First Report of Fusarium fujikuroi Causing Root Rot of Reineckia carnea in the World

Pink reineckia (Reineckia carnea [Andrews] Kunth) is an evergreen herbaceous perennial plant widely grown as groundcover or for medicinal purposes in eastern Asia (Wu et al. 2009). In June 2016, symptoms of root rot were observed in 3-year-old pink reineckia in Jingzhou, Hubei Province, China (111°15′ N, 29°26′ W) with an average disease incidence of about 40%. Chlorotic, stunted, and wilted leaves and necrosis of vascular tissue in the root zone with red-brown discoloration were observed. Some severely affected plants entirely decayed with only fibrous vascular bundles remaining. Fifty symptomatic seedlings were sampled and analyzed in the laboratory. Thirty tissues (3 × 2 mm) from symptomatic roots and stems were surface-sterilized with 70% ethanol for 45 s plus 1% sodium hypochlorite for 3 min, rinsed four times with sterile water, and incubated on potato dextrose agar (PDA) at 25°C for 3 days. Twenty-five fungal isolates were isolated from the tissues and all isolates were single-spore prior to their identification. One isolate, designated JX-1, was further characterized. The hyphae were dense, pale pinkish on PDA. Microconidia were abundant and small in size (5.1 to 11.9 µm × 2.0 to 3.1 µm), colorless, single celled, and oval to kidney shaped. Macroconidia had three to five septa and were gradually pointed or sickle shaped (17.4 to 39.9 µm × 2.5 to 3.1 µm). JX-1 was identified as Fusarium spp. based on morphology (Leslie and Summerell 2006). The internal transcribed spacer (ITS) region and translation elongation factor 1-alpha (TEF-1α) regions were sequenced after PCR amplification using rDNA universal primers ITS1/ITS4 (White et al. 1990) and EF-728F/EF-986R (Carbone et al. 1999), respectively. The ITS sequence (KX772393) had 99% identity to F. fujikuroi (AB237662) with 540 out of 545 bp matching. TEF-1α sequence (KX772392) showed 100% identity to F. fujikuroi (KX656206) with all 251 bp matching. Also, the β-tub sequence (KY914575) had 100% identity to F. fujikuroi (KC964142) with all 1,310 bp matching. H3-1 sequence (KY914574) showed 99% identity to F. fujikuroi (AF291063) with 512 out of 514 bp matching. The other isolates were identified as F. sambucinum or F. tricinctum by morphology and PCR. To validate Koch’s postulates, a pathogenicity test was performed on 6-month-old healthy R. carnea plants grown in sterile plastic pots (22 cm diameter) with a 1:1:1 autoclaved mixture of sand, soil, and commercial substrate. Each of 20 plants was inoculated by drenching with 25 ml of conidial suspension (1 × 10⁶ CFU/ml). Ten noninoculated plants served as controls. All plants were kept continuously at 25°C and 70% relative humidity in a growth chamber (12 h light/12 h dark). Thirty days later, F. sambucinum and F. tricinctum had no symptoms, but root rot symptoms were visible on the inoculated plants of JX-1, and identical to the samples collected from field. Control treatments remained asymptomatic. The morphological and molecular identification of the reisolated pathogen was similar to JX-1. The pathogenicity test showed that JX-1 was capable of causing root rot on R. carnea. F. fujikuroi has been primarily reported from rice but also on other host species (Leslie and Summerell 2006). Overgrowth of rice plants and typical rice Bakanae symptoms caused by JX-1 were observed. To the best of our knowledge, this is the first report of root rot caused by F. fujikuroi on R. carnea in the world.