The seed ecology of an ornamental wattle in South Africa — Why has Acacia elata not invaded a greater area?

Australian Acacia species introduced to South Africa as ornamentals have notably smaller invasive ranges than those introduced for forestry or dune stabilization. We asked whether the relatively small invasive extent of Acacia elata, a species used widely for ornamental purposes, is due to low rates of reproduction. Age at reproductive maturity, seed dispersal, annual seed production, seed bank dynamics and seed germination and viability were assessed at five sites in the Western Cape. Results indicate that A. elata has similar traits to other invasive Australia Acacia species: annual seed input into the leaf litter was high (up to 5000 seeds m^− 2); large seed banks develop (> 20,000 seeds m^− 2) in established stands; seed germinability is high (> 90%); seeds accumulate mostly in the top soil layers but can infiltrate to depths of 40 cm; and seed germination appears to be stimulated by fire. However the age at the onset of reproduction (~ 4 years) is longer than most widespread invaders (~ 3 years) and dispersal is fairly limited (seeds fell up to distances of 6 m from the parent canopy; the highest density of seed rain was found directly under the canopy with over 20% of seeds falling directly under the terminal branches). We suggest that the current limited distribution of invasive A. elata populations is the result of the relatively small size of initial populations (cf. large plantations and widespread plantings for forestry and dune stabilization species), the species' apparent lack of secondary dispersal vectors, and the planting of trees in gardens and urban settings offer limited opportunities for recruitment, proliferation and spread. The species is, however, increasing in abundance and range. We propose methods to improve management of invasions of the species. Management to reduce seed production of this species through classical biological control, as has been achieved for other Australian Acacia species in South Africa, should be prioritised.     

Soil seed bank in and between vegetation patches in arid Patagonia,Argentina

This study was conducted at two sites, 1.5 km from 1 to another in arid Argentina (39°S, 69°W). Vegetation is distributed in patches. Four microenvironments can be identified in the soil surface of these patches, and the bare interspaces among them. Hypotheses were that (1) at any time during the sampling periods, buried (viable + damaged) seeds of the most common vegetation in the patches, Larrea divaricata Cav., Atriplex lampa Gill ex Moquin, Stipa neaei Nees ex Steudel and Leymus erianthus (Phil.) Dubcovsky, are present in the soil seed bank at all four microenvironments within any vegetation patch and its associated interspace, and (2) natural plant recruitment from the soil seed bank occurs for L. divaricata, A. lampa, S. neaei, L. erianthus, Bromus tectorum L. and Poa lanuginosa Poiret ap. Lamarck in all study microenvironments. In undisturbed field areas, 32 soil samples were periodically taken using an auger in 1999. Viable and damaged seeds contained in the soil organic matter were counted for L. divaricata, A. lampa, S. neaei, and L. erianthus. In a further study, emergence and subsequent growth of L. divaricata, A. lampa, S. neaei, L. erianthus, B. tectorum and P. lanuginosa from the soil seed bank were evaluated in the various microenvironments; permanent plots (0.04 m²) were placed on each of the two study sites using four vegetation patches and their associated interspaces per site. Results supported the first hypotheses only for L. divaricata and A. lampa. However, natural recruitment from the soil only included S. neaei and P. lanuginosa through asexual, and B. tectorum through sexual reproduction. Despite the presence of buried seeds of L. divaricata and A. lampa in microenvironment 4 during most of the sampling period, bare interspaces among vegetation patches can be naturally vegetated through sexual reproduction by B. tectorum, during years of abundant, higher than long-term, annual precipitation.     

