Strong Competitive Ability Research Articles

Niche specialization and functional traits regulate the rarity of charophytes in the Nordic countries

Abstract Charophytes are benthic macroalgae that live in fresh and brackish waters. Given the historic deterioration of their habitats and their competitive inferiority relative to tall rooted plants under eutrophic conditions, it is hypothesized that charophytes are among the most threatened autotrophs. Also, it is expected that charophytes with generalist niches and functional traits, such as tolerance of a broad salinity range and large height, should thrive owing to available habitats and stronger competitive ability. These hypotheses were tested comparing the rarity of charophytes in the Nordic countries with other autotrophs and analysing the relationship to species niche specialization and functional traits. A value on a rarity–commonness scale was assigned to each species based on their Red List status. Niche specialization was evaluated by the Outlying Mean Index using a large Danish dataset while traits were derived from the literature. Supporting the hypotheses, 50–87% of charophyte species were Red Listed, which is much greater than for vascular aquatic (30–35%) and terrestrial plants (18–28%). Commonness of charophytes decreased significantly with niche specialization in separate analyses of brackish and freshwater sites. For brackish water species, the most influential parameter determining species distribution was salinity while for freshwater species, alkalinity, lake size and chlorophyll concentration played a major role. Four functional traits: shoot height, salinity tolerance, bulbil production and flexible life cycle duration were significantly positively related to commonness. In conclusion, charophytes contain a larger fraction of threatened species compared with other groups of autotrophs. The few common charophytes are generalists tolerant of a wide range of conditions, while specialists often have short stature, restricted life cycle variability and are rare in the disturbed contemporary landscape. It is thus a conservation priority to delineate accurately the environmental conditions preferred by the threatened species and protect or restore proper habitats. Copyright © 2015 John Wiley & Sons, Ltd.

Yield and Agronomic Advantages of Pea Leaf Type Mixtures under Organic Management

Field pea (Pisum sativum L.) is an important organic crop due to its contribution to soil fertility and other rotational benefits. Leafed (wild‐type) pea cultivars tend to be more weed suppressive, but their poor standing ability limits yield compared with semi‐leafless cultivars. Growing mixtures of leafed and semi‐leafless cultivars may improve weed suppression and yield compared with monocultures of the same cultivars by altering canopy morphology. To test this hypothesis, replicated field experiments were conducted under weedy, organic conditions in Saskatchewan, Canada, in 2011 and 2012. Mixtures of a leafed and semi‐leafless cultivar, CDC Sonata and CDC Dakota, were sown in ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 leafed to semi‐leafless pea, at target seeding rates of 88 and 132 plants m−2. Mixtures that included 50% or more semi‐leafless pea had similar lodging resistance and weed biomass suppression to the agronomically superior semi‐leafless cultivar grown alone. The strong competitive ability of the semi‐leafless cultivar was unexpected based on previous accounts. The combined yield of the two cultivars grown in a 75% semi‐leafless mixture exceeded the seed and biomass yield of either single cultivar by at least 18 and 12%, respectively. Yield enhancement was attributed to the leafed cultivar, whose seed yield increased by more than two and a half times in this mixture relative to its monoculture. Results suggest that breeding of leafed cultivars specifically for mixture with semi‐leafless pea may be a future source of yield gains in organic and low‐input systems.

Pricing and alliance selection for a dominant retailer with an upstream entry

Abstract We consider the problem of pricing and alliance selection that a dominant retailer in a two-echelon supply chain decides when facing a potential upstream entry. The two-echelon supply chain consists of a dominant retailer, an incumbent supplier and an “incursive” vendor, where both the incumbent supplier and “incursive” vendor sell substitutable products to the common market through the dominant retailer. Our objective is to discuss whether the dominant retailer should sell the “incursive” vendor's products and, if so, how the dominant retailer strategically selects the alliance structure to maximize his/her own profit. We also present how all the members make their pricing decisions and analyze the impact of competitive intensity between two products on their pricing strategies after the entry of the vendor in possible alliance settings. Our results show that: (1) the introduction of the upstream vendor always benefits the retailer, and more interestingly, benefits the incumbent suppler in many cases, too; (2) in this paper, we define the competitive ability as the price dominance of one player over another when both are competing for the same customer market, if the price competition between the incumbent supplier and the “incursive” vendor is relatively fierce, the dominant retailer should ally with the one who has a relatively strong competitive ability rather than the other who has a relatively weak competitive ability; otherwise, he/she should ally with both upstream members. Finally, using numerical examples, we analyze the impact of different parameters and provide some management insights.

