Phlyctema Vagabunda Research Articles

Lenticel hydration alters the susceptibility of apple fruit to infection by Phlyctema vagabunda

Bull’s eye rot, caused by Phlyctema vagabunda, is an important postharvest rot of apples. A combination of laboratory and field trials were conducted to examine the relationship between infection and status of apple lenticels. Fruit were hydrated and then inoculated, and climatic factors were compared with inoculations and natural infections in the field. In laboratory trials it was shown that increased lenticel density and size led to more infections. Hydration distended lenticel diameter, and dehydration contracted lenticels. A strong relationship with wind run, leaf wetness and temperature were shown to be important for laboratory inoculations of monthly harvested fruit, natural infections in trap fruit experiments, and monthly field inoculations. It was hypothesised that high wind run (> c. 240 km/day) reduced fruit susceptibility by promoting lenticel closure, and when lenticels were open, temperature limited the formation of an infection stroma. If the stroma did not form, postharvest expression of disease was negligible. Leaf wetness over 28 days was also an important factor for infection, probably because of the effect on micro-crack formation and resealing of lenticels during maturation by components of the cuticle. From these results, pre-harvest application of compounds that close lenticels could provide some control of bull’s eye rot without the need for fungicides.

Antifungal Activity of Propolis Extracts against Postharvest Pathogen Phlyctema vagabunda

Phlyctema vagabunda is one of the main postharvest pathogens in late-harvest apples in Chile. The control of this pathogen is mainly through synthetic fungicides or copper-based compounds; however, there are concerns about the residues of these products in food and the environment. Therefore, there is a need for seeking alternative control strategies, in which propolis, a resinous substance collected by bees with antimicrobial properties, could be an environmentally friendly and safe alternative to control for P. vagabunda. The aim of this study was to characterize and determine the pathogenicity of Chilean isolates of P. vagabunda and to evaluate the antifungal activity of propolis against P. vagabunda in vitro and in vivo conditions. The Chilean isolates were identified as P. vagabunda through morphological and molecular characterization. The concentrations of propolis of 0.5% and 0.05% significantly decreased the mycelial growth and germination of conidia by 88.5% and 100%, respectively. The incidence and severity of the disease in apples also decreased by 57.2% and 61.3%, respectively. The use of propolis extract could be a promising alternative for the control of P. vagabunda in apples.

New insight into morphological and genetic diversity of Phlyctema vagabunda and Neofabraea kienholzii causing bull's eye rot on apple and pear

AbstractFungi of genera Phlyctema and Neofabraea are the causal agents of bull's eye rot, a major postharvest disease of pome fruits. To investigate their morphological and genetic diversity, isolates obtained in Italy and Chile from decayed fruit and rainwater between 2014 and 2019 were grown on two agar media, inoculated onto four fruit cultivars and compared using four marker genes. Consistent intra‐ and interspecies phenotypic differences were recorded among isolates identified as P. vagabunda (two main morphotypes, PvM‐I and PvM‐II, were distinguished) and N. kienholzii. In particular, the Chilean isolates belonging to PvM‐I showed low sporulation in vitro, while isolates belonging to PvM‐II showed the most abundant sporulation and also formed conidiomata deep within fruit tissue. Host cultivar influenced the disease incidence in unwounded, inoculated fruit. Cripps Pink and Golden Delicious apples favoured the formation of P. vagabunda conidiomata and macroconidia, while Granny Smith apples and/or Kaiser pears restricted sporulation of some isolates of PvM‐I. Mycelial cords of P. vagabunda and N. kienholzii were consistently recorded in inoculated fruit, suggesting their possible involvement as a source of inoculum. Propagules of P. vagabunda were present in rainwater collected from apple plants from September to October in Italy. According to sequence analysis of ITS, EF‐1α, TUB2 and ACT1 regions of the fungi, 12 distinct sequence types were identified, three of which were characteristic of isolates from the Southern Hemisphere. The condensed maximum‐likelihood phylogenetic tree separated the 50 P. vagabunda isolates into six phylogroups, suggesting a correlation with their geographical distribution.