Experimental evidence for a delayed response of the above-ground vegetation and the seed bank to the invasion of an annual exotic plant in deciduous forests

Invasions by alien plants significantly affect native biodiversity and ecosystem functioning. We conducted a 5-year field experiment to investigate potential effects of the annual invasive plant Impatiens glandulifera on both the native above-ground vegetation and the soil seed bank in a deciduous forest in Switzerland. Eight years after the establishment of I. glandulifera, we set up plots in patches invaded by the alien plant, in plots from which the invasive plant had been manually removed and in plots which were not yet colonized by the invasive plant. We examined plant species richness, diversity and plant species composition in the above-ground vegetation and soil seed bank in all plots one year and five years after the initiation of the experiment. The 36 plots (3 plot types × 6 replicates × 2 sites) were equally distributed over two forest sites. Neither the native above-ground vegetation nor the soil seed bank was influenced by the presence of I. glandulifera one year after the start of the field experiment. After five years, however, plant species richness of both the above-ground vegetation and the soil seed bank was reduced by 25% and 30%, respectively, in plots invaded by the alien plant compared to plots from which I. glandulifera had been removed or uninvaded plots. Furthermore, plots invaded by the alien plant had a lower total seedling density (reduction by 60%) and an altered plant species composition in the soil seed bank compared to control plots. Our field experiment indicates that negative effects of the annual invasive plant on the native above-ground vegetation and soil seed bank of deciduous forests become visible with a delay of several years.     

Seed rain and seed bank of Chinese yew (Taxus chinensis var. mairei) population in Tianmu Mountain☆

Seed rain and seed bank of a Chinese yew (Taxus chinensis var. mairei) population in Tianmu Mountain were researched in 2008 and 2009. The seed rain lasted from 16th–23th of October to 5th–14th of December, and the heaviest seed falling period was from 2nd to18th of November. The intensity of seed rain showed a great inter-annual variation, with a good harvest in 2008. The fallen seeds were composed of 49.9% proportion of immature seed, 33.8% proportion of chewed seed and 16.3% proportion of mature seed. The analysis on the soil seed bank under mother forest showed that the number of intact seeds was 122.75 ± 108.08 grain/m² in October, 279.25 ± 210.73 grain/m² in December 2008, and 166.5 ± 165.34 grain/m² in October, 322.5 ± 275.73 grain/m² in December 2009. The increased number of seed was 156.5 ± 222.723 grain/m² in 2008 and 156 ± 275grain/m² in 2009, which showed a significant variation. Large number of intact seeds added into soil seed bank after seed rain each year. The number of intact seeds in soil seed bank decreased 112.75 ± 47.74 grain/m² from December 2008 to October 2009. Large number of intact seeds lost from seed rot and seed predation by animals. The number of seeds in soil bank under bamboo forest was much lower than that of mother tree forest, and the increased number of seeds was 0.63 ± 1.60 grain/m² in 2008 and 2.88 ± 1.86 grain/m² in 2009. The number of seedling was 0.73 ± 1.10 trees/m² in mother tree forest and 0.09 ± 0.35 trees/m² in bamboo forest. Seedling survival ratio was 0.37% in mother tree forest and 10.23% in bamboo forest. The micro-habitat in bamboo forest was fit for seed germination. Birds transported seeds to bamboo forest, and had an important effect on the regeneration of Chinese yew.     

Invasion by Solidago species has limited impacts on soil seed bank communities

Increasing attention in invasion biology is being paid to measuring and understanding the impacts of invasive species. For plant invasions, however, the impact of invasion on soil seed bank communities has been under-studied. At six sites in southern Germany, we investigated whether areas invaded by Solidago gigantea and Solidago canadensis experienced a reduction in seed bank species richness, size and diversity, and a change in species composition compared to adjacent uninvaded areas. We found no overall effect of invasion on seed bank size, or on species richness and diversity. Seed bank size significantly decreased from 0–5 cm to 5–10 cm depth in both invaded and uninvaded areas. A significant amount of variation in species composition was explained by invasion, but it was only one-tenth of that explained solely by site effects. Our study suggests that invasion by Solidago species may not have the same impacts on the soil seed banks of native species as other invasive perennial forbs that have so far been studied.     

