Integrated responses of hydraulic architecture, water and carbon relations of western hemlock to dwarf mistletoe infection

Dwarf mistletoe (Arceuthobium spp.) is a hemiparasite that is said to be the single‐most destructive pathogen of commercially valuable coniferous trees in many regions of the world. Although its destructive nature is well documented in many respects, its effects on the physiology of its host are poorly understood. In the present study, water and carbon relations were characterized over a range of scale from leaf to whole tree in large (40‐ to 50‐m‐tall) individuals of western hemlock (Tsuga heterophylla (Raf.) Sarg.) that were either heavily infected, or uninfected with hemlock dwarf mistletoe (Arceuthobium tsugense). Specific hydraulic conductivity (k_s) of infected branches was approximately half that of uninfected branches, yet leaf‐specific conductivity (k_L) was similar because leaf area : sapwood area ratios (A_L : A_S) of infected branches were lower. Pre‐dawn and minimum leaf water potential and stomatal conductance (g_s) were similar among infected and uninfected trees because adjustments in hydraulic architecture of infected trees maintained k_L despite reduced k_s. Maximum whole‐tree water use was substantially lower in infected trees (approximately 55 kg d^?1) than in uninfected trees (approximately 90 kg d^?1) because reduced numbers of live branches in infected trees reduced whole‐tree A_L : A_S in a manner consistent with that observed in infected branches. Maximum photosynthetic rates of heavily infected trees were approximately half those of uninfected trees. Correspondingly, leaf nitrogen content was 35% lower in infected trees. Foliar δ¹³C values were 2.8‰ more negative in infected than in uninfected individuals, consistent with the absence of stomatal adjustment to diminished photosynthetic capacity. Adjustments in hydraulic architecture of infected trees thus contributed to homeostasis of water transport efficiency and transpiration on a leaf area basis, whereas both carbon accumulation and photosynthetic water use efficiency were sharply reduced at both the leaf and whole‐tree scale.     

Comparison of Reproduction by Meloidogyne graminicola and M. incognita on Trifolium Species

The reproductive potential of Meloidogyne graminicola was compared with that of M. incognita on Trifolium species in greenhouse studies. Twenty-five Trifolium plant introductions, cultivars, or populations representing 23 species were evaluated for nematode reproduction and root galling 45 days after inoculation with 3,000 eggs of M. graminicola or M. incognita. Root galling and egg production by the two root-knot nematode species was similar on most of the Trifolium species. In a separate study, the effect of initial population densities (Pi) of M. graminicola and M. incognita on the growth of white clover (T. repens) was determined. Reproductive and pathogenic capabilities of M. graminicola and M. incognita on Trifolium spp. were similar. Pi levels of both root-knot nematode species as low as 125 eggs per 10-cm-d pots severely galled white clover plants after 90 days. Meloidogyne graminicola has the potential to be a major pest of Trifolium species in the southeastern United States.     

淡水养殖太平洋鲑循环饥饿后补偿性生长效果研究

用16.1%脂肪,38.1%蛋白质含量日粮饲养108尾初始重约为240g的太平洋鲑(Oncorhynchusspp.)于0.25m3的水族箱中64d,水温为15.5±3.7℃。实验分6组,分别为对照组(每天投喂),实验1组(隔天投喂),实验2组(隔2天投喂2天),实验3组(隔4天投喂4天),实验4组(隔8天投喂8天),实验5组(隔16天投喂16天)。每组设3个平行水族箱,每箱6尾鱼。研究淡水养殖太平洋鲑多重周期饥饿后补偿性生长效果。实验结果表明:(1)各试验组太平洋鲑成活率均为100%。实验1、2、3组太平洋鲑鱼体增重接近对照组,其恢复摄食期间特定生长率、摄食率、食物转化率均显著或极显著高于对照组(P<0.05或0.01)。而实验4、5组鱼恢复摄食期间虽摄食率极显著高于对照组(P<0.01),但其鱼体增重、特定生长率、食物转化率均极显著低于对照组(P<0.01);(2)实验各组鱼肥满度、肝体比、肝脏脂肪和糖原含量、肌肉中脂肪含量较对照组均有不同程度下降,肝脏脂肪中总饱和脂肪酸比例上升,而总多不饱和脂肪酸比例下降;(3)实验1、2、3组血浆中甘油三酯、胆固醇和低密度脂蛋白显著低于对照组,而葡萄糖、血清中甲状腺激素T4浓度显著高于对照组(P<0.05)。实验结果表明,初重约240g太平洋鲑饥饿1—4d,再循环投喂相同时间64d后,获得了接近完全补偿生长效果,表现为其恢复摄食期间摄食率和食物转化率明显上升,生长速率明显加快,饲料报酬明显提高,鱼体增重接近持续喂食的对照组,养殖效益明显提高。但饥饿8—16d再循环投喂相同时间后,表现为无补偿生长效应,食物转化率和生长速率明显下降,鱼体增重极显著低于持续喂鱼的对照组。     

