Screening brassicaceous plants as biofumigants for management of Phytophthora cinnamomi oak disease

Brassicaceous plants rich in glucosinolates have been used as biofumigants for the management of soilborne pathogens. Efficacy of Brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon the hydrolysis of glucosinolates. Management of Phytophthora cinnamomi, the causal agent of oak root rot in rangeland ecosystems using biofumigation, is promising, but requires further validation. The biofumigation activity of 14 brassicaceous plants was evaluated under experimental conditions. All evaluated plants rich in sinigrin suppressed (100%) the mycelial growth of P. cinnamomi, while plants rich in aromatic or other aliphatic glucosinolates had little or no suppressive effect. Simulating soil amendment in field conditions, the effects on natural soil artificially infested with P. cinnamomi chlamydospores were examined with Brassica juncea, Eruca vesicaria and Lepidium sativum, three species with different glucosinolate profiles. Only B. juncea decreased the viability of chlamydospores significantly in comparison with untreated soil only 1 day after biofumigation, whereas E. vesicaria needed 8 days to reach significance and L. sativum had no effect at all. Despite the decreases in soil inoculum, biofumigation with B. juncea did not prevent the root infections in a highly susceptible host (Lupinus luteus). However, biofumigation with plants rich in sinigrin, such as B. juncea, decreased P. cinnamomi soil inoculum under the experimental minimum threshold for oak disease expression. Although biofumigation should be considered as an effective measure to be incorporated in integrated control of the oak disease, biofumigation by itself would not be effective enough for the substantial suppression of P. cinnamomi inoculum.     

Biotic interactions in a Mediterranean oak forest: role of allelopathy along phenological development of woody species

Plant–plant chemical interactions in forests can have a strong impact on the biodiversity and dynamics of these ecosystems, particularly in Mediterranean forests where plants exhibit a high secondary metabolite diversity. Allelopathic interactions in Mediterranean ecosystems have been mostly studied in the first stages of ecosystem dynamics, shrublands and pine forests, but little is known about these interactions in mature oak forests. In this study, the allelopathic effect of three main woody species of downy oak forests (Quercus pubescens, Acer monspessulanum and Cotinus coggygria) on germination and growth of two herbaceous species (Festuca ovina and Linum perenne) was tested through aqueous extracts obtained from different leaf phenological stages (green, senescent and litter). The germination velocity of the two target species was inhibited by the aqueous extracts of senescent leaves from all the woody species. The growth of F. ovina seedlings was affected by aqueous extracts of green leaves of all the woody species, while the growth of L. perenne was only affected by aqueous extracts of green leaves of A. monspessulanum. This shows that (i) allelochemicals released by leaf leachates of the dominant woody species could control the dynamic of the herbaceous species, and then their potential competition with trees and (ii) allelopathic effects of woody species are related to their phenological stage and seem consistent with the development stage of target species.

     

Rosellinia necatrix attack according to soil features in the Mediterranean environment

A study was carried out on Rosellinia necatrix attack on young woody plants, as possibly affected by selected soil features under three water regimes. Six different soil systems representing five agro‐environments and one forest in the Puglia Region (southern Italy – Mediterranean climate) were compared. R. necatrix attack on sweet cherry trees was simulated using artificial inoculum and saplings of Prunus mahaleb, the most widely used rootstock of sweet and sour cherries, monitored during the spring period. Soil features significantly influenced disease score, which did not differ from one water regime to another, even though disease level in the different soils was affected by water content. Rosellinia mahaleb saplings grown in forest soil showed the highest disease score, which differed significantly from that observed in all the agricultural soils tested in this study. Amongst these, disease score was lower in sandy soils than in soils that were richer in loamy fraction.     

