Alternaria Rot Research Articles

Fungicide Resistance in Alternaria alternata from Blueberry in California and Its Impact on Control of Alternaria Rot.

Alternaria rot caused by Alternaria alternata is one of the major postharvest diseases affecting blueberries in California. The sensitivity profiles of A. alternata from blueberry field to quinone outside inhibitors (QoIs), boscalid, fluopyram, fludioxonil, cyprodinil, and polyoxin D in California were examined in this study. EC50 values of 51 A. alternata isolates for boscalid varied greatly among the isolates, ranging from 0.265 to >100 μg/ml. EC50 values of 51 A. alternata isolates to fluopyram, fludioxonil, cyprodinil, and polyoxin D were 5.188 ± 7.118, 0.078 ± 0.021, 0.465 ± 0.302, and 6.238 ± 7.352 μg/ml, respectively. In total, 143 isolates were screened for resistance at 5 and 10 μg/ml for fludioxonil, cyprodinil, and fluopyram, 10 μg/ml for polyoxin D, and 10 and 50 μg/ml for boscalid. Based on the published discriminatory concentrations for phenotyping resistance, of the 143 isolates, all were considered resistant to boscalid; 32, 69, and 42 were sensitive, low resistant, and resistant to fluopyram, respectively; and all were sensitive to fludioxonil and cyprodinil. In a PCR-restriction fragment length polymorphism method for phenotyping, 60 out of the 143 isolates were classified as resistant to QoIs. Control tests on detached blueberry fruit inoculated with different Alternaria isolates showed that fludioxonil and cyprodinil significantly reduced disease incidence and severity; however, pyraclostrobin, boscalid, fluopyram, and polyoxin D significantly reduced only disease severity. The obtained results will be helpful in making decisions on fungicide programs to control A. alternata isolates with resistance or reduced sensitivities to multiple fungicides.

Characterization, pathogenicity, and fungicide sensitivity of Alternaria isolates associated with preharvest fruit drop in California citrus

Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their seasonal patterns during 2019 and 2020. On fruits, latent infections were more associated with the stem end than with the stylar end, except during spring when a significantly high percentage of flowers (86%) had latent infections. Latent infections on twigs varied markedly between years (28% in 2019 and 9.5% in 2020), while Alternaria spp. were also recovered from citrus leaves. Alternaria isolates collected during the survey were identified based on multigene sequence analysis, confirming that Alternaria alternata and Alternaria arborescens are the two species associated with infections of citrus fruits. Of the 23 isolates, 19 were identified as A. alternata and demonstrated the dominance of this species over A. arborescens. Isolates representing populations of these two species were selected as representative isolates for physiological and morphological studies. A. alternata and A. arborescens showed similar conidial dimensions but differed in the number of conidia produced. Growth rates demonstrated that A. alternata grows faster than A. arborescens at all the temperatures evaluated, except at 25 and 35 °C. The growth patterns were similar for both species. The sporulation rate of the Alternaria isolates was influenced differently by temperature. This parameter also influenced conidial germination and appressorium formation, and no significant differences were observed between Alternaria species. Pathogenicity and aggressiveness tests on detached fruit demonstrated the ability of A. alternata and A. arborescens to cause internal lesions and produce fruit drop in the orchards with no quantitative differences between them (disease severity indexes of 58 and 68%, respectively). The fungicide sensitivity tests showed that DMI fungicides are the most effective fungicides in reducing mycelial growth. The SDHI fungicides had intermediate activity against the mycelial growth but also suppressed spore germination. The spore germination assay suggested that some of the isolates included in this study might have some level of resistance to QoI and SDHI fungicides. The findings of this study provide new information about the pathogens associated with the excessive fruit drop recently observed in some California citrus groves.