Phlyctema vagabunda is the main causal agent of apple bull’s eye rot in New Zealand

Bull’s eye rot is a postharvest storage disease of apples. Until now the cause of this disease in New Zealand was not clear. A survey of 6880 apples from five regions of New Zealand over two seasons was conducted. Neofabraea malicorticis and N. perennans were not found. One hundred and seventy-nine isolates were identified as Phlyctema vagabunda by specific polymerase chain reactions and/or sequencing the β-tubulin gene region followed by phylogenetic analysis. Two isolates were identified as N. kienholzii. Previous records of the presence of N. malicorticis and N. perennans in New Zealand were based on spore morphology and presence in pruning wound cankers. There is overlap in spore morphology for N. malicorticis, N. perennans and P. vagabunda, accounting for misidentifications. Based on our results it is likely that previous records were P. vagabunda, which can also infect pruning wounds.

Endophytic Yeasts for the Biocontrol of Phlyctema vagabunda in Apples

Bull’s-eye rot, produced by Phlyctema vagabunda, is an important postharvest disease in apples. Current measures to control infection include synthetic fungicides, in addition to the application of copper hydroxide and potassium phosphite. However, growing public concern regarding fungicide residues in food has generated interest in developing non-chemical alternative control methods; biological control is one of the most promising alternatives. In this research, native endophytic yeasts were isolated and evaluated for the biocontrol of P. vagabunda in apples. The mechanisms of action involved were also determined. Our research found 2 isolates, Vishniacozyma victoriae EPL4.5 and EPL29.5, which exhibited biocontrol activity against P. vagabunda at 20 °C in apples, the incidence of bull’s-eye rot was reduced by 39% and 61%, respectively, and the severity of the disease was decreased by 67% and 70%, respectively, when apples were inoculated with these yeasts 24 h before applying the pathogen. The main mechanisms that could be involved in the observed biocontrol activity are the ability to form biofilms and the production of volatile organic compounds.

Automated Ribosomal Intergenic Spacer Analysis to Detect Pathogenic Fungi in Dark-Colored Spots on Apple Fruits

Dark-colored spots (DCSs) found on apples at harvest time worldwide significantly reduce the commercial value of the fruits. In this study, we conducted an automated ribosomal intergenic spacer analysis (ARISA) to reliably detect fungal pathogens in these lesions. The fragment sizes of peaks for eight species and two species complexes that might cause DCSs on apples in northern Honshu Island, Japan, were determined on the basis of the ARISA. The fragment sizes for six species ( Botryosphaeria kuwatsukai, Diplocarpon mali, Mycosphaerella pomi, Neonectria galligena, Phlyctema vagabunda, and Venturia inaequalis) were unique, enabling their detection in a single ARISA trial. However, two other species and two species complexes had similar fragment sizes. To identify these fungi, PCR amplifications using species- or genus-specific primers were needed. Using this method to examine the fresh tissue of DCSs (i.e., after removing the epidermis) on commercially produced apples resulted in the detection of six fungal species and two Colletotrichum species complexes. Because the pathogenic fungi in the tissue underlying lesions are most likely the causal agents, these fungi could be responsible for the DCSs on apple fruits. An automated analysis of the PCR products amplified for the ARISA enables the rapid examination of many samples. These results indicate that the ARISA-based technique developed in the present study is useful for the accurate, reliable, and comprehensive detection of the pathogens causing DCSs on apple fruits. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Phylogenetic Diversity and Phenotypic Characterization of Phlyctema vagabunda (syn. Neofabraea alba) and Neofabraea kienholzii Causing Postharvest Bull's Eye Rot of Apple in Northern Italy.

