Phosphite-mediated enhancement of defence responses in Agrostis stolonifera and Poa annua infected by Microdochium nivale

The ascomycete fungus Microdochium nivale is one of the most damaging pathogens of cool season turfgrass. Prevention of and recovery from infection is costly to many sports facilities each year. In recent years, use of many chemical plant protectants has been restricted and turfgrass managers have increasingly sought alternative measures for disease control. The use of phosphite has been shown to be effective in reducing M. nivale disease symptoms in Agrostis stolonifera and Poa annua. The aim of this research was to assess initial defence responses in M. nivale-infected turfgrass, specifically total phenolic content and hydrogen peroxide generation, to determine the effect phosphite treatment has on these responses and on suppression of symptoms. Phenolic compounds and H₂O₂ are shown to be components of host responses. Phosphite treatment led to enhanced accumulations of total phenolic content, and when applied sequentially or singly to greenhouse plants, it led to significant reductions in M. nivale disease symptoms compared to phosphate-treated plants or controls. H₂O₂ extractions indicated that while phosphite treatment increased H₂O₂ generation compared to controls, the effect was no different to the responses in phosphate-treated plants.     

Effect of cold‐induced changes in physical and chemical leaf properties on the resistance of winter triticale (×Triticosecale) to the fungal pathogen Microdochium nivale

This study showed that several mechanisms of the basal resistance of winter triticale to Microdochium nivale are cultivar‐dependent and can be induced specifically during plant hardening. Experiments and microscopic observations were conducted on triticale cvs Hewo (able to develop resistance after cold treatment) and Magnat (susceptible to infection despite hardening). In cv. Hewo, cold hardening altered the physical and chemical properties of the leaf surface and prevented both adhesion of M. nivale hyphae to the leaves and direct penetration of the epidermis. Cold‐induced submicron‐ and micron‐scale roughness on the leaf epidermis resulted in superhydrophobicity, restricting fungal adhesion and growth, while the lower permeability and altered chemical composition of the host cell wall protected against tissue digestion by the fungus. The fungal strategy to access the nutrient resources of resistant hosts is the penetration of leaf tissues through stomata, followed by biotrophic intercellular growth of individual hyphae and the formation of haustoria‐like structures within mesophyll cells. In contrast, a destructive necrotrophic fungal lifestyle occurs in susceptible seedlings, despite cold hardening of the plants, with the host epidermis, mesophyll and vascular tissues being digested and becoming disorganized as a result of the low chemical and mechanical stability of the cell wall matrix. This work indicates that specific genetically encoded physical and mechanical properties of the cell wall and leaf tissues that depend on cold hardening are factors that can determine plant resistance against fungal diseases.     

Fungicide seed treatment efficacy against Microdochium nivale and M. majus in vitro and in vivo

BACKGROUND: Seed-borne Microdochium majus (Wollenweber) and M. nivale Fries are the primary pathogens responsible for Fusarium seedling blight in the UK. The two species show differences in pathogenicity, host preference and sensitivities to temperature, but their relative sensitivities to fungicide seed treatments are unknown. The aim was firstly to determine the efficacy of fungicide seed treatments towards single-spore isolates of M. majus and M. nivale using in vitro experiments, and subsequently to determine efficacy in vivo over a range of temperatures. RESULTS: Differences in EC(50) values between all seed treatments were evident from the in vitro experiments and ranged from 0.028 mg L(-1) for fludioxonil to 22.8 mg L(-1) for carboxin + thiram. The two seed treatments that showed best performance in vitro were used to examine efficacy towards seed-borne infection in vivo at 4, 8, 12 and 16 degrees C. Generally, seedling emergence improved and the severity of stem-base disease symptoms on emerged seedlings was reduced for both species through the use of the fungicides. The combination of fludioxonil + difenconazole showed improved performance compared with fludioxonil alone. Significantly less severe symptoms were observed through the use of fludioxonil and fludioxonil + difenconazole compared with bitertanol + fuberidazole at 12 degrees C and for all except one M. nivale infected seed lot at 8 degrees C. CONCLUSIONS: Differences in fungicide sensitivity between the two species in vitro were not evident in vivo. This is the first report of the effect of fungicide seed treatments on the control of seedling blight caused by M. majus and M. nivale.     