Comprehensive evaluation of chiral pydiflumetofen from the perspective of reducing environmental risks

The spatial structures of chiral pesticide enantiomers can affect their activity, toxicity and behavior, thereby altering exposure risk. Identifying enantiomer differences and developing high-efficiency green enantiopure pesticide is an important strategy for reducing the negative effects of pesticides. In this study, after confirming the absolute configuration of pydiflumetofen enantiomers, fungicidal activity evaluation indicated that the activity of S-(+)-pydiflumetofen was 81.3–421 times higher than R-(−)-pydiflumetofen on three kinds of phytopathogens that control Fusarium wilt (Fusarium spp.), Alternaria rot (Alternaria alternata) and Southern blight (Sclerotinia rolfsii), which might be caused by the stronger binding ability of S-(+)-pydiflumetofen with the active site of the target protein. The coexistence of R-(−)-pydiflumetofen would enhance the toxicity of S-(+)-pydiflumetofen on zebrafish through synergistic effect. Low-activity R-(−)-pydiflumetofen was preferentially dissipated in soybean, soybean plants, cabbage and celery, which was opposite in soil. The persistence of S-(+)-pydiflumetofen in crops and degradability in soil were advantageous for pesticide effects and environmental protection. Based on the maximum residue limit (MRL) and hazard quotient (HQ), the dietary risks were determined to be acceptable for all crops. Thus, developing enantiopure S-(+)-pydiflumetofen products might be a high-efficiency and low-risk strategy, and more studies should be conducted in this aspect.

Melatonin enhanced the disease resistance by regulating reactive oxygen species metabolism in postharvest jujube fruit

Melatonin (MT), as a putative pleiotropic signal molecule, could participate in inducing postharvest disease resistance and inhibiting postharvest pathogen infection in fruit. In this study, we investigate the mechanism of induced resistance by MT treatment against Alternaria rot of jujube. The results showed that 2 and 20 μmol/L MT did not have direct antimicrobial activity, 200 μmol/L MT had little influence on antifungal activity against Alternaria alternata in vitro. MT significantly reduced the lesion area of fruit inoculated with A. alternata. MT decreased the relative electrolytic leakage, malondialdehyde content, hydrogen peroxide, and the rate of superoxide anion production, while enhanced the ascorbic acid and reduced glutathione contents. Furthermore, MT observably increased the defensive enzyme activities of superoxide dismutase, the catalase, ascorbate peroxidase, peroxidase. Accordingly, these results indicated that MT treatment increased the disease resistance of jujube fruit by regulating reactive oxygen species metabolism. Novelty impact statement The results showed that MT treatment could inhibit the expansion of lesion diameter, reduce the decay rate of winter jujube, and reduce the accumulation of reactive oxygen species by activating the oxidase system, thus enhancing the resistance of winter Jujube fruit to Alternaria alternata infection by adjusting the ROS mechanism.

Arginine induces the resistance of postharvest jujube fruit against Alternaria rot

Abstract In order to explore the effects of arginine (Arg) treatment on postharvest rot of jujube caused by Alternaria alternata (A. alternata), winter jujube was treated with different concentrations of Arg (0, 20, 200, and 1000 μmol/L). Results showed that Arg treatment substantially inhibited the expansion of lesion diameter, and jujubes treated with 200 μmol/L Arg had the smallest lesion diameter. In vitro experiments demonstrated that Arg could not inhibit spore germination and mycelial growth of A. alternata. Further experimental results showed that Arg treatment reduced the production rate of O2–. and H2O2 content and improved the activities of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase in comparison with the control; Arg treatment enhanced the activities of chitinase and β-1,3-glucanase. Furthermore, Arg treatment significantly increased the activity of phenylalamine ammonia lyase and the contents of flavonoids, phenolics, and lignin. Results indicated that, although Arg could not directly inhibit the growth of pathogenic fungi as a fungicide, it can induce resistance to Alternaria rot by maintaining the balance of reactive oxygen species, increasing the activities of pathogenesis-related protein, and promoting the phenylpropane metabolism in jujube fruit tissue. Therefore, Arg treatment can be a novel measure for inducing the resistance of jujube to postharvest Alternaria rot.

Antifungal Activity and Biocontrol Mechanism of Fusicolla violacea J-1 against Soft Rot in Kiwifruit Caused by Alternaria alternata

