Impact of laurel wilt,caused by Raffaelea lauricola,on xylem function in avocado,Persea americana

Laurel wilt, caused by Raffaelea lauricola, is a lethal, vascular disease of avocado, Persea americana. Its impact on xylem function was examined in artificially inoculated plants of the ‘Simmonds’ cultivar. Three, 7, 14, 21 and 42 days after inoculation (dai), plants were rated externally and internally for disease severity on a subjective one (asymptomatic) to 10 (dead or 100% symptomatic) scale. Stems were then cut under water, 15 cm below the inoculation point, and placed in 0.1% aqueous solutions of acid fuschin in a greenhouse. After 48 h, the percentage of functional xylem was estimated 10 and 5 cm above and below the inoculation point by quantifying acid fuschin‐stained portions of digitized stem cross‐sections. Hydraulic conductivity was determined by placing the proximal end of 5‐cm‐long stem sections, harvested between 5 and 10 cm above the inoculation point, in water and quantifying the volume of water that was drawn over time through the distal end under partial pressure (350 mm Hg). Functional xylem decreased by 3 dai, well before the development of vascular discoloration (7 dai) and wilting of foliage (14 dai). By 14 dai, extensive vascular discoloration had developed and there was a dramatic reduction in functional xylem; plants with internal disease severities of 7 or greater had <20% functional xylem. Hydraulic conductivity decreased exponentially as non‐functional xylem and disease severity increased. In plants with internal severities >7, mean flow rates of water were 0.07 ml^?1 min^?1 cm^?2vs. 42 ml^?1 min^?1 cm^?2 in mock‐inoculated plants. The rapid development of these changes suggests that it may be difficult to manage laurel wilt in avocado once plants are infected by R. lauricola. Better understanding of the temporal and spatial development of infection and how the host responds to infection may assist efforts to select laurel wilt‐tolerant avocado cultivars.     

Response of swamp bay,Persea palustris,and redbay,P. borbonia,to Raffaelea spp. isolated from Xyleborus glabratus

Laurel wilt is a devastating invasive disease of members of the Lauraceae plant family. It is caused by the fungus Raffaelea lauricola, which is a nutritional symbiont of its ambrosia beetle vector, Xyleborus glabratus. In the United States, six Raffaelea spp., in addition to R. lauricola, have been recovered from mycangia of X. glabratus. We compared the response of two laurel wilt suspects, swamp bay (Persea palustris) and redbay (Persea borbonia), to five of these species, another undescribed Raffaelea sp., and R. lauricola. Six weeks after inoculation, only R. lauricola caused significantly greater symptoms than water inoculations. The fungi varied in their ability to move systemically and be recovered from the host at the end of the experiment. Stem hydraulic conductivity was decreased by R. lauricola, but none of the other taxa. Although the roles these fungi play in the life cycle of X. glabratus are not known, they do not appear to be pathogens on these host tree species.     

Partitioning of photoassimilates in avocado (Persea americana Mill.) during flowering and fruit set

To assess competition for photoassimilates among developing inflorescences, fruitlets and vegetative shoots in avocado (Persea americana Mill.), the distribution of recent photoassimilates was examined before and during flowering, fruit set, and the transition from sink to source of developing vegetative shoots. Mature leaves, located proximal to developing reproductive organs, and developing leaves, located distal to those organs, were exposed to a one-hour pulse of (14)CO(2). Translocation of radiolabeled assimilates was monitored over time and among organs. Overall distribution of assimilates was dependent on dry mass of tissues regardless of organ type. Flowers and fruitlets did not demonstrate greater sink strength than non-autotrophic leaves. Organs receiving assimilates were in phyllotactic alignment with source leaves. Photoassimilates were never limiting, although flower and fruitlet abscission occurred during and long after this competitive period. Carbohydrate availability was sufficient to support the growth of both developing fruitlets and leaves during early stages of reproductive development, and it did not limit fruitlet growth or stimulate fruitlet abscission.     

