Pectic Enzymes and Phenolic Substances in Apples Rotted by Fungi

The activities of pectic enzymes in extracts from sound applesand from apples rotted by different fungi are described. Sclerotiniafructigenaand Botrytis cinerea rots had little or no polygalacturonaseor macerating enzyme activity, but Penicillium expansum rotswere very active in these respects. Extracts from each of therots had very high pectinesterase activity, and contained galacturonicacid. None of the rots had any cellulase activity. Each of thefungi produced polygalacturonase, macerating enzymes, and pectinesterasein liquid media. The effects of adding extracts of apples tothese media are described. Filtrates from cultures of S. fructigenaand P. expansum liberated galacturonic acid from apple fruitfibre which had been thoroughly extracted with cold water. The phenolic jsubstances present in healthy and rotted tisueswere estimated. B. cinerea and S. fructigena rots containedvery little, but P. expansum rots contained as much as healthytissue which had been allowed to brown. An extract of healthyapple tissue reduced the activity of the polygalacturonase ina culture filtrate of S. fructigena. The substances responsiblefor this were tentatively identified as leuco-anthocyanins whichhad been changed to other compunds following the action of polyphenoloxidase.Thej significance of these results is discussed.     

Studies in the Physiology of Parasitism: XX. The Pathogenicity of Botrytis cinerea, Sclerotinia fructigena, and Sclerotinia laxa, with special reference to the part played by pectolytic enzymes

1. Though Sclerotinia fructigena, S. laxa, and Botrytis cinereacause rotting of apple tissue and death of the protoplasts,little or no pectolytic activity was detectable in extractsof the rotted tissue. 2. Pectic materials were extracted from normal and parasitizedapple tissue in three fractions and precipitated as calciumpectate. There was a loss of total, total insoluble, and solublepectic substances in the invaded tissues. This was most markedwith B. cinerea and S. laxa and least with S. fructigena. 3. Pectolytic activity was measured by methods involving (a)maceration of plant tissues, (b) viscosity and reducing groupdeterminations in pectic substrates, (c) increase in acidityof pectin. By these methods it was shown that pectolytic enzymeswere produced by all three fungi in synthetic media. With S.fructigena, which was the only fungus studied in detail, replacementof glucose by pectin increased the formation of pectolytic enzymes. 4. When various apple extracts were used as culture media, littleor no pectolytic activity was detectable. With all three fungithe presence of apple juice in a culture medium, which by itselfwas suitable for enzyme formation, resulted in the suppressionof pectolytic activity. 5. Oxidized apple juice had a pronounced effect in deactivatingcertain pectolytic enzymes, an effect which was especially markedwith B. cinerea. This points to an interaction between the pectolyticand oxidizing systems and introduces a new line of approachto the study of the biochemical interaction between host andparasite.     

Studies in the Physiology of Parasitism: XXV. Some Propertles of the Pectic Enzymes secreted by Pythium debaryanum

The pectic enzymes of Pythium debaryanum have been comparedwith those from two other soft-rot causing organisms, Erwiniaaroideae and Botrytis cinerea, by their effects (viscosity reduction,acid production, and reducing power) on 1 per cent, solutionsof (a) high methoxyl pectin, (b) sodium polypectate, and (c)sodium pectate (2 types). The Pythium debaryanum preparationdiffered particularly in giving no increase in reducing poweror evidence of galacturonic-acid-like derivatives. It maceratedthe walls of potato-tissue freely but had nopolygalacturonaseor pectinesterase activity.     

Role of the Polygalacturonidase Inhibitor Protein in the Ripening of Apples and Their Resistance to Monilia fructigena, a Causative Agent of Fruit Rot

We investigated the dynamics of the activity of the polygalacturonidase inhibitor protein (PGIP) in apple fruits of six cultivars differing in ripening time and correlated it with the degree of damage by the causative agent of fruit rot, Monilia fructigena. The apple cultivars studied differed significantly in PGIP activity and degree of damage by Monilia fructigena. The rate of dissemination of the fungus over fruit tissues was inversely related to PGIP activity. The resistance of apples to M. fructigena increased with ripening. The simultaneous increase in PGIP activity suggests its important role in the reduction of apple damage by fruit rot.     

