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1.
Pine pitch canker (PPC), caused by Fusarium circinatum, affects Pinus species worldwide. Although no effective solutions have yet been found to control it, there is a growing interest in using biological control agents (BCA) such as Trichoderma to avoid the application of chemical-based products. Using species with an increasing level of susceptibility to PPC (Pinus pinea, Pinus pinaster and Pinus radiata), this study aimed to evaluate the effect of Trichoderma viride pre-inoculation on disease development, assessing several physiological and hormonal parameters. A 2-week period elapsed between T. viride and F. circinatum inoculation. Sampling for each species was performed independently when at least 50% of the plants of one of the inoculated groups developed disease symptoms. Fusarium circinatum infection reduced water status and photosynthesis, but increased proline, abscisic acid and jasmonic acid concentrations in plants of P. radiata and P. pinaster with symptoms; while in P. pinea water relations were maintained and anthocyanin accumulation occurred in the presence of F. circinatum. In P. radiata, T. viride pre-inoculation accelerated disease progression, with some PPC-induced responses augmented (decreased water potential and photosynthesis; increased substomatal CO2 concentration) and novel changes not found in seedlings inoculated exclusively with F. circinatum (increased electrolyte leakage and salicylic acid; decreased relative water content). This suggests that T. viride may be initially recognized as an invading organism, subverting the plant defence mechanisms for successful root colonization. If seedlings are not allowed to recover from this state, pathogen infection may thus be facilitated, highlighting the importance of application timing in BCA strategies.  相似文献   

2.
In recent years, Pinus plantation forestry has been significantly hampered by outbreaks of pitch canker caused by the fungus Fusarium circinatum. This study investigated the role of Pinus host, geographic origin and reproductive mode in structuring the F. circinatum populations in plantations. For this purpose, 159 isolates originating from diseased plantation trees in the Western and Eastern Cape Provinces of South Africa were genotyped using 10 microsatellite markers. Analyses of these data revealed 30 multilocus haplotypes and that the populations were distinct based on geographic origin as well as host. However, shared haplotypes were observed between populations, showing that these populations are connected, possibly through the movement of haplotypes. A second aim was to determine whether the genetic variation found in these populations of the fungus could be attributed to outbreaks of the seedling disease caused by this pathogen in Pinus nurseries. To achieve this goal, an additional set of 43 isolates originating from pine seedling nurseries was genotyped and analysed. The results showed that the populations of F. circinatum in plantations most probably originated from the nursery outbreaks that occurred prior to the plantation outbreak. Inferences regarding reproductive mode further showed that sexual reproduction has little impact on the genetic makeup of the F. circinatum populations and that they primarily reproduce asexually. Overall, the results of this study showed that the F. circinatum diversity in South Africa has arisen due to multiple introductions of the pathogen and is not due to sexual reproduction.  相似文献   

3.
The pitch canker pathogen Fusarium circinatum was first found to cause damage in nurseries and pine plantations in northern Spain in 2004. Since then, establishment of pine plantations in the region has decreased as a result of the prohibitions placed on planting Pinus spp. and Pseudotsuga menziesii in areas affected by the disease. However, although most pine species have been found to be susceptible to the pathogen under nursery conditions, little is known about how the fungus affects the trees in the field. Furthermore, it is not known whether some of the native or exotic species commonly planted in the area are also susceptible to F. circinatum. The aim of this study was to evaluate the susceptibility of several conifer species commonly planted in northern Spain to the pitch canker pathogen. For this purpose, two different trials were carried out, one under controlled laboratory conditions and the other in the field. Although most of the conifers were affected by the pathogen in the laboratory tests, only Pinus radiata, Pinus nigra, Pinus pinaster and Pinus uncinata were susceptible to the pathogen in the field.  相似文献   

