First report of leaf blight and petiole rot of carrot caused by Rhizoctonia solani AG-1 IB
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First report of leaf blight and petiole rot of carrot caused by Rhizoctonia solani AG‑1 IB Manami Mori1 · Taisuke Bannai2 · Tomoo Misawa3,4 Received: 6 February 2020 / Accepted: 22 May 2020 © The Phytopathological Society of Japan and Springer Japan KK, part of Springer Nature 2020
Abstract Carrot plants with leaf blight and petiole rot were found in Hokkaido, Japan, in September 2016. The causal fungus, identified as Rhizoctonia solani anastomosis group (AG)-1 IB, caused leaf blight and petiole rot on carrot but not root rot in inoculation tests. We also confirmed that it can be discriminated on the basis of symptoms and pathogenicity from the pathogen R. solani AG-2-2 IV, which causes carrot root rot. This is the first report of leaf blight and petiole rot of carrot caused by R. solani AG-1 IB. Keywords Carrot · Hokkaido · Leaf blight · Petiole rot · Rhizoctonia Approximately 50% of the carrot (cv. Koyo-2) plants in a 2,000-m2 field in the Shiribeshi region of Hokkaido in the northernmost part of Japan had diseased leaves and petioles just before harvest in September 2016. Leaf blight and petiole rot (Fig. 1a, b) appeared first. In severe cases, entire leaves became necrotic, and petioles near the soil line became constricted turned black, and leaves ultimately wilted and died. White mycelia were both on the soil surface and on the diseased plants (Fig. 1b). Roots of the plants did not have any symptoms. A root rot disease of carrot caused by R. solani AG-2-2 IV at harvest has been reported, but leaves do not develop symptoms (Nagai and Fukatsu 1971). Thus, the leaf blight and petiole rot symptoms found in 2016 were apparently a different disease from the carrot root rot. The objectives of this study were to identify the Rhizoctonia fungus that was consistently isolated from the diseased carrot leaves and to confirm the pathogenicity of the isolate from plants with leaf * Manami Mori mori‑[email protected] 1
Central Agricultural Experiment Station, Hokkaido Research Organization, Naganuma, Hokkaido 069‑1395, Japan
2
Hokkaido Prefectural Shiribeshi Agricultural Extension Center, Kutchan, Hokkaido 044‑0083, Japan
3
Donan Agricultural Experiment Station, Hokkaido Research Organization, Hokuto, Hokkaido 041‑1201, Japan
4
Present Address: Corporate Department, Hokkaido Research Organization, Sapporo, Hokkaido 060‑0819, Japan
blight and petiole rot. We also compared the pathogenicity of the isolate with that of R. solani AG-2-2 IV, the pathogen causing carrot root rot. Symptomatic carrot leaves and petioles were collected from the field and about 10 pieces (ca. 5 mm) were cut from diseased tissues, washed in running water, surface-sterilized in 1% (w/v) sodium hypochlorite solution for 1 min, and then washed with sterile distilled water. The pieces were then placed on potato dextrose agar (PDA) containing 20 μg/ml streptomycin sulfate and incubated at 25 °C for 3 days. The growing edge of the mycelium on each plate was transferred to 2% (w/v) water agar (WA) and grown for 3 days at 25 °C
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