Montpellier broom (Genista monspessulana) and Spanish broom (Spartium junceum) in South Africa: An assessment of invasiveness and options for management

The legumes (Fabaceae) Genista monspessulana and Spartium junceum are major invaders in several other parts of the world, but not yet so in South Africa. We determine their current distributions in South Africa at different spatial scales, assess population structure (soil seed banks and size at reproduction) evaluate current management activities, and provide recommendations for control (including assessing the feasibility of nation-wide eradication). G. monspessulana occurs at nine localities in three quarter-degree cells, covering a total of 22.7 ha. S. junceum is much more widespread, occurring in 33 quarter-degree cells and is frequently cultivated in private gardens. All naturalised or invasive populations are in disturbed areas, mostly along roadsides. Once established, G. monspessulana and S. junceum accumulate large, persistent soil-stored seed banks, ranging in size between 909 and 22,727 (median 1970) seeds/m² and 0 and 21,364 (median 455) seeds/m² for the two species respectively. Both species resprout vigorously after cutting and stump herbicide application (60% of G. monspessulana and 43% of S. junceum plants resprouted) which necessitates regular follow-ups. We estimate that over 10 years, at a cost of about ZAR 81,000 (1 ZAR = 0.114 US$ as on 6 October 2012), G. monspessulana could be extirpated from South Africa. S. junceum is far more widespread and coupled with low effectiveness of control, abundance of seeds and seed longevity, eradication is unfeasible. We recommend that control methods used for S. junceum be improved to prevent resprouting, and that areas are managed to limit the movement of seeds and avoid further spread and establishment. Further studies are required to understand why these two species have failed to replicate the invasiveness shown in other parts of the world.     

Microhabitat variations and seed bank-vegetation relationships in a desert wadi ecosystem

Due to extreme variability in patterns of rainfall, plant seed banks are an important component of desert habitats. Here I report on effects of standing vegetation and three different microhabitats (channel, bank and terrace) on the soil seed bank of a desert wadi ecosystem in the Eastern Desert of Egypt. A total of 450 soil samples at 45 stands were collected to represent the different wadi microhabitats. The germinable seed bank was estimated by controlled counts of seedling emergence. The floristic composition, functional properties and diversity of the soil seed bank, as well as its similarity with the standing vegetation varied among wadi microhabitats. Such variation could be attributed to differences in disturbance intensity among microhabitats (terrace < bank < channel) and variation of soil factors along the microtopographic gradient. Channel showed the highest species richness and size of soil seed bank, followed by bank and then terrace. Moreover the Shannon index of diversity of the seed bank and its similarity with standing vegetation were significantly greater in both channel and bank microhabitats than in terrace. At the level of plant functional groups, number of seeds of annuals was higher in both channel and bank than in terrace. Shrubs were more abundant in seed banks of channel compared to terrace. The size and species richness of seed bank were increased with the total plant cover, annual/perennial ratio and species richness of the standing vegetation.     

A sampling design strategy to reduce survey costs in forest monitoring

High-quality data and long-term time series are the basis of any research activity dealing with natural resources analysis. Adequate sampling designs are fundamental to allow a robust statistical analysis to be representative of a relevant set of target variables. In this work, the sampling strategy of ICP-Forests Level II European network has been proposed to define more efficient and cost-effective procedures under the hypothesis that the average value of single-tree growth (increment) is a proxy of forest health. ICP plots have a fixed spatial structure consisting of a square of 50 × 50 m framed into 25 squared sub-plots. To estimate basal area (G) and increase over time (ΔG), two different sub-sampling methods have been implemented based on a measure of (i) the dominant layer only (i.e. a subset of the highest trees in the plot), and (ii) a random sample of squared sub-plots. While the vertical sampling procedure was performed using a progressive threshold, the horizontal sampling followed a bootstrapping procedure with random extraction without replacement. The mean absolute relative error (MARE) was used to evaluate quality of the two sub-sampling methods. Results highlighted a low predictive power with both methodologies, preventing the possibility to reduce the sampling efforts when estimating ΔG directly. In this context, the vertical sampling was strictly related to species-specific ecology, spatial structure and forest age, being influenced by vertical distribution of trees. The use of horizontal sampling for direct ΔG estimation led to systematically high errors. However, the use of horizontal sampling for total G estimation and indirect estimation of ΔG may reveal as a more effective procedure for a coherent representation of horizontal distribution of trees. Estimate ΔG as the difference between G values at time t and t + Δt finally allows for a sensible reduction of costs with a controlled estimation error. An adequate level of MARE should be decided a-priori to select the number of sub-squares to be randomly sampled.     