4.
Survival of Fusarium circinatum in colonized pine needles and wood pieces was measured. Naturally colonized branches and their needles were cut into small pieces and placed in mesh bags on the soil surface at two locations in northern Spain. Pieces were recovered periodically, cultured on a selective medium, and microscopically examined to identify the species. After 507 days, F. circinatum was recovered from 0 to 27% of the wood pieces and from none of the needles. After 858 days, F. circinatum was not recovered from any wood pieces but was found to be present on 1 out of 220 needle pieces analysed. Artificially infested pieces of wood and needles were placed on 5‐mm sieved soil either in plastic boxes at controlled temperature or in mesh bags under field conditions. No survival was recorded after 794 days under field conditions and the decline over time occurred more rapidly in inoculated pieces under field conditions. Soil was also infested with conidia of F. circinatum and survival was estimated. No conidia were recovered after 224 days at 30 °C, although at 20 and 5 °C the respective populations were 20 and 3700 cfu/g soil. Fusarium circinatum was not recovered from 2‐mm‐sieved soil collected under pitch canker‐infected pines. Results indicate that branch segments and needles naturally colonized by F. circinatum will not be a potential source of inoculum, and the fungus in soil is not likely to contribute to reinfection of new plantations after 2 years.  相似文献   

5.
The relative importance of beetle species associated with Fusarium circinatum‐infected Monterey pines was investigated in three Monterey pine forests along the coast of central California, USA from April to November in 2004 and 2005. Fusarium circinatum was frequently isolated from Ips mexicanus and I. plastographus. The mean percentage isolation based upon numbers of I. mexicanus and I. plastographus carrying propagules of F. circinatum was 17·7 and 10·9% in 2004 and 16·7 and 17·3% in 2005, respectively. The mean percentage isolation was high in the spring and early summer and low in late summer and autumn in all three locations for both species. Isolation was higher from beetles emerging from harvested F. circinatum‐infected pine‐stems than for trapped beetles, 42·4% for I. mexicanus and 45·9% for I. plastographus. The mean (± SE) propagule load of trapped I. mexicanus was 269·5 (± 14·1) in 2004 and 281·7 (± 35·7) in 2005 and was 216·1 (± 28·9) in 2004 and 251·9 (± 28·4) in 2005 for I. plastographus. Mean propagule loads decreased from May to November in all locations for both species. Propagule loads of beetles emerged from infected stems were lower than that of trapped beetles, with means of 89·4 (± 23·2) and 93·0 (± 23·2) for I. mexicanus and I. plastographus, respectively. Thus beetles must acquire fungal propagules from more than one infected host. These results also suggest that higher contamination rates and propagule loads in spring and early summer may indicate a higher risk of pitch canker transmission, relative to late summer or autumn.  相似文献   

6.
Fusarium circinatum causes pitch canker of Pinus species in many parts of the world. The fungus was first recorded in South Africa in 1990 as a pathogen of P. patula seedlings and emerged later as a pathogen of established plantation trees, especially P. radiata in the Western Cape Province (WCP). In this study the population biology of F. circinatum in the WCP was explored. The aim was to determine the possible origin and reproductive mode of the pathogen, with the ultimate intention of informing disease management strategies in the region. Vegetative compatibility assays, sexual mating studies and amplified fragment length polymorphism analyses were used. For comparative purposes, an isolate collection obtained from diseased P. radiata seedlings in a commercial nursery in the region, as well as a set of isolates from commercial seedling nurseries in the central and northern parts of South Africa, were included. The results showed that the WCP population of F. circinatum employs a predominantly asexual mode of reproduction and that it is highly differentiated from populations of the fungus elsewhere in South Africa. However, limited genetic structure was found within the respective WCP isolate collections. Overall these findings suggest that pitch canker in the WCP originates from one or more separate introductions of the pathogen and that its movement in the region is not restricted. More effective strategies are thus required to limit and manage the effects of F. circinatum in plantations in this region of South Africa.  相似文献   

