Crown Rot Disease Research Articles

Influence of native endophytic bacteria on the growth and bacterial crown rot tolerance of papaya (Carica papaya)

The native plant microbiome is composed of diverse microbial communities that influence overall plant health, with some species known to promote plant growth and pathogen resistance. Here, we show the antibacterial and growth promoting activities of autoclaved culture metabolites (ACM) from native endophytic bacteria (NEB). These NEB were isolated from a papaya cultivar (var. Cariflora) that is tolerant to bacterial crown rot (BCR) caused by Erwinia mallotivora. In this cultivar, bacterial colonization in tissues recovering from the disease was observed before onset of tissue regeneration or ‘regrowth’. We further isolated and characterized these bacteria and were able to identify two culturable stem NEB related to plant endophytic genera Kosakonia sp. (ex. Enterobacter sp., isolate EBW), and to Sphingomonas sp. (isolate EBY). We also identified root NEB under genus Bacillus (isolates BN, BS, and BT). Inhibition assays indicated that ACM from these NEB promptly (within 18-30 h) and efficiently inhibited (60–65% reduction) E. mallotivora proliferation in vitro. When surface-sterilized papaya seeds were soaked in ACM from isolates EBY and EBW, germination was variably retarded (20–60% reduction) depending on plant genotype, but plant biomass accumulation was significantly stimulated, at around two-fold increase. Moreover, greenhouse experiments show that ACM from all isolates, especially isolate EBW, significantly reduced BCR incidence and severity in a susceptible genotype (var. Solo), at around two-fold. In general, our observations of pathogen antagonism and plant growth promotion leading to disease reduction, suggested the influence of native endophytic bacteria to increased fitness in plants, and tolerance against the re-emerging crown rot disease of papaya.

Relation Between Resistance to Leaf Rust and Fusarium Crown Rot Diseases in Some Egyptian Wheat Cultivars

Wheat (Triticum aestivum L) is the most important cereal crop worldwide. It is responsible for providing more than 40% of humans with their nutritional requirements from carbohydrates and other essential nutrients. Unfortunately, its attacked by different various air and soil borne pathogens which resulted in massive losses in both yield quantity and quality. In Egypt, wheat is not only just a nutritional cereal crop, but it is considered the food security key. There is a huge gap between the wheat grain production and national consumption levels. Therefore, saving each grain from wheat production deemed urgent need. Using resistant cultivars against important invaded pathogens is considering one of the most effective and relevant techniques that can be used in the battle between plant pathologists and hazardous pathogen i.e. Puccinia triticina and Fusarium pseudograminiarum. In the current study, the resistance potential of 29 different Egyptian wheat cultivars was assessed against 3 leaf rust races and crown rot disease individually. The results showed that the tolerance potential of the tested cultivars toward either P. triticina or F. pseudograminiarum was varied significantly. Also, the relation between the incidences of the two diseases was estimated. Results indicating that there are a positive correlation between incidence of leaf rust and incidence of crown rot diseases. These findings could lead to designing special models which can be used in the prediction of the incidence by one of the two pathogens when the other attacks the wheat plants.

Antagonistic effectiveness of some bacteria against Fusarium graminearum causing crown rot disease on wheat (Triticum aestivum)

In this study, the antagonistic effect of five bacteria genera namely Bacillus, Pseudomonas, Azotobacter, Azospirillum, and Streptomyces isolated from rhizosphere of wheat were evaluated against Fusarium graminearum as potential biocontrol agents in vitro. F. graminearum was molecularly diagnosed using the Polymerase chain reaction (PCR) technique. Each bacteria were tested for the production of catalase enzyme, oxidase enzyme, analysis of starch, analyze of gelatin, and the motility, where Azotobacter, Azospirillum, and Bacillus subtilis were positive for all tested. Fungal inhibition tests were performed by using the dual culture method and agar well diffusion technique. Among them, Streptomyces and Azospirillum exhibited potent inhibition to the growth of F. graminearum (72.14% and 66.42%) respectively, followed by B.pumillus, P.fluorescens, B. subtilis and Azotobacter ( 58.28%, 43.23%, 39.71% and 35.71%) respectively as compared with the control treatment (0.0%).The dry weight of the fungus biomass was decreased with bacteria P. fluorescens, Streptomyces sp, Azotobacter sp, Azospirillum sp, B. subtilis, and B. pumillus which reached (0.114, 0.103, 0.147, 0.101, 0.143, and 0.107 g) respectively compared to the control treatment that was 0. 665 g.

