be detected only by careful observation, or were symptomless. In tests of disease transmission from seed to seedling, seeds with slight symptoms, or those which were symptomless were responsible for 35% and 52% respectively of the total disease transmission compared to 13% for obviously infected seeds. The viability of bacteria in seed stored under relatively uncontrolled conditions (10–27 C) declined by a factor of 250 per annum over the first 3 yr with extrapolation predicting effective extinction after c . 5 yr. The pathogen survived longer under controlled conditions (7–10 C and 45–50% r.h.) but no viable bacteria were detected in seed stocks which were 10-yr-old and with one exception 6-yr-old stocks were also free of the pathogen.     

Studies on the survival and transmission of Xanthomonas manihotis on cassava seed

Cassava seed which had been stored at 5 ^oC and 60% r.h. for 2–51 months was assayed for the presence of Xanthomonas manihotis by a leaf-infiltration technique, using as inoculum the supernatant from seeds soaked in sterile water at 30 ^oC for 2–4 h. The threshold of sensitivity of the assay method was 10⁵ cells/ml. Twenty out of 50 samples yielded the pathogen. The infested seed had been in storage for 2–18 months. Bacteria reisolated from infiltrated leaves were identical to X. manihotis in cultural characteristics, phage type and pathogenicity. Surface sterilisation or hot air treatment for 24 h at 65^oC or lower did not eliminate the pathogen from infested seed. Soaking of infested seed in hot water at 60 ^oC for 20 min reduced the number of bacteria to less than the minimum detectable level without appreciably reducing germination. Cassava bacterial blight was observed in 8-wk-old seedlings which had been planted during the dry season at a site where infection from outside sources was unlikely. It is postulated that a low percentage of successful seed transmissions of X. manihotis can occur under favourable environmental conditions.     

Standard yet unusual mechanisms of long-distance dispersal: seed dispersal of Corymbia torelliana by bees

Mellitochory, seed dispersal by bees, has been implicated in long-distance dispersal of the tropical rain forest tree, Corymbia torelliana (Myrtaceae). We examined natural and introduced populations of C. torelliana for 4 years to determine the species of bees that disperse seeds, and the extent and distance of seed dispersal. The mechanism of seed dispersal by bees was also investigated, including fruit traits that promote dispersal, foraging behaviour of bees at fruits, and the fate of seeds. The fruit structure of C. torelliana , with seed presented in a resin reward, is a unique trait that promotes seed dispersal by bees and often results in long-distance dispersal. We discovered that a guild of four species of stingless bees, Trigona carbonaria, T. clypearis, T. sapiens , and T. hockingsi, dispersed seeds of C. torelliana in its natural range. More than half of the nests found within 250 m of fruiting trees had evidence of seed transport. Seeds were transported minimum distances of 20–220 m by bees. Approximately 88% of seeds were dispersed by gravity but almost all fruits retained one or two seeds embedded in resin for bee dispersal. Bee foraging for resin peaked immediately after fruit opening and corresponded to a peak of seed dispersal at the hive. There were strong correlations between numbers of seeds brought in and taken out of each hive by bees ( r =  0.753–0.992, P  < 0.05), and germination rates were 95 ± 5%. These results showed that bee-transported seeds were effectively dispersed outside of the hive soon after release from fruits. Seed dispersal by bees is a non-standard dispersal mechanism for C. torelliana, as most seeds are dispersed by gravity before bees can enter fruits. However, many C. torelliana seeds are dispersed by bees, since seeds are retained in almost all fruits, and all of these are dispersed by bees.     