7.
Surveys were conducted in the five southern rice-producing states of Arkansas, Louisiana, Mississippi, Missouri and Texas in the United States during the 2018 and 2019 cropping seasons to determine the distribution and pathogenicity of fungal pathogens associated with seedling blight in rice. A total of 349 pathogenic fungal isolates were collected and identified as belonging to four genera: Rhizoctonia solani, Fusarium spp., Sclerotium rolfsii and Marasmius graminum based on morphological characteristics, molecular analysis and Koch's postulates. R. solani (252 out of 349 pathogenic isolates) was the most prevalent fungus isolated from diseased samples. Of the 252 pathogenic R. solani isolates, 245 were further classified as anastomosis group 11 (AG-11) and 7 as AG-4. Isolates of R. solani AG-4 and M. graminum were the most aggressive, with the highest stand loss (63% to 100%) and median disease rating (DR; 5.0), followed by isolates of R. solani AG-11 (stand loss = 4% to 100% and DR = 0.6 to 5.0), Fusarium spp. (stand loss = 26% to 48% and DR = 2.0 to 5.0) and S. rolfsii (stand loss = 33% to 48% and DR = 2.0 to 3.0) in causing seedling blight in rice. R. solani (62% to 83% of total pathogenic isolates) and Fusarium spp. (10% to 24% of total pathogenic isolates) were predominant in all the five states surveyed. S. rolfsii and M. graminum were present only in Louisiana and Texas. The results of this first systematic survey of rice seedling diseases in the southern United States will help develop effective fungicide seed treatment strategies for control of stand loss caused by seedling blight, one of the major factors limiting rice production.  相似文献   

8.
Brazil is the leader in the global ranking of forest productivity; however, one of the major challenges to eucalyptus production is the existence of fungal diseases. A severe epidemic caused by pestalotiopsis-like fungi was observed in a forest nursery in Brazil, causing a huge impact on the eucalyptus micropropagation stages. The aims of the present study were to identify the causal agents associated with pestalotiopsis leaf spot and dieback in eucalyptus, assess their pathogenicity to different commercial clones, and evaluate which conditions favour conidial germination and infection by the pathogens. Multilocus phylogenetic analyses using ITS, TEF and TUB identified the isolates as members of Neopestalotiopsis and segregated them into three species. Isolates from all Neopestalotiopsis spp. caused symptoms on unwounded eucalyptus leaves and disease development was strongly dependent on long leaf wetness periods (≥72 h). All four commercial clones tested were susceptible to the pathogen. These results clearly dispute the commonly held assumption that pestalotioid fungi are weak and opportunistic pathogens. This is the first report of different phylogenetic species of Neopestalotiopsis causing dieback, leaf and stem lesions in eucalyptus cuttings and provides a basis for developing novel disease management strategies in forest nurseries.  相似文献   

9.
Mycosphaerella species that cause the ‘Sigatoka disease complex’ account for significant yield losses in banana and plantain worldwide. Disease surveys were conducted in the humid forest (HF) and derived savanna (DS) agroecological zones from 2004 to 2006 to determine the distribution of the disease and variation among Mycosphaerella species in Nigeria. Disease prevalence and severity were higher in the HF than in the DS zone, but significant (P < 0·001) differences between agroecological zones were only observed for disease severity. A total of 85 isolates of M. fijiensis and 11 isolates of M. eumusae were collected during the survey and used to characterize the pathogenic structure of Mycosphaerella spp. using a putative host differential cultivar set consisting of Calcutta‐4 (resistant), Valery (intermediate) and Agbagba (highly susceptible). Area under disease progress curve (AUDPC) was higher on all cultivars when inoculated with M. eumusae than with M. fijiensis, but significant (P < 0·05) differences between the two species were only observed on Valery. Based on the rank‐sum method, 8·3% of the isolates were classified as highly aggressive and 46·9% were classified as aggressive. About 11·5% of all the isolates were classified as least aggressive, and all of these were M. fijiensis. The majority of M. eumusae isolates (seven out of 11; 64%) were classified as aggressive. A total of nine pathotype clusters were identified using cluster analysis of AUDPC. At least one M. fijiensis isolate was present in all the nine pathotype clusters, while isolates of M. eumusae were present in six of the nine clusters. Isolates in pathotype clusters III and V were the most aggressive, while those in cluster VIII were the least aggressive. Shannon’s index (H) revealed a more diverse Mycosphaerella collection in the DS zone (H = 1·81) than in the HF (H = 1·50) zone, with M. fijiensis being more diverse than M. eumusae. These results describe the current pathotype structure of Mycosphaerella in Nigeria and provide a useful resource that will facilitate screening of newly developed Musa genotypes for resistance against two important leaf spot diseases of banana and plantain.  相似文献   