Bull's eye rot, caused by Phlyctema vagabunda and Neofabraea species, is one of the most important postharvest diseases of apple. South Tyrol (northern Italy) is the largest continuous apple-producing area in Europe, with approximately 1 million tons being produced yearly and conserved in technologically advanced storage facilities for several months. Still, studies on the pathogen species causing postharvest bull's eye rot of apple, as well as their diversity and biology, are lacking for this region. Therefore, the main purpose of the present work was to identify and characterize fungal isolates obtained from decayed apple fruit with symptoms of bull's eye rot that were collected in 2018 and 2019 in different packinghouses in South Tyrol. Among more than 1,000 fungal isolates that were obtained, 419 could be assigned to the genera Phlyctema and/or Neofabraea based on rot symptoms on apple fruit and colony morphology on potato dextrose agar. A smaller subset of 101 representative isolates was further analyzed by DNA sequencing of the internal transcribed spacer region. Furthermore, partial segments of the β-tubulin gene, the translation elongation factor 1α gene, and the 16S mitochondrial ribosomal RNA gene were studied. The phylogenetic analyses, including sequences of reference species, showed that P. vagabunda is the dominant species associated with bull's eye rot of apple in the study area, whereas Neofabraea kienholzii was found only on a small number of apple fruit samples. The combination of multilocus sequence data revealed 11 unique genotypes that belonged to P. vagabunda and four to N. kienholzii. To the best of our knowledge, this study is the first to report N. kienholzii as a postharvest pathogen of apple in Italy. Finally, a pathogenicity test demonstrated different degrees of virulence among selected isolates of P. vagabunda and N. kienholzii on the cultivar Golden Delicious. The present study emphasizes the importance of accurate species identification, because different species may vary in their biological and pathogenic characteristics, and consequently require distinct disease management strategies, both in the field and during the postharvest stages.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

<i>Phlyctema vagabunda</i>によるリンゴ果実の小黒斑症状ならびに黄腐病の発生（病原追加）

<i>Phlyctema vagabunda</i>によるリンゴ果実の小黒斑症状ならびに黄腐病の発生（病原追加）

Postharvest applications of fludioxonil and pyrimethanil to control Phlyctema vagabunda on apple in South Africa

Bull's eye rot is a postharvest disease of pome fruit caused by Neofabraea and Phlyctema species infecting the lenticels of fruit in the orchard with symptoms only becoming apparent after months in storage. Chemical control is a valuable method to manage postharvest diseases on pome fruit. In this study, the efficacy of the fungicides fludioxonil (299 mg/L) and pyrimethanil (500 mg/L) was tested on Phlyctema vagabunda Desmazières, the prevalent bull's eye rot species in South Africa. Although both fungicides are registered on pome fruit against other fungal pathogens, neither are specifically registered against bull's eye rot in South Africa. Fruit trials involved curative dip, drench, and thermofogging applications of the fungicides on P. vagabunda inoculated ‘Cripps Pink’ and ‘Fuji’ apple fruit. Furthermore, the variation of pyrimethanil (500 and 1000 mg/L) sensitivity in planta in a dip application was evaluated on six P. vagabunda isolates from the Western Cape of South Africa. The effect of incubation time before treatment was tested in relation to the efficacy of the fungicides.Fludioxonil was highly effective in controlling P. vagabunda incidence as a dip application and moderately effective as a drench and thermofog application. Pyrimethanil had moderate efficacy on both cultivars as a thermofog application. The pyrimethanil dip application was ineffective in controlling disease incidence while the drench application had little efficacy on ‘Fuji’ apples and no efficacy on ‘Cripps Pink’ inoculated fruit. There was no variation in the efficacy of pyrimethanil to P. vagabunda isolates. Incubation time had a significant effect on pyrimethanil efficacy. Delaying pyrimethanil application after inoculation significantly decreased the efficacy of the fungicide in controlling P. vagabunda incidence. The longer inoculated fruit was incubated, the less susceptible the fungicide became. As a recommendation, further investigation into the ability of the fungicides to reduce P. vagabunda as a postharvest application should be conducted on pre-harvest, naturally infected, or conidial suspension inoculated fruit.

Preharvest Detection and Postharvest Incidence of Phlyctema vagabunda on 'Cripps Pink' Apples in South Africa.

