Control Of Green Mold Research Articles

ALTERNATIVE TREATMENTS FOR POSTHARVEST DECAY CONTROL ON 'PONKAN' TANGERINES

Penicillium spp. fungi are the most frequent pathogens associated to postharvest decay in citrus fruit. Pre- and postharvest chemical sprays are the most widespread methods to reduce decay incidence, but alternative substances have been reported as promising substitutes for postharvest treatments. Here we evaluated the effects of different combinations of sodium bicarbonate and potassium sorbate and heat treatments in single or combined applications as alternative treatments for the control of green and blue mold and on the postharvest quality of ‘Ponkan’ tangerines in comparison with control treatments using chlorine dioxide and imazalil. The tangerines were evaluated for internal quality and decay incidence after 15 or 30 days of cold storage at 5°C plus 5 additional days at room temperature. Quality traits were not affected by any of the treatments. Sodium bicarbonate at 2% (w/v) and potassium sorbate at 0.5% (w/v) significantly reduced decay on ‘Ponkan’ fruit after 30 days of storage. However, using these salts at 3% and 1%, respectively, in an immersion treatment at 58°C for 30 s affected peel brightness. Further investigations on salt and heat combinations are needed to determine if these are feasible alternatives to fungicides to control postharvest decay of citrus fruit.

The Ability of the Antagonist Yeast Pichia Guilliermondii Strain Z1 to Suppress Green Mould Infection in Citrus Fruit.

In previous studies it was shown that Pichia guilliermondii strain Z1, isolated from healthy Moroccan citrus Valencia-Late oranges, was effective against Penicillium italicum. Here the effectiveness of strain Z1 was assessed against Penicillium digitatum, the causal agent of green mould, under different temperature (5-25°C) and relative humidity (RH) (45-100%) regimes for its reliable and large-scale application in packinghouse. All main effects and interactions were significant (P<0.0001). In the pathogen control, the largest lesion diameter was at an RH range between 98 and 100%, regardless of the incubation temperature. The efficacy of strain Z1 was not dependent on the environment and reduced disease incidence by >80%. Its applications as a formulated product significantly reduced the incidence of infected fruit (55%) and the percentage of infected wounds (47%) compared to the only pathogen control treatment. However, disease control with formulated product was significantly less than that obtained with thiabendazole (30%) or strain Z1 culturable cells (35%). These results highlight that strain Z1 is an effective biological control agent for control of green mould under varying environmental conditions, and control may be optimized by combining its use with other environmentally-safe post-harvest treatments or improved formulation.

Curative control of citrus green mould by imazalil as influenced by infection age, wound size, fruit exposure time, solution pH and fruit brushing after treatment

Green mould (Penicillium digitatum) is a major cause of postharvest losses in citrus. Wounds and infection can be inflicted during the harvest process and should be controlled during postharvest stages to prevent decay. Imazalil (IMZ) in the sulphate formulation is currently applied by the majority of South African packhouses through an aqueous dip treatment. In this study the effects of incubation time (infection age), exposure time, solution pH, wounds size and fruit brushing after dip treatments on residue loading and curative green mould control were investigated. Exposure time did not have a significant effect on residue loading on fruit dipped in pH 3 solutions of IMZ (<2.00μgg−1). Increasing the pH to 6 resulted in significantly increased residue loading, which increased with longer exposure time, but mostly to levels below the maximum residue level of 5μgg−1 after 180s. Post-dip treatment brushing reduced residue levels obtained in IMZ pH 3 solutions by up to 90% to levels <0.5μgg−1; however, curative control of the IMZ sensitive (S) isolate was mostly unaffected, but with poor sporulation inhibition. At pH 6, post-dip brushing reduced residues to ≈60%; again curative control of the sensitive isolate was unaffected, but with better sporulation inhibition than the pH 3 treatments. Wounded rind sections loaded higher residue levels compared with intact rind sections, and large wounds loaded higher levels than small wounds (≈10.19, ≈9.06 and ≈7.91μgg−1 for large, small and no wound, respectively). Curative control of infections originating from large wounds was significantly better than those from small wounds. The ability of IMZ to control sensitive green mould infections declined from 6 and 12h after inoculation on Clementine mandarin fruit of infections inflicted by small and large wounds, respectively; on navel orange fruit, curative control declined 18 and 36h after inoculation for the respective wound size treatments. This work shows the importance of timely fungicide treatment after harvest especially on more susceptible citrus types. Results also indicate that excess residues can be stripped from the fruit, retaining residues necessary for curative control in the wound sites. However, reduced residue loading compromised the sporulation inhibition activity of IMZ.