Alternaria alternata is the main pathogenic species of various crops, including kiwifruit (Actinidia cinensis). In this study, an antagonistic fungus, J-1, with high antifungal activity against A. alternata was isolated from A. cinensis “Hongyang.” The strain J-1 was identified as Fusicolla violacea via morphological identification and DNA sequencing. This study aimed to evaluate the antifungal activity and potential mechanism of the strain J-1 against A. alternata. The strain J-1 exhibited antifungal activity against A. alternata, with an inhibition rate of 66.1% in vitro. Aseptic filtrate (AF) produced by the strain J-1 could suppress the mycelial growth and conidia germination of A. alternata at the inhibition rates of 66.8% and 80%, respectively, as well as suppress the spread of Alternaria rot in fresh kiwifruit. We observed that many clusters of spherical protrusions appeared at the mycelial tips of A. alternata after treatment with 200 mL L−1 AF of J-1. Scanning electron microscopy analysis results showed that the mycelial structures were bent and/or malformed and the surfaces were rough and protuberant. Variations in temperature, pH, and storage time had little effect on the antifungal activity of the AF. Moreover, the AF could damage the integrity of cell membranes and cause intracellular content leakage. Meanwhile, the chitinase and β-1,3-glucanase enzyme activities increased significantly, indicating that the function of A. alternata cell wall was seriously injured. Eleven antimicrobial metabolites were identified by gas chromatography–mass spectrometry (GC–MS). The strain J-I and its AF exhibited well broad-spectrum antifungal activity against Diaporthe eres, Epicoccum sorghinum, Fusarium graminearum, Phomopsis sp., and Botryosphaeria dothidea, with inhibition rates ranging from 34.4% to 75.1% and 42.7% to 75.2%, respectively. Fusicolla violacea J-1 is a potential biocontrol agent against A. alternata and other fungal phytopathogens.

Baseline Sensitivity of Alternaria alternata and A. arborescens to Natamycin and Control of Alternaria Rot on Stored Mandarin Fruit.

Alternaria rot caused by Alternaria alternata and A. arborescens is one of the major postharvest diseases on mandarin fruit in California. In this study, natamycin, a newly registered biofungicide, was evaluated for its potential as a postharvest treatment to control Alternaria rot on mandarin fruit. The baseline sensitivities of A. alternata and A. arborescens to natamycin were determined. Effective concentration inhibiting 50% of fungal growth (EC50) values of natamycin for 70 A. alternata isolates ranged from 0.694 to 1.275 µg/ml (mean = 0.921 µg/ml) in a conidial germination assay and from 2.001 to 3.788 µg/ml (mean = 2.797 µg/ml) for 40 A. alternata isolates in a mycelial growth assay. EC50 values of natamycin for 30 A. arborescens isolates ranged from 0.698 to 1.203 µg/ml (mean = 0.923 µg/ml) in a conidial germination assay and from 2.035 to 3.368 µg/ml (mean = 2.658 µg/ml) for 20 A. arborescens isolates in a mycelial growth assay. Control tests on detached mandarin fruit showed that natamycin at both low (460 µg/ml) and high (920 µg/ml) recommended rates significantly reduced disease incidence and severity on mandarin fruit inoculated with Alternaria isolates, regardless of species. High rate of natamycin significantly reduced disease incidence and severity compared with the nontreated control even when natamycin treatment was delayed for 6, 12, and 18 h after inoculation. Our results suggested that natamycin can be an effective postharvest fungicide for control of Alternaria rot on mandarin fruit.

Effects of Peroxyacetic Acid on Postharvest Diseases and Quality of Blueberries.

Postharvest diseases are a limiting factor in the storage of fresh blueberries. Gray mold caused by Botrytis cinerea and Alternaria rot caused by Alternaria spp. are important postharvest diseases in blueberries grown in California. Control of these fungal pathogens is generally dependent on preharvest sprays of synthetic fungicides, but in California multiple fungicide resistance has already developed in those pathogens, leading to the failure of disease control. Therefore, alternatives to synthetic fungicides are needed for the control of postharvest diseases. Peroxyacetic acid (PAA) is a disinfectant agent that poses low risk to human health. In this study, we evaluated the effects of postharvest use of PAA at 24 µl liter-1 and 85 µl liter-1 on fruit decay caused by fungal pathogens and quality of stored blueberry fruit. PAA treatment was applied to four cultivars over three seasons using two methods, dipping or spraying. Dipping blueberries compared with spraying them with PAA and its application at 85 µl liter-1 were the most effective treatments. For example, when applied to 'Snowchaser' blueberries, this combination reduced naturally occurring decay after 4 weeks of storage at 0 to 1°C from 14.3% among water-treated controls to 2.7% in 2018, and from 25.7% among water-treated controls to 8.6% in 2020. In general, PAA did not adversely affect fruit quality or sensory quality of blueberries. Postharvest use of PAA appears to be a promising means to reduce postharvest decay of blueberries. To reliably obtain an acceptable level of disease control, the best use of PAA may be in combination with other practices rather than using it alone.

