Phytopath. 2., 104,13—18 (1982)© 1982 Verlag Paul Parey, Berlin und HamburgISSN 0031-9481 / InterCode: PHYZA3

University of Manchester, Manchester, England

Pathogenicity of Some Fungi Associated with Crown Rotof Bananas

By

C. KNIGHT

Received September 14, 1981

KNIGHT, CUTTS and COLHOUN (1977) established that Fusarium semi-tectum Berk. & Rav. and CoUetotrichum musae (Berk. & Curt) Arx, thedominant species associated with crown rot of banana in the WindwardIslands (GRIFFEE and BURDEN 1976), were equally pathogenic. Variousother species of Fusarium, Botryodiplodia theobromae Pat., Nigrospora sphae-rica (Sacc.) Mason and Verticillium theobromae (Turc.) Mason and Hugheswere also frequently isolated from rotting crowns of banana by GRIFFEE andBURDEN (1976) in their survey. GRIFFEE (1976) studied the status of thesefungi as wound pathogens but the results were often confused by the naturalmicroflora. SHILLINGFORD (1976) considered Fusarium spp., in particular F. se-mitectum, V. theobromae and C. musae to be the major cause of post-harvestbanana fruit rots in Jamaica, including crown rot but only on disease surveyresults. These and previous studies leave room for doubt, and for the FusariaGRIFFEE and BURDEN (1976) attributed this, in part, to confusion regardingthe taxonomy.

The present paper presents the results of experiments made to investigatethe role of these fungi in causing crown rot of bananas using the methoddeveloped by KNIGHT et al. (1977).

Materials and Methods

In the experiments made by KNIGHT et al. (1977) freshly cut crowns of commercialgreen banana hands treated at harvest with benomyl were inoculated with fungi of the crownrot complex. This permitted subsequent rot development during ripening with little con-tamination by other fungi and the species used to inoculate was very frequently re-isolated.

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14 KNIGHT

The different fungi used in the pathogenicity tests are detailed in Table 1. F.semitectumAnd C.uiusdc were iiicluded as known pathogens. Green fruit was inoculated with the Fu-sarium spp. in one scries of two experiments and the other fungi in a second series of experi-ments. Ten half hands were inoculated with each fungus in all experiments. The Fusaria weremaintained in soil cultures and the other species on potato dextrose agar (Difco) slopes.Spore suspensions were prepared from 7 day-old cultures, except B. theobromae whidi wasprepared from 14 day-old cultures. Otherwise the selection of experimental fruit, method ofinoculation, assessment of rotting and re-isolation of fungi was described by KNIGHT et al.(1977).

Table 1Isolates of banana crown rot fungi used in experiments

No.

1.2.3-4.5.

6.

7.8.9.

10.

Fungus

Fusarium graminearumF. moniliformeF. moniliforme var. subglntinansF. oxysporitmF. scmitectumBotryodiplodia theobromaeCoUetotrichum ynusaeC. musaeNigrospora sphaericaVertidllium theobromae

Origin

TPI (M834)==-)Crown tissue'"""")TPI (M/FA028)TPI(M/FA051/74)TPI (M/FA056)Crown tissueTPI (M/F009/75)Crown tissueCrown tissueCrown tissue

'•) TPI = Tropical Products Institute, London.'''"'•') Freshly isolated from crown tissue of Windward Islands bananas.

Results

Tables 2 and 3 provide a summary of the mean depths to which crownrot had developed from inoculations in each experiment and the identity ofthe fungi isolated from rots in each series of experiments. Due to variation inthe degree of rot development and the fact that the controls are not entirelyfree from contamination, the degree of rot development and the percentagerecovery of the test fungi are both used as criteria for determining patho-genicity.

The following fungi of the crown rot complex, other than the speciesused in the inoculation, were isolated as contaminants and are listed in theorder oi frequency of isolation: C. musae, F. semitectHm^ F. moniliforme,Fusarium spp., F. graminearum.