Effect of postharvest application of chitosan combined with clove oil against citrus green mold

The antifungal activity of chitosan combined with clove oil against Penicillium digitatum, the causal agent of citrus green mold, was tested in vitro and in vivo. Chitosan combined with clove oil inhibited mycelial growth more than individual treatments, which was related to the greater release of cellular material and the largest alterations in hyphal morphology of P. digitatum. However, compared to chitosan alone, 1% chitosan coatings combined with various amounts of clove oil (0.5, 1 or 2mL/L) showed no greater ability in controlling decay development on artificially inoculated citrus fruit. 1% chitosan combined with 0.5mL/L clove oil appeared to slightly reduce lesion diameter and enhanced the activities of defense enzymes, including chitinase and phenylalanine ammonia-lyase at the later stages of incubation. This study indicated that the synergistic antifungal activity of chitosan-clove oil observed in in vitro studies was not found in in vivo tests. Therefore, the data suggest that a coating of 1% chitosan alone, not combined with clove oil, can effectively contribute to the control of green mold on citrus fruit.

Postharvest efficacy of resistance inducers for the control of green mold on important Sicilian citrus varieties

The disease reducing activity of acibenzolar-S-methyl (ASM), chitosan and β-aminobutyric acid (BABA) against postharvest green mold (GM) of citrus fruit, Penicillium digitatum, was investigated by tests performed in in vitro and in vivo conditions. The inhibition of the mycelial growth of P. digitatum by ASM, chitosan and BABA at different concentrations was evaluated on potato dextrose agar and on orange peel extract agar. The pathogen was totally inhibited (100% growth inhibition) by chitosan at concentrations ≥ 0.1% and by BABA at 1000 mmol and only poorly inhibited by ASM at 0.5% (47% growth inhibition). Inhibitory effects of chitosan and BABA were confirmed by P. digitatum conidial germination tests. The performances of these chemical compounds were evaluated in vivo on artificially inoculated orange, lemon and grapefruit cultivars. On the whole, chitosan significantly reduced GM decay on ‘Valencia’ and ‘Washington Navel’ orange, ‘Femminello’ lemon and grapefruit cv. Marsh Seedless at the concentration of 0.5% (6–20% disease incidence), and BABA provided the best results on ‘Tarocco Scire’and ‘Valencia’ orange and grapefruit cv. Marsh Seedless at the concentration of 1000 mmol (12–16% disease incidence). ASM did not show any efficacy. This study demonstrated that the effects of chitosan and BABA on GM in citrus fruits may be associated with their direct fungitoxic properties against the pathogen. Treatments with chitosan and BABA could be recommended for inclusion in postharvest decay management programs for citrus packinghouses and their use may be an effective method to improve the integrated pest management strategy.

Quaternary chitosan oligomers enhance resistance and biocontrol efficacy of Rhodosporidium paludigenum to green mold in satsuma orange

This study investigated the capacity of chitosan oligomers (COS), applied before harvest singly or in combination with antagonists, in controlling postharvest green mold caused by Penicillium digitatum in satsuma orange. Oranges treated with COS or Rhodosporidium paludigenum were observed having a delay in onset and progression of disease symptoms relative to wounded controls. Preharvest application of COS at different concentrations achieved similar biocontrol efficiency rates in green mold control after 4 days storage. However, the combination of pre-COS (1%, w/v) and R. paludigenum showed a more effective decay control than any other treatments. COS (1%, w/v) alone did not negatively affect R. paludigenum growth in wounds, but severely inhibited P. digitatum spore germination than lower dose treatments in vitro. The expression levels of the defense-related genes chitinase and phenylalanine ammonia lyase increased with decreased disease symptoms. Moreover, this phenomenon was more prominent in the integrated treatments than in the individual ones.