10.
Pitch canker on plantation-grown Pinus species, caused by the fungal pathogen Fusarium circinatum, first appeared in the western and southern Cape regions of South Africa. However, outbreaks have subsequently been reported from the major plantation growing regions of KwaZulu-Natal and Limpopo in the eastern, summer rainfall regions of the country. It is more than 10 years since the last detailed population genetics studies on F. circinatum in the region were conducted. To shed light on the population biology of F. circinatum in this region of South Africa, we used microsatellite markers and mating-type assays to study a collection of 296 isolates from different nurseries and plantation sites. Our results showed that populations in the region are highly diverse, but strongly interconnected, with various genotypes shared across nursery and plantation collection sites. In contrast to nursery populations, those associated with pitch canker outbreaks were characterized by the presence of relatively small numbers of dominant genotypes that were generally widespread across the region. Opposite mating-type individuals occurred in most of the isolate collections, but multilocus linkage disequilibrium analyses pointed towards clonality being the main reproductive mode of F. circinatum in the region. Most of the pathogen's genetic variation could probably have resulted from multiple different introductions into the country and more specifically, into the summer rainfall region. Because the spread and establishment of invasive pathogens are typically driven by aggressive clones, the results of this study provide important considerations for current and future Pinus disease management strategies.  相似文献   

11.
Fusarium graminearum is a major fungal pathogen of cereals worldwide, causing seedling, stem base and floral diseases, including Fusarium head blight (FHB). In addition to yield and quality losses, FHB contaminates cereal grain with mycotoxins, including deoxynivalenol, which are harmful to human, animal and ecosystem health. Currently, FHB control is only partially effective due to several intractable problems. RNA interference (RNAi) is a natural mechanism that regulates gene expression. RNAi has been exploited in the development of new genomic tools that allow the targeted silencing of genes of interest in many eukaryotes. Host‐induced gene silencing (HIGS) is a transgenic technology used to silence fungal genes in planta during attempted infection and thereby reduces disease levels. HIGS relies on the host plant's ability to produce mobile small interfering RNA molecules, generated from long double‐stranded RNA, which are complementary to targeted fungal genes. These molecules are transferred from the plant to invading fungi via an uncharacterised mechanism, to cause gene silencing. Here, we describe recent advances in RNAi‐mediated control of plant pathogenic fungi, highlighting the key advantages and disadvantages. We then discuss the developments and implications of combining HIGS with other methods of disease control. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   

12.
A. Serfling  F. Ordon 《Plant pathology》2014,63(6):1230-1240
Fusarium culmorum causes head blight, produces toxins and reduces yield and quality of cereals. To prevent damage caused by fusarium head blight (FHB), azole fungicides are mainly applied. The occurrence of insensitivity to azoles is a major problem in agriculture. The present study shows that a tebuconazole insensitive strain of F. culmorum can be readily produced in the laboratory, but that the resulting strain of the fungus is of lower fitness in vitro. Insensitivity was confirmed microscopically and by cell viability and metabolic activity. The tebuconazole insensitive strain shows cross insensitivity to nine important azoles. In addition, plants inoculated with the insensitive F. culmorum strain showed no reduction of FHB symptoms and deoxynivalenol (DON) content after tebuconazole treatment, compared to an inoculation with the sensitive strain. Use of wheat cultivars carrying a high resistance level (i.e. cv. Toras) was the most effective method for reducing symptoms and decreasing DON content, independent from the level of fungicide insensitivity of the F. culmorum strain. In conclusion, resistant cultivars and a fungicide mixture which combines different mechanisms of action in fungal metabolism should be applied to avoid fungicide insensitivity of Fusarium spp. in future.  相似文献   