Signs and symptoms associated with Heterobasidion annosum and Armillaria ostoyae infection in dead and dying mountain pine (Pinus mugo ssp. uncinata)

Symptoms and signs associated with root rot caused by Heterobasidion annosum or Armillaria ostoyae in mountain pines (Pinus mugo ssp. uncinata) were investigated in the Swiss Alps. A sample of dying or recently dead mountain pine trees (≥12 cm d.b.h.) and saplings (<1.3 m height) was assessed for root pathogen infection by taking root samples followed by isolations in the laboratory. From a subsample, an additional core was taken from the butt of each tree and evaluated in the same fashion. A total of 157 dying or recently dead mountain pine trees and 184 saplings with roots infected by either of the two pathogens or which lacked infection were analyzed using logistic regression models. The main objectives were to determine the most prominent symptoms induced by the fungi (resinosis), signs of the fungi (mycelia, fruiting bodies and rhizomorphs), and tree characteristics (d.b.h./height and evidence of wounds) that would allow an easy and reliable determination of H. annosum and/or A. ostoyae infection of mountain pines in the field. Heterobasidion annosum caused both root and butt rot on mountain pine, whereas A. ostoyae was mostly restricted to the root systems of the trees sampled. The most discriminating sign for the presence of A. ostoyae infection was the presence of characteristic mycelial fans, and for H. annosum root rot the presence of H. annosum mycelia (sheets of paper‐thin mycelium and mycelial pustules). In addition, resinosis was a powerful predictor for A. ostoyae in trees. Symptoms and signs indicating A. ostoyae or H. annosum infections were more reliable for saplings than for mature trees. Armillaria rhizomorphs were not useful in detecting A. ostoyae infection and, if present, were often formed by saprophytic Armillaria species. Heterobasidion annosum fruiting bodies were rarely observed and poorly reflected the widespread occurrence of this pathogen in the mountain pine forests.     

The role of yellow lupin (Lupinus luteus) in the decline affecting oak agroforestry ecosystems

Phytophthora cinnamomi is a soilborne pathogen causing root rot in Mediterranean Quercus species growing in ‘dehesa’ rangeland ecosystems. Recently, it has been reported causing wilting and death of Lupinus luteus (yellow lupin), a spontaneous plant in southern Spain rangelands, but also frequently sowed for livestock grazing. In soils artificially infested with P. cinnamomi chlamydospores and planted with different cultivars of yellow lupin, a significant increase in the density of propagules was detected in comparison with the initial levels of inoculum and with the infested but not planted soil (control). In oak‐rangelands in which yellow lupine was planted, isolation and counting of colonies of P. cinnamomi from soil samples have shown the ability of this plant to maintain or even increase the inoculum density and thus facilitate the infection of trees. Results suggested that cultivation of yellow lupin in oak‐rangeland ecosystems should be avoided whether oak trees are affected by root disease caused by P. cinnamomi or not. This leguminous plant can act as an inoculum reservoir or even enhance inoculum soil levels available for oak root infections, exacerbating the oak decline severity in the region.     

Assessment of Australian native annual/herbaceous perennial plant species as asymptomatic or symptomatic hosts of Phytophthora cinnamomi under controlled conditions

Phytophthora cinnamomi is a necrotrophic pathogen of woody perennials and devastates many biomes worldwide. A controlled perlite–hydroponic system with no other hyphae‐producing organisms as contaminants present allowed rapid assessment of ten annual and herbaceous perennial plant species most of which have a wide distribution within the jarrah (Eucalyptus marginata) forest in Western Australia where this pathogen has been introduced. As some annuals and herbaceous perennials have recently been reported as symptomatic and asymptomatic hosts, laboratory screening of some of the field‐tested annuals and herbaceous perennials and additional species was used to further evaluate their role in the pathogen's disease cycle. Nine of the species challenged with the pathogen were asymptomatic, with none developing root lesions; however, Trachymene pilosa died. The pathogen produced thick‐walled chlamydospores and stromata in the asymptomatic roots. Furthermore, haustoria were observed in the roots, indicating that the pathogen was growing as a biotroph in these hosts.     