The infection of apples, cv. Bramley's Seedling, by Nectria galligena Bres

In laborator experiments germinating conidia penetrated leticels and wounds but not the intact surfaces of apples. Date of harvest had no significant effect on the numbers of apples infected with Nectria galligena but the earliest picks rotted first in barn store. Inoculations of unpicked apples resulted in small arrested lesions which only developed into progressive rots after a considerable period in store. Rots developed mosy quickly from inoculations made between mid-August and mid-September. The size of rot increased with spore number and many inoculations with 10–100 conidia remained as arrested lesions. Arrested lesions developed 10–15 days after unripe apples were inoculated and consisted of a zone of fungal colonization surrounded by suberized, necrotic cells in which compounds toxic to both N. galligena and Penicillium expansum were detected. No antifungal compounds were found in progressive rots to mature apples or in healthy apples of any age. Antifungal activity, measured by inhibition of P. expansum, was greatest 15–20 days from inoculation of unripe apples with N. galligena but decreased after a total of 35 days incubation at 20 d? C. Much less antifungal activity was produced in ripe or desert apples.     

The spread of apple brown rot (Monilinia fructigena) by insects

Field and laboratory experiments were carried out to compare the spread of apple brown rot (Monilinia fructigena) by free aerial transmission of conidia, with insect spread of the pathogen. Significantly more brown rot developed on injured apples which had been visited by insects than on unvisited ones. The results obtained suggest that insects play an important role in aetiology of the disease, especially under conditions unsuitable for abiotic spread.     

Antagonistic action of siderophores from Rhodotorula glutinis upon the postharvest pathogen Penicillium expansum

Rhodotorulic acid produced by Rhodotorula glutinis strains improved the biological control of blue rot caused by Penicillium expansum in harvested apples. The production of the siderophore was closely associated with the iron concentration in the medium. Thus, very low additions of the metal reduced the siderophore production considerably. The antagonistic effect of R. glutinis and rhodotorulic acid was studied by using in vitro and in vivo assays. In the in vitro assays, rhodotorulic acid reduced the growth of P. expansum, whereas the chelate (rhodotorulic acid plus iron) did not. Siderophore antagonism was then related to competition for iron. In biocontrol assays on apple wounds, the blue mold was more effectively controlled by the antagonistic agent plus siderophore than by the antagonistic agent alone. The disease incidence (DI: percentage of treated wounds that developed rot) was 34% when apples were protected by R. glutinis alone, whereas it was 6% when the fruits were protected by R. glutinis plus rhodotorulic acid.     

The use of a surface coating to ameliorate the rate of spread of post-harvest fungal diseases of top fruit

The impact of TAL Pro-long coatings (a sucrose-ester composition) on the development of some common post-harvest fungal rots of top fruit is reported. Coatings were not observed to be fungistatic but did diminish the incidence of fungal infections on Conference pears held in cold store. At higher temperatures coatings modified the spatial distribution and reduced the rate of spread of lesions within apples and pears. In comparison to experimental controls, TAL Pro-long had a greater effect on those rots caused by Botrytis cinerea Fr., Monilinia fructigena (Aberh. & Ruhl.) Honey and Rhizopus nigricans Lind. than those of Alternaria alternata Fr., M. laxa (Aberh. & Ruhl.) Honey and Penicillium expansum Link em. Thom. The efficacy of the treatments was related to the concentration of the preparations applied, the variety of fruit, the timing of application and the temperature to which produce were subsequently exposed.     

Pectic enzymes associated with Penicillium digitatum decay of citrus fruit

Pectin methylesterase was the only pectic enzyme detectablein extracts from rind of sound or Penicillium digitatum-infectedoranges. No pectic enzymes were detected in juice from soundor infected fruit. Extracts from infected rind, and juice frominfected fruit, had macerating activity. Chromatographic analysesof rind extracts, and juice from infected fruit, showed galacturonicacid as a possible product of the degradation of pectic substances.Orange juice contained a thermo labile inhibitor of pectic ‘chain-splitting’,and macerating enzymes.     

