Black rot in lettuce: a new disease caused by Ceratocystis fimbriata in hydroponic culture in Brazil

B.A. Halfeld-Vieira* and K.L. Nechet

*halfeld@cpafrr.embrapa.br

Accepted for publication 14/07/05

Ceratocystis fimbriata is a pathogen reported on 31 plant host species representing 14 families (Baker et al., 2003). In April 2004, a large hydroponic lettuce greenhouse reported serious losses due to root rot. The Plant Pathology Laboratory of Embrapa Roraima, Brazil, received samples of Lactuca sativa cv. ‘Vera’ exhibiting black rot symptoms on roots and hypocotyl (Fig. 1). White mycelial growth and partly embedded perithecia was observed on the diseased tissue (Fig. 2).

Figure 1: Black rot symptoms on lettuce stem	Figure 2: Perithecia growing in diseased tissue

A fungus was isolated as greenish colonies on Potato Dextrose Agar (PDA). Perithecia were dark brown, base globose, 140-210 μm, ornamented with brown hyphal hairs. Neck erect, 650-890 μm, ornamented with divergent ostiolar hyphae. Width at the base was 23-33 μm and at the apex 15-18 μm. Hyaline acospores, hat shaped, 7.3-7.8 x 2.6-4.7 μm, surrounded by a gelatinous sheath (Fig. 3). The anamorph corresponded to Chalara (Fig. 4). These characteristics permitted the identification of the fungus as Ceratocystis fimbriata (Upadhyay, 1981; Wingfield et al., 1993).

Figure 3: Hat shaped ascospores, ostiolar hyphae and perithecium of Ceratocystis fimbriata	Figure 4: Chlamydospores, conidiophore and conidia of the anamorphic state Chalara

Pathogenicity tests were carried out on wounded and unwounded 35 day-old lettuce plants cv. ‘Babá de verăo’. A 40 μl aliquot of the conidial suspension (8 x 10⁴ conidia per ml) or ascospore suspension (2 masses from the top of perithecial necks in 40 μl sterile water) was deposited on the axil of the bottom leaf. Wounding was done by puncturing the leaf axil with a needle tip through the inoculum droplet. Each treatment consisted of 6 plants; there was also a sterile water control. The plants were kept in a humidity chamber for 24 hours after inoculation and then maintained under greenhouse conditions. Black rot symptoms were observed after 4 days on wounded plants inoculated with conidia or ascospores. C. fimbriata was recovered from lesions. No symptoms were observed on unwounded inoculated plants or on controls.

To our knowledge this is the first report of C. fimbriata causing disease in lettuce or any other member of the Asteraceae.

Baker CJ, Harrington TC, Krauss U, Alfenas AC, 2003. Genetic variability and host specialization in the Latin American clade of Ceratocystis fimbriata. Phytopathology 93, 1274-1284.

Upadhyay HP, 1981. A monograph of Ceratocystis and Ceratocystiopsis. Athens, USA: The University of Georgia Press.

Wingfield MJ, Seifert KA, Webber JF, eds, 1993. Ceratocystis and Ophiostoma: taxonomy, ecology, and pathogenicity. St. Paul, USA: The American Phytopathological Society.

The British Society for Plant Pathology