Phlyctema vagabunda is responsible for significant postharvest losses in 'Cripps Pink' apples in South Africa. The first objective of this study was to determine the presence and incidence of P. vagabunda on stored commercial 'Cripps Pink' apple in five major pome fruit growing regions in the Western Cape. As the fungus remains latent until postharvest, the second objective was to develop a rapid molecular detection tool to determine the presence of P. vagabunda on asymptomatic 'Cripps Pink' apples from two commercial orchards. Postharvest disease incidence in 'Cripps Pink' apples in the Western Cape ranged from 0 to 73% in the 2010/2011, 0 to 6% in 2011/2012, and 0 to 30% in 2012/2013 seasons. P. vagabunda spores were also detected on 'Cripps Pink' fruit from December to February and from March to April. In December and January, P. vagabunda spores were detected on the 'Hillieri' crab apple pollinator. The knowledge that P. vagabunda conidia are present on the surface of 'Cripps Pink' apples and 'Hillieri' crab apples during the growing season could be applied to improving current management practices in the orchards.

Identification and Characterization of Neofabraea kienholzii and Phlyctema vagabunda Causing Leaf and Shoot Lesions of Olive in California.

California produces over 95% of the olives grown in the United States. In 2017, California's total bearing acreage for olives was 14,570 hectares producing 192,000 tons of olives valued at $186.6 million. During the early spring of 2016, unusual leaf and shoot lesions were detected in olive trees from superhigh-density orchards in the Northern San Joaquin and Sacramento valleys of California. Affected trees displayed numerous leaf and shoot lesions developing at wounds created by mechanical harvesters. The 'Arbosana' cultivar was highly affected by the disease, whereas the disease was sporadic in 'Arbequina' and not found in 'Koroneiki' cultivar. Two fungal species, Neofabraea kienholzii and Phlyctema vagabunda, were found to be consistently associated with the disease, and Koch's postulates were completed. Species identity was confirmed by morphology and molecular data of the partial large subunit rDNA, the internal transcribed spacer region, and partial beta-tubulin region. The disease signs and symptoms are described and illustrated.

Genetic control of α-farnesene production in apple fruit and its role in fungal pathogenesis.

Terpenes are important compounds in plant trophic interactions. A meta-analysis of GC-MS data from a diverse range of apple (Malus × domestica) genotypes revealed that apple fruit produces a range of terpene volatiles, with the predominant terpene being the acyclic branched sesquiterpene (E,E)-α-farnesene. Four quantitative trait loci (QTLs) for α-farnesene production in ripe fruit were identified in a segregating 'Royal Gala' (RG) × 'Granny Smith' (GS) population with one major QTL on linkage group 10 co-locating with the MdAFS1 (α-farnesene synthase-1) gene. Three of the four QTLs were derived from the GS parent, which was consistent with GC-MS analysis of headspace and solvent-extracted terpenes showing that cold-treated GS apples produced higher levels of (E,E)-α-farnesene than RG. Transgenic RG fruit downregulated for MdAFS1 expression produced significantly lower levels of (E,E)-α-farnesene. To evaluate the role of (E,E)-α-farnesene in fungal pathogenesis, MdAFS1 RNA interference transgenic fruit and RG controls were inoculated with three important apple post-harvest pathogens [Colletotrichum acutatum, Penicillium expansum and Neofabraea alba (synonym Phlyctema vagabunda)]. From results obtained over four seasons, we demonstrate that reduced (E,E)-α-farnesene is associated with decreased disease initiation rates of all three pathogens. In each case, the infection rate was significantly reduced 7 days post-inoculation, although the size of successful lesions was comparable with infections on control fruit. These results indicate that (E,E)-α-farnesene production is likely to be an important factor involved in fungal pathogenesis in apple fruit.