Presevvation of Xanthomonas campestris in Brassica oleracea seeds

Summary Brassica oleracea seeds were sterilized by gamma radiation and sodium hypochlorite washing. Xanthomonas campestris was inoculated into the seeds by incubating, under vacuum, a suspension of the bacteria with the seeds. After thorough washings with sterile distilled water, the seeds retained about 13 000 cells per seed. The seeds were maintained at 4°C during 21 months, during which the viability of the bacteria and their capacity to produce xantham gum in shake flasks, were evaluated. Bacterial viability showed oscillations but after 20 months it was 10% of the initial. When these seeds were used as a pre-inoculum for a culture to produce xanthan, the final polymer concentration increased slightly with time of seed storage and the final broth viscosity was fairly constant. The specific polymer production (per weight of final bacterial cells) increased about three-fold after 21 months of experimentation. The method, besides being able to produce xantham in quantity and quality, has the advantages of an easy inoculation procedure, no need for transfers, less contamination risk and improved growth rate of the bacteria in the inoculation medium. Correspondence to: E. Galindo     

干旱胁迫下白刺花种子大小与萌发对策

种子大小与种子萌发及其与环境因子的关系是植物种子萌发对策研究中的重要科学问题之一。采用PEG模拟干旱法研究不同干旱胁迫强度(0,5%,10%,15%,20%)下,白刺花(Sophora davidii)种子萌发进程、种子大小与种子萌发及种子命运的关系。结果表明:不同干旱胁迫下,白刺花种子具有相似的萌发进程,但中度干旱处理(10%PEG)萌发率显著高于零干旱(0%PEG)和重度干旱处理(P0.05),重度干旱处理(20%PEG)种子萌发开始时间晚于零干旱和中度干旱处理;种子大小与种子萌发开始时间的关系表现为零干旱处理下呈极显著负线性关系,中度干旱处理(5%PEG,10%PEG)下无相关关系,重度干旱处理(15%PEG,20%PEG)下呈负二次曲线关系;种子大小对种子命运的影响表现为零干旱处理有利于大、小种子萌发和小种子休眠,中度干旱处理(10%PEG)增加中等种子萌发、大种子休眠和小种子死亡风险,重度干旱处理(15%PEG,20%PEG)增加大种子死亡风险、中等种子和小种子休眠。综合分析表明,白刺花种子大小与萌发行为及种子命运的关系具有较强的环境依赖性,即种子萌发行为表现为顺境下种子越大萌发越快,逆境下小种子和大种子较中等种子萌发更快;种子命运表现为顺境增加种子死亡的风险,中度干扰有利于种子萌发,逆境则有利于种子休眠。     

Attributes of the seed bank after a century of primary succession on islands in Lake Hjälmaren, Sweden

1 A large number of islands was created when the water table of Lake Hjälmaren, south central Sweden, was lowered between 1882 and 1886. We have complete lists of vascular plant species for 40 of these islands from 1886, 1892, 1903–04, 1927–28 and 1984–85.
2 We have investigated the seed bank on nine of these islands and compared species composition at different soil depths with the species lists from the islands in 1886–1985, and with the present vegetation in the area of seed bank sampling. We have also investigated the distribution in the soil of seeds from species with different ecological attributes, including seed longevity, successional status, seed weight, seed form and species longevity.
3 Seeds in soil samples were allowed to germinate over the course of two summers with an intermediate cold storage. We found 1944 seeds representing 65 taxa. The mean seed density was 84 seeds dm ^–2 .
4 The similarity between the surface soil (0–3 cm) seed bank and the vegetation at the different vegetation analyses increased from 1886 to 1993. The similarity between the present vegetation and the seed bank decreased with increasing soil depth, and the soil at 12–15 cm had no species in common with the present vegetation. Several species now absent from the vegetation were found in the seed bank.
5 Deeply buried seeds came from early successional, annual species with long-term persistent and low-weight seeds, as expected from seed bank theories, but were slightly elongated, which was in contrast to theories. Spherical seeds were associated with the surface soil, as were short-lived and high-weight seeds from late successional, perennial species.     

Frequency-dependent seed size selection on Cryptocarya alba (Mol.) Looser (Lauraceae): testing the effect of background