When crowns were inoculated with one of the Fusarium spp. or withC. musae the species used to inoculate was very frequently re-isolated withlittle contamination by other fungi. On the other hand, inoculation with eitherB. theobromae or TV. sphaerica or V. theobromae resulted in less frequent re-lsolation of the species used to inoculate and a higher degree of contaminationby other fungi. The mean depths to which crown rot developed from inocula-

Pathogenicity of Some Fungi Associated with Crown Rot of Bananas

Tahle 2Crown rot (mean depth in mm) of bananas inoculated with Fusarium spp.

and the fungi isolated from the inoculated crowns

Fungus inoculated

Control'-"'-')

F.graminearumF. moniliformeF. moniliforme var. suhgliitinansF. oxysporumF. semitectum

Crown rot(mean depth of rot

in mm)'-")

Exp. A Exp. B

0 2.1 a

5.5 11.1c2.9 a 4.0 a3.2 a 5.6 ab8.0 5.5 ab2.2 a 8.6 be

% number of attemptedisolations in both experiments

fungusinoc-

ulated

95.097.595.097.586.3

otherfungi

55.1

3.812.56.36.3

12.5

nofungus

47.5

1.31.31.31.33.8

'•*) Means not denoted by the same letter differed significantly at P < 0.05 (Student-Newman-Keuls test).

'•"•') Sterile water.

tions with F. graminearum Schwabe, F. moniliforme Sheldon, F. moniliformevar. subglutinans Wollenw. & Reink. and F. oxysporum Schlecht. were com-parable to F. semitectum. On the whole more rotting occurred in crowns in-oculated with C. musae and V. theobromae than N. sphaerica and B. theo-bromae (Table 3) but no clear distinction is possible.

Table 3Crown rot (mean depth in mm) of bananas inoculated with various species

and the fungi isolated from the inoculated crowns

Fungus inoculated

Control'--*)

B. theohromaeC. musaeC. musae (TPI)N. sphaericaV. theohromae

Crown rot (meandepth of rot in mm)'-')

Exp. A Exp. B

0.8 a 0.2 c

1.3 a 2.8 c3.1a 10.7 a2.6 a 8.6 ab0.5 a 2.2 c3.0 a 7.3 b

'/c number of attempted isolationsin both experiments

fungusinoculated

17.591.395.047.558.0

otherfungi

46.3

61.316.311.347.636.3

no fungus

60.0

28.802.5

25.017.5

*) Means not denoted by the same letter differed significantly at P < 0.05 (StudentNewman-Keuls test).

'••"') Sterile water.

|(> KNIGHT

Discussion

The use of benomyl treated commercial fruit in experiments involvinginoculation with pathogenic fungi of the crown rot complex permits sub-sequent rot development by these species during ripening with little con-tamination by other fungi. Variation in the degree of rot development maybe the result of the naturally occurring microflora or the fruit being in dif-ferent physiological conditions related to the stage of ripeness.

In these experiments the levels of infection obtained with E. graminea-rum, F. moniliforme, E. moniliforme var. subglutinans and E. oxysporum werecomparable to E, semitectum. These may therefore be considered as primarywound pathogens, their relative involvement in the disease complex willdepend on the levels of inoculum present. Both C. musae isolates were com-parable to the Fusarium isolates in that the species inoculated was very fre-quently re-isolated from rots. This was not the case with B. theobromae,N. sphaerica and V. theobromae. It seems doubtful from these results thatthey can be considered to be primary wound pathogens m this instance, andprobably only have a minor role in the disease complex.

Apart from F. semitectum, F. moniliforme and F. graminearum were themost frequently isolated Fusaria in a disease survey in the Windward Islands(GRIFFEE and BURDEN 1976). For F. graminearum this was the first report ofIts association with the banana crown rot complex. GRIFFEE (1976) suggestedthat F. graminearum was a primary wound pathogen and this is confirmed.

F. moniliforme, on the other hand, has previously been reported as awound pathogen m inoculation tests (GREENE and Goos 1963, LUKEZIC et al.1967, GRIFFEE 1976). Re-isolation was only reported in the latter two casesand GRIFFEE (1976) was not able to determine if it was a primary pathogen.SHILLINGFORD (1976), who considered the Fusaria a major cause of post-harvest rots isolated F. moniliforme from crown rots. The results now pre-sented establish F. moniliforme as a primary wound pathogen.

The inoculation tests establish F. oxysporum and F. moniliforme var. sub-glutinans as primary wound pathogens but there are few reports in the litera-ture of either species being associated with crown rot. GRIFFEE and BURDEN

(1976) found both species only rarely in a crown rot disease survey in theWindward Islands and SHILLINGFORD (1976) isolated F. oxysporum fromcrown rots in Jamaica. GRIFFEE (1976) suggested F. oxysporum was patho-genic but his results were not conclusive. ROTH and LOEST (1965) consideredF. oxysporum to be a primary invader of crown tissue but only on diseasesurvey results. GRIFFEE (1976) did not test F. moniliforme var. subglutinansbut it has been found associated with Fusarium tip rot of banana (WARDLAW