Phylogenetic, Morphological, and Pathogenic Characterization of Alternaria Species Associated With Fruit Rot of Mandarin in California.

Alternaria rot caused by Alternaria species is one of the major postharvest diseases of mandarin fruit in California. The aims of this study were to identify these Alternaria species via phylogenetic analyses and morphological characteristics and test their pathogenicity on mandarin. Decayed mandarin fruits exhibiting Alternaria rot symptoms were collected from three citrus fruit packinghouses in the Central Valley of California. In total, 177 Alternaria isolates were obtained from decayed fruit and preliminarily separated into three groups representing three species (A. alternata, A. tenuissima, and A. arborescens) based on the colony characterization and sporulation patterns. To further identify these isolates, phylogenetic analysis was conducted based on DNA sequences of the second largest subunit of RNA polymerase II (RPB2), plasma membrane ATPase (ATPase), and Calmodulin gene regions in combination with morphological characters. Of the 177 isolates, 124 (70.1%) were identified as A. alternata, and 53 (29.9%) were A. arborescens. The isolates initially identified as A. tenuissima based on the morphological characteristics could not be separated from those of A. alternata in phylogenetic analysis and thus considered A. alternata. Pathogenicity tests showed that both Alternaria species were pathogenic on mandarin fruit at both 5°C and 20°C. Our results indicated that two Alternaria species, A. alternata and A. arborescens, were responsible for Alternaria rot of mandarin fruit in California, with A. arborescens causing fruit rot on mandarin being reported for the first time.

Post-harvest Management of Alternaria Induced Rot in Tomato Fruits With Essential Oil of Zanthoxylum armatum DC

Alternaria fruit rot is a major disease caused byAlternaria alternata(Fr.) Keissl., a prolific fungal pathogen. Among post-harvest diseases of tomato, fruit rot induced byA.alternatais the most damaging. Antifungal agents are widely used to control post-harvest management of tomato fruits. However, negative impacts of fungicidal residues in edible fruits and vegetables on human health cannot be over ruled. Eco-friendly ways of controlling Alternaria rot in tomato fruits offer a novel way of tomato rot management. The current study proposes an alternate method in controlling tomato fruit rots throughZanthoxylum armatumDC essential oil (EO) application. Gas chromatography-mass spectrometry profiling showed eucalyptol and sabinene as major components ofZ.armatumEO. Furthermore, EO applied (0.5–4.5 μl/ml) showed significant inhibition ofA. alternatagrowth (p> 0.05) at 4.5 μl concentration tested. Lipid peroxidation assays revealed significant reduction in membrane damage in tomato fruits treated by EO compared to alone inoculated fruits withA.alternata. Elevated activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase coupled with enhanced antioxidants such as ascorbic acid, glutathione, proline, and total phenols in EO-treated fruits may be linked with better fruit rot management than control fruits inoculated withA.alternata-induced rot alone. Mycelia and spore production was dramatically reduced in EO applied tomato fruits overA.alternataalone in tomato fruits (p> 0.05). Interestingly, free radical scavenging activities of EO applied tomato fruits showed significant improvement compared to only pathogen-inoculated tomato fruits. Findings propose practical utility ofZ.armatumEO as a plant-based antifungal for post-harvest management of Alternaria rot in tomato fruits.

Chemical Composition, Crystal Morphology, and Key Gene Expression of the Cuticular Waxes of Goji (Lycium barbarum L.) Berries.

The cuticular wax of fruit is closely related to quality, storability, and pathogen susceptibility after harvest. However, little is known about the cuticular wax of goji berry (Lycium barbarum L.) cultivars. In the present study, the chemical composition, crystal structures, and expression levels of associated genes of the cuticular wax of six goji cultivars were investigated. We detected 70 epicuticular wax compounds in six goji cultivars. Among them, fatty acids, alkanes, and primary alcohols were the major components of the cuticular wax of goji berries, which were related to the formation of irregular lamellar crystal structures. The terpenoid compounds in the cuticular wax of goji berries were highly resistant to Alternaria rot. Moreover, the CER1, CER6, LACS1, MAH1, LTP4, ABC11, MYB96, and WIN1 genes in goji berries might be closely related to wax synthesis. These results provide valuable information for breeding and screening goji cultivars suitable for postharvest storage.