Laccase and Tyrosinase in some Wood-rotting Fungi

Several species of wood-rotting fungi have been examined forphenol oxidases. Polystictus sanguineus, a white rot, produceslaccase, secreting it into the medium. This enzyme has beenstudied and partly purified. Phellinus cryptarum, another whiterot, shows varied production of phenol oxidase according tothe medium used for growth. Laccase only is produced on maltmedium, whereas laccase and tyrosinase result after growth ona glucose and salt medium. Lentinus lepideus, a brown rot, producestyrosinase on several media and this enzyme appears to be entirelyintracellular.     

Microbial population dynamics on Golden Delicious apples from bud to harvest and effect of fungicide applications

The microbial population dynamics on apples cv. Golden Delicious were analysed every 15 days between bud and harvest in a fully replicated experiment in northern Spain in 1994 and 1995. The total microbial populations varied with developmental stage, and with prevailing climatic conditions. The predominant mycroflora were the filamentous fungi Cladosporium and Alternaria spp. and white and pink yeasts. Other genera isolated included mainly species of Epicoccum, Fusarium and Acremonium. However, the most important post-harvest pathogens Penicillium expansum and Botrytis cinerea were seldom isolated from ripening apples. Maximum total filamentous fungal populations occurred after fruit set and during early ripening [2 × 10⁴cfu (colony-forming units) g^-1 approximately] while those of bacteria were maximum at bud stage (3.5 × 10⁵and 3.0 × 10⁴ cfu g^-1 in 1994 and 1995 respectively). White yeasts were more numerous than pink yeasts. Endophytic infection of apple buds by Alternaria spp., responsible for core rot, was found in almost all bud tissue. By contrast, Cladosporium spp. were initially isolated later from 12.5–50% of tissue samples during blooming and fruit set. The impact of a four-spray fungicide regime during apple development significantly decreased the total filamentous fungal populations in both years, and that of Cladosporium spp. in 1994. However, bacterial populations were often higher on apples from fungicide-treated plots. Fungicide sprays decreased populations of Cladosporium, Alternaria and white yeasts for a maximum of up to 15–30 days after application. Fungicide application had little effect on endophytic infection of apples by Alternaria spp. between bud and harvest.     

Antifungal activity of some plant extracts on some pathogenic fungi

The inhibitory activity of five plant extracts viz. Artemisia absinthium L., Rumex obtusifolius L., Taraxacum officinale Weber ex Wiggers, Plantago lanceolata L. and Malva sylvestris L. were evaluated against the mycelial growth of three fungi Alternaria alternata (Fr.) Keissler, Penicillium expansum Link ex Thom. and Mucor piriformis Fisher that cause rot diseases in fruits and vegetables resulting in low yield and quality of fruits and vegetables. Results revealed that all the concentrations of plant extracts brought about significant inhibition in the mycelial growth of these pathogenic fungi. However, the highest concentration caused maximum inhibition in the mycelial growth followed by lower concentrations of plant extracts. The extract of A. absinthium leaves at highest concentration (S) proved highly effective in inhibiting the mycelial growth of all these pathogenic fungi followed by other plant extracts. These plants thus may have potential as the new natural fungicide for management of fungal rot diseases.     

Lactic acid bacteria with potential to eliminate fungal spoilage in foods

Aims: To investigate antifungal activity produced by lactic acid bacteria (LAB) isolated from malted cereals and to determine if such LAB have the capacity to prevent fungal growth in a particular food model system. Methods and Results: The effect of pH, temperature and carbon source on production of antifungal activity by four LAB was determined. Pediococcus pentosaceus was used to conduct a trial to determine if it is feasible to eliminate Penicillium expansum, the mould responsible for apple rot, using an apple model. Penicillium expansum was incapable of growth during the trial on apple‐based agar plates inoculated with the antifungal‐producing culture, whereas the mould did grow on apple plates inoculated with an LAB possessing no antifungal activity. Conclusion: Partial characterization of the antifungal compounds indicates that their activity is likely to be because of production of antifungal peptides. The trial conducted showed that the antifungal culture has the ability to prevent growth of the mould involved in apple spoilage, using apples as a model. Significance and Impact of the study: The ability of an LAB to prevent growth of Pen. expansum using the apple model suggests that these antifungal LAB have potential applications in the food industry to prevent fungal spoilage of food.     