Seed size affects the probability of seed predation. Large seeds should be preferred over small seeds but the selective responses of seed predators may also be frequency-dependent. Seed predators may prefer the most common seed sizes (apostatic selection), the rarest ones (antiapostatic selection) or even be unresponsive to the size of seeds. Moreover, seed density may further modify the selective responses of seed predators. We expect that at a low seed density seed consumption should be concentrated on common seed sizes, and at high seed density it should be concentrated on rare seed sizes, as common ones act as a background that makes rare phenotypes more conspicuous (the effect of background). We tested this prediction in a field experiment with seeds of Cryptocarya alba (Lauraceae) at La Campana National Park, central Chile. We presented large and small seeds in two contrasting seed densities (ten and 100 seeds per m²) and at five frequencies of large seeds: 0.1, 0.25, 0.5, 0.75 and 0.9. After 28 days we measured the proportions of the two size classes in the remaining seeds. Large seeds were always preferred to small seeds, even when they were at low frequency. Contrary to the predictions, at low seed density consumption was antiapostatic whereas at high seed density selection was independent of frequency. We discuss the causes and consequences of such selective responses expressed by seed predators.  © 2005 The Linnean Society of London , Biological Journal of the Linnean Society , 2005, 84 , 137–142.     

Foraging and community consequences of seed size for coexisting Negev Desert granivores

We examined the effects of seed size on patch use and diet selection for three co-existing Negev Desert granivores: Allenby's gerbil ( Gerbillus allenbyi ), greater Egyptian sand gerbil ( Gerbillus pyramidum ), and crested lark ( Galerida cristata ). We manipulated size and spatial distribution of seeds in experimental food patches and quantified foraging behavior by measuring giving-up densities (GUDs: the amount of food remaining in a resource patch following exploitation by a forager). In one experiment, we presented small (<1.4 mm in diameter cracked wheat), medium (2.0–3.3 mm), and large (>3.4 mm) seeds in separate trays; in a second, we presented small and medium seeds separately and mixed together. Gerbils had a higher handling time efficiency on smaller seeds, but a much higher encounter probability on larger seeds (20 times higher on large than medium seeds, and 2–5 times higher on medium than small seeds). This led gerbils to have significantly lower GUDs on larger seeds than smaller seeds and to harvest a higher proportion of the larger seeds. When presented with rich and poor patches, G. allenbyi tended to equalize GUDs in both patches, indicating a quitting harvest rate rule for patch exploitation. In contrast, larks appeared to use a fixed time rule for patch exploitation. For larks, seed size did not influence encounter probabilities, and they showed no seed-size selectivity. Still, larks had higher handling efficiencies on smaller than larger seeds, and consequently had a significantly lower GUD on small than medium seeds. Despite large differences between the gerbils and larks in their foraging, our results do not support species coexistence via seed-size partitioning: the larks had much higher GUDs than the gerbils on all seed sizes. Nonetheless, seed size, seed abundance, seed distribution and the animal's patch use behavior all played major roles in determining gerbils' and larks' diet selectivities and GUDs.     

Synergism between gibberellic acid and low Pfr levels inducing germination of Kalanchoë seeds

Sown on water, seeds of Kalanchoëbiossfetdiana Poelln. cv. Feuerblute are absolutely light-requiring and show full red/far-red reversibility. In seeds, sown on 2 ×10^-3 M gibberellic acid, red/far-red reversibility disappears and both short red and far-red irradiations induce germination. Gibberellic acid alone does not induce germination, but it increases the physiological activity of P_fr to the extent, that the low P_fr level obtained by far-red irradiation becomes very effective. The synergism between gibberellic acid and far-red light appears after a two-day incubation; period. The nature of this lag phase was examined by measuring both germination and uptake of labelled gibberellic acid in intact seeds and seeds with a punctured seed coat. The lag phase was shown to be independent of the uptake kinetics of gibberellic acid and allows development to a specific stage, necessary for germination after phytochrome-phototransformation. The kinetics of the uptake of gibberellic acid by intact seeds and embryos of intact seeds are different. In intact seeds most of the gibberellic acid is retained in the seed coat; only a small fraction actually penetrates to the embryo where it can exert its physiological activity.     

