Strain-specific detection of two Aureobasidium pullulans strains, fungal biocontrol agents of fire blight by new, developed multiplex-PCR

In Vitro Approbation of Microbial Preparations to Shield Fruit Crops from Fire Blight: Physio-Biochemical Parameters

The need for the increasing geographical spread of fire blight (FB) affecting fruit crops to be addressed led to large-scale chemicalization of the environmental matrices and reduction of plant productivity. The current study aimed to assess the effects of novel biopreparations at different exposure durations on photosynthetic pigment content and antioxidant enzyme activity in leaves of apple and pear varieties with varying levels of resistance to FB. Biopreparations were formulated from a cultural broth containing Lacticaseibacillus paracasei M12 or Bacillus amyloliquefaciens MB40 isolated from apple trees' phyllosphere. Aseptic leaves from blight-resistant (endemic Malus sieversii cv. KG10), moderately resistant (Pyrus pyraster cv. Wild), and susceptible (endangered Malus domestica cv. Aport and Pyrus communis cv. Shygys) varieties were employed. The impact of biopreparations on fruit crop antioxidant systems and photosynthetic apparatuses was investigated in vitro. Study results indicated that FB-resistant varieties exhibit enhanced adaptability and oxidative stress resistance compared to susceptible ones. Plant response to biopreparations varied based on the plant's initial FB sensitivity and exposure duration. Indeed, biopreparations improved the adaptive response of the assimilation apparatus, protein synthesis, and catalase and superoxide dismutase activity in susceptible varieties, suggesting that biopreparations have the potential for future commercialization to manage FB in fruit crops.

SCAR marker: A potential tool for authentication of agriculturally important microorganisms

Microbial inoculants are globally recommended for plant growth promotion and control of plant pathogens. These inoculants require stringent quality checks for sustainable field efficacy. Questionable regulatory frameworks constantly deteriorate the reliability of bio-inoculant technology. Existing global regulations do not involve any rapid molecular technique for the routine inspection of microbial preparations. Sequence characterized amplified region (SCAR) marker offers rapid and precise strain-level authentication of target microbes. Such advanced molecular techniques must be exploited to accurately validate the microbial formulations. Besides, the global dissemination of plant pathogenic microbes has always been an alarming threat to food security. SCAR markers could be used at the plant quarantine centers to rapidly detect catastrophic pathogens, thereby circumventing the import and export of contagious plant materials. The current review is focused on promoting the SCAR marker technology to validate commercial bio-inoculants and predict plant pandemics.

Refinement of Nonantibiotic Spray Programs for Fire Blight Control in Organic Pome Fruit

Fire blight-susceptible, certified organic pome fruit is produced on 9,000 ha in the Pacific Northwest region of the United States with acreage continuing to expand despite a 2014 prohibition on antibiotics as allowable materials for infection suppression. Nonantibiotic practices for fire blight pathogen suppression mirror conventional management, but the full-bloom-to-petal-fall period when antibiotics are typically sprayed for fire blight control continues to receive research scrutiny owing to drawbacks and weaknesses of alternative materials. As solitary treatments, effective nonantibiotic materials (e.g., a yeast biocontrol, soluble coppers, and potassium aluminum sulfate) raise the risk of a crop-value-reducing, phytotoxic response termed "fruit russeting." Conversely, materials with less russeting risk (e.g., Bacillus-based biorationals) are less effective for fire blight control. Spray programs using a sequence of materials applied from midbloom to petal fall have the potential to provide high levels of protection with reduced russeting risk. In orchard trials, the effects of nonantibiotic spray programs on the epiphytic population size of Erwinia amylovora in flowers, yeast biocontrol population size, floral pH, infection suppression, and fruit russeting revealed strategies for sequencing sprays of nonantibiotic materials. The yeast biocontrol, Blossom Protect (Aureobasidium pullulans), sprayed at 70% bloom, was an important contributor to fire blight pathogen suppression as was the soluble copper material, Previsto, when applied at full bloom. Choice of material for the petal-fall spray timing was important to fruit russeting risk but apparently less important to overall infection incidence. Consequently, treatment programs of Blossom Protect at 70% bloom, a soluble copper at full bloom, and a Bacillus-based biorational at petal fall, best balance the quality of infection suppression with the risk of fruit russeting.

