Original article

Effect of oligochitosan on development of Colletotrichum musae in vitro and in situ and its role in protection of banana fruitsMeng XIANGCHUN1, Tang YANXIA1, Zhang AIYU1, Huang XUEMEI2, Zhang ZHAOQI2*

* Correspondence and reprints

Received 14 July 2011Accepted 25 September 2011

Fruits, 2012, vol. 67, p. 147–155© 2012 Cirad/EDP SciencesAll rights reservedDOI: 10.1051/fruits/2012008www.fruits-journal.org

RESUMEN ESPAÑOL, p. 155

Article published by EDP Sciences

Effect of oligochitosan on development of Colletotrichum musae in vitro and in situand its role in protection of banana fruits.Abstract — Introduction. Concerns about the potentially harmful effects of fungicides on humanhealth and the environment encourage the search for alternative treatments for perishable fruit pos-tharvest disease control. To this end, the potential use of oligochitosan as a natural antifungal com-pound to control postharvest anthracnose caused by Colletotrichum musae was investigated inbanana fruits from the Cavendish group (genome AAA). Materials and methods. The influence ofoligochitosan on the growth of C. musae was determined in vitro by micrographic analysis, while itsin situ antifungal activity was monitored in banana fruits that were artificially injury-inoculated withC. musae; the activities of several defense-related enzymes were measured. Results anddiscussion. Oligochitosan at (4 and 8) g·L–1 markedly inhibited radial mycelial growth of C. musaein vitro. The scanning electron micrograph of C. musae treated with oligochitosan at inhibitoryconcentrations showed distortion and thinning of the hyphal wall and reduction in fungus colonydiameter. Dipping banana fruits in oligochitosan solution at (5 to 20) g·L–1 significantly reduced thediameter of the anthracnose lesion, and 20 g oligochitosan·L–1 almost reached the same inhibitoryeffect as 0.5 g·L–1 of Sportak®, a synthetic fungicide. Activities of defense-related enzymes such asphenylalanine ammonia-lyase (PAL), β-1, 3-glucanase (GLU) and chitinase (CHT), but not polyphe-nol oxidase (PPO), increased in banana fruits treated with 0.5 g oligochitosan·L–1. Conclusion. Theinhibitory effect of oligochitosan on anthracnose development is due to the combination of a directantifungal effect on the pathogen and an indirect effect, whereby the activities of defense-relatedenzymes in the banana fruit were enhanced. To control anthracnose in harvested bananas, treatmentwith oligochitosan above 20 g·L–1 may substitute the use of synthetic fungicide.China / Musa (bananas) / postharvest losses / disease control / biological control /anthracnosis / oligochitosan / antifungal properties / induced resistance

Effet de l’oligochitosane sur le développement de Colletotrichum musae in vitro etin situ et son rôle pour la protection des bananes.Résumé — Introduction. Les préoccupations causées par les effets nocifs potentiels des fongicidessur la santé humaine et l'environnement encouragent la recherche de traitements alternatifs pour lecontrôle de maladies après-récoltes des fruits périssables. À cette fin, l'utilisation potentielle d’oligo-chitosane en tant que composé antifongique naturel contre l'anthracnose après-récolte causée par Col-letotrichum musae a été étudiée pour des bananes du groupe Cavendish (génome AAA). Matérielet méthodes. L'influence de l’oligochitosane sur la croissance de C. musae a été déterminée in vitropar analyse micrographique, tandis que son activité antifongique in situ a été suivie sur des bananesqui ont été artificiellement inoculées par blessures avec C. musae ; les activités de plusieurs enzymesde défense ont été mesurées. Résultats et discussion. L’oligochitosane à (4 et 8) g·L–1 a nettementinhibé la croissance mycélienne radiale de C. musae in vitro. La micrographie électronique deC. musae traité avec de l’oligochitosane à des concentrations inhibitrices a montré une distorsion etun amincissement de la paroi des hyphes et la réduction de diamètre des colonies du champignon.Le trempage des bananes dans une solution d’oligochitosane (de 5 à 20) g·L–1 a significativement réduitle diamètre de la lésion de l’anthracnose, et un trempage à 20 g oligochitosane·L–1 a presque donnéle même effet inhibiteur que 0.5 g·L–1 de Sportak®, fongicide de synthèse. Les activités des enzymesliés à la défense telles que la phénylalanine ammonia-lyase, la β-1, 3-glucanase et la chitinase ont aug-menté dans les bananes traitées avec 0.5 g oligochitosane·L–1, mais pas celle de la polyphénol oxydase.Conclusion. L'effet inhibiteur de l’oligochitosane sur le développement de l’anthracnose est dû à lacombinaison d'effets antifongiques directs et indirects sur le pathogène, de sorte que les activités desenzymes de défense de la banane ont été améliorées. Pour contrôler l'anthracnose dans les bananesrécoltées, leur traitement par une concentration d’oligochitosane supérieure à 20 g·L–1 pourrait rem-placer l'utilisation de fongicides de synthèse.Chine / Musa (bananes) / perte après récolte / contrôle de maladies / lutte biologique /anthracnose / oligochitosane / propriété antifongique / résistance induite