Semi-commercial hot water treatments for control of bull’s eye rot of apples

Bull’s eye rot (BER) of apples is caused by a postharvest fungal pathogen (Phlyctema vagabunda syn. Neofabraea alba). Previous laboratory experiments found hot water treatments (HWT) resulted in a significant reduction of BER incidence for artificially inoculated fruit so the feasibility of HWT to control naturally infected fruit in a semi-commercial trial was tested. One bin (1934 fruit) of naturally infected ‘Scired’ apples was harvested from a Hawke’s Bay orchard with a known high incidence of BER, then placed in a coolstore for 1 week until treated. All fruit were passed through a high-pressure water blaster then air dried. Approximately half the contents of the bin (1034 fruit) were packed into Friday trays in apple boxes with a plastic polyliner. The other half (900 fruit) were treated for 2 min with hot water at 51°C in a semi-commercial hot water bath before packing. All fruit were then coolstored for 20 weeks before assessment for BER. This HWT resulted in a 6-fold reduction of BER incidence so was an effective treatment for BER in a semi-commercial test.

Testing new PCR primers and a TaqMan™ probe for detection of <i>Phlyctema vagabunda </i>syn. <i>Neofabraea alba </i>

Phlyctema vagabunda syn. Neofabraea alba is a fungal pathogen that causes bull’s eye rot (BER) of apples. Polymerase chain reaction (PCR) primers complementary to the inter-transcribed spacer region of ribosomal DNA (ITS) and the β-tubulin gene region, and a TaqMan™ probe assay were developed to detect this pathogen. These assays were compared in quantitative PCR (qPCR) reactions for amplification of DNA extracted from several fungal species and from apple tissue. Although the ITS and the β-tubulin primers amplified all N. alba isolates, both primers also amplified a few other fungal species. The TaqMan™ probe used with published primers for N. alba only amplified N. alba isolates. The TaqMan™ assay resulted in the lowest crossing threshold (Ct) values for DNA extracted from apple fruit, leaves, and spores collected on cellophane from eight apple orchards. The TaqMan™ results were correlated with percentage BER (%BER) in a 400-apple sample harvested from the same orchards. The TaqMan™ probe assay was the most sensitive and specific qPCR protocol tested, and Ct values showed the best correlation with %BER.

Phenotypic, molecular and pathogenic characterization of Phlyctema vagabunda, causal agent of olive leprosy

Olive leprosy, caused by the fungus Phlyctema vagabunda, is a classic fruit rot disease widespread in the Mediterranean basin. From 2009 to 2013, new disease symptoms consisting of small circular necrotic leaf lesions, coin branch canker and shoot dieback were observed in Spanish and Portuguese olive orchards showing intense defoliation. Phlyctema‐like anamorphs were consistently isolated from leaves and shoots with symptoms. Representative isolates from affected leaves, shoots and fruits were characterized based on morphology of colonies and conidia, optimum growth temperature and comparison of DNA sequence data from four regions: ITS, tub2, MIT and rpb2. In addition, pathogenicity tests were performed on apple and olive fruits, and on branches and leaves of olive trees. Maximum mycelial growth rate ranged between 0.54 and 0.73 mm per day. Conidia produced on inoculated apple fruits showed slight differences in morphology among the representative fungal isolates evaluated. Phylogenetic analysis clustered all of the Phlyctema‐like isolates in the same clade, identifying them as Phlyctema vagabunda. On fruits, influence of wounding, ripening and cultivar resistance was studied, with cv. Blanqueta being the most susceptible cultivar. On branches, a mycelial‐plug inoculation method reproduced olive leprosy symptoms and caused shoot dieback. On leaves, Koch's postulates were fulfilled and the pathogen caused characteristic necrotic spots and plant defoliation. This is the first time that the pathogenicity of P. vagabunda in olive leaves has been demonstrated.