Abstract 1003: A novel anti-angiogenic compound F16 that inhibits xenograft tumor growth

Abstract Recruitment of new blood vessels, commonly referred as tumor angiogenesis, during cancer progression provides an important route by which tumor cells can enter the circulation and cause distant metastasis. Tumor cells that are overexpressing vascular endothelial growth factor (VEGF) can shift the balance towards pro-angiogenic mechanisms to favor aggressive growth and enhanced metastatic potential. In this process binding of VEGF to its receptor is very critical step for triggering kinase activation and trans-phosphorylation that can eventually lead to the activation of a complex signal cascade and completion of angiogenesis. Therefore, interference with the function of the VEGFR has become a promising strategy to inhibit tumor angiogenesis. Through the molecular modeling approach a novel isoindol-amide compound, code named F16, was identified as a potent antagonist for VEGFR. The anti-angiogenic potential of F16 was confirmed through the in vitro angiogenesis assay using HUVEC cells that were grown on ECMatrixTM gel with different concentrations (0 to 10 µM) of F16. Binding assay with fluorokine conjugated VEGF in HUVEC cells proved a strong competitive binding ability for F16 (0.001 to 1.0 µM) with VEGFR in a dose dependent manner. In the whole cell binding assay nearly 95% inhibition of fluorokine conjugated VEGF was observed at 1.0 µM concentration of F16. Also, the western blot analysis showed a strong inhibition of VEGF induced phosphorylation of VEGFR2 by F16 at the same (1.0 µM) concentration in HUVEC cells. Furthermore, In vivo experiments were conducted to confirm the extent of F16 induced tumor growth inhibition in athymic nude mice that were implanted with GI-101A breast tumor xenograft. In these experiments the tumor bearing mice were designated to experimental groups (N = 6/group), namely: Control; F16 (100 mg/kg body weight); Taxol (10 mg/kg body weight); and F16 (100 mg/kg body weight) + Taxol (10 mg/kg body weight). All treatments were given intraperitonealy once in two days for a period of 21 days. Tumor growth was assessed every week using the caliper measurement. In the xenograft mice that were treated with F16 or Taxol alone nearly 65% and 71.5% inhibition of tumor growth was observed, respectively, while combination (F16 + Taxol) treatment showed more than 85.2% inhibition when compared to the untreated controls. Results from our study confirm that F16 inhibits VEGF binding and consequently VEGFR2 phosphorylation to prevent endothelial cell proliferation, migration and sprouting of new capillaries. Our findings so far have fully validated F16 as a promising anti-angiogenic agent. (The Royal Dames of Cancer Research Inc., Ft. Lauderdale, Florida is gratefully acknowledged for their generous financial support). Citation Format: Appu Rathinavelu, Sivanesan Dhandayuthapani. A novel anti-angiogenic compound F16 that inhibits xenograft tumor growth. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1003. doi:10.1158/1538-7445.AM2014-1003

Characterization of a fungicidal substance produced by Eupenicillium brefeldianum isolated from soil for plant disease control and its significance in nature.

BackgroundA fungus identified as Eupenicillium brefeldianum was isolated from soil amended with vegetable tissues.ResultWhen grown in liquid medium prepared from the same vegetable tissues, E. brefeldianum produced a substance capable of preventing disease development of leaf spots of mustard cabbage caused by Alternaria brassicicola and inhibiting the germination of A. brassicicola conidia. The inhibitory substance was fungicidal and was very stable under high temperature and extreme pH. It was soluble in polar solvents but not soluble in non-polar solvents, and did not have charges on its molecule. This is the first discovery of the production of a fungicidal substance by this fungus.ConclusionResults from this study suggest the possession of a strong competitive saprophytic ability by E. brefeldianum, which in turn may explain the widespread occurrence of this fungus in soils.