Xyleborus glabratus attacks and systemic colonization by Raffaelea lauricola associated with dieback of Cinnamomum camphora in the southeastern United States

Laurel wilt, caused by Raffaelea lauricola, is responsible for extensive mortality of redbay and other American members of the Lauraceae in the southeastern United States. Raffaelea lauricola is a mycangial symbiont of the redbay ambrosia beetle (Xyleborus glabratus), and the beetle and fungus were accidentally introduced from Asia. Branch dieback of camphortree (Cinnamomum camphora), an Asian member of the Lauraceae, has been occasionally observed in areas where laurel wilt has decimated redbay populations, and R. lauricola was isolated from such camphortrees. However, the role of X. glabratus and R. lauricola in this branch dieback remains unclear. Examination of camphortrees on Jekyll Island, Georgia showed that healthy‐appearing trees and those with branch dieback had been attacked by X. glabratus, but the trees with branch dieback had four times as many beetle attacks. Raffaelea lauricola was routinely isolated from discoloured xylem near beetle tunnels in healthy trees and those with dieback. Single‐point inoculations with R. lauricola on stems of mature, healthy camphortree trees failed to induce wilt‐like symptoms or branch dieback, although areas of discoloration were scattered throughout the xylem, and R. lauricola was reisolated irregularly at various heights in some inoculated trees. In growth chamber experiments, single‐point inoculations with R. lauricola resulted in systemic colonization but no wilt symptoms or branch dieback in camphortree saplings. In contrast, inoculations at multiple points along the stem (simulating multiple attacks by the vector) caused branch dieback and wilt‐like symptoms, including a brownish, diffuse discoloration of the xylem. Camphortree appears to be more resistant than American species of Lauraceae to the vascular wilt caused by R. lauricola. The fungus does colonize camphortrees systemically, however, and can apparently cause branch dieback. This suggests that the fungus may provide brood material for X. glabratus in Asia as it does in the southeastern United States.     

Screening for host responses in Acacia to a canker and wilt pathogen,Ceratocystis manginecans

In Vietnam, the productivity of Acacia hybrid (Acacia mangium x A. auriculiformis) plantations is being threatened by an aggressive canker pathogen, Ceratocystis manginecans, and selection for tolerance is the main control strategy. A pot trial was established in Binh Duong province to screen for the host response of nine Acacia genotypes (six Acacia hybrid clones, two A. auriculiformis clones and mixed provenance seedlings of A. mangium) to artificial inoculation with three isolates of C. manginecans. Lesion lengths as measured on the inner bark suggested that the two A. auriculiformis clones were relatively more tolerant to C. manginecans than the A. mangium genotype. In contrast, the lesion lengths of all six Acacia hybrid clones fell between the A. auriculiformis and A. mangium genotypes. The results of this study indicate that among the Acacia hybrid clones, BV10 showed the most tolerance to C. manginecans. Chemical analysis of crude sapwood extracts sampled from the lesion provided some evidence that induced phenolic compounds, particularly tetrahydroxyflavanone and condensed tannins may have a defensive role in the Acacia—C. manginecans pathosystem. However, results were not consistent across individual Acacia hybrid clones and A. mangium genotypes.     

Analgesic and anti-inflammatory effects of the aqueous extract of leaves of Persea americana mill (lauraceae)

The aqueous extract of Persea americana leaves produced a dose-dependent inhibition of both phases of formalin pain test in mice, a reduction in mouse writhing induced by acetic acid and an elevation of pain threshold in the hot plate test in mice. The extract also produced a dose-dependent inhibition of carrageenan-induced rat paw oedema. The results obtained indicate that the extract possesses analgesic and anti-inflammatory effects.     

Occurrence of the wattle wilt pathogen,Ceratocystis albifundus on native South African trees