Effects and Mechanisms of Symbiotic Microbial Combination Agents to Control Tomato Fusarium Crown and Root Rot Disease.

This study evaluated the effects and underlying mechanisms of different combinations of plant symbiotic microbes, comprising arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), and Trichoderma spp., on tomato Fusarium crown and root rot (TFCRR) resistance. A total of 54 treatments were applied in a greenhouse pot experiment to tomato (Solanum lycopersicum) seedlings inoculated with or without Funneliformis mosseae (Fm), Rhizophagus intraradices (Ri), Trichoderma virens l40012 (Tv), Trichoderma harzianum l40015 (Th), Bacillus subtilis PS1-3 (Bs), Pseudomonas fluorescens PS2-6 (Pf), and Fusarium oxysporum f. sp. radicis-lycopersici (Fo). The symbioses on the tomato root system were well developed, and the composite symbiont generated by AMF + Trichoderma spp. was observed for the first time. Compared with other treatments, Ri + Bs + Tv and Fm + Pf + Tv stimulated the greatest improvements in tomato growth and yield. The combination Ri + Pf + Th + Fo resulted in the strongest biocontrol effects on TFCRR, followed by the treatments Th + Pf + Fo and Ri + Th + Fo. Compared with the Fo treatment, most inoculation treatments improved photosynthetic performance and significantly increased defense enzyme activity in tomato plants, of which the treatment Ri + Pf + Th + Fo showed the highest enzyme activity. Metabolome analysis detected changes in a total of 1,266 metabolites. The number of up-regulated metabolites in tomato plants inoculated with Ri + Pf + Th and Ri + Pf + Th + Fo exceeded that of the Fo treatment, whereas the number of down-regulated metabolites showed the opposite trend. It is concluded that AMF + Trichoderma + PGPR is the most effective combination to promote resistance to TFCRR in tomato. The up-regulation and down-regulation of metabolites regulated by symbiotic microbial genes may be an important mechanism by which root symbiotic microorganisms promote plant growth, increase yield, and improve disease resistance.

Biofumigation With Pellets of Defatted Seed Meal of Brassica carinata: Factors Affecting Performance Against Phytophthora nicotianae in Pepper Crops

Phytophthora nicotianaeis the pathogen that causes root and crown rot disease in open field paprika pepper crops of Extremadura (central-western Spain). A field experiment was established during spring, a period compatible with the pepper crop cycle in this region, to evaluate the effects of biofumigation with pellets ofBrassica carinatadefatted seed meal, at the rate recommended by the manufacturer (3 tons ha−1), on the survival and infectivity ofP. nicotianaechlamydospores inoculum. Furthermore, three biofumigant rates (3, 6, and 20 tons ha−1) were assayed in laboratory experiments with natural soil inoculated with chlamydospores. In the field trial, the incorporation of pellets at 3 tons ha−1did not produce remarkable changes in soil enzyme activity or soil properties. In both the field and laboratory tests, survival and infectivity in the biofumigated treatment at 3 tons ha−1did not differ from those in the untreated control. On the contrary, the same rate added to autoclaved soil completely suppressed the inoculum, suggesting that the soil microbiota degradesB. carinatapellets before being effective againstP. nicotianae. Increasing the recommended rate to 6 tons ha−1decreased inoculum survival in the laboratory test and 20 tons ha−1completely inhibited the inoculum, although the economic value of such a high rate application is a factor to be assessed. In phytotoxicity tests on radish and white mustard seeds with several concentrations (100, 50, 25, 10, 5, and 0%) ofB. carinatapellets solution, no phytotoxic effect was observed with the two lowest concentrations, and no symptoms of phytotoxicity were found in the bioassays of pepper plants.