13.
Pine root infection by Fusarium circinatum has been reported in the literature, but the underlying pathogenic interaction is poorly understood. A green fluorescent protein (GFP)‐tagged F. circinatum isolate, together with confocal microscopy, was used in order to monitor the events associated with root infection of Pinus radiata seedlings. It was found that in order to reach and successfully infect pine roots, F. circinatum employed features that are similar to those previously described for other root‐infecting pathogens, such as mycelial strands, single runner hyphae and simple hyphopodia as well as other features that are reminiscent of those that are known to be involved in biotrophic invasion, such as bulbous invasive hyphae and filamentous invasive hyphae. Abundant sporulation was observed at the root surface as well as inside tracheids both in roots and in the root collar region. The fungus can spread from the roots to the aerial parts of the plant, and once there, colonization appears to be similar to the process that occurs when the pathogen is inoculated in the stem. Wilting symptoms and plant demise may be the result of a reduction in water uptake by roots and of the blockage of the vascular system by fungal hyphae and resin.  相似文献   

14.
Fusarium head blight and fusarium ear rot diseases of cereal crops are significant global problems, causing yield and grain quality losses and accumulation of harmful mycotoxins. Safety limits have been set by the European Commission for several Fusarium‐produced mycotoxins; mitigating the risk of breaching these limits is of great importance to crop producers as part of an integrated approach to disease management. This review examines current knowledge regarding the role of arthropods in disease epidemiology. In the field, diseased host plants are likely to interact with arthropods that may substantially impact the disease by influencing spread or condition of the shared host. For example, disease progress by Fusarium graminearum can be doubled if wheat plants are aphid‐infested. Arthropods have been implicated in disease epidemiology in several cases and the evidence ranges from observed correlations between arthropod infestation and increased disease severity and mycotoxin accumulation, to experimental evidence for arthropod infestation causing heightened pathogen prevalence in hosts. Fusarium pathogens differ in spore production and impact on host volatile chemistry, which influences their suitability for arthropod dispersal. Herbivores may allow secondary fungal infection after wounding a plant or they may alter host susceptibility by inducing changes in plant defence pathways. Post‐harvest, during storage, arthropods may also interact with Fusarium pathogens, with instances of fungivory and altered behaviour by arthropods towards volatile chemicals from infected grain. Host‐mediated indirect pathogen–arthropod interactions are discussed alongside a comprehensive review of evidence for direct interactions where arthropods act as vectors for inoculum.  相似文献   

15.
Due to its high tolerance to acid rain, the North American Colorado blue spruce (Picea pungens) has been among the most frequent substitute tree species used in reforestation programmes in spruce mountain forests in the Ore and Sudeten Mountains in the Czech Republic after destruction by sulphur dioxide pollution in the second half of the last century. This species was planted on more than 8800 ha of destroyed mountain forest stands in the Ore Mountains alone. New plantations prospered until a massive outbreak of the gemmamyces bud blight, first identified in 2009. The causal agent, Gemmamyces piceae, induced massive bud blight in infected trees – bud loss progressively increased to 70–80% or more, and because the trees were not able to replace the natural loss of older needles, they quickly withered and died. Many plantations disrupted by the pathogen had to be cut down. Although several resistant genotypes have been identified, the cultivation of this species in forest stands has no future in this area. Because this disease was also identified in several ornamental plantations in the area, the bud blight epidemic haunts public green space administrators and nursery and Christmas tree plantation owners. Other pathogens and pests, such as Lophodermium piceae, Sirococcus conigenus and Elatobium abietinum, have also been identified as involved in the damage to P. pungens.  相似文献   

16.
Mycosphaerella leaf disease (MLD) is caused by species of Mycosphaerella and several anamorphic form genera that have been connected to Mycosphaerella. Until recently, MLD of eucalypts was largely ignored in Portugal. However, serious damage to Eucalyptus globulus has been reported since 1999 when frequent and severe defoliation of young trees was observed. The severity of this disease prompted a preliminary study of the Mycosphaerella species associated with major symptoms of a leaf blotch disease in commercial plantations of E. globulus in Portugal, which is presented here. The species were identified by molecular methods based on the ITS1-5.8S-ITS2 cluster, together with morphological characters. In addition to confirming the species previously recorded, Mycosphaerella vespa is reported for the first time from Portugal, while the status of Mycosphaerella grandis remains to be resolved.  相似文献   