Essential Oil of Baccharis dracunculifolia (Asteraceae) Decreases Alternaria Rot in Pitahaya

Alternaria rot, caused by Alternaria alternata, is one of the most destructive diseases of pitahaya (Hylocereus spp.). We investigated the effect of the essential oil of Baccharis dracunculifolia (Asteraceae) (EOB) in the control of A. alternata. Two studies were performed in Petri dishes containing potato dextrose agar medium amended with concentrations of the EOB ranging from 5 to 1,000 µg mL-1 (first study) and from 30 to 2,000 µg mL-1. The diameter of the fungal colony was recorded daily. These data were used to calculate the the area under the mycelial growth progress curve (AUMGPC) and mycelial growth index (MGI). In the third study, the control of Alternaria rot in pitahaya fruits by EOB was investigated by adding the EOB into an edible coat based on cassava starch and sorbitol which was prepared in Tween 20. Three treatments, containing EOB at 500, 1,000 or 2,000 µg mL-1, were assessed. Two additional treatments, one containing water and another containing only the edible coating served as controls. Pitahaya fruits were immersed in those solutions for 10 min, allowed to dry and inoculated with A. alternata 48 h later. The EOB was found to inhibit the mycelial growth and a negative and quadratic model best described the relationship of the EOB concentrations with MGI and AUMGPC. Results from the experiment performed with pitahaya fruits showed that Alternaria rot was decreased with increasing EOB concentrations. Therefore, EOB is a promising and ecofriendly method that may be included in the management of Alternaria rot in pitahya.

In vitro efficacy of fungicides on mycelial growth and spore germination of Alternaria alternata and Mucor plumbeus

Tomato fruits were infected by various pathogens especially fungal pathogens under storage conditions as well as in field conditions. It was revealed that tomato fruits are attacked by Alternaria alternata causing Alternaria rot of tomato and Mucor plumbeus causing Mucor rot of tomato. Antifungal activity of some fungicides was undertaken during the present study. Different concentrations of fungicides brought about significant reduction in the mycelial growth and spore germination of Alternaria alternata and Mucor plumbeus under in vitro conditions. Hexaconozole proved highly effective in inhibiting the mycelial growth and spore germination of Alternaria alternata followed by carbendazim and copper oxychloride respectively. However, the most effective fungicide in inhibiting the mycelial growth and spore germination of Mucor plumbeus was hexaconozole followed by carbendazim and copper oxychloride respectively. Keywords: In vitro, fungicides, Alternaria alternata and Mucor plumbeus, mycelial growth, spore germination

Epsilon-poly-l-lysine (ε-PL) exhibits multifaceted antifungal mechanisms of action that control postharvest Alternaria rot

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial poly-cationic peptide widely applied as a natural preservative in the food industry, whereas its application in preventing postharvest loss of fruit was largely absent. This study investigated the antifungal activity of ε-PL and determined the possible mechanisms involved. The in vivo results indicated that 500 mg L−1 exogenous ε-PL treatment significantly inhibited black spot rot in apple, jujube, and tomato. The lesion diameter inhibition rate was range from 20.11% to 29.09% by 500 mg L−1 ε-PL treatment. ε-PL exerts antifungal activity against A. alternata in vitro, the half-inhibition concentration is 160.1 mg L−1. ε-PL induced morphology and ultrastructure change on the pathogen, which resulted in the inhibition of A. alternata. This was accomplished by disturbing pathogen membrane integrity and functionality. The fluorometric assay confirmed that ε-PL induced endogenous reactive oxygen species formation and accumulation in A. alternata and the elicited severe lipid peroxidation that caused membrane lesions. Further, ε-PL treatment enhanced the expression of genes involved in antioxidant metabolism and pathogenesis-related responses in apple fruit. These findings illustrated that ε-PL exhibits multifaceted antifungal activity by the direct effect on the pathogen as well as induce host defense responses. ε-PL may be conducive as a promising alternative for Alternaria rot management.