1 Inst. Fruit Tree Res.,Guangdong Acad. Agric. Sci.,Guangzhou, P.R. China

2 Coll. Hortic., S. China Agric.Univ., Guangzhou, P.R. China,zqzhang@scau.edu.cn

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1. Introduction

Being a highly perishable fruit, the bananahas a short shelf life and suffers severe post-harvest losses both in terms of quality andquantity. Anthracnose caused by the fungusColletotrichum musae is a major cause ofpostharvest losses [1, 2]. The most commoncontrol method for this rot is postharvesttreatment of banana fruits with syntheticfungicides, such as benomyl and thiabenda-zole (TBZ) [3]. However, with the develop-ment of resistance of C. musae to thesefungicides, this strategy is losing its efficacyin the postharvest control of banana anthra-cnose. Besides this, concern regarding fun-gicide toxicity and potentially harmfuleffects on human health and the environ-ment is growing, and consumers aredemanding alternative treatments to reducethe use of synthetic fungicides for posthar-vest disease control in perishable fruits suchas bananas [4].

Chitosan derived from the outer shell ofcrustaceans was reported as a promisingalternative treatment due to its natural anti-fungal activity and elicitation of naturaldefensive responses in plant tissues [5–7].Chitosan effectively controlled tomato grayand blue mold rot and anthracnose in arti-ficially post-inoculated papaya and mangofruits [5, 8]. Reduced percentages of infec-tion and index severity, caused by R. stolo-nifer inoculation, were also found on peach,papaya and tomato fruit treated with chi-tosan [9]. Serving as a fruit coating, it canmaintain the quality and prolong the storagelife of many kinds of fruits, such as banana,strawberry, grape, etc. [10–11].

However, the high viscosity and insolu-bility of chitosan in a neutral aqueous solu-tion restricts its uses in practice. Oligochi-tosan, which was prepared by enzymatichydrolysis of chitosan polymer, is not onlywater-soluble, nontoxic and biocompatible,but also has versatile functional properties[12, 13]. The fungicidal activity of oligochi-tosan has been proved for 12 plant patho-gens, with the highest inhibition found onPhomopsis asparagi (sacc.a) Bubak, Fusa-rium oxysporum (Schl.) f. sp. cucumerinumOwen and Rhizoctonia solani Kuhn [14].In situ studies showed that oligochitosan

inhibited spore germination and mycelialgrowth of two fungal pathogens in pear fruitand induced activities of chitinase and β-1,3-glucanase of the fruit, indicating its elicita-tion of plant resistance against fungal dis-ease other than fungicidal activity [15, 16].

