First record of Cylindrocladium pauciramosum on Ceanothus in the UK

In August 2002, a sample of Ceanothus was submitted to the Central Science Laboratory by the Plant Health and Seeds Inspectorate with symptoms of wilt and shoot blight. The disease was affecting 10% of 200 container-grown plants at a nursery in East Anglia, England; no recent import connection was found. There were numerous dark brown-to-black diffuse lesions on the stems, with profuse white sporulation on the surface. No sporulation was observed on the leaves and roots were unaffected. Microscopic examination of the fungus revealed characters typical of the genus Cylindrocladium, primarily due to the presence of a sterile appendage on the conidiophore. Examination of the culture on carnation leaf agar, after 7 days at 25°C and 12 h UV light, revealed that vesicles were clavate to obpyriform (5-12 µm diam.; mean 6.85 µm) with the widest part below the middle on the majority of occasions (77%). Conidia were hyaline, cylindrical, rounded at both ends, one septate with a range of 44-58 x 3.5-4.5 µm (mean 49.0 x 4.0 µm). The fungus was identified as C. pauciramosum as described by Schoch et al. (1999). The 5' end of the ß-tubulin gene was amplified using primers T1 and Bt2b as described previously (Henricot & Culham, 2002). Comparison of the sequence of the ß-tubulin region (Acc. No. AY880064) with other sequences available in the Genbank database showed it was identical to C. pauciramosum (teleomorph Calonectria pauciramosa). Koch's postulates were fulfilled by inoculating young plants with a spore suspension (1 x 105 conidia per ml) of the fungus, which was successfully reisolated from the leading edge of infected stems. Control plants did not develop any symptoms.

This is the first record of C. pauciramosum in the UK and the first record on Ceanothus. The pathogen has a cosmopolitan distribution and is recorded as affecting other ornamental hosts but on several occasions has been misidentified as C. scoparium (Schoch et al, 1999; Henricot et al., 2002, 2003).