During the spring of 2015, plants of wild rocket (Diplotaxis tenuifolia) cv. Frastagliata grown under tunnel (1 ha) in the Campania region near Salerno (Southern Italy) showed symptoms of a previously unknown foliar disease. First symptoms developed at temperatures of 16 to 18°C on 14- day-old plants and consisted of small circular, sunken grey brown spots (1 mm in diameter) with a well-defined border. As the lesions expanded (up to 30 mm in diameter) they developed concentric rings, coalesced, and the affected tissues became water-soaked. Lesions appeared on both foliar sides on 4 to 7% of plants. Roots were asymptomatic. Isolations were carried out from symptomatic leaf tissues on potato dextrose agar (PDA) amended with 25 mg/l of streptomycin sulphate. A white fungus, that developed black sporodochia 7 to 10 days after plating, was obtained. Cylindrical, non- septate conidia, measuring 4.4 to 9.5 (6.9) μm and 1.1 to 2.9 (1.9) μm, showed the morphological characteristics of Myrothecium sp. (Domsch et al., 1980). The Internal Transcribed Spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4. The 510 bp product was sequenced (GenBank accession No. KX298062) and showed a 100% similarity with Myrothecium verrucaria (KT354922). Pathogenicity tests were carried out in a growth chamber (20-24°C and 12 h photoperiod), on 15-day-old wild rocket plants cv. Frastagliata transplanted in 2-liter pots. Fifteen plants per pot (5 pots/treatment) were sprayed with 1x106 conidia/ml of one representative isolate of the pathogen or with distilled water, covered with transparent plastic bags for 5 days. Spots similar to those observed on the original plants developed 5 days after inoculation. All the non-inoculated plants remained asymptomatic. M. verrucaria was consistently isolated from all the symptomatic plants. The pathogenicity test was carried out twice, showing the same results. Though M. verrucaria has a wide host range (Farr and Rossman, 2016), this is the first report on D. tenuifolia in Italy as well as worldwide.
First report of leaf spot of wild rocket (Diplotaxis Tenuifolia) caused by myrothecium verrucaria in Italy
Garibaldi, A.;Gilardi, G.;Franco-ortega, S.;Gullino, M. L.
2016-01-01
Abstract
During the spring of 2015, plants of wild rocket (Diplotaxis tenuifolia) cv. Frastagliata grown under tunnel (1 ha) in the Campania region near Salerno (Southern Italy) showed symptoms of a previously unknown foliar disease. First symptoms developed at temperatures of 16 to 18°C on 14- day-old plants and consisted of small circular, sunken grey brown spots (1 mm in diameter) with a well-defined border. As the lesions expanded (up to 30 mm in diameter) they developed concentric rings, coalesced, and the affected tissues became water-soaked. Lesions appeared on both foliar sides on 4 to 7% of plants. Roots were asymptomatic. Isolations were carried out from symptomatic leaf tissues on potato dextrose agar (PDA) amended with 25 mg/l of streptomycin sulphate. A white fungus, that developed black sporodochia 7 to 10 days after plating, was obtained. Cylindrical, non- septate conidia, measuring 4.4 to 9.5 (6.9) μm and 1.1 to 2.9 (1.9) μm, showed the morphological characteristics of Myrothecium sp. (Domsch et al., 1980). The Internal Transcribed Spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4. The 510 bp product was sequenced (GenBank accession No. KX298062) and showed a 100% similarity with Myrothecium verrucaria (KT354922). Pathogenicity tests were carried out in a growth chamber (20-24°C and 12 h photoperiod), on 15-day-old wild rocket plants cv. Frastagliata transplanted in 2-liter pots. Fifteen plants per pot (5 pots/treatment) were sprayed with 1x106 conidia/ml of one representative isolate of the pathogen or with distilled water, covered with transparent plastic bags for 5 days. Spots similar to those observed on the original plants developed 5 days after inoculation. All the non-inoculated plants remained asymptomatic. M. verrucaria was consistently isolated from all the symptomatic plants. The pathogenicity test was carried out twice, showing the same results. Though M. verrucaria has a wide host range (Farr and Rossman, 2016), this is the first report on D. tenuifolia in Italy as well as worldwide.
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