Characterization and Quantification of Postharvest Losses of Apple Fruit Stored under Commercial Conditions

The objectives of this study were to characterize and quantify postharvest losses of apples under commercial conditions in Santa Catarina state, Brazil. Two experiments were conducted using ‘Gala’ and ‘Fuji’ apples. The first experiment was to characterize and quantify the most important causes of loss of fruit treated or not treated with 1-methylcyclopropene (1-MCP) then held in controlled atmosphere (CA) storage. This experiment was conducted in commercial storage facilities from 2007 to 2010. In each year, 10 samples of ≈380 kg each for ‘Gala’ and 400 kg each for ‘Fuji’ were collected from bins of commercially harvested fruit from each of 15 ‘Gala’ and 17 ‘Fuji’ orchards. Half of the samples from each orchard were treated with 1-MCP at harvest. Fruit were stored in CA, at 0.7 °C, for 150 to 300 days. After storage, one subsample of 100 disorder-free apples were selected from each sample and held at 22 °C for 7 days to simulate shelf-life conditions. The fruit were analyzed after CA storage and shelf life for the incidence of disorders. The second experiment was conducted in 2011 to identify the main fungi causing decay during storage. In this study, apples were stored in 10 commercial CA storage rooms at 0.7 °C for 180 to 240 days. After storage, fruit with decay symptoms were collected at the commercial sorting line. A total of 10 samples of 100 decayed apples were taken throughout the sorting period for each cultivar and storage room. The fungal decays were identified by visual symptoms on each fruit. Total apple losses during storage varied from 3.9% to 12.1% for ‘Gala’ and 6.6% to 8.4% for ‘Fuji’, depending on the year and 1-MCP treatment. During storage, deterioration caused by fungal decay was ≈60% and 80% of total losses for ‘Gala’ and ‘Fuji’, respectively. During shelf life, additional losses caused by fungal decay ranged from 8.4% to 17.6% for ‘Gala’ and 12.4% to 27.2% for ‘Fuji’, depending on the year. Senescent breakdown and superficial scald were the major physiological disorders. 1-MCP treatment had no effect on losses due to decay. Bull’s-eye rot, blue mold, gray mold, and alternaria rot were the most prevalent fungal decay symptoms, accounting for 52%, 27%, 9% and 10% of ‘Gala’ losses and 42%, 25%, 18% and 5% of ‘Fuji’ losses, respectively. Sources of variability for losses among years and orchards is discussed.

Induction of defense response against Alternaria rot in Zaosu pear fruit by exogenous L-lysine through regulating ROS metabolism and activating defense-related proteins

L-lysine, an important basic amino acid, its catabolic pathway is activated upon microbial pathogen attack in plants and has a central role in plant immunity. The control effects of exogenous L-lysine treatment on Alternaria rot in postharvest ‘Zaosu’ pear fruit and possible mechanisms involved were studied. The results showed that L-lysine treatment inhibited Alternaria rot development and the effect was negatively correlated with the treatment concentration, lesion diameter of 0.1 mM L-lysine treated fruit was 43.7 % lower than that of the control 15 d after treatment. Further studies showed that L-lysine treatment significantly suppressed O2−, H2O2, Malondialdehyde (MDA) content, and enhanced catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities and gene expression in pear fruit. β-1,3-glucanase (GLU), and chitinase (CHI) activities and PbrGLU, PbrCHI, and PbrPR-1 gene expression were also induced by exogenous L-lysine. The findings suggest that postharvest L-lysine treatment effectively enhanced disease resistance through inhibiting reactive oxygen species (ROS) production and activating defense-related protein in pear fruit.

Effect of Metabolites Produced by Bacillus atrophaeus and Brevibacterium frigoritolerans Strains on Postharvest Biocontrol of Alternaria alternata in Tomato (Solanum lycopersicum L.).

In the present study, the antifungal activity of metabolites produced by Bacillus atrophaeus B5 and a new Brevibacterium strain against Alternaria alternata was evaluated. Assays in vitro and in vivo on tomato fruit during postharvest were made. Based on the 16S rDNA gene sequence analysis, the new strain (strain B7) was identified as Brevibacterium frigoritolerans. Metabolites produced by both bacterial strains reduced the spore germination of A. alternata in vitro and decreased the severity of the alternaria rot disease on tomato fruit during postharvest. This is the first report that demonstrates the potential of B. frigoritolerans B7 as a biocontrol agent against this fungal phytopathogen. The use of metabolites produced by B. atrophaeus B5 and B. frigoritolerans B7 represents a new approach to reduce the use of chemical pesticides and control fungal decay during the postharvest stage.