First occurrence of resistance to strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains

BACKGROUND: Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to strobilurins of French isolates of Microdochium and to characterise the possible mechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross‐resistance was observed between all strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of strobilurins. Two other mechanisms were also detected at lower frequencies. CONCLUSION: This is the first report of strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account. Copyright © 2009 Society of Chemical Industry     

Relationship between brown foot rot and DNA of Microdochium nivale, determined by quantitative PCR, in stem bases of winter wheat

Relationships between the incidence and severity of brown foot rot and of pathogenic fungi, determined by diagnostic and quantitative PCR, were investigated during the growth of nine winter wheat crops in three cropping seasons. Microdochium nivale vars nivale and majus were the only brown foot rot pathogens present in significant amounts. Relationships between disease symptoms and amounts of pathogen DNA were often weak in early spring (when shoot-base symptoms are usually most difficult to ascribe to particular pathogens by visual examination) because of indistinct symptoms and small amounts of pathogen. Relationships were strongest during stem elongation. The amount of M. nivale in the tissues tended to decline in the summer as the plants matured, apparently disappearing partially from necrotic lesions to which it contributed, resulting in a weakened relationship between symptoms and pathogen DNA. Regression analyses of brown foot rot on amounts of M. nivale DNA for different wheat cultivars generally produced lines with similar slopes but were often most significant for the cultivar with most eyespot resistance (i.e. with least confounding eyespot) or most apparently genuine brown foot rot. DNA of Fusarium spp. was rarely present in amounts sufficient to quantify.     

Suppression of wheat-seedling diseases caused by Fusarium culmorum and Microdochium nivale using bacterial seed treatment

Snow mould, caused by Microdochium nivale , and seedling blight caused by members of the Fusarium complex, are cereal diseases of great economic importance in many temperate zones. In a glasshouse bioassay designed to enhance disease, about 600 plant-associated bacterial isolates obtained by different methods were screened for suppressive effects in wheat against infection caused by Fusarium culmorum . Although most of the isolates tested had a neutral effect on test plants and disease development, a few were synergistic to the pathogen and about one-fifth showed > 80% disease suppression. During five consecutive growing seasons, 164 bacterial isolates were tested in field experiments against both F. culmorum and M. nivale as causal agents of seedling blight. Tests for effects on yield in experiments with spring and winter wheat, performed in different climatic regions of Sweden, showed that disease-suppressive effects were repeatable. The most efficient isolates, three fluorescent pseudomonads and a species of Pantoea , suppressed disease equal to that of the fungicide guazatine, both with respect to crop stand and yield. Seed treatment with Pantoea sp. (isolate MF 626) increased yield by an average of more than 500 kg ha⁻¹ in six field experiments.     

Suppression of clubroot by Clonostachys rosea via antibiosis and induced host resistance

The mechanism of the biofungicide Prestop^® (Clonostachys rosea) was investigated for control of clubroot (Plasmodiophora brassicae) on canola. The key product components were partitioned and assessed for their effect on pathogen resting spores, root hair infection (RHI) and disease development using light microscopy, quantitative PCR and different application treatments during infection. The whole product of Prestop was consistently more effective than the C. rosea conidial suspension or product filtrate alone in reducing RHI and clubroot development. This biofungicide showed little effect on germination or viability of resting spores. Two‐application treatments at seeding and 7–14 days after seeding achieved greater clubroot control than a single application of the biofungicide at either seeding or post‐seeding stage. This may indicate the need to maintain a high biofungicide dose in the soil during primary and secondary infection. This biocontrol fungus colonized the rhizosphere and interior of canola roots extensively, and possibly induced plant resistance based on up‐regulation of the genes that are involved in jasmonic acid (BnOPR2), ethylene (BnACO) and phenylpropanoid (BnOPCL, BnCCR) biosynthetic pathways. It is concluded that the biofungicide Prestop suppressed clubroot on canola at least via root colonization and induced systemic resistance (ISR), and the latter may be through the modulation of phenylpropanoid and jasmonic acid/ethylene metabolic pathways elicited by the fungus.     