First report of the brown root rot disease caused by Phellinus noxius,its distribution and newly recorded host plants in the Amami Islands,southern Japan

To determine whether the brown root rot disease caused by Phellinus noxius is present in the Amami islands, which are situated near Okinawa, we conducted six field surveys from 1999 to 2005. The brown root rot disease was found in 22 tree species in 17 plant families at 25 different sites in all the islands surveyed. Sixteen of these species were newly recorded as host plants of P. noxius. The disease was more common in the low elevation plains and on hills less than 100 m above sea level than in mountainous areas. This is the first report of the brown root rot disease caused by P. noxius in the Amami Islands, Japan, and Ohshima Island is currently the northern‐most distribution point of the disease in the northern hemisphere.     

Variation in herbivory-induced responses within successively flushing Quercus serrata seedlings under different nutrient conditions

Herbivore damage can induce the host plant to alter the chemical and physical qualities of its leaves, which is thought to be a plant strategy—termed “induced response”—for avoiding further herbivory. In woody plants, many studies have considered variation in induced response with resource availability, but few studies have examined this variation in relation to growth patterns of woody plants. We studied the phenotypic variability of induced response within successively flushing Quercus serrata seedlings. Q. serrata seedlings were grown under controlled conditions. The controlled factors were herbivore damage (herbivore-damaged and -undamaged) and soil fertility (low and high). At each flush stage, the concentrations of condensed tannin (CT), total phenolics (TP), and nitrogen (N) in leaves were analyzed, and the leaf mass per area (LMA) was measured. CT and TP concentrations in leaves and LMA were higher in herbivore-damaged seedlings. Leaves of the first flushes showed greater sensitivity to herbivore damage and had a higher CT concentration than leaves of the later flushes. Furthermore, seedlings growing in low-fertility soil showed a greater induced response. The results suggest that the induced response of Q. serrata seedlings was related to the contributions of the tissue to current productivity. Leaves of the first flush showed a greater induced response, possibly because they play an important role in subsequent growth. The potential of Q. serrata seedlings to adjust the properties of leaves depending on herbivory and soil fertility in relation to growth patterns may be advantageous on the forest floor, where seedlings grow in soil of heterogeneous fertility and are constantly exposed to herbivory.     

Production of <Emphasis Type="Italic">Pinus halepensis</Emphasis> seedlings inoculated with the edible fungus <Emphasis Type="Italic">Lactarius deliciosus</Emphasis> under nursery conditions

Inoculation with edible fungi bestows an added value on mycorrhized plants since production of mushrooms as a secondary crop can be an economically-valuable resource in forestry management. In order to establish a protocol for controlled mycorrhization of Pinus halepensis with the edible fungus Lactarius deliciosus, several factors such as fertilisation (35, 60 or 120 mg total N and 13.5, 27 or 54 mg total P), potting substrate (sphagnum peat or sphagnum peat/vermiculite) and fungal inoculum (mycelial slurry produced in a bioreactor, alginate beads or peat/vermiculite) were assessed. The most effective inoculum was mycelial slurry at a dose of 10 ml/plant. The two potting substrates assessed were compatible with mycorrhiza formation. The greatest number of mycorrhized seedlings was obtained with a moderate level of N (35 mg/plant) or P fertilisation (27 mg/plant). Inoculation did not produce a consistent growth effect on P. halepensis, but seedlings met the quality requirements, making them suitable for planting out.     

林木根腐病发生及防治研究进展

根腐病作为一种土传病害,主要侵染植物根部,影响植株正常生理过程,发病严重时会造成全株死亡,在草本、林木等植物中均有发生,大大降低了植物的生态、经济和社会效益。为促进林业可持续健康发展,根腐病致病菌的分离、鉴定及室内、田间防治成为近年来的研究热点。文中主要针对林木根腐病的病原菌、发生症状进行概述,并综述利用林业技术、化学药剂、生防真菌、生防细菌和放线菌防治林木根腐病的研究进展,还对根腐病防治中存在的问题及未来研究趋势进行讨论,以为今后植物根腐病的系统研究及其防治提供参考。     