Soil seed bank in different habitats of the Eastern Desert of Egypt

The floristic composition and species diversity of the germinable soil seed bank were studied in three different habitats (desert salinized land, desert wadi, and reclaimed land) in the Eastern Desert of Egypt. Moreover, the degree of similarity between the seed bank and the above-ground vegetation was determined. The seed bank was studied in 40 stands representing the three habitats. Ten soil samples (each 25 × 20 cm and 5 cm depth) were randomly taken per stand. The seed bank was investigated by the seedling emergence method. Some 61 species belonging to 21 families and 54 genera were identified in the germinable seed bank. The recorded species include 43 annuals and 18 perennials. Ordination of stands by Detrended Correspondence Analysis (DCA) indicates that the stands of the three habitats are markedly distinguishable and show a clear pattern of segregation on the ordination planes. This indicates variations in the species composition among habitats. The results also demonstrate significant associations between the floristic composition of the seed bank and edaphic factors such as CaCO₃, electrical conductivity, organic carbon and soil texture. The reclaimed land has the highest values of species richness, Shannon-index of diversity and the density of the germinable seed bank followed by the habitats of desert wadi and desert salinized land. Motyka’s similarity index between the seed bank and the above-ground vegetation is significantly higher in reclaimed land (75.1%) compared to desert wadi (38.4%) and desert salinized land (36.5%).     

Ecology of Salix variegata seed germination: Implications for species distribution and conservation in the Three Gorges region

The Three Gorges Project in China has brought significant changes to the region's riparian environment, posing serious challenges to biodiversity conservation. Salix variegata is a native shrub distributed on riverbanks in the Three Gorges reservoir region, and has important ecological function in the community. In this study, we studied the ecology of seed germination of S. variegata as efforts to understand its spatial distribution and develop conservation strategies. We found that soil type, soil moisture content and temperature all had significant effects on seed germination in S. variegata. Germination rate increased with the increasing soil moisture, while decreased in over-saturated soil. The germination rate in riverbank sand was higher than in sandy soil and clay loam. The optimal temperature for seed germination was 24 °C, under which 100% of germination was reached in 7 days. Seed viability and germination declined significantly with time after being released from fruits. The results suggest that soil moisture is the determining factor on seed germination, and influenced distribution of S. variegata. The tributary riverbanks above 175 m in the Three Gorges reservoir region can be used for the conservation of the species, as their fluvial patterns should have not been disturbed by the hydropower project.     

Comparative efficacy of different approaches to managing Meloidogyne incognita on green bean

A greenhouse study was conducted to compare the relative efficacy of different approaches to managing Meloidogyne incognita on green bean. These approaches included chemical (fumigant, non-fumigant, seed dressing, and seed dip), biological (the egg-parasitic fungus, Paecilomyces lilacinus and the mycorrhizal fungus Glomus sp.), physical (soil solarization), and cultural (chicken litter and urea) methods. Accordingly, nine different control materials and application methods plus nematode-infected and non-infected controls were compared. Two important parameters were considered: plant response (plant growth and root galling) and nematode reproduction (production of eggs and the reproduction factor Rf). The results showed that the use of chicken litter as an organic fertilizer severely affected the growth and survival of the plants. Therefore, this treatment was removed from the evaluation test. All of the other eight treatments were found to be effective against nematode reproduction, but with different levels of efficacy. The eight treatments decreased (38.9–99.8%) root galling, increased plant growth and suppressed nematode reproduction. Based on three important criteria, namely, gall index (GI), egg mass index (EMI), and nematode reproduction factor (RF), the tested materials and methods were categorized into three groups according to their relative control efficacy under the applied test conditions. The three groups were as follows: (1) the relatively high effective group (GI = 1.0–1.4, Rf = 0.07–0.01), which included the fumigant dazomet, the non-fumigant fenamiphos, soil solarization, and seed dip with fenamiphos; (2) the relatively moderate effective group (GI = 3.4–4.0, Rf = 0.24–0.60), which included seed dressing with fenamiphos and urea; and (3) the relatively less effective group (GI = 5.0, Rf = 32.2–37.2), which included P. lilacinus and Glomus sp.     