Arabidopsis thaliana,an experimental host for tomato yellow leaf curl disease‐associated begomoviruses by agroinoculation and whitefly transmission

Tomato yellow leaf curl disease is one of the most devastating viral diseases affecting tomato crops worldwide. This disease is caused by several begomoviruses (genus Begomovirus, family Geminiviridae), such as Tomato yellow leaf curl virus (TYLCV), that are transmitted in nature by the whitefly vector Bemisia tabaci. An efficient control of this vector‐transmitted disease requires a thorough knowledge of the plant–virus–vector triple interaction. The possibility of using Arabidopsis thaliana as an experimental host would provide the opportunity to use a wide variety of genetic resources and tools to understand interactions that are not feasible in agronomically important hosts. In this study, it is demonstrated that isolates of two strains (Israel, IL and Mild, Mld) of TYLCV can replicate and systemically infect A. thaliana ecotype Columbia plants either by Agrobacterium tumefaciens‐mediated inoculation or through the natural vector Bemisia tabaci. The virus can also be acquired from A. thaliana‐infected plants by B. tabaci and transmitted to either A. thaliana or tomato plants. Therefore, A. thaliana is a suitable host for TYLCV–insect vector–plant host interaction studies. Interestingly, an isolate of the Spain (ES) strain of a related begomovirus, Tomato yellow leaf curl Sardinia virus (TYLCSV‐ES), is unable to infect this ecotype of A. thaliana efficiently. Using infectious chimeric viral clones between TYLCV‐Mld and TYLCSV‐ES, candidate viral factors involved in an efficient infection of A. thaliana were identified.     

The effect of a mixture of seed-borne Microdochium nivale var. majus and Microdochium nivale var. nivale infection on Fusarium seedling blight severity and subsequent stem colonisation and growth of winter wheat in pot experiments

Greenhouse experiments were conducted in order to determine the impact of seed-borne Microdochium nivale var. nivale and var. majus inoculum, and seed treatment with a carboxin+thiram mixture, on the development of seedling blight, and on subsequent stem colonisation and growth of winter wheat (cv. Cadenza). Experiments were conducted at temperatures favourable (3°C) and unfavourable (22°C) to M. nivale. Seed-borne inoculum resulted in seedling blight symptom development when plants were grown at 3°C, but not when plants were grown at 22°C. For seedlings grown at 3°C, plants arising from heavily blighted seedlings developed more severe symptoms of stem colonisation, when compared with those arising from seedlings from carboxin+thiram treated seeds. In addition, the vigour of such plants (assessed by determining the number of tillers and ears per plant, stem length, green leaf area, dry weight and yield) was also significantly lower than for plants arising from carboxin+thiram treated seeds. Microdochium nivale var. majus and var. nivale appeared to have little effect on plant vigour from seedlings grown at 22°C. This is the first recorded incidence of seedling blight affecting subsequent plant growth. Microdochium nivale var. majus and var. nivale stem colonisation increased from growth stage (GS) 40–49 to harvest in plants raised from seedlings grown at both temperatures. Microdochium nivale var. majus and var. nivale were isolated from the second node at GS 40–49 and the third node at harvest of plants from seedlings grown at 3°C. For plants from seedlings raised at 22°C, M. nivale var. majus and var. nivale were isolated from the first node at GS 40–49 and the second node at harvest. Carboxin+thiram seed treatment decreased the extent and severity of stem colonisation on plants from seedlings grown at 22°C.     

Pathogenic variation of Mycosphaerella species infecting banana and plantain in Nigeria

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.     

Suppression of clubroot (Plasmodiophora brassicae) development in Arabidopsis thaliana by the endophytic fungus Acremonium alternatum

