First report ofRhizoctonia solaniAG 4 HG-II attacking castor bean plants (Ricinus communis) in Brazil and evaluation of two castor bean cultivars for resistance to damping-off

Abstract

Abstract. In 2006 stem rot, root rot and death of castor bean plants was widespread in parts of the São Paulo State, in Brazil. Rhizoctonia solani AG HG-II was identified as the causal agent. Two extensively grown cultivars (BRS Nordestina variety and Sara hybrid) were highly susceptible to this pathogen.Castor bean (Ricinus communis) belongs in the Euphorbiaceae and is classified as an oleaginous species due to its great production of essential oils. It is probably native to the African continent, in current Ethiopia. This region has a tropical climate, which has favoured the adaptation of this species in Brazil. As a plant with great aptitude for essential oil production, it is grown with the aim of incorporating its oil into combustible compounds such as biodiesel. This has been the motivating factor for castor bean cultivation in Brazil (Azevedo and Lima 2001).The resurgence of this crop and the agricultural expansion to regions with lower technological access has led to a plant population increase. Higher dissemination of phytopathogenic agents, including soil-transmitted pathogens such as Rhizoctonia spp. (Lima and Batista 1997), was found during the last few agronomic years. Consequently, properties with limited technology have not had great productivity, which has damaged the development of the Brazilian castor crop (Fornazieri Junior 1986).Diseases caused by soil-inhabiting fungi are detected during castor bean germination or in seedlings and lead to necrosis of stem, cotyledon and young root tissues. The main injury caused is stand reduction, which needs replanting procedures, processes that elevate crop production costs (Batista et al. 1996). The aim of this study was to verify the resistance of two cultivars largely used in Brazil to Rhizoctonia spp., as well as to characterise Rhizoctonia spp. isolates that have damaged recent castor bean crops.In March 2006, symptoms including stem rot and root rot, leading to the death of plants, were observed in castor bean plants in São Paulo State, in Brazil. White mycelium was observed in dead plants and necrotic tissue. Fragments of necrotic tissue were collected and disinfested in 70% alcohol for 30 s and 2% sodium hypochlorite for 30 s, washed in distilled water, and then plated onto PDA and incubated at 24 C in the dark for 24 h (Fenille et al. 2005). The isolated fungus showed a ramification angle of~90 , basal constriction, a septum next to the lateral hyphae and sclerotia. This morphology is consistent with Rhizoctonia spp. (Sneh et al. 1991). A culture has been deposited in the São Paulo State University Mycology Database.Twenty randomly selected cells per isolate were analysed, and the number of nuclei per cell was counted. Prior to examination, hyphae were stained with a DAPI technique in the vegetative cells (Kulik and Dery 1995) and the hyphae were stained with a safranin-O (0.03%) and KOH (3%) solution and then observed under brightfield microscopy at Â400 magnification, for the visualisation of the anastomosis reaction (Yamamoto and Uchida 1982)....

Stem Rot on Adzuki Bean (Vigna angularis) Caused by Rhizoctonia solani AG 4 HGI in China

“…capitata ) and the web blight of the snap bean ( Phaseolus vulgaris ) (Yang et al, 2007). Additionally, R. solani AG 4 HGI and the other two subgroups, HGII and HGIII, can cause stem rot or stem canker on tomato, castor bean, green amaranth and Chinese amaranth (Basseto et al, 2008; Kuramae et al, 2003; Yang et al, 2005). Our results and previous studies show that R. solani AG 4 HGI can cause various types of diseases in a wide range of hosts.…”