In November 2002, a disease was observed on eight cultivars of Asiatic hybrid lilies (Lilium sp.) in two fields in Carpinteria, CA. The same disease was observed on greenhouse grown Asiatic hybrid lilies in Nipomo, CA in an adjacent county. ‘Monte Negro’ was the most severely affected. Symptoms consisted of necrotic leaf tips as well as 5- to 10-mm ellipsoidal necrotic spots on stems and the abaxial and adaxial leaf surfaces. Lesions were initially dark brown and water soaked, becoming lighter as they dried. Although leaf spot symptoms usually began at the leaf tip, eventually the entire leaf would become blighted. Disease symptoms were not observed on Oriental hybrid lilies in the same nurseries. A Botrytis sp. was consistently associated with the disease symptoms. In pure culture, the fungus matched the description of Botryotinia sphaerosperma (Gregory) Buchw. (anamorph Botrytis sphaerosperma (Gregory) Buchw.) (1). The fungus is distinguished by its large, spherical conidia that average 23 to 25 μm in diameter at maturity. The conidia are born in compact heads on unbranched conidiophores. Conidia and conidiophores are hyaline when young. At maturity, the conidia turn dark brown, whereas the conidiophores turn blackish brown. The fungus formed abundant sclerotia on potato dextrose agar when incubated at room temperature with 12 h per day of fluorescent lighting. The sclerotia were black, ovate to sphaeroidal, had a rough surface, and were 1.5 to 2.5 × 1 to 2.5 mm. Apothecia were not observed. Pathogenicity was tested on 12 Asiatic hybrid and 12 Oriental hybrid lilies. Inoculum consisting of mycelial fragments and conidia (1 × 105 conidia per ml) was produced on lily leaf agar (500 ml of H2O, 7.5 g of agar, and 25 g of healthy, macerated lily leaves). Plants were inoculated by rubbing leaves and stems with the spore and mycelial fragment suspension using cotton swabs. Plants were maintained in a greenhouse at 25°C. After 7 days, characteristic lesions were observed on the leaves and stems of Asiatic hybrid and Oriental hybrid lilies, from which the same Botrytis sp. was consistently isolated. Three control plants each of Asiatic hybrid and Oriental hybrid lilies treated with water as a check, remained symptomless. Although studies to determine potential fungicides for controlling this pathogen have not yet been undertaken, good sanitation, a lily-free period, and steam sterilization of beds should be considered in the management of this disease. In Europe, this fungus has been reported as a pathogen on Lilium regale (2). To our knowledge, this is the first report of this pathogen in North America. Herbarium specimens were submitted to the USDA APHIS mycology laboratory in Beltsville, MD (Accession No. BPI 842231). Cultures were also submitted to the American Type Culture Collection (MYA-2890).
References: (1) P. H. Gregory. Trans. Br. Mycol. Soc. 25:26, 1941. (2) G. L. Hennebert. Friesia 9:52, 1969.