Seed size and seedling emergence in 16 temperate forest herbs and one dwarf-shrub

The impact of seed size (seed mass) on seedling emergence beneath a leaf litter layer and post-dispersal seed predation was investigated in two field experiments including 16 forest herbs and one dwarf-shrub in southeastern Sweden. In the first experiment, I studied the relationship between seed mass of eight forest herbs (0.3–16.7 mg) and seedling emergence after removal of litter and reduction of seed predation (rodents and insects). Removal of litter and reduction of seed predation did not affect seedling emergence. However, regardless of treatment, species with large seeds (> 3 mg) had a higher seedling emergence than those with small seeds (< 1 mg). In the second experiment, I investigated the relationship between seed mass of 12 species (0.007–18.4 mg) and seedling emergence after removal of litter, reduction of seed predation (insects) and seedling herbivory (molluscs). Total emergence over three years was significantly higher in species with large seeds (> 3 mg) than in those with small seeds (< 2 mg). Removal of litter increased total seedling emergence, while application of insecticide and molluscicide had no effect. Similar results were obtained from both a deciduous and a mixed coniferous forest, but seedling emergence was in general higher in the mixed coniferous forest. Seedling emergence in temperate forest herbs and dwarf-shrubs seems to be higher in species with large than in those with small seeds, and it is often enhanced by disturbance.     

EXPERIMENTS IN THE SUDAN GEZIRA ON CONTROL OF WILT OF DOLICHOS BEAN (DOLICHOS LABLAB) ASSOCIATED WITH ATTACK BY COCKCHAFER GRUBS (SCHIZONYCHA SP.)

Wilt of dolichos bean ( Dolichos lablab ) in the Sudan Gezira appeared to be due primarily to cockchafer grubs ( Schizonycha sp.) in the soil attacking the hypocotyls or roots of plants up to about 6 weeks after sowing. Many wilted plants also showed symptoms of ashy stem blight ( Macrophomina phaseoli ), but in these the fungus was probably a secondary invader rotting roots weakened or damaged by unfavourable soil conditions or insects. Wilt was often severe in dolichos sown on land cropped to sorghum ( Sorghum vulgare ) in the preceding season, sorghum roots in the soil harbouring the grubs. Under moderate grub attack seed dressings containing organomercurial and γ-benzene hexachloride (BHC) gave satisfactory-protection at 0.089%γ-BHC/seed but were inadequate when wilt was severe. Dieldrin and aldrin at 0.044 or 0.089%/seed gave excellent protection in all experiments, but their performance under exceptionally severe wilt conditions has yet to be tested, as also the relative efficiencies of seed treatment and soil treatment under such conditions. Fungicide-insecticide seed treatment also reduced preemergence rotting of germinating seeds due to grub attack.
Wilt rarely occurred in dolichos planted on land fallow in the preceding season, but, even in the apparent absence of wilt, seed treatment often appreciably improved emergence, plant populations, growth and yields. These effects possibly resulted from control of root damage by soil insects, such damage reducing growth and yields but not sufficiently severely to cause wilting. Pending further investigation a powder seed dressing containing organomercurial plus 20% dieldrin, and applied at 1:450 by weight to seed (about 5–6 g./acre of dieldrin), is recommended for dolichos bean in the Gezira.     

Effects of search experience in a resource-heterogeneous environment on the oviposition decisions of the seed beetle, Callosobruchus maculatus (F.)

Abstract.  1. This study investigates how female seed beetles, Callosobruchus maculatus , distribute their eggs on various-sized seeds when the size of seed was varied during the egg-laying period.
2. Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans ( Vigna angularis ). Each array contained four size classes of seed, ranging from small (5.0–5.5 mm diameter) to large (6.5–7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64-patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four-patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64-patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four-patch design would only rarely encounter a change in bean size.
3. Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female's recent experience.
4. Female beetles exhibited size discrimination throughout their egg-laying process; however, there was a trade-off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg-load seeds during the egg-laying process.
5. Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg-discrimination ability.     

Are predatory birds effective secondary seed dispersers?