This study investigated the ability of an endophytic fungus Acremonium alternatum to reduce clubroot formation in the model plant Arabidopsis thaliana, which is highly susceptible to Plasmodiophora brassicae . Quantitative PCR demonstrated that A. alternatum colonized the P. brassicae -infected roots and shoots of the host plant. When Arabidopsis plants were co-inoculated with P. brassicae and A. alternatum , gall formation was reduced as shown by the reduction of the disease index (DI) by up to 50% compared to plants only infected with P. brassicae, whereas the infection rate was lowered by about 20% only in several, but not all, experiments. Clubroot was similarly suppressed when plants were inoculated with autoclaved A. alternatum spores or spore extracts, showing that viable spores were not needed. However, A. alternatum spores did not inhibit P. brassicae resting spore germination. Compared to the normal root galls, the smaller root galls on A. alternatum -inoculated plants contained fewer resting spores of the clubroot pathogen. It was thus hypothesized that inoculation with A. alternatum delayed the development of P. brassicae . Using quantitative RT-PCR to monitor the expression of P. brassicae genes differentially expressed during the development of the disease, a delayed pathogen development was corroborated. Furthermore, greenhouse experiments identified a time window in which the endophyte had to be administered, where the latest effective time point was 5 days before inoculation with P. brassicae and the optimum treatment was to administer A. alternatum and P. brassicae at the same time. These results indicate that A. alternatum and perhaps similar endophytes could be useful for the management of clubroot disease.     

Role of co‐infection by Pectobacterium and Verticillium dahliae in the development of early dying and aerial stem rot of Russet Burbank potato

Potato early dying (PED) is a disease complex primarily caused by the fungus Verticillium dahliae. Pectolytic bacteria in the genus Pectobacterium can also cause PED symptoms as well as aerial stem rot (ASR) of potato. Both pathogens can be present in potato production settings, but it is not entirely clear if additive or synergistic interactions occur during co‐infection of potato. The objective of this study was to determine if co‐infection by V. dahliae and Pectobacterium results in greater PED or ASR severity using a greenhouse assay and quantitative real‐time PCR to quantify pathogen levels in planta. PED symptoms caused by Pectobacterium carotovorum subsp. carotovorum isolate Ec101 or V. dahliae isolate 653 alone included wilt, chlorosis and senescence and were nearly indistinguishable. Pectobacterium wasabiae isolate PwO405 caused ASR symptoms including water‐soaked lesions and necrosis. Greater Pectobacterium levels were detected in plants inoculated with PwO405 compared to Ec101, suggesting that ASR can result in high Pectobacterium populations in potato stems. Significant additive or synergistic effects were not observed following co‐inoculation with these strains of V. dahliae and Pectobacterium. However, infection coefficients of V. dahliae and Ec101 were higher and premature senescence was greater in plants co‐inoculated with both pathogens compared to either pathogen alone in both trials, and V. dahliae levels were greater in basal stems of plants co‐inoculated with either Pectobacterium isolate. Overall, these results indicate that although co‐infection by Pectobacterium and V. dahliae does not always result in significant additive or synergistic interactions in potato, co‐infection can increase PED severity.     

Involvement of FgMad2 and FgBub1 in regulating fungal development and carbendazim resistance in Fusarium graminearum

Resistance to carbendazim of Fusarium graminearum is conferred by point mutation in the β₂‐tubulin gene that plays an important role in spindle assembly. The spindle assembly checkpoint is a cellular surveillance system that is critical for maintaining genomic stability. Predicted protein Mad2‐ and Bub1‐encoding genes in F. graminearum (FgMad2 and FgBub1) were isolated and characterized. There was no difference in FgMad2 and FgBub1 expression levels between carbendazim‐sensitive and ‐resistant strains; however, after carbendazim treatment FgMad2 expression increased while FgBub1 expression stayed the same. Both the FgMad2 and FgBub1 deletion mutants became more sensitive to carbendazim. The FgMad2 deletion mutants grew more slowly, produced fewer conidia and both hyphae and conidia were malformed. Conversely, deletion of FgBub1 had no effect on fungal development other than a reduction in conidia production. FgMad2 deletion mutants exhibited a severe decrease in perithecia production and pathogenicity along with a down‐regulation of trichothecene production, whereas FgBub1 deletion mutants exhibited only a slight reduction in perithecia production and was accompanied by a twofold increase in trichothecene production. Overall, the results indicate that both FgMad2 and FgBub1 are involved in carbendazim resistance and trichothecene biosynthesis, and FgMad2 plays an important role in fungal development in F. graminearum.     