Thiabendazole residue loading in dip, drench and wax coating applications to control green mould and chilling injury on citrus fruit

Green mould (caused by Penicillium digitatum) is a major cause of postharvest losses in citrus. Residue loading of thiabendazole (TBZ) with application methods typically used in South African packhouses and green mould control was studied. TBZ was applied curatively and protectively in dip, drench and wax coating treatments and fruit were inoculated with a TBZ-sensitive or a TBZ-resistant isolate of P. digitatum. The dip treatments consisted of TBZ concentrations of 0–2000μgmL−1; fruit were dipped for 60s at 22°C at a pH of 7. Residues differed between fruit batches and ranged from 0.5 to 1.7μgg−1 at 1000μgmL−1 TBZ. Curative dip treatments almost completely controlled green mould (>96% at 1000μgmL−1 TBZ). The residue level needed for 75% curative control ranged from 0.06 to 0.22μgg−1, depending on citrus type. Protective treatments were unreliable and control varied from 17% to 97.9% at 1000μgmL−1 TBZ between fruit batches. Drench treatments consisted of exposure times of 30, 60 and 90s with 1000 or 2000μgmL−1 TBZ. Average TBZ residues were 2.14μgg−1 for Clementine mandarin fruit and 3.50μgg−1 for navel orange fruit. Green mould control on navel orange fruit resulted in 66–92%, 34–90% and 9–38% control for curative treatments after 6 and 24h and protective treatments, respectively, depending on fruit batch. Wax with 4000μgmL−1 TBZ was applied at 0.6, 1.2 and 1.8Lwaxton−1 fruit. Chilling injury was evaluated after fruit storage at −0.5°C for 40 days. Average TBZ residues loaded was 1.3, 1.3 and 2.7μgg−1 at the recommended 1.2Lton−1 for Satsuma mandarin, Clementine mandarin and Valencia orange fruit, respectively. Protective treatments showed lower infection levels (14–20%) than curative treatments (27–40%) for Valencia orange fruit. The same trend was observed with Satsuma (92–95% curative; 87–90% protective) and Clementine mandarin fruit (82–90% curative; 59–88% protective), but control was relatively poor. TBZ application in wax exceeded 5μgg−1 at higher wax loads (1.2 and 1.8Lton−1). Wax treatments showed a significant reduction in chilling injury; TBZ had an additive effect. TBZ resistant isolates could not be controlled.

Control of postharvest green mould of citrus by haliscosamine isolated from Haliclona viscosa sponge

The aim of this study was to evaluate the antifungal activity of haliscosamine isolated from Haliclona viscosa sea sponge from the Moroccan Atlantic coast against Penicillium digitatum, the causal agent of citrus green mould. The in vitro antifungal activity of haliscosamine, determined using the agar disc‐diffusion method, showed that haliscosamine and DESOGERME SP VEGETAUX® (reference product) have fungicidal activity with inhibition diameters of 19 and 18 mm, respectively. Haliscosamine and a positive control (DESOGERME SP VEGETAUX®) were tested in vivo in comparison with a negative control on orange fruits in normal storage conditions. This test showed that after four weeks of storage, the rate of decay of citrus fruits treated with haliscosamine or DESOGERME does not exceed 14%, whereas in the negative control the decay rate is 77%. The results of in vitro and in vivo tests indicate that haliscosamine and DESOGERME SP VEGETAUX® have an important antifungal potential against P. digitatum and that haliscosamine (a natural product) may represent an alternative to the use of chemical fungicides.