Terpenoid and lipid profiles vary in different Phytophthora cactorum – strawberry interactions

Specialized metabolites are essential components in plant defence systems, serving as signalling molecules and chemical weapons against pathogens. The manipulation of plant defence metabolome or metabolites can thus be an important virulence strategy for pathogens. Because of their central role, metabolites can give valuable insights into plant-pathogen interactions. Here, we have conducted nontargeted metabolite profiling with UPLC-ESI-qTOF-MS to investigate the metabolic changes that have taken place in the crown tissue of Fragaria vesca L. (woodland strawberry) and Fragaria × ananassa (Weston) Duchesne ex Rozier (garden strawberry) during 48 h after Phytophthora cactorum challenge. Two P. cactorum isolates were compared: Pc407 is highly virulent to F. × ananassa and causes crown rot, whereas Pc440 is mildly virulent. In total, 45 metabolites differentially accumulated between the treatment groups were tentatively identified. Triterpenoids and various lipid compounds were highly represented. The levels of several triterpenoids increased upon inoculation, some of them showing distinct accumulation patterns in different interactions. Triterpenoids could either inhibit or stimulate P. cactorum growth and, therefore, triterpenoid profiles might have significant impact on disease progression. Of the lipid compounds, lysophospholipids, linoleic acid and linolenic acid were highly accumulated in the most compatible Pc407 - F. × ananassa interaction. As lysophospholipids promote cell death and have been linked to susceptibility, these compounds might be involved in the pathogenesis of crown rot disease. This metabolite analysis revealed potential factors contributing to the outcome of P. cactorum – strawberry interactions. The information is highly valuable, as it can help to find new breeding strategies and new solutions to control P. cactorum in strawberry.

Morphogenetic identification, description and pathogenicity of novel pathogens on Iraqi wheat plant (Triticum aestivum) causing head blight and crown rot diseases

Abstract. Mohammed-Ameen MK, Minati MH, Abbas MH. 2021. Morphogenetic identification, description and pathogenicity of novel pathogens on Iraqi Wheat Plant (Triticum aestivum) causing head blight and crown rot diseases. Biodiversitas 22: 2999-3005. Wheat (Triticum aestivum L.) plant suffers from several fungal diseases, such as Fusarium head blight, root rot, and crown rot diseases that reduce the quality and quantity of grains. Two Fusarium species (Fusarium brachygibbosum and F. falciforme) have been isolated from wheat roots and rhizosphere regions showing disease symptoms in wheat fields in Al-Hwuir and Al-Qurna districts at Basra province. Each fungal species had been characterized morphologically and molecularly based on DNA sequence data for the translation elongation factor 1- ? (TEF-1 ?). Results of pathogenicity test showed that F. falciforme and F. brachygibbosum at the third week of inoculation induced head bleached symptoms with the severity of 12.46% (with significant differences P > 0.05) and 7.14%, respectively on Abu Ghraib 3 cultivar. Yellowing and necrosis symptoms were recorded in stem and crown region. The mean of disease severity (as necrosis on basal stem and crown) was 5% and 3.34% for F. falciforme and F. brachygibbosum, respectively. The two Fusarium species were identified as new pathogens on wheat plants in Iraq, causing head bleaching, stem and crown necrosis.

The use of biological selenium nanoparticles to suppress Triticum aestivum L. crown and root rot diseases induced by Fusarium species and improve yield under drought and heat stress.