Competition for space in two invasive Indo-Pacific corals — Tubastraea micranthus and Tubastraea coccinea: Laboratory experimentation

The invasive Indo-Pacific coral Tubastraea coccinea (Cnidaria, Scleractinia) dominates western Atlantic artificial reef communities. Tubastraea micranthus, a congener, recently invaded the Gulf of Mexico and threatens to become another strong invasive due to similar growth and population expansion characteristics. It also appears to have strong competitive abilities. We examined active competition for space in both of these invasive species to determine their respective capabilities using three sessile Caribbean marine anthozoans — Ricordea florida (Cnidaria, Corallimorpharia), Epicystis crucifer, and Condylactis gigantea (Cnidaria, Actinaria). Coral polyps from the target coral species were placed in contact with the experimental competitor for 3–28d. T. micranthus responded with an extracoelenteric digestion response to all three Caribbean competitors and was found to be competitively superior. The corallimorpharian R. florida and the anemone E. crucifer elicited extracoelenteric digestive responses from T. coccinea, while C. gigantea did not. The two corals displayed no aggressive interactions towards each other, implying an immune recognition of each other as “self”. Both coral species exhibited aggressive behaviors towards and dominance over their competitors for space. These are characteristics which most likely facilitated the successful invasion of T. coccinea in the western Atlantic. The scleractinian coral T. micranthus, exhibiting similar characteristics, also has the potential of becoming a successful invasive in the Atlantic.

Invasion genetics of Chromolaena odorata (Asteraceae): extremely low diversity across Asia

Chromolaena odorata is a native of America while a weed in many parts of tropical and subtropical regions in the world. Research into the invasion mechanisms of C. odorata contributes to a broader understanding of factors that facilitate plant adaptation, and also helps developing effective management strategies. In this study, we used three DNA fragments and six microsatellite loci: (1) to compare genetic diversity of C. odorata in its native and invaded regions; (2) to elucidate the invasive routes and identify possible source locations of C. odorata from America to Asia, with attempt to evaluate the possible mechanisms facilitating the successful invasion of this species. Despite two recorded independent introductions, DNA sequence data revealed only one single haplotype of C. odorata present throughout tropical Asia. All six microsatellite loci consistently exhibited extremely low genetic diversity in Asian populations compared to those from native ranges. Our results implied that there was likely only a single introduction to Asia, and Trinidad, Tobago and adjacent areas in the West Indies were the most likely source location of that introduction. The successful invasion of C. odorata in Asia may have been facilitated by the genotype with strong competitive ability.

Plant traits regulating N capture define microbial competition in the rhizosphere

Global warming and nitrogen (N) deposition promote the displacement of native plant species by neophytes which have similar ecological niches but stronger competitive abilities. It remains unclear how plants with different competitive abilities alter microbial growth and turnover in the rhizosphere under high and low N input. We hypothesized 1) slower microbial growth in the rhizosphere of plants with smaller roots and 2) restriction of microbial growth under low versus high N amendment. These hypotheses were tested on two strawberry species: Fragaria vesca (native species) and Duchesnea indica (an invasive plant in central Europe) grown under intra-specific and inter-specific competition at very low and high N levels.Species-specific traits of plant–microbial interactions mitigated N deficiency in the rhizosphere. At low N addition the native species F. vesca stimulated faster microbial growth and turnover than D. indica. F. vesca did this by increasing root mass and exudation at the expense of the shoots. In contrast, the invasive plant – D. indica – did not increase root mass under low N amendment, but did increase its N uptake rate. This resulted in N deficiency, retarding microbial growth and turnover in the rhizosphere, as revealed by the dominance of slow-growing microorganisms.A low N level in the soil promoted root growth and rhizodeposition and thus accelerated microbial turnover correspondingly to increasing root mass. Fast N uptake by roots, however, may lead to N deficiency and did retard microbial growth in the rhizosphere. In conclusion, the plant species with the stronger competitive ability at low N level controls the microbial community in the rhizosphere.

Effects of sweet potato (Ipomoea batas) cultivation on the community composition and diversity of weeds in arid fields