Although oligochitosan is regarded as aversatile biopolymer in its applications toagriculture, its potential use as an antimicro-bial or preservative compound deserves tobe further explored. No information isknown about the effects of oligochitosan onpostharvest pathogens of banana. In thisstudy, we evaluated the effect of oligochi-tosan on the development in vitro andin situ of Colletotrichum musae, and itselicitation of defense-related enzymes suchas phenylalanine-ammonia-lyase (PAL),polyphenoloxidase (PPO), β-1,3-glucanase(GLU) and chitinase (CHT) in banana fruit.

2. Materials and methods

2.1. Inoculum preparation

Colletotrichum musae, kindly supplied byProf. Liu, Aiyuan, South China AgriculturalUniversity, was maintained in potato dex-trose agar (PDA) at 28 °C. The spores wereremoved from 7-day-old PDA cultures andsuspended in sterile distilled water. The sus-pensions were filtered through three layersof muslin cloth to remove mycelial frag-ments and adjusted to 1 × 106 conidia·mL–1

with a hemacytometer according to Liu et al.[8].

2.2. Determination of effectiveconcentration of oligochitosanfor controlling fungal growth

Water-soluble oligochitosan with 95%deacetylation, average molecular weight of5 kDa, low viscosity and pH value of 7.0,was kindly provided by Hainan ZhengyeZhongnong High Technology Co., Ltd. Theeffects of oligochitosan on mycelial growthwere assayed using the method of Yao andTian [17] with some modifications. Oligochi-tosan solution was mixed with molten PDA

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to reach final concentrations of (1, 2, 4 and8) g·L–1 in a total volume of 10 mL per petriplate. After the agar had solidified, 5-mmdisks of C. musae were placed in the centerof each petri plate and were incubated at28 °C. Colony diameter was determined7 days after treatment. Each treatment wasreplicated three times, ten petri plates wereused in each treatment for measuring thecolony diameter, and the experiment wasrepeated twice with similar results.

2.3. Microscopy studies

Seven-day-old fungal cultures of C. musaeon PDA were used for scanning electronmicroscopy (SEM) to check the morpholog-ical changes caused by oligochitosan,according to the methods described byAlvindia and Natsuaki [18]. Segments(5 × 10) mm in size were cut from theperiphery of the colony cultures and imme-diately placed in a vial containing 3% glu-taraldehyde in 0.05 mol·L–1 phosphatebuffer (pH 6.8) at 4 °C. The segments werefixed for 48 h, then dehydrated for 20 mineach in an ethanol series [(30, 50, 70 and95)%] and, finally, in absolute ethanol for45 min. The samples were then critical-point dried in liquid carbon dioxide andthen mounted on SEM stubs and electro-plated with gold-palladium. The sampleswere viewed in a Philips FEI-XL300 SEMoperated at 20 kV at 2,000× magnification.

2.4. Fruit and postharvest treatment

Fresh banana fruits (genome AAA, Cavend-ish group, cv. BaXi), at the green maturitystage according to the criteria of Jullien et al.[19], with fruit firmness of around 50 N, wereharvested from a commercial orchard locatedin Zhongshan,Guangdong province. Bananahands in positions 2–3 from the top of eachbunch were cut and divided into individualfingers. Fingers without any visual defectsand of uniform size and color were ran-domly selected and used for this experi-ment.

Banana fingers were surfaced-sterilizedwith sodium hypochlorite (2%) for 3 min,rinsed with distilled water and air-dried at

ambient temperature (25–28 °C). Air-driedfruits were then dipped for 2–3 min in dif-ferent concentrations of oligochitosan [(2.5,5, 10, 20) g·L-1] solution and again kept atambient temperature for drying. Water and0.5 g·L-1 of Sportak® (Bayer CropScience,Germany) dipping were used, respectively,as negative and positive controls. One dayafter the oligochitosan treatment, three holesof 2 mm deep and 2 mm in diameter weremade on one side of each fruit, and sporesof C. musae were inoculated by placing 10 µLof a conidial suspension (106 conidia·mL–1)in each of the holes. For each treatment,twenty fruits were inoculated, namely60 inoculation replicates per treatment.After inoculation, the fruits were incubatedat 22 °C and 95% relative humidity in con-tainers wrapped by polyethylene bags withwet paper towels in the bottom of the con-tainer. Peel tissues surrounding the woundsof three fingers were sampled after (0, 3, 6,9 and 12) days for enzyme activity determi-nation. Ten days after inoculation, the decaydiameter was measured with a precisionruler Pad. The experiment was repeatedthree times.