Editorial

Last year I was honoured to be elected by representatives of the member countries as EPPO's new Director-General. One of the responsibilities that comes with that job is Editor-in-Chief of the EPPO Bulletin. In practice most of the work of producing the Bulletin is undertaken by Madeleine McMullen, who is our Managing Editor, with others in the EPPO Secretariat helping to review papers and translate abstracts. That will continue to be the case. What I would like to do in my role as Editor-in-Chief, initially, is understand what you want from the Bulletin as readers and contributors, and ensure within the broad purposes of the Bulletin and available resources that we are meeting those needs as well as we can. The EPPO Bulletin is the official gazette of our organization, publishing Standards which we have formally adopted and reports of our activities, including proceedings of our workshops and conferences. In addition, we publish submitted papers on all aspects of plant protection, in particular those of special interest to the National Plant Protection Organizations of our member countries. The current issue contains papers on a representative range of topics from across EPPO's fields of interest. It includes a datasheet on the Invasive alien plant Baccharis halimifolia, and a revised version of the Standard PM 3 on ‘Testing growing medium and plants in growing medium’. These are followed by recommendations and conclusions from 2 EPPO Workshops held in 2013 on ‘Experiences with implementation of zonal evaluation of plant protection products’ and on ‘Management of Globodera rostochiensis and G. pallida’. The rest of the issue brings together a very wide range of authored articles on plant quarantine and plant protection products. A report on furniture as a pathway for pests is included along with results from a survey on pests in wood packaging material. Pest Risk Analysis is further developed in a quantitative interpretation of the entry section of the EPPO decision-support scheme. A paper from Syria provides information on parasitoids of scale pests and recommendations for the EPPO Positive List. A potential product for the control of postharvest green mould is evaluated and semi field trials for molluscicide efficacy are presented. Several first reports provide important updates on the geographical distribution of a range of pests and information on phytosanitary status of different crops have been provided by experts from across the EPPO region. Is this the right range of topics for the EPPO Bulletin to cover? Are the papers covering the topics in the right way and at the right length for you, as readers? If you have any views on the EPPO Bulletin do let me know via hq@eppo.int so we can take them into account as we start to prepare the content for future issues.

Effect of Pichia membranaefaciens in combination with salicylic acid on postharvest blue and green mold decay in citrus fruits

The separate or combined effects of Pichia membranaefaciens and salicylic acid (SA) on the control of blue and green mold decay in citrus fruits were investigated. Results indicate that combining P. membranaefaciens (1×108CFUml−1) with SA (10μgml−1) either in a point-inoculated or dipped treatment provided a more effective control of blue and green mold than separately applying yeast or SA. SA (10μgml−1) did not significantly affect P. membranaefaciens growth in vitro but slightly increased the yeast population in fruit wounds. P. membranaefaciens plus SA effectively enhanced the phenylalanine ammonia-lyase, peroxidase, polyphenoloxidase, chitinase, and β-1,3-glucanase activities and stimulated the synthesis of phenolic compounds. The combined treatment did not impair quality parameters such as weight loss or titratable acidity, but resulted in low average natural infection incidence and increased total soluble solids and ascorbic acid contents in citrus fruits after 14d at 20°C.

Residuos en frutos de naranja del fungicida imazalil aplicado en postcosecha y su efecto en el control de moho verde