For developing ecological prevention and management techniques for invasive and dominant weed species, the screening and using of high value species with strong competitive ability (e.g., local food, native species and/or cash crops) have captured widely attention. To explore the effects of sweet potato (Ipomoea batas) cultivation on community composition and species diversity of weeds, the composition, density, importance value, species richness, diversity indices, and Pielou index were analyzed under five different cover scenarios (0%, 1–25%, 26–50%, 51–75, 76–100%). The study took place in arid cultivated fields in Jianshui County, Yunnan Province, China. A total of 25 weed species from 18 families were identified. Of these, four invasive species Ageratum conyzoides, Bidens pilosa, Eleusine indica, and Galinsoga parviflora and two native species, Digitaria sanguinalis and Portulaca oleracea had the highest population density and were most dominant. Population density and importance values of the six dominant weed species declined as sweet potato cover increased. A significant negative correlation was observed between importance values and sweet potato cover (P<0.05). Population density of two less dominant native species, Calystegia hederacea and Poa annua, increased significantly with increasing sweet potato cover. Similarly, the importance values for two additional native species Acalypha australis and Echinochloa crusgalli was positively correlated with sweet potato cover (R=0.964, R=0.891, P<0.05). Maximum values for species richness (23.5, 24.5), Simpson index (0.89, 0.85), Shannon-Wiener index (2.36, 2.35) and Pielou index (0.75, 0.73) corresponded to sweet potato cover ranges of 1–25% and 26–50% respectively. As sweet potato cover increased species richness and diversity values significantly declined. Overall, the results indicate that the cultivation of sweet po486 生 物 多 样 性 Biodiversity Science 第 22卷 tato alters the community composition and diversity of weeds limiting the occurrence of the dominant and invasive weed species. As a result, mid to low percent cover values should be considered an effective and ecologically-based weed management strategy to replace herbicide use in arid fields.

Distribution pattern of Caragana species under the influence of climate gradient in the Inner Mongolia region, China

There is a strong climate gradient in the Inner Mongolia region, China, with solar radiation and air temperature increasing but precipitation decreasing gradually from the northeast to the southwest. Sixteen Caragana species exist in the Inner Mongolia region. These Caragana species exhibit a distribution pattern across moisture zones and form a geographical replacement series. In order to examine the mechanisms responsible for Caragana species distribution pattern, we selected 12 Caragana species that exhibit a distinct distribution pattern across multiple moisture zones in the Inner Mongolia region, and determined the relationships between the leaf ecological and physiological traits of these Caragana species and the aridity index and solar radiation. Along with the climatic drought gradient and the solar radiation intensification from the northeast to the southwest, leaf ecological characteristics of Caragana species changed drastically, i.e. the leaf shape gradually turned from flat into tegular or tubbish; the leaf hair became denser, longer and lighter in color; the leaf area, leaf biomass and specific leaf area (SLA) decreased significantly; the leaf thickness and the ratio of leaf thickness to leaf area increased significantly; and the leaf chlorophyll content decreased significantly. As the climatic drought stress increased, osmotic potentials of the main osmotic adjustment substances and the cytoplasmic ion concentration of Caragana species increased significantly. Meanwhile, the total and free water contents and water potential of leaves decreased significantly; the ratio of bound to free water increased significantly; the stomatal conductance and transpiration rate reduced significantly; and the water use efficiency (WUE) increased significantly. In addition, with the intensification of climatic drought stress, peroxidase (POD) and superoxide dismutase (SOD) activities in leaves increased significantly. As a result, the malondialdehyde (MDA) content increased while the oxygen free radical content decreased. Our results showed that most of the leaf ecological and physiological traits of the 12 Caragana species varied in accordance with the climatic drought gradient in the Inner Mongolia region, which reflected the adaptation of the Caragana species to the local climate conditions. With relatively more active metabolism and faster growth, the Caragana species in the northeast had strong competitive abilities; on the other hand, with stronger resistance to climatic drought stress, the Caragana species in the southwest could survive in harsh environments. Based on our results, we concluded that both the environmental gradients and the adaptive responses of Caragana species to their environments played important roles in the formation of the Caragana species distribution pattern across the Inner Mongolia region.

Effect of crop species and mixed ratios on morphological plasticity and competitiveness of Phalaris minor Retz