Ceratocystis albifundus causes the disease known as wattle wilt of non‐native Acacia mearnsii trees in South Africa, Uganda and Kenya. Infection results in rapid wilt and death of susceptible trees and stem cankers on more tolerant trees. It has been suggested that C. albifundus is indigenous to southern Africa, possibly having spread from native Protea spp. to non‐native A. mearnsii and A. decurrens trees. Although C. albifundus has been collected from Protea spp., these reports are based on limited records for which only aged herbarium specimens exist. During surveys of wound‐infecting fungi on native tree species in South Africa, a fungus resembling C. albifundus was collected from Protea gaguedi, Acacia caffra, Burkea africana, Combretum molle, C. zeyheri, Faurea saligna, Ochna pulchra, Ozoroa paniculosa and Terminalia sericea. The identity of the fungus was confirmed as C. albifundus, using comparisons of DNA sequence data for the ITS and 5.8S gene of the rRNA operon. In pathogenicity trials, lesions were produced on C. molle and A. caffra, with some trees beginning to die at the termination of the experiment. This study represents the first report of C. albifundus from native tree species in South Africa and provides unequivocal evidence that the fungus occurs naturally on native Protea spp. The wide host range of C. albifundus, as well as its abundance on these indigenous hosts lends further support to the view that it is a native African pathogen.     

桉树枯萎病菌的生物学特性及对杀菌剂的敏感性试验

对桉树枯萎病菌的生物学研究结果显示,病菌的最适生长温度为25℃,最适pH值为5.5,光照对生长影响不大。菌丝致死温度为65℃。糖源对分生孢子萌发无明显作用。杀菌剂毒力测定显示根腐灵、宝宁对菌丝生长抑制较强,克露和宝宁对孢子发芽有较强的抑制作用。     

中国松萎蔫病病原线虫鉴定及诊断技术研究

松材线虫作为一种外来入侵物种,其致病机理尚不明确,致使该病的防治和控制工作进展缓慢。目前,该病的研究难点在于对其进行早期诊断和检疫。本文着重对我国松萎蔫病病原线虫鉴定及病害快速检测技术的研究现状进行评述,以期找到行之有效的检测方法。     

Discoloration induced by Raffaelea quercivora isolates in Quercus serrata logs and its relation to phylogeny: a comparison among isolates with and without the Japanese oak wilt incidence including outside of Japan

Japanese oak wilt (JOW) has been prevalent in Japan since the late 1980s. Infections of the fungus, Raffaelea quercivora Kubono et Shin. Ito, which is transmitted by an ambrosia beetle [Platypus quercivorus (Murayama)], can cause JOW. Although R. quercivora, P. quercivorus, and oak trees are distributed in other Asia–Pacific countries, the incidence of JOW has not been reported outside Japan. In this study, we collected R. quercivora isolates from 5 Asian countries, including Japan, and compared their ability to induce sapwood discoloration by inoculating Q. serrata logs. The tangential widths of the discoloration in sapwoods inoculated with non-Japanese isolates were equivalent to or greater than those of the 2 Japanese isolates. This indicates that a lack of JOW incidence outside Japan is not because of the lowered ability of R. quercivora to spread discoloration compared with the Japanese isolates. Statistical analyses of the relationship between discoloration and phylogeny based on DNA sequences of actin and chitin synthase showed that the discoloration width was independent of phylogenetic relatedness among the isolates. To discuss why the occurrence of JOW has not been reported outside Japan, further studies (e.g., on host susceptibility and P. quercivorus aggression) throughout Asia are needed.     

Responses ofQuercus sapwood to infection with the pathogenic fungus of a new wilt disease vectored by the ambrosia beetlePlatypus quercivorus

Quercus serrata andQ. crispula wilt during the summer in wide areas along the Sea of Japan. Mass attacks of trees by an ambrosia beetle (Platypus quercivorus) are characteristic before appearance of the wilting symptoms. This study investigated the pathogenic effects of a fungus detected specifically in the wilting trees. This hyphomycete fungus,Raffaelea sp., has a distribution that correlates with the discolored xylem area called wound heartwood in which vessels are dysfunctional. Tylosis formation around the hyphae indicates vessel dysfunction. In areas with discoloration, the fungal hyphae were invading living ray parenchyma cells from the vessel lumen. As a protective reaction the ray cells exuded yellow substances into the vessels, but these substances seemed ineffective against the fungal activity, probably because the fungus disperses along the beetle's gallery before enough substance can accumulate. It should allow wide discoloration in sapwood. Cambium was not necrotic around the fungus. The cytological process in the host was as follows: (1) synthesis of secondary metabolites by the stimuli of oak fungus; (2) exudation of yellow substances into vessels; and (3) dysfunction of vessels and wound heartwood formation. In regard to wilting of trees, the pathogenicity of the fungus should be assessed by its ability to stop sap flow.     