El control del moho verde (causado por el hongo Penicillium digitatum) en las plantas de empaque de cítricos de Uruguay se basa principalmente en el uso del fungicida imazalil (IMZ). La aplicación continuada de este fungicida generó un aumento en la frecuencia de cepas resistentes y, por tanto, de la dosis del fungicida utilizada. El objetivo del presente trabajo fue determinar la residualidad del fungicida IMZ durante el almacenamiento refrigerado de las variedades de naranja (Citrus sinensis [L.] Osbeck) Washington Navel y Valencia y su relación con el control del moho verde. Para ello, frutos de naranja var. Valencia fueron artificialmente inoculados con los aislamientos de P. digitatum sensible y resistente a IMZ y frutos de naranja var. Washington Navel solo con el aislamiento resistente. Luego de 18-20 h, los frutos fueron tratados con Imazalil a 500 y 1000 mg kg-1 aplicado en solución acuosa solo o en combinación con bicarbonato de sodio (BCS) al 3%. Con la aplicación de la cera se aplicó IMZ a una concentración de 3000 mg kg-1. Las variables analizadas fueron la incidencia del moho verde y el nivel de residuo del fungicida imazalil. Las evaluaciones fueron realizadas luego de 12, 19, 26 y 33 días de almacenamiento en frío y luego de siete días de vida comercial. En naranjas de la variedad Washington Navel, el residuo de IMZ fue menor a 2,0 mg kg-1 en todos los tratamientos, tanto aplicado en solución a 20 ºC ó 50 ºC como solo o en mezcla con BCS. La aplicación de IMZ en la cera determinó un nivel de residuos mínimo sobre la fruta de 2,48 mg kg-1y se mantuvo alto hasta el final del período de evaluación. En la variedad Valencia, los residuos de IMZ fueron menores a 0,70 mg kg-1 para dosis de 1000 mg kg-1 y se duplicaron con la aplicación a 50 ºC; mientras que los residuos de la aplicación de IMZ en cera fueron siempre mayores a 3,0 mg kg-1. En ninguna de las variedades el aislamiento resistente a IMZ fue controlado, aún con niveles de residuos de IMZ superiores a 3,0 mg kg-1. En cambio el aislamiento sensible fue controlado con un residuo promedio de IMZ superior a 2,0 mg kg-1 o cuando el fungicida fue combinado con BCS.

Effects of citrus wax coating and brush type on imazalil residue loading, green mould control and fruit quality retention of sweet oranges

Wax application plays an important role in prolonging fruit quality, and the addition of imazalil (IMZ) furthermore protects fruit against green mould caused by Penicillium digitatum. The objectives of this study were to evaluate green mould control and quality preservation effects of carnauba or polyethylene citrus coatings supplemented with IMZ, as well as the effect of synthetic or horsehair brush types used on sweet orange fruit. Single applications of IMZ at 3000μgmL−1 at rates of 0.6, 1.2 and 1.8Lt−1 resulted in residues that increased with increasing coating loads on navel oranges (1.31 to 3.32μgg−1) and Valencia oranges (3.22 to 6.00μgg−1). Coating with IMZ generally provided poorer curative control (≈14%) than protective control (≈58%), with less sporulation in treatments using horsehair (≈59%) than synthetic brushes (≈64%). More fruit weight and firmness losses were found in fruit treated with the polyethylene coating (≈1.18 and ≈0.93 ratios of treated vs. untreated, respectively) and lower in carnauba treated fruit (≈0.76 and ≈0.74 ratios, respectively). However, polyethylene coatings resulted in shinier fruit before (≈10.85 shine ratio) and after storage (11.60), whereas carnauba coatings resulted in lower shine ratios (≈7.45 and 10.15, respectively). Gas (CO2) exchange ratios remained similar for both waxes (≈0.67). Higher polyethylene coating loads (1.8Lt−1) resulted in off-tastes similar to uncoated control fruit (≈2.21 rating on a 5-point scale) and higher than the rating for carnauba coated fruit (≈1.82) at this rate. Scanning electron micrographs showed an amorphous crystallised natural wax layer with uncovered stomatal pores on the surface of uncoated fruit. The thickness of the applied wax layer increased with increasing coating load. A single application of IMZ in wax provided good protective green mould control and sporulation inhibition, with differing effects on some fruit quality parameters due to coating and brush types.

