© 2006 Plant Management Network.
First Report of Cocoicola californica on Washingtonia robusta in Florida
M. L. Elliott, Professor, and E. A. Des Jardin, Senior Biological Scientist, Fort Lauderdale Research and Education Center, 3205 College Avenue, University of Florida, Fort Lauderdale 33314-7719
Corresponding author: Monica L. Elliott. firstname.lastname@example.org
Elliott, M. L., and Des Jardin, E. A. 2006. First report of Cocoicola californica on Washingtonia robusta in Florida. Online. Plant Health Progress doi:10.1094/PHP-2006-0227-01-BR.
In April 2005, mature Washingtonia robusta H. A. Wendl. (Mexican fan palm) located in a home landscape in Pinellas Co., FL were observed with leaves exhibiting uneven necrosis of leaf segments and reddish-brown stripes extending the length of the petioles. Petiole cross-sections exhibited internal discoloration. Numerous older leaves were dying prematurely as a result of this rachis (petiole) blight (Fig. 1). The petioles had superficial blister-like regions, but no fungal structures were evident (Fig. 2).
Petiole sections were washed thoroughly with tap water, wiped clean with 95% ethyl alcohol, and placed in a plastic container lined with a wet paper towel. Other petiole sections were allowed to air dry for storage. Within 24 h, stromata with multiple ostioles and a blackened, cirrhus-like mass of discharged ascospores were observed (Fig. 3). There were no elongated ascoma beaks or necks. Ascospores were unicellular, fusiform with distinct apiculate ends, and pale reddish-brown with longitudinal striations (Fig. 4). The average size of ascospores was 19.5 + 1.4 µm × 7.9 + 0.9 µm (N = 50). We identified the fungus as Cocoicola californica (M. E. Barr, Ohr & M. K. Murphy) K. D. Hyde & P. F. Cannon (1,2).
This fungus was first reported on Washingtonia filifera (Linden ex André) H. A. Wendl. ex de Bary (California or Desert fan palm) in California as a new species of Serenomyces, with an ascospore size of 18-20 µm × 7-8 µm (1). In a taxonomic monograph on tar spot fungi of palms, Hyde and Cannon (1999) repositioned the species into the genus Cocoicola (2). Also, these authors reported an ascospore size of 16-21 µm × 5.5-6.5 µm for C. californica, even though they examined the original material from California. While the fungus observed in Florida produced ascospores that are slightly wider than those described previously, the ascospores most closely fit the characteristics of C. californica in size and shape (2).
C. californica is a member of the Phaeochoraceae, a group of fungi known only in association with members of the Arecaceae (synonym=Palmae) family (2). The common name of "tar spot," often used to describe these fungi, is derived from the black coloration of their fruiting bodies. These fungi invade either the leaf segments and leaflets or the leaf petiole, costa, and rachis. In general, these fungi are biotrophic, and anamorphs are unknown. Although Barr et al. reported that the C. californica was culturable (1), our attempts to obtain pure cultures of this fungus were unsuccessful. Since the vast majority of palm tar spot fungi remain unculturable, including other Cocoicola spp., our unsuccessful attempts were not surprising. Fulfilling Koch’s postulates with the tar spot fungi associated with rachis (petiole) blight of palms has not been accomplished, and we were unable to fulfill them either. Pathogenicity has been assumed based on symptom expression, observation of the fungi in direct association with the symptoms, and the biotrophic characteristics of the fungi.
Until now, C. californica has only been reported from southern California and only from W. filifera. However, importation of mature palms occurs frequently from California into Florida, which would allow for transfer of biotrophic pathogens also. A specimen of the C. californica-infected W. robusta petiole was deposited with the University of Florida’s Mycological Herbarium in Gainesville, FL as accession number FLAS F58687.
1. Barr, M. E., Ohr, H .D., and Murphy, M. K. 1989. The genus Serenomyces on palms. Mycologia 81:47-51.
2. Hyde, K. D., and Cannon, P. F. 1999. Fungi causing tar spots on palms. Mycol. Pap. 175.