The Potential Efficacy of Glycyrrhizic Acid and Its Nanostructure Against Brown Rot of Peach fruits

Production of peaches (Prunus persica (L.) Batsch) for both local market and export is increasing each year in Egypt. Brown rot disease, caused by Monilinia laxa and Monilinia fructigena, is considered one of the most important postharvest rots affecting peaches in Egypt and economic losses are increasing. Antifungal activity of glycyrrhizic acid nanoparticles (GA-NPs) and glycyrrhizic acid (GA) at 0.2 and 0.4 mmol/L was investigated as a control for both these brown rot pathogens on peach fruits in both in vitro and in vivo studies. In the in vitro studies, GA-NPs were the most effective as shown by the ability to decrease linear growth of both brown rot pathogens in potato dextrose agar (PDA) amended with 0.4 mmol/L GA-NPs. Micrographs of M. fructigena exposed to 0.4 mmol/LGA showed mycelial deformations, nodule formation, detachment of the cell wall, shrinkage and inhomogeneous cytoplasmic materials with large vacuoles. Mycelium of M. laxa exposed to 0.4 mmol/ LGA-NPs resulted in thinner and distorted hyphae, nodule formation, cell wall thinning, and swellings. The GANPs and GA treatments improved fruit quality by maintaining firmness and total soluble solids (TSS). GA-NPs were more effective in decreasing decay incidence than their bulk material. The 0.4 mmol/L GA-NPs completely inhibited the disease on naturally infected peach fruits for both seasons of 2018 and 2019. Furthermore, 0.4 mmol/L GA-NPs reduced the disease incidence in inoculated fruits by 95 (M. laxa) and 88% (M. fructigena) in 2018 season and 96 (M. laxa) and 85% (M. fructigena) in 2019 season. In conclusion, GA-NPs could enhance the resistance of peaches against brown rot caused by M. laxa and M. fructigena.     

Facultative parasites and host respiration. I. Healthy tissue adjacent to the site of infection

Summary The respiration, as measured by oxygen uptake, was higher for healthy tissue adjacent to soft rots of apple (var. Bramley) caused byPenicillium expansum Link andThom. andBotrytis cinerea Fr. and of potato tuber (var. Arran Banner) caused byErwinia aroideae Townsend, than tissue at a more distant site. The respiration of tissue adjacent to a physiological rot caused by bruising was not affected. It was concluded that there is diffusion of a substance(s) from the site of infection which causes an increase in the rate of respiration of the adjacent tissue.This work formed part of a Ph. D. thesis submitted to the University of London, July 1961.     

Fungal Assciations: II. Cultural Studies on Rhizoctonia solani Kuhn, Fusariutn solani Snyder and Hansen, and Other Fungi, and Their Interactions

Several types of interaction between Rhizoctonia solani, Fusariumsolani, and Phoma foveata were found when these fungi were grownon potato-dextrose agar. After being used by Rhizoctonia a potatomash medium gave better growth of Rizoctonia and Fusarium thanit did when the medium was initially used by Fusarium; and thiswas so whether the reaction of the spent medium was readjustedor not. It is suggested that potato mash medium used by Fusariumcontains a thermostable factor(s) affecting the subsequent growthof Rhizoctonia or Fusarium. The range of pH values suitable for Rhizoctonia growth was narrowerthan that for Fusarium, optimum values being approximately 5•9for the former and 7•8 for the latter. In mixed culturesof the two fungi on potato-dextrose agar adjusted to differentpH values, the fungus for which the reaction of the medium wasmore suitable usually became visually predominant after sometime. A study of various carbon sources showed that poor growth ofRhizoctonia was obtained when pectin was used as the sole sourceof carbon. On a pectin-agar medium, the rate of growth of aRhizoctonia colony increased on the sector which lay towardsan adjacent Fusarium colony; also, after the two fungi camein contact, there was more rapid growth of Rhizoctonia roundthe Fusarium colony than elsewhere. On a synthetic liquid mediumwith pectin as the carbon source better Rhizoctonia growth wasobtained when Fusarium-spent medium was added to it than whenRMzoctoma-spent medium was added. Rhizoctonia showed partial deficiencies in thiamine, biotin,and inositol. Both the extract of Fusarium mycelium, grown onvitamin-free medium, and the Fusarium-spent medium, stimulatedthe growth of Rhizoctonia on vitamin-free medium.     