Effect of different nitrogen and carbon sources and concentrations on the mycelial growth of ectomycorrhizal fungi under in-vitro conditions

Effect of different nitrogen and carbon sources and their concentrations in liquid media on the mycelial growth of six different ectomycorrhizal (ECM) fungal species was studied. Differences were found in the utilization of the different nitrogen and carbon sources between the fungal species. All the species showed better mycelial growth in the medium containing ammonium as nitrogen source. Growth was low in all species in medium in which nitrogen was supplied in nitrate form. All the ECM isolates investigated showed reduced growth in the medium containing maleic acid as the carbon source. The effect of glucose and di-ammonium hydrogen orthophosphate concentrations on mycelia growth of all the six fungal species was studied with ranges for glucose of 2–40 g/l, and for di-ammonium hydrogen orthophosphate of 2–20 g/l. Cortinarius fulvoconicus and Cortinarius flexipes showed maximal mycelial growth at a glucose concentration greater than 20 g/l. Suillus luteus, Scleroderma citrinum, Laccaria laccata, and Tricholoma aurantium showed maximal growth at a glucose concentration of 20 g/l. All six species showed maximal mycelial growth at 5–10 g/l of di-ammonium hydrogen orthophosphate concentration and with increased concentration mycelial growth in all species decreased.     

香格里拉普朗尾矿区工程边坡植被恢复调查研究

为研究香格里拉市高寒山区工程边坡迹地植物群落结构,以香格里拉普朗尾矿区工程边坡迹地为研究对象,研究其植物群落的物种组成、物种相似性及物种多样性。结果表明：工程迹地乔木层的优势种主要是丽江云杉,灌木层优势种以川滇高山栎为主,其次是滇西北小檗和西南蔷薇,草本层优势种以苔草、蒿等植物为主,未受破坏的自然林地植物优势种更为多元化;工程迹地1年自然恢复样地与自然群落样地物种相似性指数较小,为0.03~0.30;工程迹地多年自然恢复样地物种与自然群落样地物种相似性系数较高,最高为0.43;F1样地草本层Simpson多样性指数、Shannon-Wiener多样性指数均较大,但不同工程迹地之间差别较小。草本层自然恢复较快,在演替早期,草本植物中的蒿、苔草、野青茅及西南鸢尾等植物,可作为工程迹地植被恢复的先锋植物。     

Management of fungal root‐rot pathogens in tropical Acacia mangium plantations

Acacia mangium is a fast‐growing tree species. It is mainly planted in large monocultures for pulpwood in South‐East Asia. Root rot has become the most economically damaging disease of this species with high tree mortality rates observed during second and third rotations. Two main types of root rots have been found in A. mangium, viz. brown root‐rot and red‐root disease caused by Phellinus spp. and Ganoderma spp., respectively. To assess the future management options for root rot of A. mangium, we review past and current disease‐management strategies for root rot in different temperate and tropical industrial tree crops. The efficacies of a wide range of silvicultural, chemical and biological options are detailed, and their potential utilization in managing root rot of A. mangium is discussed. We conclude that the current gaps in knowledge regarding identification, biology and disease epidemiology of the root‐rot pathogens will need to be addressed so that effective management options can be developed.     

Occurrence of brown root rot in Ocean Expo Park,Okinawa, Japan: Infection route and preventive control measures

