569 research outputs found
Genetics of resistance to Stemphylium leaf blight of lentil (Lens culinaris) in the cross barimasur-4 x CDC milestone
Stemphylium blight of lentil caused by Stemphylium botryosum Wallr., is a serious problem in Bangladesh, northeast India and Nepal causing more than 60 % yield losses under epidemic conditions. The pathogen started to appear on lentil in Saskatchewan in recent years and is widely distributed throughout western Canada but it is not well understood. An investigation of inheritance of resistance to stemphylium blight was done in the lentil cross Barimasur-4 × CDC Milestone. In order to develop a reliable indoor screening technique for this inheritance study, a suitable isolate of Stemphylium botryosum, a suitable culture medium for inoculum production and an appropriate plant age for indoor inoculation were identified. The maximum differential of disease severity was observed when lentil genotypes were inoculated at 14 days after planting (DAP). At 14 DAP, lentil plants rapidly defoliated but were capable of regrowth which caused variability in scoring for disease reaction. Inoculation at 42 DAP, close to the flowering stage, was found to be better for consistently scoring disease reaction. V8P medium was most suitable for inducing conidia production. Based on ability to sporulate, the isolate SB-19 from Saskatchewan was identified as suitable for conducting genetic studies of resistance to stemphylium blight. It was compared to isolate SB-BAN from Bangladesh for aggressiveness on two lentil cultivars. The SB-BAN isolate was found to be more aggressive. A preliminary screening of local and exotic germplasm done with the two isolates revealed considerable variability for disease resistance. Resistance to S. botryosum appeared to be quantitatively inherited in the cross Barimasur-4 × CDC Milestone according to both field and indoor screenings. The results of this study also confirmed that Precoz, one of the parents of Barimasur-4, was resistant to S. botryosum
Field-applied fungicides and postharvest treatments to control asparagus diseases posing biosecurity threats to New Zealand
Collaborative research between New Zealand and Australia has investigated field-applied fungicides and postharvest treatments for control of asparagus rust (caused by Puccinia asparagi) and phomopsis stem blight of asparagus (caused by Phomopsis asparagi) in Queensland. In a 2004 field trial, the fungicides difenoconazole and propiconazole reduced the incidence of asparagus rust. In a 2005 field trial, four fungicides (carbendazim, chlorothalonil, iprodione and propiconazole) reduced the severity of phomopsis stem blight. Postharvest disinfection with sodium hypochlorite or with calcium hypochlorite at 150 ppm was highly effective at reducing Pu. asparagi and Ph. asparagi spore germination on water agar. Integrated disease management based on field and postharvest methods are suggested to reduce the risk of importation of the diseases to New Zealand. Similar methods could be used for controlling these diseases if they establish
Ecological interactions of Fusarium species and the meal beetle <em>Tenebrio molitor</em>
Contamination of stored grains by moulds and their mycotoxins results in quality and nutritional reduction. Ingestion of contaminated products and feed poses a significant hazard to human and animal health. The moulds deterioration and storage insects are of major concern in poor post-harvest management conditions. Theinteractions between the storage moulds (Fusarium spp.) and insects (T. molitor) are bilateral.Fusarium species colonized wheat kernels affected the feeding behaviors, weight gain and survival rate of T. molitor mature larvae. Wheat kernels colonized by F. proliferatum and F. poae attracted T. molitor larvae significantly more than untreated (control) kernels; whereas kernels colonized with F. avenaceum or Beauveria bassiana were avoided by the larvae. However, larvae fed on F. culmorum, F. avenaceum or B. bassiana colonized kernels had enhanced larvae mortality. Our results indicated that