Control of Microdochium majus in winter wheat with botanicals – from laboratory to the field

The fungal pathogen Microdochium majus, causing snow mould, seedling blight and foot rot, results in severe yield losses in small grain cereals. There are few options to control this pathogen in organic production. In this study, aqueous extracts or botanical powders prepared from chamomile, meadowsweet, thyme and Chinese galls were tested in vitro against M. majus conidia germination and mycelial growth, respectively. Subsequently, three botanicals were chosen, applied as powders with different seed coating adhesives, and tested for their effect on the incidence of M. majus from naturally infected wheat seed lots and on seedling emergence from soil under controlled environmental conditions. Furthermore, seed treatments with warm water, a bacterial product or one chosen botanical were tested in a growth chamber and in a field experiment over three consecutive years. Of the botanicals tested, Chinese galls showed the highest efficacy in controlling M. majus, reducing conidia germination and mycelial growth by up to 97 and 100%, respectively, and reducing the incidence from infested seeds by up to 59%. In two growth chamber experiments, total seedling emergence increased by up to 30 and 59% compared with the control treatments following an application with Chinese galls. Under field conditions, yield increase through Chinese galls, the bacterial product and the warm water treatment was 19, 10 and 37% compared with the untreated control, respectively. This study demonstrates the potential of Chinese galls to control M. majus in wheat. Options for improved formulations or combinations of heat‐based treatments with Chinese galls are discussed.     

Isolation and characterization of Streptomyces species from potato common scab lesions in Norway

The present survey was conducted to isolate and characterize Streptomyces species from common scab lesions of potato in Norway. Bacteria were isolated from scab lesions on tubers sampled in two consecutive years at different locations in Norway spanning ～1400 km from south to north. In total, 957 independent isolations from individual tubers were performed, with 223 putative pathogenic isolates obtained from 29 different potato cultivars and 130 different fields. Streptomyces europaeiscabiei was the most abundant species isolated from common scab lesions (69%), while 31% of the isolates obtained were S. turgidiscabies. Streptomyces scabies was not found. Pathogenicity of selected Streptomyces isolates was tested on potato. The ability of the bacterial isolates to infect potato was consistent with the presence of the txtAB operon. The results revealed no pattern in geographical distribution of S. europaeiscabiei and S. turgidiscabies; both could be found in the same field and even the same lesion. Four different pathogenicity island (PAI) genotypes were detected amongst the txtAB positive isolates: nec1+/tomA+, nec1–/tomA+, nec1+/tomA? and nec1?/tomA?. The current findings demonstrate that there is genetic variability within species and that the species are not spread solely by clonal expansion. This is thought to be the most comprehensive survey of Streptomyces species that cause common scab of potato in a European country.     

Spatial genetic structure and dispersal of the cacao pathogen Moniliophthora perniciosa in the Brazilian Amazon

Moniliophthora perniciosa is the causal agent of witches’ broom in Theobroma cacao (cacao). Three biotypes of M. perniciosa are recognized, differing in host specificity, with two causing symptoms on cacao or Solanaceae species (C‐ and S‐biotypes), and the third found growing endophytically on lianas (L‐biotype). The objectives of this study were to clarify the genetic relationship between the three biotypes, and to identify those regions in the Brazilian Amazon with the greatest genetic diversity for the C‐biotype. Phylogenetic reconstruction based on the rRNA ITS regions showed that the C‐ and S‐biotypes formed a well‐supported clade separated from the L‐biotype. Analysis of 131 isolates genotyped at 11 microsatellite loci found that S‐ and especially L‐biotypes showed a higher genetic diversity. A significant spatial genetic structure was detected for the C‐biotype populations in Amazonia for up to 137 km, suggesting ‘isolation by distance’ mode of dispersal. However, in regions containing extensive cacao plantings, C‐biotype populations were essentially ‘clonal’, as evidenced by high frequency of repeated multilocus genotypes. Among the Amazonian C‐biotype populations, Acre and West Amazon displayed the largest genotypic diversity and might be part of the centre of diversity of the fungus. The pathogen dispersal may have followed the direction of river flow downstream from Acre, Rondônia and West Amazon eastward to the rest of the Amazon valley, where cacao is not endemic. The Bahia population exhibited the lowest genotypic diversity, but high allele richness, suggesting multiple invasions, with origin assigned to Rondônia and West Amazon, possibly through isolates from the Lower Amazon population.     