1972).In these experiments the levels of infection obtained with B. theobromae,

N. sphaerica and V. theobromae were not such that they can be consideredprimary wound pathogens. The results agree with the observation of GRIFFEE

(1976) that although involved in the crown rot disease complex, V. theo-bromae is not very pathogenic in its own right- SHILLINGFORD (1976) con-

Pathogenicity of Some Fungi Associated with Crown Rot of Bananas I 7

sidered V, theobromae a major cause of post-harvest rots but only on diseasesurvey results where it was frequently isolated from crown rots. GRIFFEE

(1976) also considered it doubtful that 7V. sphaerica is a primary woundpathogen, and SHILLINGFORD (1976) suggested it only had a minor role in thedisease complex. B. theobromae on the other hand, was considered by GRIFFKE

(1976) to be primarily involved in the disease complex. SHILLINGFORD (1976)assigned it a minor role in the disease complex and these results along withother unpublished data support this, even though it is well documented as awound pathogen of bananas (GREEN and Goos 1963, LUKEZIC et al. 1967,WARDLAW 1972).

Summary

Growns of commercial green banana hands treated at harvest withbenomyl were inoculated with a number of fungi associated with crown rotm the Windward Islands. Durmg ripening, rots developed following mocula-tion with Fusarium graminearum, F. moriilijormG, F. moniliforme var. sub-glutinans and F. oxysporum with very frequent re-isolation of the speciesinoculated. They were therefore considered primary wound pathogens. Botry-odiplodia theobromae, Nigrospora sphaerica and Vertidllium theobromaewere generally less pathogenic and it is doubtful if they should be regardedas primary wound pathogens in this instance.

Zusammenfassung

Pathogenitat einiger Pilze verbunden mit der Kronenfaule von Bananen

Die Kronen von kommerziellen, grlinen Bananenhanden, die zur Erntemit Benomyl behandelt worden waren, wurden mit einer Anzahl von Pilzeninokuliert, die mit der Kronenfaule auf den Windward-Inseln in Verbindungstehen. Wahrend der Reife entwickelten sich die Faulen nach der Inokulationmit Fusarium graminearum, F. moniliforme, F. moniliforme var. subglutinansund F. oxysporum. Die Reisolation der inokulierten Art war sehr haufig mog-lich. Deshalb wurden diese Pilze als primare Wundpathogene angesehen,Botryodiplodia theobromae, Nigrospora sphaerica und Vertidllium theo-bromae waren gewohnlich weniger pathogen, und es erscheint deshalb fraglich,ob sie in diesem Beispiel als primare Wundpathogene betrachtet werden sollten.

I wish to thank Professor J. COLHOUN for useful advice, the Tropical Products Institute,London for financial support and Gcest Associated Ltd. and the Windward Islands BananaGrowers Association for supplies of fruit.

Literature

GREENE, G. L., and R. D. Goos, 1963: Fungi associated with crown rot of boxed bananas.Phytopathology 53, 271-^275.

GRIFFEE, P. J., 1976: Pathogenicity of some fungi isolated from diseased crowns of bananahands. Phytopath. 2. 85, 206—216.

Phytopath. Z., Bd. 104, Heft 1 2

18 KNIGMI", Pathogenicity ot Some Fungi Associated with Crown Rot of Bananas

, and O. J. BURDEN, 1976; Fungi associated with crown rot of boxed bananas in theWindward Islands Phytopath. Z. S5, 149—158.

KNIGHT, C , D . F . CUTTS, and J. COLHOUN, 1977: The role of Fusarium semitectum in causingcrown rot of bananas. Phytopath. Z. 89, 170—176.

LuKEZic, F. L., W. J. KAISER, and M. M. MARTINEZ, 1967: The incidence of crown rot ofboxed bananas in relation to microbial populations of the crown tissue. Canad. J. Bot.45,413—421.

ROTH, G., and F. C. LOEST, 1965: Collar rot of banana hands and its associated micro-organisms. Dept. Agric. Techn. Serv. South Africa, Tedin. Comm. 44, 1—14.

SHILLINGFORD, C . A., 1976: Occurrence of banana fruit-rot fungi in Jamaican boxing plants.Plant Dis. Reptr. 60, 788—793.

WARDLAW, C . W., 1972: Banana Diseases including Plantains and Abaca. Longman, London.

Author's address: Dr. C. KNIGHT, National Institute oi Agricultural Botany, Hunting-don Road, Cambridge CB3 OLE (UK).