17.
Leaf blight, sheath blight, and web blight are major diseases caused by Rhizoctonia species on both Fabaceae and Poaceae plant hosts in the Brazilian Amazon agroecosystem. To determine the diversity of Rhizoctonia species associated with foliar diseases on fabaceous (cowpea and soybean) and poaceous (rice and signal grass [Urochloa brizantha]) hosts, a broad survey was conducted in Pará, Rondônia, Roraima, and Mato Grosso, in the Amazon, from 2012 to 2013. We extended our survey to Cerrado areas of Mato Grosso, and the lowlands of Paraíba Valley, in São Paulo, where these Rhizoctonia foliar diseases have not been reported so far. Our findings revealed that these diseases are caused by a diversity of Rhizoctonia solani AG-1 complex. We detected that R. solani AG-1 IA (sexual phase Thanatephorus cucumeris) was the predominant pathogen associated with signal grass leaf blight and collar rot diseases in the Amazon, especially in Rondônia and northern Mato Grosso. In addition, a subgroup of R. solani (AG-1 IF), not previously reported in Brazil, was associated with leaf blight on cowpea and soybean, in Roraima. Another subgroup (AG-1 ID) was also detected in Roraima. In Mato Grosso Cerrados we did not find any of the major Rhizoctonia foliar pathogens. Instead, R. oryzae (Waitea circinata) was the predominant species associated with a collar rot on U. brizantha. In the lowlands of São Paulo, R. oryzae-sativae (Ceratobasidium oryzae-sativae) was the predominant pathogen detected causing the rice sheath spot disease.  相似文献   

18.
The aim of this study was to examine the disease development of quambalaria shoot blight, caused by the fungal pathogen Quambalaria pitereka, in plantation‐grown spotted gum (Corymbia citriodora subsp. citriodora, C. citriodora subsp. variegata, C. henryi and C. maculata) in south‐east Queensland, Australia. The results showed that native spotted gums are a primary source of inoculum followed rapidly by the production of secondary inoculum from infected trees in the plantation. The rate of spread and development of Q. pitereka within plantations increased exponentially over time as additional trees became infected and produced secondary inoculum. Spore concentration was shown to play an important role in disease development, with disease severity increasing with increasing disease incidence on individual trees and incidence across the plantation.  相似文献   

19.
The control of seedborne rice seedling diseases in the seed beds is important to avoid epidemics in rice nurseries and paddies, which may result in severe yield loss. Recently, irradiation with plasma containing electrons, creating positive or negative ions and neutral species, has been shown to have an antimicrobial effect, probably via generation of reactive oxygen species. This study examines whether two seedborne rice seedling diseases, bakanae disease caused by the fungal pathogen Fusarium fujikuroi, and bacterial seedling blight caused by Burkholderia plantarii, are suppressed by irradiation of infected rice seeds with atmospheric plasma. Seed germination and seedling growth were not inhibited in plasma‐treated healthy seeds. When F. fujikuroi‐infected rice seeds were irradiated with plasma after being immersed in sterile distilled water, bakanae disease severity index and the percentage of plants with symptoms were reduced to 18.1% and 7.8% of non‐irradiated control, respectively, depending on the duration of plasma irradiation. The bacterial seedling blight disease index was also reduced by plasma irradiation in vacuum‐inoculated seeds to 38.6% of the non‐irradiated control, and in infected seeds harvested from spray‐inoculated heads of rice plants to 40.1% of the control. Therefore, plasma irradiation seems to be effective in controlling two independent seedborne rice seedling diseases.  相似文献   

20.
Historical records report Fusarium moniliforme sensu lato as the pathogen responsible for Fusarium diseases of sorghum; however, recent phylogenetic analysis has separated this complex into more than 25 species. During this study, surveys were undertaken in three major sorghum‐producing regions in eastern Australia to assess the diversity and frequency of Fusarium species associated with stalk rot‐ and head blight‐infected plants. A total of 523 isolates were collected from northern New South Wales, southern Queensland and central Queensland. Nine Fusarium species were isolated from diseased plants. Pathogenicity tests confirmed F. andiyazi and F. thapsinum were the dominant stalk rot pathogens, whilst F. thapsinum and species within the F. incarnatum–F. equiseti species complex were most frequently associated with head blight.  相似文献   

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