T. molitor larvae have the ability to sense potential survival threats of kernels colonized with F. avenaceum or B. bassiana.T. molitor acted as vehicle for Fusarium spp.dissemination within grains. After feeding on Fusarium mycelia and conidia for 24 h, live conidia were traceable in beetles’ excreta. Beetles were capable of contaminating a high proportion of wheat kernels up to 20 days. Kernels contamination and fungal colony forming unit density of F. proliferatum were higher than other tested Fusarium species. T. molitor beetles disseminated tested Fusarium fungal conidia internally and externally. Fungal contamination by beetle copulation to eggs was first described in our present research.F. proliferatum drew our research attention for its attracting meal beetles property. Pathogenicity of different F. proliferatum strains on T. molitor was assessed according to mortality on 4th instar larvae. Radiate growth rate, sporulation, and DNA biomass in larvae tissue were evaluated as parameters to determine the contribution to pathogenicity. For pathogenicity on wheat plants, we demonstrated that F. proliferatum strains can systemically colonize the wheat plant (cv. Taifun) from soak-inoculation of mature wheat seeds to stem, leaf and then to wheat kernels. The pathogenicity on T. molitor larvae and wheat plants was not consistent, which indicated different pathogenicity mechanisms.Ökologische Interaktion zwischen Fusarium Spezies und dem Mehlkäfer T. molitor Die Kontamination eingelagerten Getreides mit Vorratspilzen und deren Mykotoxinen sowie der Befall mit Vorratsschädlingen führen zur Minderung von Qualität und Nährwert. Durch die Aufnahme kontaminierter Nahrungs- und Futtermittel entstehen erhebliche Gefahren für die menschliche und tierische Gesundheit. Die Interaktionen zwischen Vorratspilzen (Fusarium spp.) und Insekten (T. molitor) sind bilateral. Von Fusarium besiedelte Weizenkörner beeinflussten Nahrungsaufnahme, Gewichtszunahme und Überlebensrate von T. molitor Larven. Von F. proliferatum und F. poae befallene Körner lockten signifikant mehr T. molitor Laven an als unbehandelte Körner, während Körner mit F. avenaceum oder Beauveria bassiana von den Larven gemieden wurden. Larven, die mit F. culmorum, F. avenaceum oder B. bassiana befallen Körner gefressen hatten, wiesen eine höhere Sterblichkeit auf. Unsere Ergebnisse deuten darauf hin, dass T. molitor Larven die Fähigkeit haben, potentielle Schadwirkungen von Körnern mit F. avenaceum oder B. bassiana zu erkennen. T. molitor fungierte als Vehikel für Fusarium spp. Nachdem die Käfer 24 h mit Fusarium Myzel und Konidien gefüttert worden waren, waren lebende Konidien in ihren Exkrementen nachweisbar. Die Käfer waren 20 Tage lang in der Lage, große Anteile exponierter Weizenkörner zu kontaminieren. Die Menge der durch die Käfer kontaminierten Weizenkörner und die Dichte der koloniebildenden Einheiten waren bei F. proliferatum höher als bei den anderen untersuchten Fusarium Spezies. T. molitor verbreitete die Konidien von Fusarium intern und extern. Die Kontamination von Eiern durch die Kopulation wird erstmals in unserer vorliegenden Arbeit beschrieben. Die Pathogenität verschiedener F. proliferatum Stämme wurde anhand der Sterblichkeitsrate des vierten Larvenstadiums von T. molitor bewertet. Als Parameter der Pathogenität wurden radiale Wachstumsrate, Sporulation und Pilz-DNA in Larvengewebe untersucht. Es konnte gezeigt werden, dass F. proliferatum Stämme in der Lage sind, ausgehend von einer Tauchinokulation von Saatgut die daraus entstehenden Pflanzen systemisch über Stängel und Blätter bis zu den Körnern zu besiedeln. Die Pathogenität für Weizenpflanzen korrelierte nicht mit der für T. molitor Larven, was auf unterschiedliche Mechanismen der Pathogenität hinweist
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Biological management of Fusarium crown rot of asparagus seedlings with saprophytic microorganisms.
Thesis (M.S.
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Interactions between clonal asparagus plantlets and virulent and avirulent isolates of Fusarium.