Fusarium species threaten wheat crops around the world and cause global losses. The global trend is toward using biological materials such as selenium (Se) in nano form to control these fungi. Bulk selenium is toxic and harmful at high doses; however, selenium nanoparticles are safe; therefore, the aim of this study to employ the biological selenium nanoparticles (BioSeNPs) synthesized by Lactobacillus acidophilus ML14 in controlling wheat crown and root rot diseases (CRDs) induced by Fusarium spp., especially Fusarium culmorum and Fusarium graminearum, and their reflection on the growth and productivity of wheat. The ability of BioSeNPs to suppress the development and propagation of F. culmorum and F. graminearum and the CRDs incidence were also investigated. The obtained BioSeNPs were spherical with a size of 46nm and a net charge of -23.48. The BioSeNPs significantly scavenged 88 and 92% of DPPḢ and ABTṠ radicals and successfully inhibited the fungal growth in the range of 20-40µg/mL; these biological activities were related to the small size of BioSeNPs and the phenolic content in their suspension. Under greenhouse conditions, the wheat supplemented with BioSeNPs (100µg/mL) was significantly reduced the incidence of CRDs by 75% and considerably enhanced plant growth, grain quantity and quality by 5-40%. Also, photosynthetic pigments and gas exchange parameters were significantly increased as compared to chemical selenium nanoparticles (Che-SeNPs) and control. This study results could be recommended the use of BioSeNPs (100µg/mL) in reducing CRDs incidence and severity in wheat plants, enhancing their tolerance with drought and heat stress, and increasing their growth and productivity as compared to control and Che-SeNPs.

Biological Control of Strawberry Crown Rot Disease (Pestalotiopsis sp.) using Trichoderma harzianum and Endophytic Bacteria

Strawberry crown rot is one of the diseases caused by several soil-borne pathogens. Control of the disease is quite difficult, especially on unhealthy soil condition. The study was conducted to examine the potential of Trichoderma harzianum and consortium endophytic bacteria application to control strawberry crown rot disease and resistance of strawberry varieties to crown rot disease based on control treatment. The research stages were isolation and identification of the pathogen, antagonist test of T. harzianum against the pathogen, potency test of both biological control agents to control crown rot disease on three strawberry varieties (Dorit, Rosalinda and the hybrid of Early Bright and Tokii varieties). This study used a Randomized Block Design. The results indicated that Pestalotiopsis sp. was one of the pathogens causing strawberry crown rot. The pathogen was inhibited by T. harzianum using antagonistic mechanism. Although, based on the percentage inhibition of radial growth, only 32 % of inhibition of T. harzianum against Pestalotiopsis sp. when both isolates laid out on PDA in same time. Application of both biological controls lead to the increasing resistance of three strawberry varieties against crown rot disease. The hybrid of Early Bright and Tokii variety was the most resistant varieties compared than 2 others varieties after biological control application.

Bipolaris sorokiniana-Induced Black Point, Common Root Rot, and Spot Blotch Diseases of Wheat: A Review.

Wheat is among the ten top and most widely grown crops in the world. Several diseases cause losses in wheat production in different parts of the world. Bipolaris sorokiniana (teleomorph, Cochliobolus sativus) is one of the wheat pathogens that can attack all wheat parts, including seeds, roots, shoots, and leaves. Black point, root rot, crown rot and spot blotch are the main diseases caused by B. sorokiniana in wheat. Seed infection by B. sorokiniana can result in black point disease, reducing seed quality and seed germination and is considered a main source of inoculum for diseases such as common root rot and spot blotch. Root rot and crown rot diseases, which result from soil-borne or seed-borne inoculum, can result in yield losses in wheat. Spot blotch disease affects wheat in different parts of the world and cause significant losses in grain yield. This review paper summarizes the latest findings on B. sorokiniana, with a specific emphasis on management using genetic, chemical, cultural, and biological control measures.

Identification and Chemical and Biological Management of Phytopythium vexans, the Causal Agent of Phytopythium Root and Crown Rot of Woody Ornamentals.