The seed bank in a subtropical freshwater marsh: implications for wetland restoration

Seed bank samples were collected from Huli Marsh, a subtropical shallow water mountainous marsh in Hunan Province, South China. Core samples were divided into upper and lower layers (each 5 cm in depth) and allowed to germinate in three water levels (0, 5 and 10 cm) over a 4-month period. A total of 51 species germinated and the mean density was 9211 ± 7188 seedlings m⁻². In the top 5 cm 41 species and 5747 ± 5111 seedlings m⁻² germinated, whereas 40 species and 3464 ± 3363 seedlings m⁻² did so from 5–10 cm. Germinated seedling density was significantly higher in the upper layer, largely due to differences in eight species. With increasing experimental water depth, less seedlings germinated: respectively, 9788 ± 7157 m⁻², 2050 ± 2412 m⁻² and 1978 ± 2616 m⁻², of 44, 21 and 19 species, submerged under 0, 5 or 10 cm. Seven species could emerge only in 0 water level. Vallisneria natans occurred only in 5 cm water, whereas Ottelia alismoides occurred in 10 cm water. In the vegetation survey of the marsh, 25 species were recorded, which was less than half of the species recorded in the seed bank. The top 10 dominants in the standing vegetation, accounting for 89% of vegetation abundance, represented only 10% in the seed bank. Twenty germinated species that also occurred in the standing vegetation accounted for 56% of the total seed bank. Our observed number of species germinating from a Chinese wetland seed bank is within the range observed elsewhere in the northern hemisphere (15–113 species).     

Controlling the seed bank of the invasive plant <Emphasis Type="Italic">Acacia saligna</Emphasis>: comparison of the efficacy of prescribed burning,soil solarization,and their combination

Reducing the seed bank of invasive plants is a prerequisite for successful restoration of invaded ecosystems. The Australian legume tree Acacia saligna is one of the worst invasive plants in Mediterranean climate regions. This fire-adapted species possesses a large persistent seed bank characterized by physical dormant seeds. The present research was aimed to compare the efficacy of prescribed burning, soil solarization by solar heating of moist soil, and their use in combination on A. saligna seed bank reduction, using the buried seed method, and on seedling emergence from the natural seed bank, as a model of controlling fire-adapted plants. The data obtained show that the direct effect of prescribed burning on the buried seed dynamics was highly variable, and it only reduced seed viability from 98% to about 56%. Soil solarization, particularly in combination with prescribed burning, was much more effective than prescribed burning alone, reducing seed viability to about 29 and 4%, respectively. These results were confirmed by recording seedling emergence from the natural seed bank during two successive germination years following the treatments. Only a relatively very small number of seedlings emerged in the soil solarization treatment and none in the combined treatment. Based on the above data, it is recommended to apply prescribed burning as a pretreatment for soil solarization, or to utilize wild fires followed by soil solarization to reduce the seed bank of invasive fire-adapted plants. In situations in which fire cannot be used as a pretreatment, soil solarization alone is reasonably effective.     

Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Density and distribution of seeds in bottom sediments in Zostera marina beds in Ago Bay,central Japan

The density of Zostera marina L. seeds in bottom sediments was examined to study the reproductive patterns of the Z. marina population in Ago Bay, Mie Prefecture, central Japan.Seeds and seed coats were numerous in Tategami, where the annual type of Z. marina grows. In contrast, seeds were scarce in Hamajima, where the perennial type of Z. marina grows. Bottom sediment was sampled with sediment cores at Tategami in November 2004 and March 2005 to examine density and depth distribution of the seeds. Seeds were found as deep as 8 cm, but no deeper. On the other hand, empty seed coats were found as deep as 16 cm in both months. In the upper layers of the sediment to a depth of 8 cm, the average number of seed coats was 7960 ± 2997 m⁻² in November and 16,318 ± 2922 m⁻² in March. Deeper than 8 cm, the number of seed coats gradually decreased owing to decomposition, and none was found below 16 cm. We used the density of reproductive shoots and number of seeds per spadix in Tategami to estimate the fate of seeds and seed coats of the annual type of Z. marina in bottom sediments: out of the 6000 seeds m⁻² produced annually, 72% disappears from the stand and 28% is buried locally. The density and distribution of Z. marina seeds are among the most important factors in maintenance and propagation of the annual population at Tategami.     

Evaluation of biological seed treatments in combination with management practices for the control of Fusarium dry rot of potato

Seed-borne diseases of potato represent a significant constraint to potato production in the US. The use of an effective fungicide in combination with good management practices during cutting and storage, prior to planting, is essential to reducing disease. The efficacy of two biocontrol agents (Bacillus subtilis and Trichoderma harzianum), and a commercially formulated mixture of the chemicals fludioxonil plus mancozeb, applied as seed treatments in combination with different management practices, were evaluated over two years for the control of seed piece decay and sprout rot caused by Fusarium sambucinum. Treatments were made 10 days prior to planting and at planting, and tubers were re-stored at either 18 °C and 95% RH with forced air ventilation at 5950 l min⁻¹ (optimal conditions), at 25 °C in the dark without ventilation (sub-optimal), or not stored at all prior to planting. Seed piece and sprout health were evaluated in vitro and agronomic impacts evaluated in field experiments. Results showed that the biological control agents B. subtilis and T. harzianum provided good control of sprout rot and seed piece decay caused by F. sambucinum, when seed was re-stored under optimal conditions or not re-stored at all. Under optimal conditions, treatment with B. subtilis reduced sprout rot and seed piece decay on average by 66% and 84%, respectively. Treatment with T. harzianum reduced sprout rot and seed piece decay on average by 70% and 81%, respectively. Treatment with fludioxonil + mancozeb reduced sprout rot and seed piece decay under both re-storage regimes. Under optimal conditions, disease incidence and severity was reduced on average by 81% and 97%, respectively. Neither biological control agent reduced seed piece decay incidence under either re-storage regime compared to the untreated controls.     

Local and microscale distributions of Cenococcum geophilum in soils of coastal pine forests

To clarify the local and microscale distribution patterns of Cenococcum geophilum at soil surfaces in coastal pine forests, we collected soil samples in Pinus thunbergii stands. To investigate the local distribution of C. geophilum, five soil samples were collected randomly to obtain roots of P. thunbergii at four study sites. To examine the microscale distribution of fungi, 19 soil samples were collected from a 5 × 5 m quadrat at a minimum interval of 15 cm. Ectomycorrhizas of P. thunbergii were examined and identified morphologically. C. geophilum mycorrhizas were retrieved from all the sites at the local scale and from all sampling points within a site at the microscale. The occurrence frequency of C. geophilum ectomycorrhizas ranged from 20.0 to 62.6 % at the sites studied. These results suggest that C. geophilum is the dominant ectomycorrhizal fungus and is distributed ubiquitously in coastal pine forests of Japan.     

Modifying orchard planting sites conserves entomopathogenic nematodes,reduces weevil herbivory and increases citrus tree growth,survival and fruit yield