Avaliação de microrganismos antagônicos, Saccharomyces cerevisiae e Bacillus subtilis para o controle de Penicillium digitatum

Os frutos cítricos são afetados por diversas doenças, especialmente as fúngicas, as quais afetam a produtividade e a qualidade, principalmente quando se visa ao mercado de frutas frescas, seja para o mercado interno, seja para a exportação. Dentre as doenças fúngicas que ocorrem na fase de pós-colheita, destaca-se o bolor verde, causado por Penicillium digitatum. As medidas de controle baseiam-se, principalmente, no tratamento de frutos com diferentes combinações de fungicidas no packing-house. Devido às restrições quanto à presença de resíduos de fungicidas em frutos de citros e ao crescente desenvolvimento de linhagens resistentes dos patógenos a tais fungicidas, torna-se necessária a busca de alternativas de controle, como o controle biológico. Portanto, este trabalho teve por objetivos: (i) verificar o efeito antagônico de agentes de controle biológico (ACBs), sendo 06 isolados de Saccharomyces cerevisiae e 13 isolados de Bacillus subtilis contra P. digitatum; (ii) estudar as interações in vitro entre ACBs e o fitopatógeno; (iii) verificar o efeito da integração dos antagonistas com bicarbonato de sódio e cera de carnaúba no controle do bolor verde. Os resultados mostraram que a maioria dos isolados bacterianos e todos os isolados de levedura inibiram o crescimento micelial do fitopatógeno. Somente um isolado de Bacillus subtilis (ACB-84) foi capaz de inibir a germinação de P. digitatum com 72% de inibição, enquanto ACB-K1 e ACB-CR1 (S. cerevisiae) foram os mais eficientes com inibições de 78 e 85,7%, respectivamente; a adição de sacarose (a 0,5%) favoreceu ainda mais a inibição da germinação dos conídios pelos isolados da levedura. Os resultados de controle in vivo mostraram a viabilidade de S. cerevisiae ACB-K1 e ACB-CR1 para o controle de P. digitatum, em frutos de lima-ácida 'Tahiti' e laranja 'Hamlin', respectivamente; a associação de bicarbonato de sódio com agentes de biocontrole não resultou em melhorias no controle curativo do bolor verde; cera de carnaúba (18% de SST) favoreceu a atividade antagonística de S. cerevisiae, e tal efeito dependeu da variedade dos frutos cítricos em estudo e do isolado da levedura utilizado para o biocontrole.

Control of green mould of citrus by using Trichoderma harzianum, humic acid or garlic

Penicillium digitatum, an aggressive fungus causes post-harvest decay of mandarin sweet orange and Washington navel. In vitro Trichoderma harzianum or humic acid (HA) or powdered cloves of garlic caused inhibition of fungal growth of isolates P1 and P2. Under storage conditions, the fruit citrus is protected by using T. harzianum with standard volume 2.0 ml (9.6 × 106 conidia/ml) and application 24 h before inoculation reduces disease incidence and disease severity after seven days from inoculation with P. digitatum spore suspension (1.0 × 106 spores/ml) compared to control. Spraying the fruit citrus by standard volume of 2.0 ml of either HA or powder cloves of garlic 1% on each fruit 24 h before inoculation reduces disease incidence and disease severity after seven days from inoculation with P. digitatum (1.0 × 106 spores/ml) compared to control. The lowest percentage of disease incidence and disease severity were associated with powder of cloves garlic and followed by HA and T. harzianum during two growing seasons compared with the untreated and control.

De-novo assembly and characterization of the transcriptome of Metschnikowia fructicola reveals differences in gene expression following interaction with Penicillium digitatumand grapefruit peel

BackgroundThe yeast Metschnikowia fructicola is an antagonist with biological control activity against postharvest diseases of several fruits. We performed a transcriptome analysis, using RNA-Seq technology, to examine the response of M. fructicola with citrus fruit and with the postharvest pathogen, Penicillium digitatum.ResultsMore than 26 million sequencing reads were assembled into 9,674 unigenes. Approximately 50% of the unigenes could be annotated based on homology matches in the NCBI database. Based on homology, sequences were annotated with a gene description, gene ontology (GO term), and clustered into functional groups. An analysis of differential expression when the yeast was interacting with the fruit vs. the pathogen revealed more than 250 genes with specific expression responses. In the antagonist-pathogen interaction, genes related to transmembrane, multidrug transport and to amino acid metabolism were induced. In the antagonist-fruit interaction, expression of genes involved in oxidative stress, iron homeostasis, zinc homeostasis, and lipid metabolism were induced. Patterns of gene expression in the two interactions were examined at the individual transcript level by quantitative real-time PCR analysis (RT-qPCR).ConclusionThis study provides new insight into the biology of the tritrophic interactions that occur in a biocontrol system such as the use of the yeast, M. fructicola for the control of green mold on citrus caused by P. digitatum.