2.5. Measurement of defense-relatedenzyme activity

One gram of peel tissue was homogenizedwith 10 mL cold borate buffer (50 mmol·L–1,pH 8.8) and sodium phosphate buffer(50 mmol·L–1, pH 6.0) containing 1% (w/v)polyvinyl-polypyrrolidone (PVP) for pheny-lalanine-ammonia-lyase (PAL) and polyphe-noloxidase (PPO) crude enzyme extraction,respectively. For β-1,3-glucanase (GLU) andchitinase (CHT) enzyme extraction, ten mLof 50 mmol·L–1 sodium acetate buffer(pH 5.0) were used. The homogenate wascentrifuged at 4 °C for 15 min at 13,000 × gand the supernatant was used for enzymeassay.

The phenylalanine-ammonia-lyase activ-ity was assayed according to the method byLisker et al. [20] with slight modifications.The enzyme extract (1 mL) was incubatedwith 2 mL of borate buffer (50 mmol·L–1,pH 8.8) and 1 mL of L-phenylalanine(20 mmol·L–1) for 60 min at 37 °C. The reac-tion was stopped with 1 mL HCl (1 mol·L–1).

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PAL activity was determined by the produc-tion of cinnamic acid measured in a spec-trophotometer at 290 nm. The blank was thecrude enzymepreparationmixedwith L-phe-nylalanine and without incubation. Theenzyme activity was expressed as nmol cin-namic acid·h–1·mg–1 protein.

The determination of the polyphenoloxi-dase activity was carried out by adding0.5 mL of enzyme preparation to 3.0 mLof catechol substrate (500 mmol·L–1 in50 mmol·L–1 sodium phosphate buffer,pH 6.0) and the increase in absorbance at420 nm was measured immediately. Theactivity of PPO was expressed as U·mg–1

protein, where one unit corresponds to anincrease of 0.001 in absorbance per min.

The β-1,3-glucanase activity was deter-mined using 0.4% laminarin in 0.05 mol·L−1

sodium acetate buffer (pH 5.0) as substrate.The amount of glucose released was calcu-lated based on a glucose standard curve.Reducing sugars were measured at 540 nmusing dinitrosalicylic acid reagent. Enzymeactivity was expressed as mmol glucose·min–1·mg–1 protein.

The chitinase activity was assayed follow-ing the method of Deepak et al. [21] with

N-acetyl glucosamine as the standard. Col-loidal chitin in 0.05 M sodium acetate buffer(pH 5.0) was used as substrate. The concen-tration of N-acetyl glucosamine releasedafter incubation was measured spectropho-tometrically at 585 nm using dimethylamino-benzaldehyde reagent. Enzyme activity wasexpressed as nmol N-acetyl glucosamine·h–1·mg–1 protein.

2.6. Data collection and analysis

The experiments were laid out in a com-pletely randomized design with three repli-cations per treatment. Analysis of variancewas done using the DPS software and dif-ferences between means were determinedusing Duncan’s Multiple Range Test (DMRT)at P = 0.05.

3. Results

3.1. Effect of oligochitosan onmycelial growth of C. musae in vitro

The radial mycelial growth of C. musae onpotato dextrose agar (PDA) medium sup-plemented with oligochitosan was evalu-ated 7 days after inoculation. As comparedwith the control, obvious inhibition in thegrowth of C. musae was observed in theplates with oligochitosan at (4 and 8) g·L–1,in which the colony diameters were mark-edly reduced by 65.4% and 71.6%, respec-tively, when compared with the diameter ofthe control colony (figure 1). No significantinhibition of mycelial growth was obtainedat oligochitosan concentrations of (1 and2) g·L–1.