Soilborne diseases caused by pathogens such as Phytophthora, Rhizoctonia, Fusarium, Verticillium, and Pythium species are the most important diseases of woody ornamentals. Ginkgo (Ginkgo biloba) and red maple (Acer rubrum 'October Glory') plants grown in containers and fields in Tennessee showed root and crown rot symptoms with dark brown to black lesions in 2017 and 2018. The objective of this research was to isolate and identify pathogens affecting ginkgo and red maple plants in Tennessee nurseries and to develop fungicide/biofungicide management recommendations for nursery producers. Isolations were made from the infected roots. Several Phytophthora-like colonies with spherical zoospores, filamentous to globose oogoni, and whitish mycelium were isolated on V8-PARPH medium. To confirm identity, total genomic DNA was extracted, followed by sequence analysis of the internal transcribed spacer regions, large subunit of nuclear rRNA, and cytochrome c oxidase subunits I and II of mitochondrial DNA. Based on morphological and molecular analysis, Phytopythium vexans was described as a causal agent of crown and root rot from the infected ginkgo and red maple plants. To complete Koch's postulates, a pathogenicity test was performed by drenching 100 ml of V8 agar medium slurry of Phytopythium vexans inoculum on 1-year-old potted ginkgo plant root systems as well as red maple October Glory. Necrotic lesion development was observed in the root system 45 days after inoculation and Phytopythium vexans was reisolated from the roots of both ginkgo and red maple. All control ginkgo and red maple plants remained disease free and no pathogen was reisolated. In addition, the efficacy of fungicides, biofungicides, fertilizer, and host plant defense inducers (traditionally recommended for management of oomycete diseases) for control of Phytopythium crown and root rot was evaluated on ginkgo and red maple October Glory seedlings in greenhouse and field trials. Fungicides such as Empress Intrinsic, Pageant Intrinsic, Segovis, and Subdue MAXX were effective in both greenhouse and field trials, and the biofungicide Stargus reduced disease severity caused by pathogen Phytopythium vexans on ginkgo and red maple plants in greenhouse trials. These results will help nursery producers make proper management decisions for newly reported Phytopythium crown and root rot disease of ginkgo and red maple plants.

Erwinia mallotivora is the causal agent of papaya bacterial crown rot disease in Lampung Timur, Indonesia

Sixteen bacterial strains showing oval, convex with a white colony colour were obtained from the water-soaked lesions on the petioles and leaves of infected papaya (cv. calina) collected from a papaya field in Lampung Timur, Indonesia. The pathogenicity test showed that all the strains produced the same symptoms with those found in the field. Four representative strains were then chosen for further investigation. The phenotypic characteristics revealed that the strains resembled Erwinia mallotivora. Two representative strains were further identified using a 16SrDNA sequence analysis. The result showed that the strains were placed within the group of the type strain and the reference strains of E. mallotivora. To the best of our knowledge, this is the first finding of E. mallotivora as the causal agent of papaya crown rot disease in Indonesia. Among the sixteen plants used for the host range test, the symptom was only observed on eggplants, but not on the other fifteen plant species.

Effects of Genotype, Sowing Time and Seed Fungicide Pre-Treatments on Root and Crown Rot and Grain Yield in Bread Wheat

This study was carried out to investigate the effects of sowing time, cultivar and seed fungicide applications on root and crown rot disease and grain yield of bread wheat with different earliness traits (Esperia, mid-early; Genesi, late and Anapo, early) in the experiment station of the Department of Field Crops, Faculty of Agriculture, Tekirdağ Namık Kemal University. Four different fungicides pre-treatments (prothioconazole + tebuconazole, carboxin + thiram, prochloraz + tiriticonazole and control) were applied to the seeds of the varieties before sowing in three different times, on 1 November, 15 November and 30 November 2016. The experiment was designed as a split-split-plot with 3 replications. The results of the variance analysis showed that the effect of applying different seed fungicide pre-treatment root and crown rot of bread wheat varieties was statistically significant. Prothioconazole + tebuconazole application caused the lowest root and crown rot with 2.714 %, followed by prochloraz + tiriticonazole with 3.31%. The highest root and crown rot was determined with a value of 3.64% for the earliest sowing on 01 November. Among the four different fungicide pre-treatments, the highest root and crown rot (5.59%) was obtained in the control application, while the lowest root and crown rot was obtained in prothioconazole + tebuconazole, carboxin + thiram and prochloraz + triticonazole, with 1.96%, 2.10% and 2.89% root and crown rot, respectively. These data indicate that early sowing may increase root and crown rot severity.