Responses of two closely related oak species, Quercus robur and Q. petraea, to excess manganese concentrations in the rooting medium

Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field.     

Calonectria metrosideri,a highly aggressive pathogen causing leaf blight,root rot,and wilt of Metrosideros spp. in Brazil

The genus Metrosideros includes several tree, shrub and vine species, native to the Pacific Islands. Seedlings from 25 seed lots of Metrosideros polymorpha and two seed lots of M. tremuloides with symptoms of root rot, stem girdling, wilting and round, purple leaf spots were observed in the Forestry Nursery at the Universidade Federal de Viçosa, Brazil. In the original disease site, seedling mortality reached up to 71% in M. polymorpha and 34% in M. tremuloides. Single conidial cultures obtained from infected leaf, root and stem samples of M. polymorpha were used to identify the fungal species. Morphological characters and DNA sequences of four loci, containing partial sequences of β‐tubulin (TUB2), histone H3 (HIS3), calmodulin (CAL) and the elongation factor (tef‐1α) genes of three isolates, indicated that they belong to a new species, described here as Calonectria metrosideri sp. nov. Potting medium infestation and inoculation of seedlings of M. polymorpha with an inoculum suspension at 1 × 10⁴ conidia ml^?1 induced typical symptoms of the disease (leaf spots, root rot and wilt), similar to those observed under natural conditions. Calonectria metrosideri was re‐isolated, which fulfilled Koch's postulates, and confirmed its status as a pathogen.     

Vegetation and its relation to soil nutrient and salinity in the Calabar mangrove swamp,Nigeria

The study examines vegetation – environment relationships. Vegetation measurements included species frequency, density, diameter and tree height, while environmental measurements were soil particle size distribution, acid properties (pH, Al, SO₄), nutrient cations (Ca, Na, Mg, K), organic carbon, nitrogen, phosphorus and chloride content. Nypa fruticans was the dominant species in the A stratum (> 3 m tall) while Rhizophora mangle was dominant in the B stratum (1–3 m tall). The C stratum (< 1 m tall) was dominated by mangrove, Nypa and Raphia saplings. Silt was dominant and the most variable particle size fraction. A principal components analysis of the soil data indicated the first three dominant components influencing the vegetation were salinity, nutrient and soil texture. Tree height and density correlated highly with the salinity and soil texture gradients (P < 0.01), while basal area correlated with salinity and nutrient gradients (P < 0.01). While Avicannia africana in the A stratum was influenced largely by the salinity and soil texture gradients. Nypa fruticans in the B stratum was influenced by salinity and nutrients.     

Responses of conifer species of the Great Lakes region of North America to inoculation with the pitch canker pathogen Fusarium circinatum

Five conifer species grown in the Great Lakes region of North America were examined for their susceptibility to Fusarium circinatum, (syns. Fusarium subglutinans f. sp. pini and F. moniliforme var. subglutinans), the causal agent of pitch canker. Three‐year‐old (3‐0) seedlings of red (Pinus resinosa), jack (P. banksiana) eastern white (P. strobus), Scots (P. sylvestris) and Austrian (P. nigra) pine were planted in 4 l pots in a greenhouse at Auburn University in November 1998. In April and June 1999, seedlings were inoculated by removing a needle fascicle approximately 5 cm from the terminal bud and placing a drop containing F. circinatum conidia on the wound. Resin production, canker length and seedling mortality were recorded 12 weeks later. Jack, Scots and eastern white pine were the most susceptible with Austrian and red pine more resistant to the fungus. F. circinatum was re‐isolated from 37% to 96% of inoculated seedlings. The susceptibility of jack, Scots and eastern white pine indicates a potential risk to these important species of the region if F. circinatum were to be introduced into the area.     

