Characterization of a New Subgroup of Rhizoctonia solani Anastomosis Group 1 (AG-1-ID), Causal Agent of a Necrotic Leaf Spot on Coffee

Abstract

A new foliar disease on coffee leaves was observed in Mindanao, Philippines, in 1996. The symptoms appeared as large circular or irregularly shaped necrotic areas with small circular necrotic spots (1 mm or less in diameter) usually found around the periphery of the large necrotic areas. Rhizoctonia solani was consistently isolated from these diseased coffee leaves. Isolates obtained were multinucleate (3 to 12 nuclei per hyphal cell), had an optimum temperature for hyphal growth at 25 degrees C, prototrophic for thiamine, and anastomosed with tester isolates belonging to R. solani anastomosis group 1 (AG-1). Mature cultures on potato dextrose agar (PDA) were light to dark brown. Sclerotia, light brown to brown, were formed on the surface of PDA and covered the whole mature colony culture. Individual sclerotia often aggregated into large clumps (3 to 8 mm in diameter) and their color was brown to dark brown. In pathogenicity tests, isolates from coffee caused necrotic symptoms on coffee leaves, whereas isolates of AG-1-IA (not isolated from coffee), 1-IB, and 1-IC did not. The results of analyses of restriction fragment length polymorphism of ribosomal DNA internal transcribed spacer, random amplified polymorphism DNA, and fatty acid profiles showed that R. solani isolates from coffee are a population of AG-1 different from AG-1-IA, 1-IB, and 1-IC. These results suggest that R. solani isolates from coffee represent a new subgroup distinct from AG-1-IA, 1-IB, and 1-IC. A new subgroup ID (AG-1-ID) is proposed.

General Description of Rhizoctonia Species Complex

“…Note: this subgroup was recently reported in the Philippines (Priyatmojo et al, 2001) Undetermined subgroup: buckwheat, flax, spinach, radish, and durian (Durio zibethinus Murr. ).…”

“…Note: This group includes the AG-2-1 tulip strain (former AG-2t) and the AG-2-1 tobacco strain (former homogenous Nt-isolates) (Kuninaga et al, 2000). Priyatmojo et al, 2001;Naito, 2004).…”

The advancing identification and classification of Rhizoctonia spp. using molecular and biotechnological methods compared with the classical anastomosis grouping

“…Subgroups of the following MNR AGs were differentiated with this method: AG 2 Matsumoto and Matsuyama 1999), AG 3 , and AG 4 (Johnk and Jones 2001). However, AG 1-IA could not be differentiated from AG 1-IB, although AG 1-IC isolates were distinct (Johnk and Jones 1994;Priyatmojo et al 2001). FAME profiles coupled with another molecular method could differentiate AG 1 (the coffee necrotic leaf spot pathogen) as a new AG 1 subgroup named AG 1-ID (Priyatmojo et al 2001).…”

A Comprehensive Overview on Black Scurf of Potato

“…At present, 13 AGs (designated AG-1 through AG-13) and 21 subgroups (designated AGs 1-IA, 1-IB, 1-IC, 1-ID, 2-1, 2-2-IIIB, 2-2-IV, 2-2-LD, 2-3, 2-4, 2-BI, 3-IIA, 3-IIB, 3-IIC, 3-TB, 4-HG-I, 4-HG-II, 6-GV, 6-HG-I, 9-TX, 9-TP) are recognised (Ogoshi, 1987;Naito and Kanematsu, 1994;Carling, 1996;Hyakumachi et al, 1998;Carling et al, 1999Carling et al, , 2002aKuninaga et al, 2000a;Priyatmojo et al, 2001). Subgroups within AGs are partially based on differences in one or more biochemical, genetic, or pathogenic characteristic (Ogoshi, 1987).…”