Fusarium oxysporum was isolated most frequently, followed by F. moniliforme, and F. solani from infected asparagus plants grown in the field. In pathogenicity tests both with seedlings and plantlets, F. moniliforme showed slightly higher virulence than Fusarium oxysporum did in general. Fusarium moniliforme showed more consistent virulence on both seedlings and plantlets than F. oxysporum did. Fusarium oxysporum showed slightly higher virulence on plantlets than on seedlings. Fusarium solani showed very weak or no sign of virulence on seedlings and plantlets, respectively, in both tests. In protection tests with plantlets, most protection of asparagus against virulent fusarial infections occurred when challenge isolates were inoculated five or seven days after inoculation of protective fusarial species. Avirulent F. oxysporum was a more effective protective agent against infection of F. moniliforme than it was against F. oxysporum. Fusarium solani was more effective against infection of F. oxysporum than it was against F. moniliforme. Virulent fusarial species showed significant increase in conidial populations on asparagus plantlet root and stem segments, and showed higher root and stem rot ratings than avirulent fusarial species did. Avirulent fusarial species showed minimal increase in conidial populations on both root and stem segments, and showed low to very low root and stem rot ratings. All fusarial species infected asparagus plantlets through primary and lateral root tips, natural wounds, and between the walls of the epidermal cells directly. Some penetration was appressorium-like and direct. It was assumed that the meristematic region could act as a major infection site. Virulent fusarial species were growing faster and more abundantly inside and outside of the plantlet epidermal areas than were avirulent fusarial species. Fusarium solani was the slowest growing species. Within a short period, virulent fusarial species caused cortical rots. However, over extended periods, they invaded tracheary elements eventually, and caused extensive damages. Avirulent F. oxysporum accumulated heavily on and around the epidermal areas even if it invaded part of cortical cells inside the epidermal regions. Fusarium solani caused proliferation of lateral roots and increased the surface area of primary and secondary roots
Characterization of the stemphylium blight pathogens and their effect on lentil yield
The disease stemphylium blight has become common in lentil fields in Saskatchewan, but the effect of this disease on developing lentil plants, has not been studied under field conditions. Even though Stemphylium botryosum is suspected to be the pathogen causing stemphylium blight in lentil around the world, there is no confirmation of the pathogenic species involved in stemphylium blight of lentil in Saskatchewan. The objectives of this study were to determine the effect on lentil seed quantity and quality of S. botryosum infection at the seedling, the early-flowering, the mid-flowering or the podding stages, and to characterize the pathogen or pathogens causing stemphylium blight in Saskatchewan lentil fields.
Three field experiments were conducted over two years using green polyethylene low tunnels to create conducive environments and control the timing of infection. Cumulative disease severity, measured as area under the disease progress curve, in lentil treatments inoculated at the seedling stage was higher compared to treatments inoculated at later growth stages or to uninoculated control treatments, in which some stemphylium blight developed due to natural inoculum. Neither the amount of harvested seed, nor seed weight or seed size were reduced compared to the uninoculated control, even though disease severity was higher in inoculated versus uninoculated treatments. Seed infection levels of 2.6 to 3.4% in seed harvested from treatments that were inoculated at the seedling, early and mid-flower stages were significantly higher than those observed in seeds from uninoculated control treatments (0.6%) or from treatments inoculated at podding (1.2%).
Field isolates of Stemphylium spp. were compared to the ex-type isolate by morphology, and additionally to sequence data of five Stemphylium spp. and one Alternaria sp. obtained from GenBank by molecular phylogenetic analyses of the internal transcribe spacer (ITS) and the glyceraldehyde 3 – phosphate dehydrogenase (gpd) gene regions. Morphology of colony and conidia were not informative since features overlapped except for three isolates. Results of the molecular phylogenetic analyses revealed that S. botryosum is one of two possible Stemphylium spp. involved in the development of stemphylium blight in lentil. The three isolates with different morphology were also consistently clustered as a species distinct from the Stemphylium species.
Although yield loss could not be demonstrated here, further studies on the epidemiology of the pathogens causing stemphylium blight in Saskatchewan lentil fields are warranted in view of the fact that more than one candidate species was identified as the causal agent
Epidemiology of Stemhylium blight on lentil (Lens culinaris) in Saskatchewan
Stemphylium blight is a defoliating fungal disease caused by Stemphylium botryosum. It has become more prevalent in Saskatchewan. Although not much is known about the biology of the fungus, increasing lentil (Lens culinaris) yield losses of up 62% have been reported in Bangladesh and India. The infection of lentil by S. botryosum was investigated under a range of temperatures (5 to 30°C), wetness periods (0 to 48 h) and wetness periods interrupted by dry periods of 6 to 24 h. The experiments involved testing the impact of environmental conditions on germination of conidia on glass slides and stemphylium blight infection on lentil (cv. CDC Milestone). Generalised linear models and non-parametric tests were used to determine the effects of these factors on conidial germination and disease development. Infection levels increased with increasing temperature and wetness duration. A latent period of 48 h was observed at 25°C and 30°C under continuous wetness. The duration of the latent period increased with decreasing temperatures and decreasing wetness duration. S. botryosum required warm temperatures (above 25°C) and a minimum wetness period of 8 h for optimal disease development. Low levels of infection were observed within the first 2 h of incubation at 10°C and increased with longer wetting periods up to 48 h and temperatures up to 30°C. The pathogen could maintain infectivity during interrupted wetness periods despite its requirement for prolonged wetness periods. Infection levels were not significantly affected by interrupting dry periods of 6 to 24 h although long dry periods (24 h) combined with higher temperatures (30°C) resulted in a decrease in stemphylium blight severity. Germination studies on glass slides supported these findings. Response surface models were developed that provided a good fit for the response of conidial germination to temperature and wetness duration. The coefficients of determination for the regression of observed against predicted effects ranged from 0.88 to 0.97. The general additive model could also be used to predict stemphylium blight severity responses to temperature and wetness duration (scaled deviance = 1.04). However, that model tended to overestimate infection levels especially at lower temperatures. The coefficients of determination for the observed against predicted effects at 5 to 30ºC ranged from 0.77 to 0.92 for the general additive model
Comparative Metabolome and Transcriptome Analyses of Susceptible Asparagus officinalis and Resistant Wild A. kiusianus Reveal Insights into Stem Blight Disease Resistance.