The effect of oligochitosan on the mor-phological changes of C. musae wasexamined by scanning electron micrograph(SEM) (figure 2). In the control, normalgrowth of C. musae mycelia on PDA wasobserved. The hyphae were homogeneouswith smooth cell walls and clear develop-ment of conidiophore. In the treatment at2 g oligochitosan·L–1, a slightly distortedmycelium was observed. At the highestoligochitosan concentration (4 g·L–1),

Figure 1.In vitro culture ofColletotrichum musae on PDAmedia supplemented withdifferent concentrations ofoligochitosan and radial growthof C. musae mycelia. Colonydiameter was measured 7 dafter incubation. Bars withdifferent letters are significantlydifferent at P = 0.05 (Duncan'sMultiple Range Test).

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Effect of oligochitosan on development of C. musae on banana

distortion, indentation, rupture, thinning ofthe hyphal cell wall and reduction of thehyphal diameter of C.musae were observed.

3.2. Effect of oligochitosan dippingon banana anthracnose development

Oligochitosan at 5 g·L–1 and above consid-erably reduced banana fruit lesion diametercaused by inoculation of C. musae (fig-ure 3). The higher the concentration of oli-gochitosan, the smaller the lesions observed.

Oligochitosan at 20 g·L–1 reduced thelesion diameter on the fruit by 67.2% com-pared with the water control. No significantdifference was obtained between 2.5 g·L–1

oligochitosan dipping and the control (fig-ure 3). Oligochitosan at 20 g·L–1 showedalmost the same inhibiting effect on anthra-cnose lesion development as Sportak®, asynthetic fungicide, at a concentration of0.5 g·L–1. Other than inhibiting the develop-ment of anthracnose, oligochitosan appearedto delay ripening, as indicated by inhibitionof the fruit degreening (figure 3), respira-tion and pulp softening (data not shown).

3.3. Effect of oligochitosanon defense-related enzymes

The effect of oligochitosan treatment indelaying the anthracnose development wasfurther investigated with respect to the activ-ities of several defense-related enzymes inthe banana peel tissue. The activity of phe-nylalanine-ammonia-lyase (PAL) increaseddramatically during the first 3 days thendecreased in both control and oligochi-tosan-treated fruits. Higher PAL activitieswere recorded in the treated fruits from the3rd up to the 12th day of storage than in thecontrol fruit, where up to two-fold higheractivity was observed on the 9th and 12thdays (figure 4).

No significant difference in the polyphe-noloxidase (PPO) activity was observedbetween the treated and control fruits dur-ing the whole incubating time, except that,on day 3, lower activity was detected in thetreated fruits. An increase in PPO activityfrom 20 U·mg−1 protein at 0 d to almost40 U·mg−1 protein on day 6 was recorded inboth treated and control fruits (figure 4).

A constant increase in the β-1, 3-gluca-nase (GLU) activity was observed in bothtreated and control fruits. However, thetreated fruits displayed more markedenhancement in the activity, with (37, 49and 39)% higher activity on the 6th, 9th and12th days, respectively, than in untreatedfruits. In all evaluations, a higher chitinase(CHT) activity was observed in the treatedfruits, when compared with the control (fig-ure 4).

4. Discussion

The growing concern regarding the poten-tially harmful effect of synthetic fungicideson the environment and human health

FS(hc42vS2Tdt

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igure 2.canning electron micrograph

SEM) of Colletotrichum musaeyphae exposed to waterontrol and (2 and) g oligochitosan·L–1 for 6 d at8 °C. The samples wereiewed in a Philips FEI-XL300EM operated at 20 kV at,000 × magnification.he white arrows showistortion, indentation andhinning of the hyphal wall.