Controle em pós-colheita de Penicillium digitatum EM laranja-pera com microrganismos e tratamento térmico

O mercado consumidor está exigindo alimentos sem a presença de resíduos de agrotóxicos. Assim, o trabalho teve como objetivo avaliar o controle do bolor verde, em laranjas-Pera, com agentes de biocontrole (Bacillus subtilis e Bacillus licheniformis, Bacillus subtilis (QST 713)), associados ou não ao tratamento térmico. Para tanto, os frutos foram adquiridos em "packinghouse" antes do processamento, sendo lavados e desinfestados com hipoclorito de sódio. Os frutos submetidos a esses tratamentos foram armazenados, por 11 a 28 dias, em temperatura de 10 ºC e UR 90%±5 ou por oito dias a 20 ºC e UR 90%±5. De modo geral, o tratamento térmico reduziu a severidade da doença determinada pela área abaixo da curva do progresso da doença nos frutos e a incidência natural de doenças em pós-colheita de laranja-Pera. Por outro lado, os agentes de biocontrole não controlaram a doença, mostrando que os organismos testados não apresentaram atividade curativa contra o bolor verde.

Control of postharvest green mold of citrus fruit with yeasts, medicinal plants, and their combination

The use of bio-fungicides and a plant extracts to control postharvest disease was investigated as an alternative to chemical control. The combination of a promising plant extract and yeast were selected through in vitro and in vivo techniques. A combination of Candida utilis TISTR 5001 and Eugenia caryophyllata crude extract was the best combination to attain a reduction in disease incidence and disease severity of Penicillium digitatum on citrus fruit. Colonization was the lowest on fruit treated with the combination of E. caryophylata crude extract and C. utilis TISTR 5001, and survival of C. utilis TISTR 5001 was the highest. The combination of E. caryophylata crude extract and C. utilis TISTR 5001 significantly reduced the natural development of green mold of citrus fruit, and had no effect to fruit quality. The active compound of E. caryophylata was found to be eugenol, based on HPLC and NMR (1H and 13C). Hence, the results indicate that a combination of plant extracts and yeasts posses antifungal activity that can be exploited as an ideal treatment for future plant disease management.

Evaluation of curative and protective control of Penicillium digitatum following imazalil application in wax coating

Imazalil (IMZ) is widely used in citrus packhouses to manage green mould, caused by Penicillium digitatum. The aim of this study was to investigate green mould control efficacy of IMZ applied in a wax coating, and the combination of aqueous dip and coating IMZ applications. Single application of IMZ at 3000μgmL−1 in carnauba wax coating at rates of 0.6, 1.2 and 1.8Ltonne−1 of fruit gave better protective (mean 13% infection) than curative (mean 70% infection) control of the sensitive isolate. Imazalil residue levels increased (0.85 to 1.75μgg−1) with increasing coating load. However, the resistant isolate could not be controlled (>74% infection). Dip only treatment (IMZ sulphate at 500μgmL−1 for 45s and 90s) gave good curative control (≈77%) of the sensitive isolate at residue loading of 0.12–0.73μgg−1. Wax coating only treatment (IMZ at 3000μgmL−1 at 1.8L wax tonne−1) gave good protective control and improved sporulation inhibition (≈80%) at residue loading of 1.32–7.09μgg−1. The MRL of 5μgg−1 was exceeded at higher wax loads on navels and clementines. Double application with dip (45s in IMZ sulphate at 500μgmL−1) followed by 2000μgmL−1 IMZ in wax coating at 0.6, 1.2 and 1.8L wax tonne−1 resulted in residue loading of 1.42 to 2.83μgg−1, increased protective control (≈69%) as well as curative control (≈83%). In all treatments, poor curative and protective control of the resistant isolate was observed (<46% and <55%, respectively). Double application demonstrated superior green mould control by giving good curative and protective control and sporulation inhibition.