The effect of fungicides on spore germination, mycelial growth and lesion development of <i>Phlyctema vagabunda</i> (syn: <i>Neofabraea alba</i>) (bull’s eye rot of apples)

Phlyctema vagabunda (syn: Neofabraea alba) is a plant pathogenic fungus that causes bull’s eye rot on apples and pears. Phlyctema vagabunda fruit infections occur in orchards predominantly pre-harvest, and eventually express as a fruit rot after 4—5 months of cool storage. Twelve fungicides (captan, carbendazim, copper hydroxide, cyprodinil, difenoconazole, dithianon, dodine, isopyrazam, metiram, lime sulphur, sulphur and trifloxystrobin) were tested in vitro for their effects on spore germination and mycelial growth of P. vagabunda. Spore germination was inhibited by metiram, captan, dodine, dithianon, lime sulphur, carbendazim and isopyrazam, in order of effectiveness. Carbendazim, isopyrazam, difenoconazole and cyprodinil, in order of effectiveness, inhibited mycelial growth when used at label rates. Wettable sulphur was ineffective in both assays. On detached apple fruit, carbendazim, cyprodinil, trifloxystrobin and isopyrazam (in order of effectiveness) inhibited lesion development.

A simple method for conidial production and establishing latent infections of apples by <i>Phlyctema vagabunda</i> (syn: <i>Neofabraea alba</i>)

A method was developed to inoculate and establish infection of detached apple fruit with the bull’s eye rot pathogen, Phlyctema vagabunda (syn: Neofabraea alba), without wounding. Mycelial cultures of P. vagabunda did not produce conidia on commonly used potato dextrose agar, or several other tested media. Growth on corn meal agar resulted in the highest conidial yield, and maximum production was achieved after 5 days. These conidia were placed on water agar, and apple fruit were placed on these spores for at least 5 days for establishment of infections. Reliable infection of 66—100% of apples required 14 days of contact. The ability to rapidly produce copious quantities of conidia and inoculate without wounding facilitates a number of other postharvest control and epidemiology studies.

First Report of Neofabraea alba Causing Fruit Spot on Olive in North America.

Olive (Olea europaea) is a widely planted evergreen tree primarily grown for its oil, fruit for pickling, and landscape appeal in Mediterranean and temperate climates. California produces most of the olives grown in the United States; its industry was valued at $53 million in 2011 (4). In 2005 and 2008, fruit spotting occurred on coratina and picholine cultivars in two commercial orchards in Sonoma County. The spots were scattered, slightly sunken and brown, and surrounded by a green halo. Many of the spots were associated with lenticels. A slow to moderate growing, cream to rose-colored fungus was isolated from the spots onto potato dextrose agar (PDA) amended with 0.01% tetracycline hydrochloride. Sporulation was observed in vitro on PDA after 40 days under near-UV light. Macroconidia, produced from conidiomata, were hyaline, aseptate, cylindrical to fusiform-allantoid, slightly curved, and 17 to 27 × 2.5 to 3.5 μm (average 21.1 × 2.9 μm). Microconidia were aseptate, strongly curved, hyaline, and 14 to 18 × 0.75 to 1 μm (average 16.1 × 0.9 μm). rDNA sequences of the internal transcribed spacer (ITS) region of the isolate (GenBank KC751540), amplified using primers ITS1 and ITS4, were 99.8% identical to Neofabraea alba (E.J. Guthrie) Verkley (anamorph Phlyctema vagabunda) (=Gloeosporium olivae) (AF141190). Pathogenicity was tested on detached, green fruit (cv. frantoio). Olives were surface sterilized in 10% sodium hypochlorite for 5 min and air dried. Five olives were wounded with a needle and 10 μl spore suspension (105 spores/ml) was placed on each wound. An equal amount of spore suspension was placed on five unwounded olives. Water was also placed on wounded and unwounded olives to serve as a control. The olives were placed on racks in 22.5 × 30 cm crispers lined with wet paper towels and incubated at 23°C. After 21 days, the olives began to turn red. Olives wounded and inoculated with N. alba had a distinct green ring around the inoculation point where maturity was inhibited. Control olives uniformly turned red. After 35 days, wound-inoculated olives began to form a sunken, brown lesion at the inoculation point where aerial mycelium was visible. After 51 days, lesions were visibly sunken and immature conidiomata began to form in concentric rings giving a bull's eye-like appearance. Unwounded fruit exhibited uneven maturity and green spots associated with the lenticels throughout the experiment but did not develop sunken lesions. Control fruit showed no symptoms and ripened normally. After 56 days, fruit was surface sterilized in 10% sodium hypochlorite for 5 min and plated onto PDA. N. alba was isolated from the sunken and green areas of all of the wounded and unwounded fruit. No fungi grew from the control fruit. The experiment was repeated once with similar results. N. alba has been reported to cause an anthracnose disease on fruit and leaves of olives in Spain and Italy (1,2). In North America, N. alba causes a bull's eye rot on fruit of Malus and Pyrus spp. in the Pacific Northwest and coin canker of Fraxinus spp. in Michigan and Canada (3). To our knowledge, this is the first report of N. alba causing disease on olive in North America.