Flooding affects the development of Plasmodiophora brassicae in Arabidopsis roots during the secondary phase of infection

Clubroot, a disease of Brassicaceae species, is caused by the soilborne pathogen Plasmodiophora brassicae. High soil water content was previously described to favour the motility of zoospores and their penetration into root cells. In this study, the effect of irrigation regimes on clubroot development during the post‐invasive secondary phase of infection was investigated. Three irrigation regimes (low, standard, high) were tested on two Arabidopsis accessions, Col‐0 (susceptible) and Bur‐0, a partially resistant line. In Col‐0, clubroot symptoms and resting spore content were higher under the ‘low irrigation’ regime than the other two regimes, thus enhancing the phenotypic contrast between the two Arabidopsis accessions. Clubroot severity under high and low irrigation regimes was evaluated in near‐isogenic lines derived from a Col‐0 ×  Bur‐0 cross, to assess the effect of soil moisture on the expression of each of four quantitative trait loci (QTL) controlling partial resistance. The presence of the Bur‐0 allele at the QTL PbAt5.2 resulted in reduced severity only under low irrigation, whereas the Bur‐0 allele at QTL PbAt5.1 was associated with partial resistance only under high irrigation. QTL PbAt4 reduced the number of resting spores in infected roots, but was not associated with reduced clubroot symptoms. The results indicated that soil moisture could have consequences for the secondary phase of clubroot development, depending on plant genotype. Future genetic studies may benefit from using combinations of watering conditions during the secondary stage of infection, thus opening up the possibility of identifying genetic factors expressed under specific environmental conditions.     

Effect of wheat spike infection timing on fusarium head blight development and mycotoxin accumulation

Fusarium head blight in wheat spikes is associated with production of mycotoxins by the fungi. Although flowering is recognized as the most favourable host stage for infection, a better understanding of infection timing on disease development and toxin accumulation is needed. This study monitored the development of eight characterized isolates of F. graminearum, F. culmorum and F. poae in a greenhouse experiment. The fungi were inoculated on winter wheat spikes before or at anther extrusion, or at 8, 18 and 28 days later. Disease levels were estimated by the AUDPC and thousand‐kernel weight (TKW). The fungal biomass (estimated by qPCR) and toxin concentration (deoxynivalenol and nivalenol, estimated by UPLC‐UV‐MS/MS) were measured in each inoculated spike, providing a robust estimation of these variables and allowing correlations based on single‐individual measurements to be established. The toxin content correlated well with fungal biomass in kernels, independently of inoculation date. The AUDPC was correlated with fungal DNA, but not for early and late infection dates. The highest disease and toxin levels were for inoculations around anthesis, but early or late infections led to detectable levels of fungus and toxin for the most aggressive isolates. Fungal development appeared higher in kernels than in the chaff for inoculations at anthesis, but the opposite was found for later inoculations. These results show that anthesis is the most susceptible stage for FHB, but also clearly shows that early and late infections can produce significant disease development and toxin accumulation with symptoms difficult to estimate visually.     

Disease protection and growth promotion of potatoes (Solanum tuberosum L.) by Paenibacillus dendritiformis

One of the challenges in developing plant‐beneficial bacterial agents for agricultural application is ensuring that an effective selection and screening procedure is in place. The sporadic success of using bacterial agents in the field is usually due to the inability of added bacteria to compete with the local microorganisms. In the present study, the effectiveness of Paenibacillus dendritiformis, a unique pattern‐forming, Gram‐positive, soil bacterium, to reduce disease indices and increase yield in potato crops was examined. This bacterium was chosen as a potential agent based on genome analysis carried out in previous studies. In vitro laboratory experiments, as well as three greenhouse and one field experiment, were conducted. The results show that, in agreement with the hypothesis, P. dendritiformis significantly reduced the maceration area of tuber slices infected by Pectobacterium carotovorum subsp. carotovorum, significantly reduced disease indices in greenhouse experiments and significantly increased tuber yield of infected plants in the field. This work demonstrates the potential of preliminary screening based on genome analysis to identify effective biocontrol agents.