Screening Subterranean Clover (Trifolium spp.) Germplasm for Resistance to Meloidogyne species

This study was conducted to identify lines of subterranean clover (Trifolium spp.) with resistance to Meloidogyne arenaria (Neal, 1989) Chitwood, 1949, race 1; M. incognita (Kofoid and White, 1919) Chitwood, 1949, race 3; and M. javanica (Treub, 1885) Chitwood, 1949. A collection of 134 subterranean clover lines was evaluated and all had intermediate to high susceptibility. Root galling was negatively correlated with both seed and dry matter yields. Soil fumigation significantly reduced the nematode population in the field. Results indicate there is limited genetic resistance to root-knot nematodes among subterranean clover lines. Alternative sources of variation for this trait should be investigated.     

越冬和复苏时期太湖水体蓝藻群落结构的时空变化

为研究太湖蓝藻在越冬与复苏时期群落结构的时空变化规律,于2008年11月,2009年2月,2009年4月,在太湖富营养化较严重的湖区选取8个采样点 (梅梁湾、竺山湾、贡湖湾、大浦、西太湖、南太湖、湖心和湖湾交汇处),分3层采水样,过滤并提取样品DNA经PCR扩增蓝藻16S rDNA序列,采用T-RFLP(末端标记的限制性酶切片段长度多样性)技术分析蓝藻群落结构和多样性变化。共得到87个不同的T-RFs(末端限制性酶切片段),表明太湖蓝藻具有丰富的基因多样性。T-RF相对丰度和聚类分析结果表明,太湖蓝藻群落结构在垂直空间上相似性较高,相似度 > 50%;在水平空间,与Microcystis spp.对应的信号峰在8个采样点均为最强峰(相对丰度为17.7% 47.5%)。竺山湾蓝藻多样性最低,西太湖最高,但其余采样点间蓝藻群落和Shannon多样性指数没有显著差异(P>0.05)。Microcystis相对丰度与Shannon多样性指数呈显著负相关(皮尔逊相关系数为-0.958)。在时间尺度上,相似性分析(Analysis of similarity,ANOSIM)结果显示太湖蓝藻群落结构存在极显著差异( P<0.01) 。春季复苏时蓝藻多样性最高,秋季衰亡时最低。聚类分析表明样品聚成两大特征类群,秋季衰亡时样品独自聚为1支,而春季复苏期和冬季越冬期样品彼此混杂。     

Labidocera aestiva and L. scotti in Tamiahua Lagoon,Veracruz, Mexico

Labidocera aestiva and L. scotti were found in the Tamiahua Lagoon, Veracruz, Mexico. Fleminger (1957) found that the populations of these species may overlap geographically, although L. aestiva has affinity to the Carolinian province and L. scotti to the Caribbean province. This study describes the seasonal behavior and succession of this species in the Tamiahua Lagoon, a brackish water system with a high marine influence. A qualitative and quantitative analysis of samples was made in March, July, and September 1985 and January 1986. L. aestiva was found in temperatures below 26 °C in a wide salinity range. At temperatures above 26 °C and up to 32 °C, L. aestiva was present also with euryhaline character. In the Tamiahua Lagoon these two species did not overlap during this study. Both species are considered temporary inhabitants of this estuarine system in the Western Gulf of Mexico.     