Control of Neofabraea alba by plant volatile compounds and hot water

Fumigation by plant volatile compounds and hot water treatment were tested in vitro and in vivo for their activity against Neofabraea alba (anamorph Phlyctema vagabunda), the cause of lenticel rot in apple fruit. In vitro trials with volatile compounds showed a consistent inhibition of pathogen growth by carvacrol, trans-cinnamaldehyde, citral and trans-2-hexenal, while (−)-carvone, hexanal, p-anisaldehyde, 2-nonanone and eugenol showed progressively lower inhibition. The greatest inhibition of mycelial growth was demonstrated by carvacrol (effective doses for 50 and 95 inhibition [ED 50 and ED 95] = 5.9 and 17.0 μL L −1, respectively; minimum inhibitory concentration [MIC] = 36.9 μL L −1) and of conidial germination by trans-2-hexenal (ED 50 and ED 95 = 4.1 and 6.9 μL L −1, respectively; MIC = 9.2 μL L −1). Hot water showed a complete inhibition of conidial germination in vitro after 10, 2 and 1 min of exposure at 40, 45 and 50 °C, respectively, and a complete inhibition of mycelial growth after 20 min of exposure at 75 °C. Among the volatile compounds tested, only 25 μL L −1 of carvacrol slightly reduced fungal infection on artificially infected apples (11.4% efficacy). Hot water treatment at 45 °C for 10 min showed high efficacy in the control of lenticel rot on apples. Reduction of infection was 80% in artificially inoculated fruit (cv Golden Delicious) and 90% in naturally infected fruit (cv Pink Lady) after 90 and 135 d of storage, respectively.

In vitro and in vitro activity of eugenol oil ( Eugenia caryophylata) against four important postharvest apple pathogens

The activity of eugenol oil was evaluated in vitro and in vivo against four apple pathogens namely Phlyctema vagabunda, Penicillium expansum, Botrytis cinerea and Monilinia fructigena. The minimum inhibitory concentration (MIC) of eugenol incorporated in malt extract agar medium was found to be 2 mg ml − 1 . Mycelial growth of the four test pathogens was completely inhibited when treated with 150 µl l − 1 of volatile eugenol whether at 4 or 20 °C. Conidia of P. vagabunda, P. expansum, M. fructigena and B. cinerea suspended for 2 min in eugenol solution at 2 mg ml − 1 heated to 50 °C germinated at rates of 19, 37, 38 and 39%, respectively. Three different eugenol formulations (Tween 80, ethoxylate and lecithin) were tested for their in vivo efficacy against the tested pathogens on apples. Ethoxylate– and Tween 80–eugenol formulations applied at room temperature were ineffective in reducing disease incidence. When heated to 50 °C, both formulations induced phytotoxicity on apple surface and caused cuticle damages as revealed by scanning electronic microscopic observations. A mixture of eugenol at 2 mg ml − 1 and soy lecithin at 50 mg ml − 1 suppressed the phytotoxic symptoms produced by eugenol on apples and reduced the disease incidence of P. expansum, P. vagabunda, B. cinerea and M. fructigena to less than 7, 6, 4 and 2% respectively after 6 months of storage at 2 °C. The application of heated lecithin-formulated eugenol could become a successful alternative to the traditional fungicides used in postharvest disease management of apple fruit.