Leaf loss and plant decline in some heliconia fields were investigated. A Cylindrocladium species was isolated and determined to be pathogenic. Experience in controlling C. spathiphylli on spathyphyllum suggested some control approaches, although fungicides had not been found effective. Further studies on the heliconia pathogen were indicated

Aragaki, M.

Uchida, J.Y.

Yahata, P.S.

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·~~• BQIEfNooo85 Hawaii Institute of Tropical AgrIculture and Human R~urcesCollege of Tropical AgrIculture and Human R~urcesUniversity of Hawaii at ManoaHELICONIA ROOT ROT AND FOLIAR BLIGHT CAUSED BY CYLINDROCLADIUMJ. Y. Uchida, M. Aragaki, and P. S. Yahata*IntroductionThe tropical cut flower market has increased markedlyin -the past few years. Novel heliconia cultivars havedelighted North American and European floral designers, andthese appealing exotic flowers have been well received byconsumers. While demand for new plants and cut flowerscontinues to increase, growers have noticed a major prob-lem in some of their plantings. Diseased plants in thesefields or sections of fields showed excessive leaf loss andgeneral plant decline. The cause of heliconia declineappeared to be parasitic, and a study was undertaken todetermine the pathogens involved.Disease and SymptomsDiseased plants had dry, papery leaf spots, "firing" ordrying of leaf margins, sheath and petiole blights, varyingamounts of leaf yellowing, and severe root rot. Leaf scorchand firing of leaf edges are symptoms of water stress, whichresulted from sheath and petiole blights, and severe root rot.This was followed by premature loss of leaves, which led toweak and stunted plants. Floral quality and quantity werereduced as a consequence of this decreased photosyntheticcapacity of diseased plants.Rhizomes were generally healthy internally, althoughthere was blackening of the vascular bundles traceable toinfected roots.Cause and SpreadEarly isolations made from diseased petioles and drysheath tissue yielded Cylindrocladiwn. but only saprophyteswere recovered from scorched leaf blades. Cylindrocladium,a known fungal pathogen of spathiphyllum, fern, palm,alfalfa, papaya, ohia, and many woody plants, was subse-quently isolated from rotted heliconia roots as well as fromspots on leaf blades, leaf sheaths, and petioles. A survey ofseveral commercial heliconia fields, in which the same spe-cies of Cylindrocladium was found associated with poorlygrowing plants, demonstrated the widespread nature of thisproblem. The fungus was isolated from root rots of the fol-lowing heliconia cultivars: 'Parakeet', 'Parrot', 'ChristmasRed', 'Firebird', 'Wagnerana Rainbow', 'Red Caribea', and'Kamehameha'. Since heliconia is vegetatively propagated,it is not surprising that the disease was found in so manyvarieties and locations.In controlled greenhouse studies, the pathogenicity ofthe Cylindrocladium from heliconia was confirmed on heli-conia 'Red Caribea'. Spores of the fungus produced in pureculture were applied to healthy plants, and symptoms of thedisease, such as leaf spots, petiole and sheath blights(Figures I, 2), and severe root rot (Figure 3), developed.The sheath and roots were especially susceptible.Morphologically, the Cylindrocladium species fromheliconia closely resembles Cylindrocladium spathiphylli, avery destructive pathogen on commercial spathiphyllUlri.Two isolates of Cylindrocladium from diseased heliconiawere not pathogenic to healthy spathiphyllum plants, how-ever. Similarly, isolates of Cylindrocladium spathiphylliobtained from spathiphyllum were not pathogenic to heti-conia (Figure 3). On the basis of morphological andphysiological similarities and host specificity, the fungusfrom heliconia is tentatively named Cylindrocladiwn spathi-phylli f. sp. heliconiae.Cylindrocladium produces large numbers of spores,which are spread by splashing water. Movement of the fun-gus is relatively slow, because its dispersal depends uponwater or soil movement. On the other hand, contaminationof clean areas can take place rapidly if contaminated plants,diseased plant parts, and infested tools, soil, and equipmentare not properly disposed of or treated. When infested areasof the field are cleaned by removing dead leaves, rhizomes,and roots, this debris should be destroyed, not compostednor dumped in a waste pile.The fungus also produces microsclerotia, which serveas resistant survival structures; these persist for extendedperiods in decomposing diseased leaves, roots, or corms.Replanting in an area previously cropped with badly dis-eased heliconia should be avoided, since infections ofhealthy plants would likely occur again. Cylindrocladiumcrotalariae, a close relative that also produces micro-sclerotia, has been reported to survive in fallowed fields fortwo years.ControlAlthough therapy or curing of diseased plants is usuallyuneconomical, rare, valuable heliconia plants that becomediseased can be rescued by careful trimming and peeling ofthe corms and removal of all dark areas. These trimmedcorms should be soaked in a freshly prepared lO-percentliquid household bleach solution for five minutes and thenplanted in clean vermiculite or commercial potting mix.After these are rooted and growing vigorously, they shouldbe transplanted into clean fields. Any plant that appearsweak or is suspect should not be planted out in the field.Every effort should be taken to avoid field introduction ofheliconias that may be diseased, as eradication of the patho-gen from the field is virtually impossible.Because of a lack of information on this disease, morework is needed to develop basic control procedures. In theThe authors thank the Governor's Agricultural Coordinating Committee for financial assistance making this research possIble.• Assistant Professor of Plant Pathology, Professor of Plant Pathology, and Research Associate in PlantPathology, respectively.meantime, it is crucial for growers who are eSlablishingnew fields 10 use only disease-free planting material. Whengrowers are not certain if the planting material is healthy,rhizomes should be washed, peeled completely, dipped in asurface disinfestant (as menlioned above), and planted infresh commercial potting mix or sterilized media inindividual containers. Plants that grow vigorously with noevidence of poor growth associated with rOOI rOI can thenserve as slock for new healthy plantings.Fungicides have not been successful in controlling rootrOl of spalhiphyllum caused by Cylindroc/adiumFigure 1. Young lesioll8 on leaf and sheath ofheliconia inoculated with Cylindrocladium.pcdhiphylli f. &p. heliconiue,spathiphy/li. This indicales Ihat a successful heliconia rOOlrol control program must be based on careful inuoductionof disease-free slack plants. Species of Cylindrocladiumare inhibited by benomyl, and disease prevention of leafspots and peliole blighl may be obtained with thischemical.The burrowing nematode (Radopholus simifis) andthree root-fouing fungi, Pylhium splendens, P. aphani-dermatum, and P. myrioty/um, have been found inassociation with heliconia root rol Their roles in heliconiadiseases need investigation.Figure 2, BlighHng of sheath and leaves afterfoliar inoculation. New leavel! produced after theinoculation are unaffected.Figure 3. Root rot caused byCytindrvcladium .palhiphylli f. &p.heliconiae. From left: uninoc-ulated control; plant inoculated withCylindrvcladium from spathiphyl.lum; two plants inoculated withCyJindrocladium from heliconia,Issued in furtherance of Cooperative Extension work, Acts 01 May 8 and June 30, 1914, in cooperation with the U. S. Department ofAgriculture. Noel P. Kefford, Director ollhe Institute and Dean 01 the College, Cooperative Extension service, College 01 Tropical Agricultureand Human Resources, University 01 Hawaii at Manoa, Honolulu, HI 96822. An Equal Opportunity Employer providing programs and services tocitizens of Hawaii without regard to race, color, national origin, or sex. 12189

Heliconia Root Rot and Foliar Blight Caused by Cylindrocladium

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Heliconia Root Rot and Foliar Blight Caused by Cylindrocladium

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