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requires efforts to explore alternative strat-egies to reduce postharvest rotting of vege-tables and fruits. Among the naturalcompounds, oligochitosan offers a greatpotential as a water-soluble and biodegrad-able substance that has antifungal activity[10, 15, 22]. Previous studies have shownthat oligochitosan could induce resistance inplants against fungal diseases on vegetablecrops and pear fruit [14, 22]. We studied thepotential postharvest use of oligochitosan asan antifungal agent and elicitor of defensereactions to reduce anthracnose caused byC. musae in banana fruit.

Our results showed that oligochitosaninhibited mycelial growth of C. musaein vitro, and delayed anthracnose develop-ment caused by C. musae in bananas, vali-dating its antifungal activity [10, 15, 22].Meng et al. reported that 5 g·L–1 of oligo-chitosan or chitosan presented 100% inhibi-tion in mycelial growth of two fungi

pathogens from pear fruit, Alternariakikuchiana and Physalospora piricolain vitro. Higher concentration was requiredfor in situ control of black spot disease inpears caused by A. kikuchiana, and around50% inhibition was obtained by 10 g·L–1 ofoligochitosan treatment 96 h after inocula-tion [15]. In our study, a concentration of 8 goligochitosan·L–1 reduced the in vitro my-celial growth by 71.6%, and (10 and 20) goligochitosan·L–1 induced more than 50%inhibition of anthracnose caused byC. musae in situ 10 days after inoculation.Moreover, we observed that the oligochi-tosan treatment resulted in cell wall distor-tion and fragmentation of C. musae, whichwas expressed as reduced mycelial growthin vitro. These results proved the directinhibitory effect of oligochitosan on thepathogen.

Besides its antifungal effect, the chitosanor oligochitosan treatment was also foundto elicit defense responses in postharvestfruits. In tomato fruit, postharvest chitosantreatment induced a significant increase inthe activities of polyphenoloxidase (PPO)and peroxidase (POD), and enhanced thecontent of phenolic compounds [8].Increase in the activities of chitinase (CHI),β-1,3-glucanase (GLU) and peroxidase(POD) was reported in oligochitosan-treated pear fruit [15]. In our study, we foundthat the activities of phenylalanine-ammo-nia-lyase (PAL), β-1,3-glucanase (GLU) andchitinase (CHT) in oligochitosan-treatedbanana fruit increased significantly, indicat-ing that oligochitosan is also an effectiveagent for inducing defense responses. PALis involved in the biosynthesis of phytoalex-ins and lignins, thus contributing to the pro-duction of physical and chemical barriersagainst infection. The observed increase inPAL activity could have triggered the phe-nylpropanoid pathway, resulting in therelease of toxic phytoalexins at the site ofC. musae penetration.

Higher expression levels of hydrolasessuch as β-1,3-glucanase and chitinase havebeen shown to provide enhanced resistanceto fungal pathogens. The direct effect ofthese enzymes on the pathogen is degrada-tion of fungal cell wall components. Theindirect effect is the release of some elicitors

Figure 3.Fruit lesion diameters onbanana fruit treated withdifferent concentrations ofoligochitosan or with Sportak®

(0.5 g·L–1) and inoculated withColletotrichum musae (bottom),and anthracnose symptoms onthe fruit (top). Bars withdifferent letters are significantlydifferent at P = 0.05 (Duncan'sMultiple Range Test).

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Effect of oligochitosan on development of C. musae on banana

from the decaying fungal cell wall that mightstimulate other plant defense mechanismssuch as phytoalexin accumulation in thehost plants [23]. Fruits treated with oligochi-tosan resulted in increased levels of β-1,3-glucanase and chitinase activity followingthe pattern of induction observed in chi-tosan- or harpin-treated melon, mango andapple fruits [15, 24]. The observation in thisstudy that oligochitosan treatment did notresult in significant change in PPO activityneeds further investigation.