入侵植物小子虉草(<i>Phalaris minor</i> Retz.)为农田恶性杂草, 对其科学、有效的控制与管理是世界性难题。本文以小子虉草为试验对象，在温室条件下采用de Wit取代法，研究了其与小麦、蚕豆和油菜3种农作物在不同混种比例下, 小子虉草的表型可塑性与竞争效应, 以提高农田生态系统对该入侵物种的预警和控制能力。结果表明, 除混种比例对小子虉草的分枝数和主穗长度影响不显著外(<i>P</i>≥0.05), 作物种类、混种比例以及二者交互对小子虉草的株高、主穗种子数、剑叶面积和生物量有显著或极显著影响(<i>P</i>≤0.05或0.001)。在油菜混合种群中, 小子虉草的株高显著大于按同等比例与小麦、蚕豆的混合种群及其单一种群的株高, 但分枝数、主穗长、主穗种子数、剑叶面积和生物量则显著小于按同等比例与小麦、蚕豆混种时植株的上述指标。3种作物按不同比例与小子虉草混种时, 小麦、蚕豆和油菜的相对产量均小于1.0, 表明3种作物与小子虉草在田间以种间竞争为主; 小子虉草与蚕豆以各种比例混种、与小麦以1∶1和1∶2混种时, 其相对产量均大于1.0, 表明此时以其种内竞争为主; 油菜混合种群中小子虉草的相对产量均小于1.0, 表明此时以种间竞争为主。在混种比例大于1∶1时, 小子虉草与油菜的竞争平衡指数显著小于0, 表明此时油菜的竞争能力大于小子虉草, 而供试其他条件下小子虉草与供试作物的竞争平衡指数均显著大于0, 说明小子虉草对小麦、蚕豆及低密度种植条件下的油菜具有很强的竞争能力。本研究结果显示油菜对小子虉草具有较强的竞争抑制作用, 在油菜混合种群小子虉草的分枝数、主穗长、主穗种子数、剑叶面积和生物量显著降低, 因此在小子虉草入侵地大面积种植油菜有抑制小子虉草的效果。

Effect of Low Temperature on Purple Nutsedge (Cyperus rotundus) Reproductive Biology

Purple nutsedge is considered to be the worst weed in the tropical and subtropical regions of the world. Although the plant is a low grower it has very strong competitive abilities. The influence of initial tuber size and cold treatment on tuber sprouting, accumulation of plant biomass and new tubers formation was studied. Tubers sprouted continuously over 30 to 50 d with significantly lower sprouting ability of small tubers (0.1 to 0.2 g). Short cold treatment (4 C for 4 d) significantly stimulated sprouting process. The early sprouting of cold treated tubers led to increased number of shoots and inflorescences and therefore more intensive biomass accumulation, as well as more intensive formation of new tubers. The increase in total biomass accumulation raises the reproductive and spreading potential of the weed.

A comparative study of competitiveness between different genotypes of weedy rice (Oryza sativa) and cultivated rice

Competition from weedy rice can cause serious yield losses to cultivated rice. However, key traits that facilitate competitiveness are still not well understood. To explore the mechanisms behind the strong growth and competitive ability, replacement series experiments were established with six genotypes of weedy rice from different regions and one cultivated rice cultivar. (1) Weedy rice from southern China had the greatest impact on growth and yield of cultivated rice throughout the entire growing season. Weedy rice from the northeast was very competitive during the early vegetative stage while the competitive effects of eastern weedy rice were more detrimental at later crop-growth stages. (2) As the proportion of weedy rice increased, plant height, tillers, above-ground biomass, and yield of cultivated rice significantly declined; the crop always being at disadvantage regardless of proportion. (3) Weedy biotypes with greater diversity as estimated by their Shannon indexes were more detrimental to the growth and yield of cultivated rice. Geographic origin (latitude) of weedy rice biotype, its mixture proportion under competition with the crop and its genetic diversity are determinant factors of the outcome of competition and the associated decline in the rice crop yield. © 2013 Society of Chemical Industry.

Crown plasticity reduces inter-tree competition in a mixed broadleaved forest

The objective of the study was to analyse to which extent horizontal crown plasticity reduces inter-tree competition at stand scale, and how it relates to species growth strategy. Two components of crown plasticity defined at the individual tree level (crown shape distortion, CSD and crown displacement relative to stem, CRD) were analysed and their relative importance in the reduction of competition was quantified. Inter-tree competition at stand scale was estimated using spatial pattern analysis and crown overlap estimation. Measurements were performed in a mixed broadleaved stand of Western Europe. Crown plasticity was shown to regularise the spatial distribution of crowns in comparison with the corresponding stems and to reduce inter-tree competition by optimising space occupation. A significant reduction in crown overlap was observed, mainly due to CRD and secondarily to CSD. At the species level, CSD and CRD were positively correlated. In addition, both were negatively correlated with species shade-tolerance scores. In particular, three European temperate tree species showed contrasting responses, which were related to their known specific ecological strategies. Fagus sylvatica, known to be a highly shade-tolerant species, showed large crowns, low CSD and CRD, indicating a low plasticity and suggesting a strong competitive ability. At the opposite, Quercus sp., known to be clearly less shade-tolerant, exhibited a reduced growth, associated with high CSD and CRD, indicating high crown plasticity and probably a lower competitive ability. For this species, plasticity could be described as passive. Last, Carpinus betulus, known to have a relatively good shade-tolerance, showed a contrasting behaviour with high CSD and CRD and a strong presence in the stand, suggesting high crown plasticity and a good competitive ability. In that case, plasticity was described as rather adaptive.