Decomposition of leaves of huisache (Acacia tortuoso) and mesquite (Prosopis spp) in soil of the central highlands of Mexico

In the central highlands of Mexico, mesquite (Prosopis spp) and huisache (Acacia tortuoso), N₂ fixing trees or shrubs, dominate the vegetation and are used in an alley cropping system to prevent erosion and restore soil fertility. We investigated how much the leaves of both trees contribute to dynamics of carbon (C) and nitrogen (N) in soil by adding leaves of both species to soil sampled under the canopy of mesquite and huisache, outside their canopy and from fields cultivated with maize at three different sites and monitoring microbial biomass C, production of carbon dioxide (CO₂), and dynamics of inorganic N (ammonium and nitrate) in an aerobic incubation. The soluble fraction and N content of the mesquite leaves were larger than in the huisache leaves, but lignin and polyphenol content were lower. Evolution of CO₂ increased 2.7-times when mesquite and 2.4-times when huisache leaves were added to soil. During all stages of decomposition and in all treatments, C mineralization of leaves from mesquite was greater than from huisache leaves. Mesquite leaves induced an increase in mineral N of 25.6 mg N kg^–1 soil after 56 days and those of huisache 9.8 mg N kg^–1. Twenty-six percent of N from mesquite leaves and 11% of huisache was mineralized, if no priming effect was considered. Nitrogen release from the leaves was greater when the soil organic matter content was lower. It was found that soil under the canopy of mesquite and huisache effectively accumulated organic material, micro-organisms and valuable nutrients. In an alley cropping system huisache might be a better choice than mesquite as huisache grows faster than mesquite and sheds its leaves twice a year while mesquite only once, although the amount of N mineralized was larger from mesquite leaves than from those of huisache.     

Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.     

In vitro and in vivo antagonism of biocontrol agents against Colletotrichum lindemuthianum causing bean anthracnose

Bean anthracnose caused by Colletotrichum lindemuthianum is a serious seed borne disease. For devising an effective management strategy, the efficacy of different bioagents, viz. Trichoderma viride, Trichoderma harzianum, Trichoderma hamatum and Gliocladium virens conducted under in vitro and in vivo conditions revealed maximum inhibition of mycelial growth in dual culture (59.48%) and inverted plate (55.98%) with T. viride. All the bioagents overgrew the pathogen and the principal mechanism of mycoparisitism observed was coiling, brusting and disintegration of pathogen hyphae. Culture filtrate from T. viride was found best as it completely inhibited radial growth at 25 and 50% concentration and reduced the spore germination of test fungus significantly. However, lower concentrations of culture filtrate from all bioagents showed little effect on spore germination. Seed application of bioagents was found better as compared to soil application. A maximum increase in seed germination and inhibition of seed borne infection was observed with T. viride followed by T. harzianum under pot culture conditions. T. viride has the maximum potentiality to suppress the spore germination, mycelial growth, seed borne infection of C. lindemuthianum and increased seed germination when compared with the other biocontrol agents.     

rDNA analysis of the Red Sea seagrass,Halophila, reveals vicariant evolutionary diversification

The effects of opening the Suez Canal as a connection between the Red Sea and the Mediterranean Sea were reported for a number of marine species. However, the evolutionary origin of the seagrasses in the Red Sea and the linking population genetics of seagrasses between the Arabian Sea, the Gulf of Aden, the Red Sea and the Mediterranean Sea have not yet been investigated in detail. The invasion of Halophila stipulacea Asch. from the Red Sea into the Mediterranean Sea after the opening of the Suez Canal was already recorded. We hypothesize that Halophila ovalis populations in the Red Sea developed through long-term historical processes such as vicariant evolutionary diversification. Seagrass samples were collected along the Egyptian coastline of the Red Sea and analysed by the molecular marker ITS. The sequences were compared with published ITS sequences from seagrasses collected in the whole area of interest. In this study, we reveal the linking population genetics, phylogeography and phylogenetics of two dominant seagrass species, Halophila stipulacea and Halophila ovalis, among species collected in the Red Sea and worldwide. The results indicate that the Red Sea Halophila ovalis populations do not group to Halophila ovalis worldwide, and Halophila major, Halophila ovalis collected worldwide and Halophila ovalis collected at the Red Sea are sister clades. Hence, vicariant evolutionary diversification for Halophila ovalis may occur in the Red Sea.