In conclusion, the current study showedthat the control of anthracnose in bananafruit with oligochitosan treatment was dueto the direct inhibition of growth ofC. musae and indirectly through enhancedactivity of enzymes involved in the biosyn-thesis of phenolic compounds that impartdisease resistance. The results suggest thatoligochitosan, which is nontoxic and bio-compatible, might be a promising substitutefor banana anthracnose control, and mighthave potential in enhancing the activity ofchemical fungicides currently used to con-trol C. musae on bananas, allowing lowerconcentrations of fungicide to be used.There is a need for commercial applicationtrials of oligochitosan, singly or integratedwith fungicides or other postharvest diseasecontrol methods, to be carried out onbanana anthracnose control. According tothe in situ results presented here, above20 g·L–1 is recommended as the commercialtrial concentration of oligochitosan, becausea more complicated pathogen and fruitquality or maturity background may occurin commercial use.

Acknowledgements

This research was supported by the researchand demonstration of key technologies forpromoting the banana industry develop-ment program (No. 2009B020201011)and the introduction and application dem-onstration of postharvest preservationtechnologies in tropical fruits program(No. 2009B050300006) of Guangdong Sci-ence and Technology Department, and theNational Natural Science Foundation of

China (30771515). We thank Dr. EldaB. Esguerra, from the Postharvest Horticul-ture Training & Research Center in theUniversity of the Philippines Los Baños, forher help with the language modification ofthis manuscript.

FAapβcp(c5ro

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igure 4.ctivities of phenylalaninemmonia-lyase (PAL),olyphenol oxidase (PPO),-1,3-glucanase (GLU) andhitinase (CHT) in bananaericarp treated with waterontrol) andg oligochitosan·L–1. Bars

epresent standard deviationsf the means.

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Efecto del oligoquitosano en el desarrollo de Colletotrichum musae in vitro ein situ y su papel para la protección de las bananas.

Resumen — Introducción. Las preocupaciones que provocan los potenciales efectos noci-vos de los fungicidas en la salud humana y en el medioambiente fomentan que se investigueen tratamientos alternativos para el control de enfermedades posteriores a la cosecha de losfrutos perecederos. Con este fin, se estudió para las bananas del grupo Cavendish (genomaAAA) el uso potencial de oligoquitosano, como compuesto antifúngico natural contra laantracnosis posterior a la cosecha, causada por Colletotrichum musae. Material y métodos.Se determinó in vitro, por análisis micrográfico, la influencia del oligoquitosano en el creci-miento de C. musae, mientras se hizo el seguimiento in situ de su actividad antifúngica enbananas inoculadas artificialmente por heridas con C. musae. Se midieron las actividades devarias enzimas de defensa. Resultados y discusión. El oligoquitosano de (4 y 8) g·L–1 inhi-bió considerablemente el crecimiento micelial radial de C. musae in vitro. La micrografía elec-trónica de C. musae tratado con oligoquitosano en concentraciones inhibidoras mostró unadistorsión y un adelgazamiento de la pared de las hifas y la reducción de diámetro de lascolonias del hongo. La inmersión de las bananas en una solución de oligoquitosano (de 5 a20) g·L–1 redujo significativamente el diámetro de la lesión de la antrácnosis, y una inmersióncon 20 g oligoquitosano·L–1 ofreció casi el mismo efecto inhibidor que 0.5 g·L–1 de Sportak®,fongicida de síntesis. Las actividades de las enzimas relacionadas con la defensa, tales comola fenilanalina amonio-liasa, la β-1, 3-glucanasa y la quitinasa aumentaron en las bananas tra-tadas con 0.5 g oligoquitosano·L–1, mientras que la de la polifenol oxidasa no lo hizo.Conclusión. El efecto inhibidor del oligoquitosano en el desarrollo de la antrácnosis esdebido a la combinación de efectos antifúngicos directos e indirectos en el patógeno, demodo que las actividades de las enzimas de defensa de la banana se han mejorado. Paracontrolar la antrácnosis en las bananas cosechadas, el uso de fungicidas de síntesis podría serreemplazado por un tratamiento con una concentración de oligoquitosano superior a 20 g·L–1.

China / Musa (bananos) / pérdidas postcosecha / control de enfermedades /control biológico / antracnosis / oligoquitosano / propiedades antimicosicas /resistencia inducida

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