lotiopsis and Pestalotia De Not. spp. are common because dark, multicelled spores with appendages are common on many decaying or diseased plant tissues. While these genera are easily identifiable as a general group, the nomenclatural confusion between these genera and the superficial similarity of these genera make a review difficult.
Symptoms Leaf spots associated with Pestalotiopsis spp. begin as tiny, black spots that expand to about 2 mm long and are elongate, elliptical to circular lesions, depending on the host. These lesions may expand to form small blights that are bordered by black tissue, with some chlorosis between lesions (Plate 62). Lesions also occur on the rachis and petioles (Plate 63). Dead tissue is often tan to light gray and very thin. In addition to leaf spots, blights on a Chamaerops sp., Roystonea regia, and Syagrus romanzoffiana; a crown rot of Phoenix roebelenii (Plate 64) and a Syagrus sp.; and a general decline of Butia capitata have been associated with Pestalotiopsis spp. Pestalotiopsis spp. invade the trunks, sheaths, and petioles of Areca catechu (betel nut palm) by infecting wounds created by insects (Plates 65 and 66).
Causal Organism Fungi casually identified as Pestalotia spp. may be Pestalotiopsis spp. Fungi identified as Pestalotiopsis spp. may have two or more, unbranched, apical, conidial appendages and four conidial septations (five-celled) with a hyaline basal cell. Conidia are distinctive with three dark cells in the middle of the spore and two to four appendages at the apical end. Conidia are produced on groups of conidiophores. Pestalotia spp. are taxonomically described as having three to nine, simple or branched, apical appendages; five septations (six-celled); and branched appendages on the basal cell. There are other important differences between these two genera, such as conidial wall structure, that are used less frequently. While there are numerous Pestalotiopsis spp. associated with palms, Pestalotiopsis palmarum (Cooke) Steyaert is the most common. Conidia are fusiform, are usually straight, have four septations with slight constrictions at the septa, and are 4.5–7.5 × 17–25 µm. The apical appendages are 5–25 µm long.
Host Range and Epidemiology Pestalotiopsis palmarum has been recovered from numerous palms in the United States and from Cocos nucifera and Elaeis guineensis worldwide. Records of Pestalotia spp. can also be found, and many of these may have been of the genus Pestalotiopsis. Pestalotia spp. have been reported on more than 28 palms. Pestalotiopsis spp. have been reported on 39 palm species in Florida, with Pestalotia palmarum listed as synonymous to Pestalotiopsis palmarum in 35 of the 39 listed species. Leaf spots associated with Pestalotiopsis palmarum have been reported on Adonidia merrillii, Arenga spp., Bismarckia nobilis, Butia capitata, Caryota mitis, an unidentified Caryota sp., Chamaedorea elegans, Chamaedorea erumpens, Chamaerops humilis, Coccothrinax spp., Cocos nucifera, Dictyosperma album, Dypsis decaryi, Dypsis lutescens, a Hyophorbe sp., Livistona chinensis, Phoenix canariensis, Phoenix dactylifera, Phoenix reclinata, Phoenix roebelenii, Pinanga spp., Pseudophoenix spp., Ptychosperma elegans, Ptychosperma macarthurii, Rhapidophyllum hystrix, Rhapis excelsa, an unidentified Rhapis sp., Roystonea regia, Sabal palmetto, Serenoa repens, Syagrus romanzoffiana, Thrinax spp., Trachycarpus fortunei, and Washingtonia robusta. Additionally, an unidentified species of the genus Pestalotiopsis has been reported on Areca catechu and on Carpentaria, Howea, Ravenea, and Syagrus spp. Pathogenicity was confirmed for a Pestalotiopsis sp. on wounded Areca catechu and Howea forsteriana. The fungus did not penetrate nonwounded tissue. Secondary Pestalotiopsis invasion of leaf spots caused by Bipolaris incurvata (C. 28
Bernard) Alcorn was also confirmed on Cocos nucifera. In this study, the Pestalotiopsis sp. did not invade Cocos nucifera leaves without existing lesions. In the Philippines, Pestalotiopsis spp. invaded wounds caused by a leaf miner on Cocos nucifera. Based on the known disease cycles of other imperfect fungi and the presence of spores borne on acervuli on older lesions, these spores are likely to splash to wounded leaves or other damaged tissue and invade palm hosts. Since Pestalotiopsis spp. are associated with insect wounds, spores are likely to be dispersed by insects also. High humidity is expected to favor invasion by Pestalotiopsis spp. In general, Pestalotiopsis spp. do not penetrate leaves without wounds in pathogenicity studies. B. incurvata lesions are secondarily invaded by Pestalotiopsis spp. and became enlarged, changing from a dark brown spot to a straw-colored lesion with a broad, dark brown margin. Thus, health of the foliage and protection from other leaf pathogens must be a priority.
Diagnostic Techniques Pestalotiopsis spp. are readily isolated from diseased tissue. Infected leaves should be washed, sectioned into pieces about 2–4 mm long, disinfested in 0.5% sodium hypochlorite solution, blotted dry, and placed on the surface of water agar or acidified water agar. Single hyphal tips can be transferred from water agar plates to various nutrient agars, such as V8 juice agar and potato dextrose agar. Colonies are white. Sporulation begins after 1 week or longer, and spores are produced on groups of conidiophores. If isolation media are not available, the diseased tissue should be washed well, placed in a moist chamber (glass dish or plastic bag with a moist tissue), and incubated at 24–26°C in the light. Conidia form in 1–3 days on older lesions.
Management Severely diseased leaves should be removed and destroyed on palms grown in greenhouses for the ornamental trade. Cultural controls such as increasing air movement to reduce humidity, increasing plant spacing, removing weeds or trimming surrounding vegetation, using solid-covered greenhouses, and timing water application to avoid prolonged periods of leaf wetness should be used. Application of protective, broad-spectrum fungicides should help to keep young leaves healthy. Given the known invasion by Pestalotiopsis spp. of leaf spots caused by B. incurvata, a disease management program that controls B. incurvata and other known fungal leaf pathogens should be used. For palms in the landscape, the cultural controls suggested above should be used to reduce disease levels. Palms should be kept nutritionally healthy and insect pests should be controlled to avoid invasion of damaged tissue by Pestalotiopsis spp. Insecticides and fungicides should be applied to wounds invaded by Pestalotiopsis spp. The time for trimming operations should be selected to allow wounded tissue to dry as rapidly as possible, e.g., trimming mature trees during periods of wet conditions should be avoided. If wet weather cannot be avoided, fungicide should be applied immediately on trimmed petioles or trunks. Selected References Alfieri, S. A., Langdon, K. R., Kimbrough, J. W., El-Gholl, N. E., and Wehlburg, C. 1994. Diseases and Disorders of Plants in Florida. Florida Dep. Agric. and Consumer Service, Div. Plant Industry. Bull. 14. Brown, J. S. 1975. Investigation of some coconut leaf spots in Papua New Guinea. Papua New Guinea Agric. J. 26:31-42. Sutton, B. C. 1980. Pages 263-265 in: The Coelomycetes: Fungi Imperfecti with Pycnidia, Acervuli and Stroma. Commonwealth Mycological Institute, Kew, U.K.
(Prepared by J. Y. Uchida)