Relationships of Native Desert Plants with Red Brome (Bromus rubens): Toward Identifying Invasion-Reducing Species

AbstractThe interactions between native and exotic species occur on a continuum from facilitative to competitive. A growing thrust in invasive species science is differentiating where particular native species occur along this continuum, with practical implications for identifying species that might reduce the invasibility of ecosystems. We used a greenhouse experiment to develop a competitive hierarchy of 27 native species with red brome, an invasive annual grass in the arid lands of the southwestern United States, and a field study to assess in situ responses of brome to native perennial species in the Mojave Desert. Native species most competitive with brome in the competition experiment included the annuals Esteve's pincushion and western fiddleneck and the perennials eastern Mojave buckwheat, sweetbush, and brittlebush, which reduced brome biomass to 49 to 70% of its grown-alone amount. There was no clear difference in competitive abilities with brome between annual and perennial natives, and competiveness was not strongly correlated (r= 0.15) with the biomass of the native species. In the field, sweetbush and brittlebush supported among the least cover of brome, suggesting congruence of the strong early competitive abilities of these species with in situ patterns of brome distribution. At the other extreme, brome attained its highest average cover (19%) below littleleaf ratany, significantly greater than all but 3 of the 16 species evaluated. Cover by brome was only weakly related (r= 0.19) to the area of the perennial canopy, suggesting that factors other than the sizes of perennial plants were linked to differences in brome cover among species. Results suggest that (1) interactions with brome differ substantially among native species, (2) these interactions are not as closely linked to biomass production as in more temperate regions, and (3) there is potential for identifying native species that can reduce invasion of desert ecosystems.

Characterization of a fungistatic substance produced by Aspergillus flavus isolated from soil and its significance in nature

A fungus capable of using vegetable tissues for multiplication in soil was isolated and identified as Aspergillus flavus based on morphological characteristics and sequence similarity of ITS and 28S. When grown in liquid medium prepared from the same vegetable tissues used in soil amendment, the isolate of A. flavus produced a substance capable of preventing disease development of black leaf spot of mustard cabbage caused by Alternaria brassicicola and inhibiting the germination of A. brassicicola conidia. The inhibitory substance was fungistatic, and was very stable under high temperature and high or low pH value. It was soluble in ethanol or methanol, moderately soluble in water, and insoluble in acetone, ethyl acetate or ether. The inhibitor is not a protein and has no charges on its molecule. This is the first discovery of the production of a fungistatic substance by this deleterious fungus. Results from this study suggest the possession of a strong competitive saprophytic ability by A. flavus, which in turn may explain the widespread occurrence of this fungus in soils. Production of a fungistatic substance when A. flavus was grown in medium prepared from vegetable tissues suggests the importance of antibiotic production in its competitive saprophytic colonization of organic matters in soils.

Forage Yield, Growth Rate, and Nitrogen Uptake of Faba Bean Intercrops with Wheat, Barley, and Rye in Three Seeding Ratios

ABSTRACTAnnual cool‐season grain legumes like faba bean (Vicia faba L.) grown in mixtures with winter cereals such as wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), or rye (Secale cereale L.) may offer advantages over cereal‐alone crops grown for forage production. A 2‐yr field study was conducted to evaluate the effects of intercropping faba bean with each of the above cereals in three seeding ratios (i.e., 75:25, 50:50, and 75:25) on growth rate, plant height, chlorophyll content, forage yield, and N uptake. Growth rate of faba bean and cereals was lower in the mixtures than in the monocultures, especially in the faba bean–barley mixtures because of the strong competitive ability of barley. Chlorophyll content was lower in faba bean compared with the cereals, and there was no difference among seeding ratios. Plant height of faba bean was higher in the intercrops compared with its monocrop at 3 wk after tillering (WAT), whereas at 6 WAT, the trend was different since faba bean plants in the monocrop were higher than in the intercrops. Rye monocrop and rye–faba bean intercrops provided the greatest forage yield. Although the three intercrops of faba bean with rye had lower crude protein (CP) content than the faba bean monocrop, they provided the highest CP yields per hectare because of their higher forage yield than the faba bean monocrop.