Development of a Strain-Specific Quantification Method for Monitoring Bacillus amyloliquefaciens TF28 in the Rhizospheric Soil of Soybean

Bacillus amyloliquefaciens TF28 can be used to control soybean root disease. To assess its commercial potential as a biocontrol agent, it is necessary to develop a strain-specific quantification method to monitor its colonization dynamics in the rhizospheric soil of soybean under field conditions. Based on genomic comparison with the same species in NCBI databases, a strain-unique gene ukfpg was used as molecular marker to develop strain-specific PCR assay. Among three primer pairs, only primer pairs (F2/R2) could specifically differentiate TF28 from other strains of B. amyloliquefaciens with the detection limit of 10 fg and 100 CFU/g for DNA extracted from pure culture and dry soil, respectively. Then, a colony count coupled with PCR assay was used to monitor the population of TF28 in the rhizospheric soil of soybean in the field. The results indicated that TF28 successfully colonized in the rhizospheric soil of soybean. The colonization population of TF28 changed dynamically within the 120-day growth period with high population at the branching (V6) and flowering stages (R2). This study provides an efficient method to quantitatively monitor the colonization dynamics of TF28 in the rhizospheric soil of soybean in the field and demonstrates the potential of TF28 as a biocontrol agent for commercial development.

Inhibition of Erwinia amylovora by Bacillus nakamurai

A variety of potential inhibitors were tested for the first time for the suppression of Erwinia amylovora, the causal agent of fire blight in apples and pears. Strain variability was evident in susceptibility to inhibitors among five independently isolated virulent strains of E. amylovora. However, most strains were susceptible to culture supernatants from strains of Bacillus spp., and particularly to the recently described species B. nakamurai. Minimal inhibitory concentrations (MICs) were 5-20% (vol/vol) of culture supernatant from B. nakamurai against all five strains of E. amylovora. Although Bacillus species have been previously reported to produce lipopeptide inhibitors of E. amylovora, matrix-assisted laser desorption time of flight mass spectrometry (MALDI-TOF MS) and column chromatography indicated that the inhibitor from B. nakamurai was not a lipopeptide, but rather a novel inhibitor.

Floral Colonization Dynamics and Specificity of Aureobasidium pullulans Strains Used to Suppress Fire Blight of Pome Fruit

Aureobasidium pullulans is used as a biocontrol agent for fire blight protection in organic apple and pear production. We assessed colonization of pome flowers by A. pullulans in orchards located near Corvallis, OR and Wenatchee, WA. Blossom Protect, a mix of A. pullulans strains CF10 and CF40, and its citrate-based companion, Buffer Protect, were sprayed at 70% bloom. Later in bloom, the population size of putative A. pullulans on flowers was estimated by dilution plating; plate scrapings of putative A. pullulans were then sampled and subjected to a PCR analysis. Sequenced PCR amplicons of the internal transcribed spacer region and the elongase gene confirmed the presence of A. pullulans, whereas a multiplex PCR with primers specific to CF10 and CF40 was used to determine the presence of the introduced strains. At Corvallis, a wet spring environment, A. pullulans, was recovered from most (>90%) Bartlett pear and Golden Delicious apple flowers sampled from experimental trees, regardless of whether the trees were treated with Blossom Protect. Nevertheless, population size estimates of A. pullulans on the flowers were correlated with the number of times Blossom Protect was sprayed on the trees. At Wenatchee, an arid spring environment, A. pullulans was detected on most flowers from trees treated with Blossom Protect, but only on a minority of flowers from nontreated controls. In both locations, the combined incidence of strains CF10 and CF40 on flowers averaged 89% on Blossom Protect-treated trees, but only 27% on adjacent, nontreated trees. During subsequent trials, the efficacy of Blossom Protect for fire blight control was compared with alternative yeast isolates, with each applied with Buffer Protect; local isolates of A. pullulans and Cryptococcus neoformans and a postharvest biocontrol strain of Cystofilobasidium infirmominiatum were used All yeast strains suppressed fire blight to a degree; however, in each of four trials, the level of suppression was highest with Blossom Protect, and it was significantly superior (P ≤ 0.05) to other yeast isolates in two of the trials. Because A. pullulans strains CF10 and CF40 were detected primarily on flowers on trees treated with Blossom Protect, and because they were detected much less frequently on nearby nontreated tress, we recommend treating every tree row with Blossom Protect at least once for organic fire blight suppression.