Occurrence of<Emphasis Type="Italic">penicillium expansum</Emphasis> and patulin in apples as raw materials for processing of foods — case study

The contamination of apples Gloster variety withPenicillium expansum was investigated in the case study. The apples serve as a raw material in thefood industry for processing of baby foodstuffs and other apple products. The core of 3 – 5 % apple samples has been contaminated with spores and mycelium of untested microfungi. The surface tissue of stored apples has not been damaged. Penicillium expansum was isolated in all tested apple samples. Patulin has been found at levels tens to hundreds of üg/kg in tested apple samples. Patulin was primarily associated with core and areas of decomposing tissue and can penetrate up to approx. 1 cm of the surrounding healthy tissue. The production of patulin after the experimental contamination of apples was tested after 14 days of storage (21 °C, dark). The maximum value of patulin was found 110 mg/kg of rotten part of apple sample.     

花魔芋软腐病原真菌分离鉴定

魔芋软腐病是魔芋生产过程中的重要病害,也是限制魔芋产业发展的主要因素。目前,已有报道魔芋软腐病主要由细菌引起,鲜有真菌引起魔芋球茎软腐发病的报道。为明确云南曲靖市花魔芋(Amorphophallus konjac)软腐病的病原种类和侵染特征,该研究通过组织分离法,对采集自云南曲靖市的花魔芋病样进行了真菌的分离,通过形态学结合基于ITS与LSU序列分析的分子鉴定方法对分离真菌进行鉴定,并根据柯赫氏法则进行致病性测定,并对鉴定出的病原真菌同魔芋软腐病原细菌进行了双回接试验分析。结果表明:(1)从形态学和分子水平鉴定了轮纹镰刀菌(Fusarium concentricum)、尖孢镰刀菌(F. oxysporum)和F. ambrosium 3种镰刀菌,1种毛霉属真菌(Mucor sp.),1种根霉属真菌(Rhizopus sp.),1种青霉属真菌(Penicillium sp.)和1种粉红螺旋聚孢霉属真菌(Clonostachys sp.)。(2)统计分析发现,轮纹镰刀菌的相对丰度最高,为45.45%。(3)柯赫氏法则检测发现轮纹镰刀菌具有致病性。(4)轮纹镰刀菌和病原细菌胡萝卜果胶杆菌(Pectobacterium aroidearum)双接种魔芋球茎发现软腐病发病更快,病变组织重量显著高于单接种轮纹镰刀菌或果胶杆菌处理。综上表明,魔芋软腐病可能是由真菌和细菌复合侵染引发。该研究结果为魔芋软腐病的防治提供了理论依据。     

A Comparison of the Seasonal Rates of Dry Matter Production of Three Coniferous Species with Contrasting Patterns of Growth

Seasonal rates of growth and dry-matter production were examinedin second-year seedlings of Larix leptolepis, Pinus contorta,and Pinus radiata grown in an unheated glasshouse. The deciduousLarix had a higher rate of production of dry matter than eitherof the two species of Pinus until the time of leaf fall, andthis was accompanied by a greater height and diameter increment.However, between the time of leaf fall in Larix and the endof the growing season, the species of Pinus increased in dryweight by more than 25 per cent, and in consequence Larix, becauseof its deciduous habit, lost much of the advantage of its fastgrowth-rate. Comparison of the two pine species showed thatP. radiata, while making nearly 3.5 times as much height incrementas P. contorta, had only a 45 per cent higher dry weight thanthat species at the end of the experiment. The dry-weight differenceswere due to differences in relative growth-rate (RGR). The RGR differences between the two pine species resulted fromdifferences in net assimilation rate (NAR) rather than differencesin the ratio of photosynthetic to non-photosynthetic tissue,and P. radiata gained most of its dry-weight advantage duringthe two months of October and November. It seems possible thatthe higher NAR of P. radiata at this time was a reflection ofthe difference in growth habit between the two pine species,and possible mechanisms by which growth may have affected NARin this experiment are briefly considered.