First Report of Anthracnose Caused by Colletotrichum acutatum on Tamarillo in the United States

An aggressive anthracnose disease was identified on greenhouse and home garden cultivated tamarillo (Solanum betaceum). Large angular lesions eventually engulfed leaves of mature, fruit bearing trees. Additional lesions were seen on petioles and stems, resulting in stem girdling. Flower clusters were also attacked, but there were no fruit lesions. In greenhouse conditions young plants were found infected in the foliar and apical regions, resulting in death of young plants. Cultures obtained from multiple disease samples each resulted in a single fungal isolate. Molecular identification was carried out by analysis of the ITS1/ITS4 region. Full matches were found to Glomerella acutata (anamorph Colletotrichum acutatum Simmonds). Cultures were reddish-gray, with masses of mucilaginous orange-brown spores. Conidia were fusiform, measuring 14.0 +/-2.3 by 5.7+/-0.7 micrometers. No setae were present, but structures resembling immature perithecia were present, embedded in the agar, a characteristic of C. acutatum Group D isolates. Six immature plants (5 months old) and three mature plants (2 year old) were inoculated with 1x 104 conidia into apical regions and on the upper foliage. Plants were enclosed in clear plastic bags and incubated for three days. Bags were removed and plants maintained in the greenhouse. Within two weeks all plants expressed disease symptoms. Lesions on the foliage were evident as well as the apical regions. Lesions progressed, killing the upper regions of the plant within a month. Isolations consistently resulted in cultures of C. acutatum. Anthracnose of tamarillo has been reported in South America and New Zealand, where commercial production is concentrated, however it is primarily a fruit disease. Our isolate is principally a foliar and stem pathogen. Host range for C. acutatum is wide enough that our isolate likely originated from another host as there is not widespread tamarillo production in the US. Interestingly, solanaceous crop plants are not generally subject to infection by C. acutatum, however, this may be changing.