Identification of Codonopsis pilosula Crown Rot Disease and Its Sensitivity to Fungicides

Identification of Codonopsis pilosula Crown Rot Disease and Its Sensitivity to Fungicides

Plant mitochondria and chloroplasts are targeted by the Rhizoctonia solani RsCRP1 effector

The fungal species Rhizoctonia solani belongs to the Basidiomycota division and is a ubiquitous soil-borne pathogen. It is the main agent of the damping-off disease in seedlings and causes the root and crown rot disease in sugar beets. Plant pathogens deploy small secreted proteins, called effectors, to manipulate plant immunity in order to infect the host. Here, a gene (RsCRP1) encoded a putative effector cysteine-rich protein was cloned, expressed in Cercospora beticola and used for virulence assays. The RsCRP1 gene was highly induced upon the early-infection stage of sugar beet seedlings and disease was promoted. Confocal microscopy demonstrated localization to the chloroplasts and mitochondria upon transient expression of RsCRP1 in leaves of Nicotiana benthamiana. Further, this effector was unable to induce necrosis or to suppress hypersensitive response induced by the Avr4/Cf4 complex in N. benthamiana. Overall, these data indicate that RsCRP1 is a novel effector targeting distinct plant cell organelles in order to facilitate a successful infection at the early stages of the disease development.

Situation of Fusarium root and crown rot disease of wheat in Iran

Situation of Fusarium root and crown rot disease of wheat in Iran

Evaluation of potassium salt of phosphonic acid in Nagpur mandarin with special reference to Phytophthora management

Phytophthora parasitica var. nicotianae is a major fungal pathogen that causes foot rot, root rot, crown rot, gummosis, leaf fall, and brown rot diseases in Nagpur mandarin in the entire Vidarbha region of Maharashtra. For the efficient management of root rot and gummosis due to Phytophthora, the potassium salt of phosphonic acid (PSPA) was evaluated under field and laboratory conditions. In field trials, infected plants were treated with different concentrations of PSPA by foliar spray and soil drenching. The results revealed that foliar spray + soil drenching of PSPA at 3 ml/liter water was better with respect to the average reduction in no. of lesion with oozing (28.39%), minimum in feeder root index (2.17), increase in canopy volume (11.15%) and higher fruit yield (65.89 kg/ per tree). The effect of PSPA was assayed at three different concentrations against P. nicotianae under in vitro. PSPA was found most effective in arresting the growth of P. nicotianae as complete (100%) inhibition observed in tested doses.

Evaluation of potassium salt of phosphonic acid in Nagpur mandarin with special reference to Phytophthora management


 
 
 Phytophthora parasitica var. nicotianae is a major fungal pathogen that causes foot rot, root rot, crown rot, gummosis, leaf fall, and brown rot diseases in Nagpur mandarin in the entire Vidarbha region of Maharashtra. For the efficient management of root rot and gummosis due to Phytophthora, the potassium salt of phosphonic acid (PSPA) was evaluated under field and laboratory conditions. In field trials, infected plants were treated with different concentrations of PSPA by foliar spray and soil drenching. The results revealed that foliar spray + soil drenching of PSPA at 3 ml/liter water was better with respect to the average reduction in no. of lesion with oozing (28.39%), minimum in feeder root index (2.17), increase in canopy volume (11.15%) and higher fruit yield (65.89 kg/ per tree). The effect of PSPA was assayed at three different concentrations against P. nicotianae under in vitro. PSPA was found most effective in arresting the growth of P. nicotianae as complete (100%) inhibition observed in tested doses.
 