In Florida, a root weevil pest of citrus, Diaprepes abbreviatus, is more damaging and attains higher population density in some orchards on fine textured, poorly drained “flatwoods” soils than in those on the deep, coarse sandy soils of the central ridge. Previous research revealed that sentinel weevil larvae were killed by indigenous entomopathogenic nematodes (EPNs) at significantly higher rates in an orchard on the central ridge, compared to one in the flatwoods. We hypothesized that filling tree planting holes in a flatwoods orchard with sandy soil from the central ridge would provide a more suitable habitat for EPNs, thereby reducing weevil numbers and root herbivory. Fifty trees were planted in oversized planting holes filled with coarse sand and 50 trees were planted in native soil in a split plot design where whole plots were species of introduced EPNs and split plots were soil type. Each of Steinernema diaprepesi, Steinernema riobrave, Heterorhabditis indica, Heterorhabditis zealandica, or no EPNs were introduced into the rhizospheres in 10 plots of each soil type. During four years, EPN numbers in soil samples and the relative abundance of seven species of nematophagous fungi associated with nematodes were measured three times using real-time PCR. The efficacy of EPNs against sentinel weevil larvae was also measured three times by burying caged weevils in situ. EPN species richness (P = 0.001) and diversity (P = 0.01) were always higher in sand than native soil. Soil type had no effect on numbers of EPNs in samples, but EPNs were detected more frequently (P = 0.01) in plots of sandy soil than native soil in 2011. Two nematophagous fungi species, Paecilomyces lilacinus and Catenaria sp. were significantly more abundant in nematode samples from sandy soil on all three sampling dates. Efficacy of EPNs against weevil larvae was greater in sandy soil inoculated with S. diaprepesi (P = 0.03) in June 2010 and in all treatments in sandy soil in May 2011 (P = 0.03). Sixty-eight percent more adult weevils (P = 0.01) were trapped emerging from native soil during two years than from sandy soil. By May 2011, the cumulative number of weevils emerging from each plot was inversely related (P = 0.01) to the numbers of EPNs detected in plots and to EPN efficacy against sentinels. Three trees in sandy soil died as a result of root herbivory compared to 21 trees in native soil. Surviving trees in sandy soil had trunk diameters that were 60% larger (P = 0.001) and produced 85% more fruit (P = 0.001) than those in native soil. Although it is not possible to characterize all of the mechanisms by which the two soil treatments affected weevils and trees, substitution of sand for native soil was an effective means of conserving EPNs and shows promise as a cultural practice to manage D. abbreviatus in flatwoods citrus orchards with a history of weevil damage to trees.     

Formulation of a soil biofungicide for control of damping-off of Chinese cabbage (Brassica chinensis) caused by Rhizoctonia solani

A granulate biofungicide named PBGG was developed by combining Pseudomonas boreopolis with Brassica seed pomace, glycerin and sodium alginate. Application of 1.0% (w/w) of PBGG to the soil infested with Rhizoctonia solani AG-4 significantly reduced the percentage of colonization of cabbage seeds by the pathogen and stimulated proliferations of actinomycetes. Among Streptomyces populations, Streptomyces padanus (strain SS-07) and Streptomyces xantholiticus (strain SS-09) were the two most effective strains with strong antagonistic effects to R. solani. Application of 1% (w/w) PBGG in soil significantly increased population densities of S. padanus and S. xantholiticus. Treating soil with S. padanus (strain SS-07) or S. xantholiticus (strain SS-09) alone or in combination with 1% (w/w) PBGG significantly reduced the percentage of colonization of cabbage seeds by R. solani, compared to untreated controls. S. padanus was the most effective agent in reducing the percentage of seed colonization by the pathogen. Results of greenhouse tests showed that the most effective treatment was the amendment of pathogen-infested soil by S. padanus + 1% (w/w) PBGG which resulted in a disease incidence of 6.5–8.6%, compared to 27.8–31.7% for the treatment of S. xantholiticus + 1% (w/w) PBGG, 36.9–38.6% for the treatment of 1% (w/w) PBGG alone, and 61.8–64.8% for the treatment of control (unamended soil). Results of greenhouse and field tests also showed that soil amendment of 1% (w/w) PBGG alone or 1% (w/w) PBGG mixed with S. padanus (strain SS-07) or S. xantholiticus (strain SS-09) was not harmful to seed germination of Chinese cabbage. The study suggests that amendment of R. solani infested soil with S. padanus + 1% (w/w) PBGG prior to sowing is an effective method for control of damping-off of Chinese cabbage.