In June 2010 and July 2011, celery (Apium graveolens) samples cv. Tango were submitted to the Penn State Plant Disease Clinic from Franklin and Dauphin Counties, PA, respectively. Plants exhibited curling and twisting of leaves and petioles and dark, brownish-black necrotic lesions at the base of the plant, extending up the petioles. A fungal organism with morphology consistent to Colletotrichum acutatum J.H. Simmonds was isolated from plant lesion tissue excised from the Dauphin Co. sample. Grown on half strength potato dextrose agar (PDA), the colony had gray aerial mycelium and a pink reverse. Conidia were 5.1 to 14.5 × 2.6 to 5.1 μm, aseptate, hyaline, elliptical, with one or both ends slightly pointed, and formed from the mycelium or in dense orange masses of acervuli on the aerial surface of the culture. Setae were not present. To test pathogenicity, five 23-week-old plants of the cv. Sonora and five 11-week-old plants each of the cvs. Tango and Tall Utah were sprayed until runoff with a conidial suspension (1.3 × 106 conidia/ml and 1.4 × 106 conidia/ml, respectively) and 0.025% Tween. One plant of each cv. was sprayed with milliQ water and 0.025% Tween as a control. Plastic bags were sprayed with the conidial suspension (milliQ water for the control), and secured over the individual plants for 24 h to create a humidity chamber. Plants were incubated in a growth chamber with a 16-h photoperiod, 25°C day/18°C night temperatures, and 70% humidity. Post-inoculation, all of the cv. Tango plants exhibited leaf cupping and curling after 7 days and most plants had dark stem lesions after 3 weeks, consistent with celery leaf curl symptoms. Plants of cvs. Tall Utah and Sonora developed malformed leaves and leaf curl symptoms 16 days and 10 days post-inoculation, respectively. None of the control plants developed symptoms. Infected tissue was excised from diseased plants, surface disinfested in 0.5% sodium hypochlorite for 45 s and plated on half strength PDA. Fungal colonies consistent with C. acutatum were recovered from all inoculated celery tissues (except two of the five inoculated cv. Tall Utah plants and the negative controls). To verify morphological identification, the internal transcribed spacer (ITS) rDNA region was amplified and sequenced for our original isolate and those recovered from the inoculated plants using ITS1 and ITS4 primers (2) (GenBank Accession No. JQ794875). Sequence homology revealed 99 to 100% similarity to accessioned isolates of C. acutatum, which included the holotype and a paratype of C. acutatum (Accession Nos. AF411700 and AF411701, respectively). Celery leaf curl has been reported to have caused devastating crop losses on celery in Australia (1, 3) and to our knowledge, C. acutatum causing leaf curl of celery has not been officially reported in the United States. Infected celery plants are unmarketable because of the leaf malformation and eventual plant necrosis caused by C. acutatum. As such, this disease could have serious negative implications for celery growers in the United States.
References: (1) J. B. Heaton and S. R. Dullahide. Australas. Plant Pathol. 22:152, 1993. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990. (3) D. G Wright and J. B. Heaton. Australas. Plant Pathol. 20:155, 1991.