First report of head rot of cabbage and web blight of snap bean caused by Rhizoctonia solani AG‐4 HGI

Abstract

During July 2004, head rot of cabbage ( Brassica oleracea var. capitata ) and web blight of snap bean ( Phaseolus vulgaris ) were frequently observed in Dehong district in southern Yunnan Province, China. Affected cabbages had a dark, sometimes wet decay at the bases of outer leaves and on emerging cabbage heads. The outer leaves later collapse. A brown mycelium appeared on affected parts after damp weather with occasional small brown sclerotia on the cabbage head. The first symptoms on snap bean were small, circular, watersoaked spots on stems, pods, and foliage, later tan-brown with a dark border, up to 2 cm across. Irregular, light brown sclerotia and a fine mycelium develop as plants become seriously blighted. Affected plant parts from cabbage and snap bean were surface-sterilized and incubated on potato dextrose agar (PDA). Rhizoctonia solani was recovered consistently. All cabbage and snap bean isolates anastomosed with tester isolates of subgroups HGI, HGII, and HGIII within AG-4, giving a C2 hyphal fusion reaction (Carling, 1996). The 5·8 s rDNA-ITS of four cabbage and snap bean isolates (CA-04 -1, CA-04 -2, SB-04 -1 and SB-04-2 respectively) matched isolates of R. solani AG-4, subgroup HGI (Kuninaga et al ., 1997).Cabbage heads and snap bean green pods were inoculated with two of their respective isolates grown for 4 days on PDA. After covering with moist cotton to avoid drying out, test plants were held in a greenhouse with ∼ 28 ° C-16 h day and 15 ° C-8 h night. Plugs of sterile PDA were placed on cabbage and snap bean plants as controls. These remained healthy while, within one week, inoculated cabbage and snap bean plants showed similar symptoms to those seen naturally. Rhizoctonia solani was reisolated from these plants, confirming its pathogenicity. This is first report of Rhizoctonia solani AG-4 HGI in China causing head rot of cabbage and web blight of snap bean. AG-A infects snap bean in China (Yang et al ., 2005) and AG-4 in Iran (Balali & Kowsari, 2004), but through root infections. Rhizoctonia solani routinely affects cabbages and further study is needed to compare the pathogenicity of isolates in relation to their sub-groups.

Genetic Characterization and Pathogenicity of Rhizoctonia solani Associated with Common Bean Web Blight in the Main Bean Growing area of Argentina

“…Rhizoctonia solani complex identification is based on the mycelial compatibility between isolates, which makes it possible to assign them to anastomosis groups (AGs) (Sneh et al 1991;Carling 1996). Isolates of AG 1, AG 2 and AG 4 have been associated with WB in common bean (Galvez et al 1989;Tu et al 1996;Godoy-Lutz et al 2003Yang et al 2007;Dubey et al 2014). Isolates of AG 1, AG 2 and AG 4 have been associated with WB in common bean (Galvez et al 1989;Tu et al 1996;Godoy-Lutz et al 2003Yang et al 2007;Dubey et al 2014).…”

Cropping Systems and Cultural Practices Determine the Rhizoctonia Anastomosis Groups Associated with Brassica spp. in Vietnam

“…In our study, AG 1-IB isolates were only recovered from Lam Dong, a province in the cool Central Highlands of Vietnam and the main lettuce production region of Vietnam, suggesting that the presence of this AG is associated with cool climates. The presence of AG 4 has also been reported on Brassica oleracea [21] and B. rapa subsp. chinensis [38] in China, B. oleracea in the UK [23], B. napus L. and B. campestris L. in Canada [39], and B. oleracea [18] and B. napus L. in the US [40].…”

Molecular identification and pathogenicity of Rhizoctonia spp. recovered from seed and soil samples of the main bean growing area of Argentina

“…Most of the R. solani isolates recovered from bean plants showing root and hypocotyl rot symptoms collected in Brazil, Cuba, Iran and Turkey were characterized as AG 4 HG-I based on different techniques including sequencing of the rDNA-ITS region (Meinhardt et al, 2002;Nerey et al, 2010;Kiliçoğlu and Özkoç, 2013;Haratian et al, 2013). AG 4 isolates have also been reported to be associated with web blight in common bean (Gálvez et al, 1989;Tu et al, 1996;Godoy-Lutz et al, 2003Yang et al, 2007;Dubey et al, 2014). Moreover, R. solani AG 4 can attack other commercial crops including maize and tobacco (Bacharis et al, 2010;Mercado-Cárdenas et al, 2015), which are grown in rotation with bean in northwestern Argentina.…”