Chemical Composition of Essential Oil of Ocimum basilicum L. and Its Potential in Managing the Alternaria Rot of Tomato

: The essential oil obtained by hydro-distillation of leaves of Ocimum basilicum (basil essential oil) was analyzed for its potential to manage the Alternaria alternata causal agent of Alternaria rot of tomato, in vitro and in vivo. Further, the chemical composition of the extracted basil oil was analyzed by the GC/MS. A total of 20 chemical compounds were identified in the hydro-distilled basil essential oil. The primary constituents of the basil essential oil were methyl chavicol (38.2 %) and linalool (28.7 %). In vitro, the basil essential oil successfully constrained the growth and conidia germination of A. alternata. The highest concentration of basil essential oil (10 %) provided maximum growth reduction (88.0 %) of the fungus. Likewise, the highest concentration of basil essential oil (10 %) caused a 90 % reduction in conidia germination. In vivo, the tomatoes treated with 4 % and 6 % basil essential oil had 33.3 % and 55.5 % respectively, reduction in the infected wounds as compared to control (untreated inoculated). Also, there were 52.9 % and 62.3 % less A. alternata infected fruits when treated with 4 % and 6 % basil essential oil respectively as compared to control (untreated inoculated). This proves that the basil essential oil was able to manage the Alternaria rot of tomato successfully. Therefore, the basil essential oil can substitute the synthetic fungicides to manage the Alternaria rot of tomato.

Inhibitory effect of postharvest yeast mannan treatment on Alternaria rot of tomato fruit involving the enhancement of hemicellulose polysaccharides and antioxidant metabolism

In order to study the effects of yeast mannan (YM) treatment on postharvest infection of tomatoes, the fruit were vacuum-infiltrated and coated with different concentrations of YM. The YM treatment at 1.0 g L−1 effectively reduced the decay of tomatoes caused by Alternaria alternata, and suppressed fruit color change and ethylene biosynthesis during storage. The YM-treated tomatoes retained a high level of tightly bonded hemicellulose (TBH) in cell wall materials, and compared to the control, the TBH possessed many structural polymers rich in xylose and mannose. YM treatment reduced lipid peroxidation and hydrogen peroxide accumulation in tomato by enhancing the activities of antioxidant enzymes including peroxidase, superoxide dismutase and catalase. The alleviation of oxidative stress by YM helped inactivate the nonenzymatic cleavage of TBH polysaccharides in the cell wall architecture, which could enhance fruit resistance against pathogenic infections and thereby suppress postharvest quality deterioration of tomatoes during storage.

Postharvest use of natamycin to control Alternaria rot on blueberry fruit caused by Alternaria alternata and A. arborescens

Abstract Alternaria rot caused by Alternaria alternata and A. arborescens is a major postharvest disease affecting blueberries in California. The effectiveness of natamycin, a newly registered biofungicide in the United States, was evaluated for its potential as a postharvest treatment to control Alternaria rot. The baseline sensitivities to natamycin in A. alternata and A. arborescens were established. The effective concentrations of natamycin for 50 % reduction in growth relative to control (EC50) of 34 A. alternata isolates ranged from 0.640 to 1.032 mg L−1 with a mean of 0.778 ± 0.097 mg L−1 for conidial germination, and from 2.660 to 4.330 mg L−1 with a mean of 3.390 ± 0.435 mg L−1 for mycelial growth. EC50 values of natamycin for 34 A. arborescens isolates ranged from 0.540 to 1.335 mg L−1 with a mean of 0.950 ± 0.162 mg L−1 for conidial germination, and from 0.610 to 3.430 mg L−1 with a mean of 1.920 ± 0.637 mg L−1 for mycelial growth. For A. alternata isolates, the minimum inhibitory concentrations (MICs) for conidial germination were 5 mg L−1 for 27 isolates and 10 mg L−1 for 7 isolates, and the MICs for mycelial growth were 25 mg L−1 for all 34 isolates. For A. arborescens isolates, the MICs for conidial germination were 10 mg L−1 for 5 isolates and more than 10 mg L−1 for 29 isolates, and the MICs for mycelial growth were 10 mg L−1 for 6 isolates and 25 mg L−1 for 28 isolates. Control tests on blueberry fruit inoculated with four isolates of each Alternaria alternata and A. arborescens showed that even a quarter concentration of the label rate of natamycin significantly reduced disease incidence and severity of Alternaria rot, regardless of application method or incubation condition. Our results suggest that natamycin can be an effective tool for control of postharvest Alternaria rot in blueberry.