Responses of oaks and tanoaks to the sudden oak death pathogen after 8 y of monitoring in two coastal California forests

Sudden oak death, caused by Phytophthora ramorum, is widely established in mesic forests of coastal central and northern California. In 2000, we placed 18 plots in two Marin County sites to monitor disease progression in coast live oaks (Quercus agrifolia), California black oaks (Q. kelloggii), and tanoaks (Lithocarpus densiflorus), the species that are most consistently killed by the pathogen in these areas. Through early 2008, the numbers of newly infected trees increased for all species. The infection rate for trees that were asymptomatic in 2000 was 5.0% y⁻¹ for coast live oaks, 4.1% y⁻¹ for black oaks and 10.0% y⁻¹ for tanoaks. Mortality rates were 3.1% y⁻¹ for coast live oaks, 2.4% y⁻¹ for black oaks, and 5.4% y⁻¹ for tanoaks. Mortality not attributed to P. ramorum was 0.54% y⁻¹ for coast live oaks, and 0.75% y⁻¹ for tanoaks. Weibull survival models of trees that were asymptomatic in 2000 provided overall median survival times of 13.7 y for coast live oaks, 13.8 y for black oaks, and 8.8 y for tanoaks. Survival of infected (bleeding) trees declined to 9.7 y for coast live oaks, 6.2 y for black oaks, and 5.8 y for tanoaks. Ambrosia beetle attacks on bleeding trees further reduced modeled survival times by 65–80%, reaffirming the earlier finding that beetle attacks on bleeding cankers considerably reduce survival. Across all plots, the modeled time for 90% of trees that were asymptomatic in 2000 to become infected is 36.5 y for coast live oaks and 15.4 y for tanoaks. There was a trend toward higher infection rates as tree diameter increased. Greater than 90% of living coast live oaks that failed during the study had extensive beetle tunneling at the site of the break. Disease intensity in coast live oaks at the plot level was positively associated with bay laurel (Umbellularia californica) basal area and negatively associated with Pacific madrone (Arbutus menziesii) basal area. This study demonstrates the use of survival modeling to characterize the effects of epidemic disease on different species and to project the future of forests infected with tree pathogens.     

沼泽红假单胞菌的分离鉴定及对蕹菜生长的影响

从引进的日本土壤改良剂中富集分离得到1株光合细菌,通过形态学观察及生理生化特性鉴定,鉴定为该菌株属于红假单胞菌属。以泰国柳叶蕹菜为试验材料,用GRH-507菌液稀释500倍在蕹菜幼苗期、生长期进行叶面喷施,以等量的清水作对照,在成熟期调查蕹菜的产量。结果表明,喷施500倍GRH-507菌液稀释液能提高蕹菜的产量,两次收割产量分别比对照增产31.03%、20.74%。     

松兰山景区松材线虫病综合治理研究

研究分析了浙江宁波市象山松兰山景区松材线虫病发生规律与防治效果。结果表明：只采取“封锁”措施，会使松材线虫病迅速爆发毁灭全林。从1992年到1998年，松兰山枯死松树从6株增到5893l株，增长了9820．8倍；采用皆伐松林防治松材线虫病并改造成板栗、杨梅的方法，会导致逆向演替，使松林最后成为以疏花野青茅为主的荒山。而采取综合防治措施就可有效地控制松材线虫病的危害。从1998年到2002年，松兰山枯死松树下降到137株，缩小了430倍，使松兰山仍然保持着葱郁的松林群落。     

科尔沁沙质草地生物量对水、氮、磷添加的响应(英文)

为探寻科尔沁沙地东南部草地生产力自然恢复的主要限制因素,该文采用3因素2水平析因设计研究了水、氮、磷添加对沙质草地的影响。8种处理分别为添加水(W)、加氮肥(N)、加磷肥(P)、加水+氮肥(WN)、加水+磷肥(WP)、加氮肥+磷肥(NP)、加水+氮肥+磷肥(WNP)和对照(CK),每种处理6次重复,随机分配在48个4m×4m的样方中,样方之间留2m缓冲带。研究结果表明:科尔沁沙质草地生产力的恢复受氮素的限制,与水和磷无关;2005年生长季所有添加氮肥的样方,生物量和地上净初级生产力均较对照明显增加(P<0.05);禾本科根量在地下生物量中占优势。受限于地下生物量测定,目前的研究可能低估了我国北方草地的净初级生产力。