Ocean Expo Park, established in 1976 on subtropical Okinawa Island, Japan, has approximately 8000 planted or naturally grown trees in an area of 77.2 ha. Windfall of these trees occurs mainly due to typhoons; wood chips made from the trunks and roots of windfall trees are commonly used as mulching material throughout the park areas, despite possible infection by pathogenic fungi such as Phellinus noxius, the pathogen causing brown root rot. P. noxius is distributed in tropical and subtropical areas worldwide and has a broad host range. The fungus can infect host plants with mycelia via root-to-root contact or with basidiospores. Here, we report the current status of tree damage caused by brown root rot in the park and infer the infection routes of P. noxius based on microsatellite markers. Among a total of 294 trees surveyed in the park, P. noxius was isolated from 13 trees of five species. P. noxius was observed more frequently on Ficus microcarpa than on other tree species. Ficus superba var. japonica was identified as a new host species, and Bombax ceiba was first recorded as a host plant of P. noxius in Japan. Among the 13 P. noxius isolates from the diseased trees, 2 isolates from adjacent diseased trees were considered to be of the same genet, while the other 11 isolates were different genets, indicating that infection by basidiospores occurred frequently among trees in the entire park, although spread via root systems also occurred between at least two adjacent trees. An identical genet was not detected at distant locations, which suggests that the disease does not spread via chips. However, mulching with chips can lead to wood decay due to decaying fungi other than P. noxius. Therefore, in accordance with the precautionary principle, the park currently prohibits the chipping and mulching of windfall or damaged trees and is considering disposal methods such as burning.     

Butt rot ofChamaecyparis obtusa (Sieb. et Zucc.) Endlicher trees caused byPerenniporia subacida in Shikoku district, Japan: Pathogen, distribution of damaged trees in the stand, and soil investigation

The rot ofChamaecyparis obtusa (hinoki) trees was studied in the northern part of Kagawa Prefecture, Japan. Among 158 hinoki examined, butt rot was found in 28.6, 58.3, and 100% of trees in the 29, 30, and 34-year-old stands, respectively. All trees with butt rot, and 11 trees without it had rotted roots. Thirteen hinoki were peeled byCervus nippon (sika deer) and all of them were infected with butt rot. The maximum height of rot in deer-damaged trees was 2.6 m from the ground level, but was 1.9 m in undamaged trees. About eighty-two percent of rotted trees showed rotted areas of less than 40 cm² on the cross section of stems at the ground level. White mycelia and black flecks sometimes appeared in the rotted wood. Basidiocarps of polyporaceous fungus were often found on felled logs and rotted stumps of hinoki and identified asPerenniporia subacida. Basidiomycetous fungus was isolated frequently from rotted wood of roots and stems, and determined to beP. subacida by comparative study on cultural characteristics. An inoculation experiment and wood-decay test proved that the fungus was the cause of the rot of hinoki. Few absorbing roots of living trees were found in the clayey subsurface soil of the high dry bulk density and the less soil aeration. Some absorbing roots had root rot and the rot spread from the base of the absorbing root to the central part of the woody root. This is the first report on the rot of hinoki caused byP. subacida in Japan.     

Studies in Forest Pathology Root Rot due to Rhizoctonia solani Kühn

A root rot disease of Phyllanthus emblica, Quercus serrata and Citrus sp. due to Rbizoctonia solani has been observed in the two tropical forests of Meghalaya in May to August. Seedling mortality was 39.4% in P. emblica, 38.6% in Q. serrata and 17.1% in Citrus sp. Older plants were resistant to this disease. High temperature and rainfall favour the disease development. The disease was observed in silt and clay soil with pH 6.10 and 6.38 and moisture content 22.8 and 24.6% respectively. The fungus grows over a broad temperature ranges (5 to 40°C) with optimum temperature at 20 to 35°C. The pathogenicity of the fungus was established. The fungus possesses quick and wide powers of saprophytic colonization of dead and healthy roots and soil. This is a new host record for this fungus on P. emblica and Q. serrata in India.     

Behaviour and survival of Phytophthora cambivora inoculum in soil‐like substrate under different water regimes