Allelopathic effect of itchgrass (Rottboellia cochinchinensis) on seed germination and plant growth

Herbicides produce a wide range of toxic side‐effects that pose a potential hazard to the environment. The development of natural allelochemicals is one method of addressing these issues. Here, we describe the allelopathic activity of itchgrass (Rottboellia cochinchinensis), which can inhibit the seed germination and growth of weeds. Farmers in Lampang, northern Thailand, have been cultivating itchgrass and using it as a mulching material to control other weeds in vegetable fields. It has long been observed that itchgrass interferes with the growth of other plants. This study showed that the density of weed species in the itchgrass‐infested areas was lower than that in the itchgrass‐uninfested areas. The shoot and root growth of Bidens pilosa, Mimosa pudica, Ageratum conyzoides, Echinochloa crus‐galli, Oryza sativa var. RD 6, and Lactuca sativa var. OP were significantly reduced in soil previously planted with itchgrass. Water‐soluble extracts from all parts of itchgrass had inhibitory effects on the growth of some test plants. Allelochemicals from itchgrass can inhibit seed germination and plant growth better at a 1 cm distance than at a 3 cm and 5 cm distance from itchgrass. Our results suggest that itchgrass has a strong competitive ability and possible allelopathic activity to other plant species. The allelopathic activity of itchgrass in the soil can influence the germination of adjacent species, causing reduced growth of seedlings.

Production of a Fungistatic Substance by Pseudallescheria boydii Isolated from Soil Amended with Vegetable Tissues and Its Significance

Four fungal isolates that were able to use vegetable tissues for multiplication in soil were isolated and identified as Pseudallescheria boydii based on morphological characteristics and ITS sequence similarity. When grown in broth prepared from the same vegetable tissues used in soil amendment, all these isolates of P. boydii produced a substance capable of reducing the disease incidence of black leaf spot of spoon cabbage caused by Alternaria brassicicola and inhibiting the germination of A. brassicicola conidia. The substance, which was fungistatic, was very stable under high temperature and high or low pH value. It was soluble in polar solvents and insoluble in non-polar solvents. Molecular weight estimation and ion exchange ability tests suggest that the fungistatic compound has a molecular weight between 500 and 1,000 and has no charge on its molecule. Results from this study suggest the possession of a strong competitive saprophytic ability by P. boydii, which in turn may explain the widespread occurrence of this human pathogen in soil. Production of a fungistatic substance when P. boydii was grown in broth prepared from vegetable tissues suggests the importance of antibiotic production in its competitive saprophytic colonization of organic matters in soil.

Mechanisms of invasive population establishment and spread of pinewood nematodes in China

This paper summarizes the results of our study of the pinewood nematode (Bursaphelenchus xylophilus). By population genetic analysis, it was determined that there was no genetic bottle caused by the founder effect and genetic drift in the Chinese invasive population. Multiple invasions with large amounts of nematodes from different sources led to rich genetic diversity in the invasive population. Keeping high genetic diversity in the invasive process may be one of the genetic mechanisms in its successful invasion. By testing interspecies competition, it was shown that, with high fecundity and a strong competitive ability, B. xylophilus outcompeted the native species B. mucronatus in the natural ecosystem during the invasion process. Competitive displacement may be one of the ecological mechanisms of B. xylophilus's invasion. In addition, an unequal interspecific hybridization with introgress was in favor of the invasive species which also accelerated the replacement of B. mucronatus by B. xylophilus. The structures, functions and evolutions of a few important genes that are closely related to the ecological adaptation of pinewood nematodes were studied to explore the molecular mechanism of its ecological adaptations. Further, the resistance and resilience mechanism of the pine ecosystem invaded by pinewood nematodes was also investigated. The results of these studies uncovered a portion of the genetic and ecological mechanisms of PWN's successful invasion and laid a foundation for further study to obtain a comprehensive interpretation of the mechanisms of the nematode invasion. The results also provided a scientific basis for effectively controlling the occurrence and spread of pine wilt disease which is caused by nematodes. Various aspects requiring further investigation are considered.