First Report of Fusarium lateritium as the Agent of Nut Gray Necrosis on Hazelnut in Italy

Abstract

Hazelnut (Corylus avellana) is a traditionally cultivated nut species in Italy. Italy is the second largest producer of hazelnut in the world after Turkey. In early summer of 2000, a severe fruit drop (up to 60%) was observed in several hazelnut orchards located in the Latium Region in central Italy. The severity of yield losses led to investigating the etiology of the disease subsequently named nut gray necrosis (NGN) based on symptoms observed on the affected fruit. Symptoms consisted of a brown grayish necrotic spot/patch on the nut shell and bracts, sometimes involving the petiole (1). Isolations of the potential pathogen were from tissue that was sampled starting from bloom of female flowers to fully ripened fruit. Isolations from symptomatic tissue consisted of placing onto potato dextrose agar (PDA) small tissue fragments (approximately 3 mm) cut from the margin of lesions, while asymptomatic material (entire flowers or young fruit) was sectioned into small pieces. All the material was previously surface disinfected with 1% NaOCl. Slow-growing, dark grayish olive colonies were obtained consistently within 14 days of incubation at 20 to 22°C from symptomatic and asymptomatic material. Sporodochia were rarely produced on PDA, but never on carnation leaf agar. Dark grayish olive colonies were assigned to a Fusarium sp. Detached hazelnut fruit exposed to 20 μl of a mycelial suspension (105 CFU/ml) and incubated in a moist chamber at room temperature for 10 days produced orange sporodochia bearing 3 to 5 septate macroconidia (35 × 4 μm). On the basis of morphology, the fungus was identified as Fusarium lateritium Nees. (3,4). The identity was confirmed by internal transcribed spacer rDNA sequence comparison with BBA65248 (GenBank Accession No. AF310980). The sequences of two isolates, ISPaVe1874 and ISPaVe1976, were deposited in GenBank (Accession Nos. FN547420 and FN547445, respectively). Pathogenicity tests were performed in planta by inoculating, with the aforementioned isolates, young to fully formed fruit (approximately 24 mm in diameter) either with a drop of mycelial (106 CFU/ml) or conidial (106 conidia/ml) suspension. Drops were placed between the nut and leafy involucre. Controls were treated with sterile water only. Within 2 weeks after inoculation, a grayish necrosis developed on all the inoculated fruit and was similar to symptoms originally observed in the field. No differences were observed between the two methods of inoculation. On full-sized fruit, lesions extended from the shell to inner tissues. The pathogen was consistently reisolated from lesions. Controls showed no symptoms. To our knowledge, this is the first report of F. lateritium as the causal agent of nut gray necrosis on hazelnut in Italy, and this pathogen has never been reported as an agent of necrosis and drop of hazelnut fruit, but it was previously reported as an agent of twig cankers (2). References: (1) A. Belisario et al. Inf. Agrario 59:71, 2003. (2) A. Belisario et al. Plant Dis. 89:106, 2005. (3) J. F. Leslie et al. The Fusarium Laboratory Manual. Blackwell Publishing Press Ltd, Oxford, UK, 2006. (4) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, 1983.