감귤 녹색곰팡이병 방제를 위한 천산용 추출물의 실용적 적용

This study tested the antifungal compound obtained from a medicinal plant, Dioscorea quinqueloba Thunb., in order to search the possibility of practical application of this product in agriculture through evaluating its activity using the citrus fruits. The extract of D. quinqueloba Thunb., which has the strongest antifungal activity, was selected as a candidate among 101 plant extracts. Based on this examination concerning antifungal activity of the product on Penicillium digitatum in vitro, it was confirmed its effect of mycelial growth inhibition showed over 87% at 0.5 mg/ml concentration. This natural product showed the stability of the substance, as it was not significantly influenced by pH, temperature, or ultraviolet radiation. While citrus fruits were stored at room temperature, P. digitatum was inoculated into them in order to prepare a similar environmental conditions with epidemic occurrence of the mold. As the result of our investigation, the disease preventive effects of the active antifungal substance evidenced a 100% at 0.5 mg/ml. When the phytotoxicity of the selected natural product on citrus at 2 mg/ml was assessed, we noted no toxic effects. Based on the superior preventive effects from this natural product extracted from the plant, it is presumed to be very useful in agricultural applications for the control of green mold, P. digitatum, which has been occurred often the biggest problem in the storage of citrus fruits.

Imazalil residue loading and green mould control on citrus fruit as affected by formulation, solution pH and exposure time in aqueous dip treatments

Green mould, caused by Penicillium digitatum, is responsible for major postharvest fruit losses on the South African fresh citrus export market. Some of these losses as well as fungicide resistance development can be attributed to sub-optimal imazalil (IMZ) residue loading on citrus fruit (<2μgg−1), which is commonly the case in South African packhouses. This will result in loss of control and sporulation inhibition on decayed fruit. IMZ formulation [IMZ sulphate and emulsifiable concentrate (EC)], solution pH (IMZ sulphate at 500μgmL−1 buffered with NaHCO3 or NaOH to pH 6 and 8) and exposure time (15–540s) were investigated in order to improve IMZ residue loading and the green mould control on Clementine mandarin, ‘Eureka’ lemon, and navel and Valencia orange fruit. Exposure time had no significant effect on residue loading in the unbuffered IMZ sulphate solution (pH 3). No differences were observed between the pH buffers used, but residue loading improved with increase in pH. The maximum residue limit (MRL) of 5.0μgg−1 was exceeded following dip treatment in the IMZ EC (after 75s exposure time), and IMZ sulphate at pH 8 using NaHCO3 (77s) or NaOH (89s) as buffer. The MRL was exceeded after 161s in IMZ sulphate solutions buffered at pH 6 with either NaHCO3 or NaOH. An IMZ residue-loading curve was prepared from which residue levels can be predicted for the control of IMZ-sensitive and IMZ-resistant isolates of P. digitatum. From this model the benchmark residue level for 95% control of an IMZ-sensitive isolate and of an IMZ-resistant isolate were predicted to be 0.81 and 2.64μgg−1, respectively. Residue loading can be improved by adjusting the pH level of an IMZ sulphate solution to 6 or by using the IMZ EC formulation, but exposure time should be restricted to 45s so as not to exceed the MRL. Conversely, sufficient exposure time of ≈90s in an unbuffered IMZ sulphate solution (pH 3) will result to improved green mould control, but with residue loading below 2μgg−1. The resistant isolate could not be controlled adequately with residue levels below the MRL, therewith indicating the practical relevance of IMZ resistance.