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First Report of Crown Rot and Root Rot Caused by Cylindrocladium pauciramosum on Feijoa (Feijoa sellowiana) in Italy

Feijoa sellowiana (O. Berg) O. Berg is native to South America and grown in Italy as an ornamental plant and for its fruit. During 2006, 2007, and 2008, a severe wilting was noticed on ∼ 10,000 potted 6-month to 3-year-old plants obtained from seeds and produced by three commercial nurseries in Catania Province (southern Italy). Wilting was always associated with root rot and brown discoloration at the base of the stem. Leaf spots or stem lesions were not observed. A Cylindrocladium sp. was isolated consistently from the crown, basal stem, and roots of symptomatic plants on potato dextrose agar (PDA). Ten isolates of a Cylindrocladium sp. were obtained from single-spore colonies made from a 14-day-old culture grown on PDA and subsequently subcultured on carnation leaf agar (CLA). Cultures were incubated at 25°C under near-UV light with a 12-h light/dark regimen and examined after 7 days (1). Only fungal structures occurring on the carnation leaf tissue were examined. Isolates were identified based on morphological traits and mating type responses (2,4). Isolates were mated with opposite mating tester strains of C. pauciramosum (DISTEF-G128 [MAT1-1] and DISTEF-G87 [MAT1-2]) and C. scoparium (DISTEF-GCs7 = CBS 120892 [MAT1-1] and DISTEF-GP0 = CBS 119669 [MAT1-2]) selected from an Italian collection. Plates were parafilmed, sealed in plastic bags, incubated in a chamber at 25 ± 1°C with a photoperiod of 16 h of light and 8 h of darkness, and examined weekly until perithecia developed. Successful crosses were determined after 2 months of incubation and were regarded as those isolate combinations that produced perithecia with viable ascospores. Conidia were observed to be 30 to 60 × 3.5 to 5.0 μm while conidiophores mostly had two to three series of branches and stipes terminated in obpyriform to broadly ellipsoidal vesicles, which is characteristic of C. pauciramosum C.L. Schoch and Crous (teleomorph Calonectria pauciramosa C.L. Schoch and Crous). Fertile perithecia containing viable ascospores were similar to Calonectria pauciramosa. They were obtained only from crosses of the examined isolates with mating type testers of C. pauciramosum. Six isolates (when paired with DISTEF-G128) and four isolates (when mated with DISTEF-G87) provided fertile progeny. No perithecia were obtained in pairings of the 10 isolates with tester strains of C. scoparium. One representative isolate was deposited at the Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (DISTEF-AS4 = CBS-120618). Koch's postulates were fulfilled by inoculating 30 6-month-old seedlings of feijoa with a spore suspension (10⁵ conidia per ml) of one isolate of the pathogen (DISTEF-AS4) grown on CLA for 14 days. The same number of seedlings was used as a control. Following inoculation, plants were maintained in a growth chamber at 25 ± 1°C and 90 to 95% relative humidity. Wilting, crown rot, and root rot symptoms identical to those observed in the nurseries appeared within 15 to 50 days. Symptoms were not observed on the control plants. C. pauciramosum was previously reported to cause leaf spots on feijoa (3). To our knowledge, this is the first report of wilting due to crown and root rot caused by C. pauciramosum in this host. The disease is a limiting factor for feijoa cultivation in Sicilian nurseries.

References: (1) P. W. Crous et al. Mycologia 84:497, 1992. (2) P. W. Crous and M. J. Wingfield. Mycotaxon 51:341, 1994. (3) G. Polizzi and V. Catara. Plant Dis. 85:803, 2001. (4) C. L. Schoch et al. Mycologia 91:286, 1999.