Authors
P. Baiswar,
S. Chandra,
R. Kumar, and
S. V. Ngachan, ICAR Research Complex for NEH Region, Umiam-793103, Meghalaya, India; and
D. D. Rosa, São Paulo State University, College of Agronomic Science, Department of Plant Production--Plant Health Protection Sector, P.O. Box 237, Botucatu, SP 18610-307, Brazil
Ctenanthe oppenheimiana (= Maranta oppenheimiana) is a common foliage plant also known as “never never” plant. Plants grow best in high-humidity conditions. Potted plants in Barapani, Meghalaya, India were found to be infected with a foliar disease. Initial symptoms were leaf margin necrosis that expanded to cover large areas of the leaf blade during March and April of 2007. Leaf portions from the margin of infected and healthy tissue were washed with sterile water and then surface sterilized with 4% sodium hypochlorite for 30 s. These bits were again washed twice with sterile water, blotted dry, plated on water agar, and maintained at 25°C. After 24 h, mycelial growth was transferred to potato dextrose agar. Fungal colonies were brown with fluffy, aerial mycelium Hypha was branched at 90° with lateral branches having constriction at the point of origin. Hyphal cells were determined to be multinucleate when stained with 4′,6-diamidino-2-phenylindole. Sclerotia were 3 to 5.6 mm in diameter (average 4.1 mm) and were not differentiated into cortex and medulla. The above characteristics were consistent with a Rhizoctonia sp. (2). Anastomosis group (AG) was determined by pairing isolates with tester isolates of R. solani and its subgroups (AG 1-1A, AG 2-1, AG 2-2 IIIB, AG 3, AG 4HG-II, AG 5, AG 6, AG 7, AG 8, AG 9, AG 10, AG 11, AG 12, AG 13, and AG BI) and staining hyphae with Safranin-O 0.03% and KOH 3% solutions. Anastomosis was positive only between the Ctenanthe isolate and AG 2-1 tester strain. (1). The Ctenanthe isolate was grown on potato dextrose broth for 8 days. The broth culture was blended in a Waring blender for 2 min and 10 ml was mixed with 90 ml of sterile water. The mycelium suspension was sprayed on five healthy plants of C. oppenheimiana Noninoculated plants served as a control. Inoculated leaves developed initial symptoms of marginal leaf necrosis after 6 to 8 days and expanded leaf necrosis, similar to the original symptoms, after 12 to 15 days. No symptoms developed on noninoculated plants. R. solani was isolated from leaf lesions of the inoculated plants, confirming Koch's postulate To our knowledge, this is a new report from India.
References: (1) G. C. MacNish et al. Phytopathology 83:922, 1993. (2) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St Paul, MN, 1991.