We have studied the unusual phenomenon of secondary seed dispersal of Lycium intricatum seeds on a small oceanic Atlantic island (Alegranza, Canarian Archipelago) in which a small frugivorous lizard ( Gallotia atlantica ) and two different predatory birds participate, a shrike ( Lanius excubitor ) and a kestrel ( Falco tinnunculus ). Endemic lizards that are common prey of both bird species consume Lycium fruits. Lizard remains were significantly matched with the presence of Lycium fruits in the regurgitation pellets of the two predatory birds. Seeds were found in 7.3% of the lizard droppings, 31.0% of kestrel pellets and 55.7% of shrike regurgitations. The mean number of seeds per dropping or pellet was 4.8 ±4 in lizard, 20.2 ±34.5 in shrike and 6.7 ±8.1 in kestrel. The percentage of viable seeds showed significant differences among all four treatments, decreasing in the following direction: seeds collected directly from plants (98.0%), shrikes (88.0%), lizards (72.3%), and kestrels (31.7%). Seeds from Lycium fresh fruits and shrike pellets showed significantly higher germination rates than those from lizard droppings and kestrel pellets. While lizards and shrikes are effective seed dispersers, kestrel gut treatment decreases seed viability. Seed viability is always higher than seed germination in each of the four treatments. In this island environment, Lycium seeds are under an important random influence during the seed dispersal process. Secondary seed dispersal seems to acquire a relevant dimension in small and remote insular environments or isolated continental systems where interactions among the different elements involved are intense, all of them are abundant native residents, and they have been coexisting for a long time. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 345–352.     

Serotiny and seed germination in three threatened species of Mammillaria (Cactaceae)

Individuals of some species of Mammillaria (Cactaceae) store some seeds on the plant over periods exceeding 1 year (serotiny). We examined the phenomenon of serotiny and germination behaviour of three rare and endangered Mammillaria species that occur in central Mexico. The species with the highest seed retention was Mammillaria solisioides, whose individuals kept on average 24% of their total seed crop throughout their observable lifetime. Individuals of Mammillaria napina and Mammillaria hernandezii did not differ in their degree of seed retention (about 5%). In M. solisioides and M. hernandezii, seed germination declined significantly with seed age, whereas in M. napina germination increased slightly. In all three species, over 70% of retained seeds were still alive after 8 years. Increasing fractions of dormant seeds were observed with seed age in M. solisioides and M. hernandezii, whereas in M. napina this fraction followed the opposite trend. All three species showed strict light dependence for germination. Serotiny was positively correlated with the harshness of the environment when species and populations were assumed independent. However, these correlations were not significant at the 5% level when the degree of relatedness of species and populations was taken into account using phylogenetically independent constrasts. We hypothesise that serotiny in these species represents a mechanism by which they can cope with a harsh, unpredictable environment. To our knowledge, this is the first assessment of serotiny in cacti.     

Tree Seed Fate in a Logged and Fragmented Forest Landscape, Northeastern Costa Rica1

We compared the seed fate of two animal‐dispersed, large‐seeded timber species (Dipteryx panamensis [Fabaceae] and Carapa guianensis [Meliaceae]) in logged and fragmented forests with that for continuous forest in northeastern Costa Rica. For both species, we quantified rates of seed removal (an index of vertebrate predation) and the fate of dispersed seeds (those carried away from their original location that either germinated or were not subsequently removed within three months). We predicted that (1) fewer seeds would be dispersed by vertebrates in fragmented forest than in continuous forest due to low population abundances after hunting and/or loss of suitable habitat, and (2) seed predation rates would be higher in forest fragments than in continuous forest due to high abundance of small‐bodied seed consumers. We compared three forest fragments currently managed for timber (140–350 ha) and a large reserve of continuous forest (La Selva, 1500 ha and connected to a national park). An exclusion experiment was performed (seeds placed in the open vs. seeds within semipermeable wire cages; 5 cm mesh size) to evaluate the relative roles of large and small animals on seed removal. Seed germination capacity did not differ among all four sites for both species. Removal of Dipteryx seeds was higher in forest fragments (50% removal within 10 days and related to the activity of small rodents) compared to La Selva (50% removal after 50 days). Also, more Dipteryx seeds were dispersed at La Selva than in fragmented forests. Contrary to our predictions, removal of Carapa seeds was equally high among all four sites, and there was a trend for more seeds of Carapa to be dispersed in fragments than in La Selva. Our results suggest that fragmentation effects on tree seed fate may be specific to species in question and contingent on the animal biota involved, and that management strategies for timber production based on regeneration from seed may differ between forest patches and extensive forests.     