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Ecology and Management of Stemphylium Leaf Spot of Spinach
Stemphylium leaf spot of spinach has re-emerged as a disease of economic concern for fresh market, processing, and seed production. The two main causal agents, Stemphylium beticola and S. vesicarium, are seedborne and seed transmitted. The overall objective of this study was to elucidate the biology and epidemiology of these pathogens, and to refine management options for the disease by: i) identifying Stemphylium species and development of their teleomorphs associated with Stemphylium leaf spot in spinach seed crops, and species colonizing seed grown in key countries of seed production; ii) screening spinach cultivars for resistance to S. vesicarium; iii) determining the prevalence of resistance to the fungicides azoxystrobin and pyraclostrobin that have been used widely to control this disease; iv) evaluating genetic differences of pathogenic vs. non-pathogenic seedborne isolates of S. vesicarium; and v) sequencing the genome of S. beticola isolates to complement genomes available for S. vesicarium. Isolates of S. beticola, S. vesicarium, and S. drummondii were pathogenic to spinach, but eight other Stemphylium species associated with spinach were not. Cultivars with resistance to S. vesicarium were identified for fresh market and processing spinach production. In vitro and in vivo assays confirmed resistance to azoxystrobin and pyraclostrobin for all spinach leaf and seed isolates of S. vesicarium tested, but not isolates of S. beticola. Resistant isolates all had the G143A mutation in the cytochrome b gene that confers this resistance. The proportion of seedborne S. vesicarium isolates pathogenic to spinach varied among seed lots, and was negatively correlated with genetic diversity of the isolates. Seed populations of S. vesicarium were structured genetically based on pathogenicity to spinach, not by seed lot or country of seed production. Genotypes of pathogenic S. vesicarium isolates from leaf spots were detected on seed lots used to plant the crops, and seed populations were more diverse genetically than foliar populations. The sequenced genomes of two S. beticola isolates from spinach will facilitate genetic comparison of species that cause Stemphylium leaf spot, and development of molecular detection tools. This research provides new insights into Stemphylium leaf spot of spinach with implications for enhanced management of this disease
Arbuscular mycorrhizal fungi
The potential disease suppressiveness of arbuscular mycorrhizal (AM) fungi of various origins on Bipolaris sorokiniana in barley has been investigated. Firstly, a survey considering the occurrence of AM fungi in arable fields in Sweden were conducted with the aim to exploit site specific genetic resources in relation to disease suppressiveness. Arbuscular mycorrhizal fungi were present at all 45 sampling sites surveyed all over Sweden at densities ranging from 3 up to 44 spores per gram air dried soil. The highest spore density was found in a semi-natural grassland and the lowest were found in a cereal monoculture. The AM fungi were then multiplied in trap cultures in the greenhouse with the aim to use these for studying potential disease suppressiveness. Thus, the effects of the AM fungi trap cultures on the transmission of seed-borne B. sorokiniana in barley were investigated, using the trap culture inocula, but also including inocula consisting on spore mixtures. The arbuscular mycorrhizal fungi were able to suppress the transmission of B. sorokiniana in aerial parts of barley plants. The degree of suppression varied with the origin of the AM fungal trap cultures. The trap culture inoculum with the highest suppression of the B. sorokiniana transmission originated from an organically managed barley field with undersown ley. The two spore-inocula with the best suppression of the pathogen originated from fields with winter wheat and spring barley, respectively. Eventually, an in vitro method was developed for studying the effect of AM fungal colonisation of roots on the development of foliar diseases and the reaction of the actual host plant of the disease causing organism. Using the developed method, it was indicated that AM fungal colonisation of barley plant suppressed the development of leaf necroses due to B. sorokiniana. Further in vitro studies on the interaction between B. sorokiniana and arbuscular mycorrhizal fungi showed that B. sorokiniana decrease the germination of the AM fungal spores. In conclusion, AM fungi suppress the development of B. sorokiniana in barley. My data suggest that for biocontrol of B. sorokiniana AM fungi should be considered
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