Imported Hawaiian Ti Cordyline plants (Cordyline fruticosa) ‘Tipsy Pink’ with anthracnose symptoms were found in Gainesville, FL, in 2013. A Colletotrichum spp. was isolated from symptomatic Cordyline plants and Koch’s postulates were fulfilled. The colony color on acidified potato dextrose agar (PDA) was orange with slight shades of pink and light gray aerial mycelium. Sclerotia and setae were absent. Conidia were one-celled, hyaline, guttulate, and cylindrical with round ends. The mean size of the conidia was 14.7 × 5.0 μm and ranged from 12.5 to 17.5 × 3.8 to 7.5 μm. Polymerase chain reaction (PCR) was performed on the internal transcribed space (ITS) and 28S rDNA regions of the isolate, and the sequences were compared with those of Colletotrichum spp. in GenBank. Sequence analysis indicated that the isolate belonged to C. cordylinicola. This is the first report of C. cordylinicola on C. fruticosa in Florida and the United States. Anthracnose symptoms developed on healthy-looking, latently infected Hawaiian Ti plants within 2 to 3 months, and 34% to 44% of the non-inoculated plants became diseased in 3 months. Reactions of several Dracaena and Cordyline species and varieties including Hawaiian Ti to C. cordylinicola were assessed. Several Dracaena and Cordyline species and varieties including Hawaiian Ti exhibited a differential response when inoculated with C. cordylinicola, but none of them was resistant. Hawaiian Ti was the most and lucky bamboo (Dracaena sanderiana) the least susceptible [area under the disease progress curve (AUDPC) = 71 vs. 10 cm2·d–1] to C. cordylinicola. The slope of the log-transformed disease progress regression line was steepest on Hawaiian Ti and D. marginata variety ‘Colorama’ plants, intermediate on varieties ‘Tarzan’ and ‘Magenta’, and least on lucky bamboo [slope = 0.046, 0.044, 0.036, and 0.034 vs. 0.020 log(cm2 + 1)/d, respectively, with a mean se of 0.0006].
Kalpana Sharma, Erica Goss and Ariena H.C. van Bruggen
Kalpana Sharma, Joyce L. Merritt, Aaron Palmateer, Erica Goss, Matthew Smith, Tim Schubert, Robert S. Johnson and Ariena H.C. van Bruggen
International trade in ornamental plants has increased worldwide. Dracaena is the genus most frequently imported into the United States and many pests and pathogens currently not in the United States could be imported with Dracaena plant materials. In 2009, lucky bamboo (Dracaena sanderiana) with anthracnose symptoms was found in Florida. The associated fungus, putative Colletotrichum dracaenophilum, is considered a reportable pathogen that originated from Asia. Imported D. sanderiana plants with anthracnose symptoms were collected from a nursery in south Florida in 2011 and retail stores in north Florida in 2012 and 2013. Five isolates of Colletotrichum spp. were isolated from symptomatic D. sanderiana plants and Koch’s postulates were fulfilled for the first time. Polymerase chain reaction was performed on the internal transcribed space (ITS) and 28S rDNA regions of three original isolates and re-isolates and these sequences were compared with sequences of Colletotrichum spp. in GenBank. Sequence analysis indicated that the Colletotrichum isolates obtained from D. sanderiana in Florida belonged to C. dracaenophilum or the C. gloeosporioides species complex. Latent infections on healthy-looking lucky bamboo developed anthracnose lesions within 2 to 3 months. The reaction of several Dracaena species and varieties to the two Colletotrichum species was tested. Colletotrichum dracaenophilum caused the most severe disease on lucky bamboo, whereas one isolate of the C. gloeosporioides species complex was least pathogenic to all of the Dracaena spp. and varieties. Hot water treatments were not effective at controlling latent infections, but application of Azoxystrobin at 0.075 g a.i./L significantly reduced anthracnose development on both latently infected and inoculated lucky bamboo plants.