 

Anti-microbial Effect of Cocoa Leaf Extracts on Botryodiplodia theobromae; Leading Causative Organism of Crown Rot Disease of Banana (Musa acuminata)

An investigation was carried to assess in-vitro management of crown rot disease on Banana using extracts of cocoa leaves. The causative organism (Botryodiplodia theobromae) was sub cultured and the concentration determined through microbial count. Different cocoa leaves extracts were prepared using two different solvents. A conventional fungicide known as Mancozeb was used as a positive control and the nutrient broth only served as negative controls to help in assessment of the antimicrobial effect of the cocoa leave extracts. Phenolic Methanol Extracts (PME), Crude Cocoa Leaves Aqueous Extracts (CCAE) and Mancozeb were employed to prepare aqueous solutions through serial dilution with varied concentration. The nutrient broth (100 µL of double strength), 100 µL each of the plant extract concentrations, and 20 µL of inoculums were dispensed in a sterile micro-titre plate containing 96 wells. Incubation of the micro-titre plate was carried out at a temperature of 37°C for 1 day (24 hours). Susceptibility or otherwise of the microorganism (B. theobromae) from four sample stations was analyzed with 20 µL of a 5% solution of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide MTT. The presence of blue-black wells indicated the growth of B. theobromae. The experiment was conducted in triplicates for PME (refined), CCAE and Mancozeb. The minimum inhibition concentrations (MICs) of PME (refined) that inhibited the growth of B. theobromae collected from four different locations were 5mg/ml, 2.5 mg/ml, 10 mg/ml and 2.5 mg/ml respectively for B. theobromae (B1)(Offinso), B. theobromae (B2)(Effiduase), B. theobromae (B4)(Kejetia) and B. theobromae (B5)(Ejisu) which was lower compared to the MICs of CCAE which was 30 mg/ml for the four sample stations. Comparatively, the MIC of the PME (5 mg/ml, 2.5 m g/ml, 10 mg/ml and 2.5mg/ml) was almost equivalent to the MIC of the conventional fungicide (Mancozeb) (2.5 mg/ml) for all the four sample stations of B. theobromae.

Disease responses of hexaploid spring wheat (Triticum aestivum) culms exhibiting premature senescence (dead heads) associated with Fusarium pseudograminearum crown rot

Hexaploid spring wheat (Triticum aestivum) may exhibit significant crown rot disease responses to infection by Fusarium pseudograminearum, with a range of susceptibility levels available in commercial cultivars. Dry conditions during grain-fill may lead to the expression of prematurely senescing culms, which typically fail to set grain. Assessment of hexaploid spring wheat plants exhibiting both non-senescent and prematurely senescent culms was performed using visual discolouration, F. pseudograminearum biomass and vascular colonisation in culm sections sampled at three different heights above the crown and at the peduncle. Samples from six commercial cultivars were collected at milk development in 2014 from Narrabri and Tamworth, New South Wales and Wellcamp, Queensland. Prematurely senescent culms exhibited greater visual discolouration, F. pseudograminearum biomass and vascular colonisation than non-senescent culms in each cultivar. A further comparison of the parameters across four time points from milk development, when senescent culms are first observed, to maturity was conducted for cultivar Sunlin. F. pseudograminearum biomass and vascular colonisation were significantly different between culm conditions prior to maturation, while visual discolouration was not significantly different between culm conditions at any single time point. Colonisation of xylem and phloem tissue was extensive in the basal portions of prematurely senescent culms (36 to 99%) prior to maturation, and suggests significant impacts on water and nutrient movement during crown rot disease. Despite a range of resistance ratings being assessed, cultivars were not reliably separated based upon responses to severe disease pressure, demonstrating the continuing need for improved crown rot resistance in commercial wheat.