Population biology of Senecio integrifolius (Compositae), a rare plant in Sweden

In a study of natural populations of Senecio integrifolius in southern Sweden (1979–1983) seeds were found to disperse from mid-June to late July and most of them germinated in autumn. No soil seed bank was observed. On a heavily grazed site few seeds were produced but the percentage of estimated germination was high (c. 75%). In two moderately grazed habitats 8–10% of the estimated number of seeds produced in permanent plots germinated. In a lightly grazed habitat many seeds were produced but only a small percentage germinated (1.4%). In field experiments the average germination was 50–53% when newly harvested seeds were sown where the vegetation had been removed, and 20–33% when sown in undisturbed vegetation at a moderately grazed site. Germination was much lower in a lightly grazed habitat (3–12%). Survival of seedlings was much higher in heavily and moderately grazed habitats than in lightly grazed habitats. Mortality tended to be higher during the growing season (mid-April to early November) than during the winter, and increased markedly during a drought period in the summer of 1982. The half-life of plants established in 1980 varied from 39.3 years at the most intensively grazed site to 7.2 at the lightly grazed site. The number of flowering stems varied between years mainly according to weather. Few plants in the permanent plots flowered every year, the flowering being most frequent at heavily grazed sites. It is concluded that heavy grazing by cattle after seed dispersal is the appropriate management for maintaining S. integrifolius in Sweden.     

Oxidative stress, phospholipid loss and lipid hydrolysis during drying and storage of intermediate seeds

The biochemical and physiological basis of intermediate seed storage behaviour was examined by investigating the effects of equilibrium drying under relative humidities (RHs) of 9–81% and of storage at 20 or 5°C on coffee seed viability and antioxidant, lipid and sugar status. Slow drying induced a significant decrease in the concentrations of the pools of two major antioxidants, glutathione and ascorbate, and an increase in the free fatty acid (FFA) content of seeds, independent of the RH employed. Seeds stored at 81% RH and 20°C lost their viability very rapidly and showed an extensive loss and oxidation of antioxidants, an accumulation of FFA and a selective loss of phospholipids, in particular phosphatidylethanolamine (PE). Interestingly, the changes in PE content were not due to fatty acid de-esterification and the increase in FFA levels resulted from neutral lipid hydrolysis. Decreasing the storage temperature to 5°C considerably slowed both the loss of seed viability and the level of oxidative stress as well as the rates of lipid hydrolysis. No decline in seed viability was observed under storage conditions of 45% RH/20°C. After 1 year under 45% RH/5°C, the loss of seed viability was found to be due to imbibitional damage and could be circumvented by pre-humidifying or pre-heating seeds before sowing.     

Effect of fire on the topsoil seed banks of rehabilitated bauxite mine sites in the jarrah forest of Western Australia

Summary Germinable seed stores of 5- and 8-year-old rehabilitated bauxite mine pits in south-west Western Australia were assessed before and after burning. These seed stores were compared to those of adjacent unmined Jarrah ( Eucalyptus marginata ) forest, to identify at what age fire can be reintroduced, in order to measure restoration success and reduce fire hazard. Soils were sampled in early summer (before fire) and late autumn (after fire). Before fire, the mean topsoil seed bank of 5-year-old sites was 2121 seeds per m² while 8-year-old sites had a mean of 1520 seeds per m². Only the 5-year-old sites were significantly different from the forest mean of 1478 seeds per m² for the same season. After summer burns (and possibly due to seasonal effects) topsoil seed banks of rehabilitated areas (sampled in autumn) decreased by an average of 53 per cent. Topsoil seed banks of 5–8-year-old sites were resistant to lower intensity burns, with 362 seeds per m² of native species surviving mild burns and 108 seeds per m² of native species surviving after an intense summer fire. The topsoil seed reserve of 5–8-year-old rehabilitated areas had a high proportion of annual weed species while the forest sites had high levels of subshrubs and native annuals. Low-intensity burns did not alter the composition of life-forms in the soil seed bank, while intense burns favoured annual weed and shrub species. The results indicate that it is not appropriate to introduce fire to rehabilitated areas before 8 years, due to limited fuel reduction benefits and possible adverse effects on obligate seeding species. The large proportion of weed species in the soil seed bank of young rehabilitated areas is a concern, and remains a major consideration for future disturbance of these areas.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

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.