Molecular characterization by PCR-RFLP of indigenous fungal isolates from hypersaline stream water in România

This is the first exhaustive report on the fungal community biodiversity in hypersaline water in România. A total of 27 fungal strains (19 molds and eight yeast) have been isolated from Lopătari hypersaline water, Buzau County. Based on classical investigation, these strains have been identified as belonging to the genera Aureobasidium, Alternaria, Aspergillus, Penicillium, and Fusarium. The molecular characterization of fungal isolates at species level was performed using PCR-RFLP analysis of the 5.8S-ITS region. PCR products were digested with different combinations of endonucleases. The most frequently isolated species were Aspergillus niger (14.81% of all isolates), A. versicolor, (14.81%) and Penicillium crustosum (14.81%). In addition, ribosomal restriction patterns which exhibited profiles specific to Aureobasidium pullulans were derived, and to discriminate between Aureobasidium isolates, the elongase-encoding gene (ELO) was chosen as a genetic marker followed by digestion with endonuclease HhaI. Five yeast isolates displayed restriction patterns corresponding to Aureobasidium melanogenum (18.52%) and three isolates to Aureobasidium pullulans (11.11%). In addition, the RFLP types of Aureobasidium pullulans varieties with HhaI are clearly distinguished and could be applied to assess the intraspecific variability.

A method of multiplex PCR for detection of field released Beauveria bassiana, a fungal entomopathogen applied for pest management in jute (Corchorus olitorius)

The fungal entomopathogen Beauveria bassiana is a promising biocontrol agent for many pests. Some B. bassiana strains have been found effective against jute pests. To monitor the survival of field released B. bassiana a rapid and efficient detection technique is essential. Conventional methods such as plating method or direct culture method which are based on cultivation on selective media followed by microscopy are time consuming and not so sensitive. PCR based methods are rapid, sensitive and reliable. A single primer PCR may fail to amplify some of the strains. However, multiplex PCR increases the possibility of detection as it uses multiple primers. Therefore, in the present investigation a multiplex PCR protocol was developed by multiplexing three primers SCA 14, SCA 15 and SCB 9 to detect field released B. bassiana strains from soil as well as foliage of jute field. Using our multiplex PCR protocol all the five B. bassiana strains could be detected from soil and three strains viz., ITCC 6063, ITCC 4563 and ITCC 4796 could be detected even from the crop foliage after 45 days of spray.

Disseminated histoplasmosis in a domestic cat imported from the USA to Austria

We present a case of disseminated histoplasmosis in a domestic cat imported from the USA to Austria. Histopathological examination revealed a systemic mycosis with most severe involvement of the lungs suggestive of Histoplasma (H.) capsulatum-infection. Molecular confirmation was based on polymerase chain reaction (PCR) and sequence analysis of a fungal culture from liver samples. This is the first case of feline histoplasmosis proven by molecular diagnostic technique in Europe and reported in Austria, etc.

Evaluation of Strategies for Fire Blight Control in Organic Pome Fruit Without Antibiotics

Apple and pear produced organically under the U.S. National Organic Program (NOP) standard can be treated with antibiotics for suppression of fire blight caused by Erwinia amylovora. Recent regulatory actions by the NOP, however, have lessened the likelihood of antibiotic use after the 2014 season. In response, western U.S. organic apple and pear stakeholders identified two immediate-need research objectives related to fire blight control: development of effective non-antibiotic control programs based on combinations of registered biological products; and, in apple, integration of these products with lime sulfur, which is sprayed at early bloom to reduce fruit load. In orchard trials in Oregon, increasing the frequency of treatment with biological products improved suppression of floral infection. In apple, fruit load thinning with 2% lime sulfur plus 2% fish oil (LS+FO) at 30 and 70% bloom significantly (P ≤ 0.05) reduced the proportion of blighted flower clusters in four of five orchard trials. Moreover, lime sulfur significantly (P ≤ 0.05) suppressed epiphytic populations of E. amylovora after their establishment on apple flowers. Over four trials, treatment with Aureobasidium pullulans (Blossom Protect) after LS+FO reduced the incidence of fire blight by an average of 92% compared with water only; this level of control was similar to treatment with streptomycin. In three seasons, a spray of a Pantoea agglomerans product after the 70% bloom treatment of LS+FO established the antagonist on a significantly (P ≤ 0.05) higher proportion of flowers compared with a spray of this bacterium before the thinning treatment. Consequently, in apple, biological treatments for fire blight control are not advised until after lime sulfur treatments for fruit load thinning are completed.

Genetic diversity among isolates of Paenibacillus larvae from Austria

Genetic diversity of 214 Paenibacillus larvae strains from Austria was studied. Genotyping of isolates was performed by polymerase chain reaction (PCR) with primers corresponding to enterobacterial repetitive intergenic consensus (ERIC), BOX repetitive and extragenic palindromic (REP) elements (collectively known as rep-PCR) using ERIC primers, BOX A1R and MBO REP1 primers. Using ERIC-PCR technique two genotypes could be differentiated (ERIC I and II), whereas using combined typing by BOX- and REP-PCR, five different genotypes were detected (ab, aB, Ab, AB and alphab). Genotypes aB and alphab are new and have not been reported in other studies using the same techniques.