Phytophthora cambivora is a soil‐borne pathogen responsible for root and collar rot of woody species including Castanea spp., on which it causes Ink disease. P. cambivora does not produce chlamydospores, and the prevalence of a single mating type in nature limits the production of oogonia and oospores. Thus, survival of P. cambivora, in the absence of suitable hosts, relies mainly on sporangia, zoospores and mycelium. However, inoculum survival in soils or substrates represents a major factor in disease epidemics and is probably dependant on environmental factors. The aim of this article was to study the behaviour of P. cambivora in a peat‐based substrate (PbS) in the absence of a host, under controlled conditions, and by varying the substrate water regimes. Total inoculum in the substrate was quantified by qPCR, using customized rDNA primer sets, whilst zoospores were quantified after elution, and their vitality was determined by a specific staining procedure. Inoculum infectivity was assessed using chestnut root baits. Results indicated that during the initial 48 h after infestation (matric potential, pF 1.2; 70% water content), the inoculum level increased producing microsporangia and mycelium before decreasing, regardless of the water regime applied. The number of free zoospores increased over a period of (maximum) 7 days after substrate inoculation. Vitality of zoospores declined to 45% at day 18, with no statistical differences amongst water regime treatments. Both rDNA and zoospore number increased in flooded samples at day 23, illustrating the vitality of the inoculum. Inoculum was able to infect chestnut root baits up to 45 days at pF 1.2 and 3.5, before and after flooding, but at pF 6.3, only in the absence of flooding. Although based on experiments carried out in microcosms, these results highlight an unexpected resistance of P. cambivora zoospores to environmental constraints. Furthermore, the infectivity ability of the inoculum to survive in PbS over time even in the absence of the host adds relevance to the risk of movement of soil and substrates associated with plant trading worldwide.     

Effect of three species of bacteria on damping-off,root rot development,and ectomycorrhizal colonization of lodgepole pine and white spruce seedlings

Interactions between three species of bacteria (Burkholderia cepacia, Pseudomonas chlororaphis and Pseudomonas fluorescens), an ectomycorrhizal fungus (Paxillus involutus), and three root pathogenic fungi (Fusarium moniliforme, Fusarium oxysporum and Rhizoctonia solani) were studied. Burkholderia cepacia significantly reduced the in vitro mycelial growth of P. involutus, whereas, B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. involutus reduced the mycelial growth of F. moniliforme, F. oxysporum and R. solani. Culture filtrates of B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. involutus reduced conidial germination and increased the formation of chlamydospores of F. moniliforme and F. oxysporum. Burkholderia cepacia also reduced the formation of ectomycorrhizal short roots by P. involutus on lodgepole pine (Pinus contorta) and white spruce (Picea glauca) seedlings 2 months after inoculation. However, no significance difference in mycorrhizal short roots was observed after 4 months. The fungicide Anchor (a mixture of carboxine and thiram) significantly reduced root rot severity and increased the survival of lodgepole pine seedlings grown in a growth mix infested with F. moniliforme, F. oxysporum and R. solani. Control of the diseases of white spruce caused by these pathogens was not as successful. Treatment of seeds with either B. cepacia or P. involutus alone significantly increased the survival of seedlings grown in a mix that was inoculated with F. moniliforme and reduced the root rot severity caused by F. moniliforme and F. oxysporum, but not R. solani. Higher seedling survival and lower root rot severity were observed when conifer seeds were concomitantly inoculated with one of the bacterial species, P. involutus and Anchor.     

Changes in water status in seedlings of six species in the Fagaceae after inoculation with Raffaelea quercivora Kubono et Shin-Ito

To clarify the differences in susceptibility of six species in the Fagaceae (Quercus crispula, Quercus serrata, Quercus acutissima, Quercus phillyraeoides, Quercus glauca, and Castanopsis cuspidata var. sieboldii) to Raffaelea quercivora, we inoculated this fungus on seven potted 5-year-old seedlings of each species, observed symptom development, and measured xylem pressure potential (XPP) after inoculation. The first death was observed on the 11th day in Q. crispula and on the 56th day in Q. serrata. The number of dead seedlings of Q. crispula and Q. serrata were five and one, respectively, whereas no mortality was observed in the other four species. The XPP of inoculated seedlings in both Q. crispula and Q. serrata decreased after inoculation. In contrast, the XPP of inoculated seedlings of the other four species remained almost the same as in the control seedlings. These results indicate that R. quercivora is pathogenic to Q. crispula and Q. serrata and that the susceptibility of the six Fagaceae species in our study differed among species.