Hypovirulence and Double-Stranded RNA in Botrytis cinerea

Abstract

Twenty-one strains of Botrytis cinerea isolated from 13 species of plants grown in China were compared for pathogenicity on Brassica napus, mycelial growth on potato dextrose agar, and presence of double-stranded (ds)RNA. The results showed that the strain CanBc-1 was severely debilitated in pathogenicity and mycelial growth, compared with the 20 virulent strains. A dsRNA of approximately 3.0 kb in length was detected in CanBc-1 and 4 hypovirulent single-conidium (SC) isolates of CanBc-1, but was not detected in the 20 virulent strains of B. cinerea and 4 virulent SC isolates of CanBc-1. Results of the horizontal transmission experiment showed that the hypovirulent trait of CanBc-1 was transmissible and the 3.0-kb dsRNA was involved in the transmission of hypovirulence. Analysis of a 920-bp cDNA sequence generated from the 3.0-kb dsRNA of CanBc-1 indicated that the dsRNA element was a mycovirus, designated as B. cinerea debilitation-related virus (BcDRV). Further analyses showed that BcDRV is closely related to Ophiostoma mitovirus 3b infecting O. novo-ulmi, the causal agent of Dutch elm disease. Mitochondria and cytoplasm in hyphal cells of CanBc-1 became degenerated, compared with the virulent isolate CanBc-1c-66 of B cinerea. This is the first report on the occurrence of Mitovirus-associated hypovirulence in B. cinerea.

Characterization of a Novel Bipartite Double-Stranded RNA Mycovirus Conferring Hypovirulence in the Phytopathogenic Fungus Botrytis porri

“…For simplicity, the names of strains GarlicBc-16, GarlicBc-38, GarlicBc-72, OnionBc-95, and GP72SC35 of B. porri were abbreviated here as Bc-16, Bc-38, Bc-72, Bc-95, and SC35, respectively. Maintenance of the stock cultures and establishment of working cultures of these strains of B. porri were carried out as described in our previous study (51). Mycelial agar plugs (6 mm in diameter) removed from the colony margin of a 3-to 5-day-old culture of each strain or isolate were placed on potato dextrose agar (PDA) in petri dishes (9 cm in diameter) at one plug per dish.…”

“…Individual conidia on the PDA surface were picked up using a sterilized fine glass needle under a light microscope and transferred to fresh PDA plate at one conidium per plate. The plates were incubated at 20°C for 5 days, the resulting cultures were identified, and those belonging to B. porri were individually tested for the mycelial growth rates on PDA (20°C), pathogenicity on detached garlic leaves (20°C, 72 h), and the presence of the two dsRNA segments in mycelia using previously described methods (51,57,58). The hypovirulent strain Bc-72 and the virulent strain Bc-16 of B. porri were used as controls in this experiment.…”

“…Horizontal transmission refers to transmission hypovirulence-associated dsRNAs from hypovirulent to virulent fungal strains through hyphal anastomosis (38). The experiment was done on PDA in petri dishes using the pairing culture technique (51,52,56). In the contact culture in each dish (9 cm in diameter), the dsRNA-containing hypovirulent strain Bc-72 served as the donor, whereas strains Bc-38, SC35, or Bc-95 served as recipients.…”

Effect of putative mitoviruses on in vitro growth of Gremmeniella abietina isolates under different laboratory conditions

“…They lack true virions, and have a (+) ssRNA genome of approximately 2.5 kb (Boland, 2004). Mitoviruses have been recorded in several phytopathogenic fungi such as Cryphonectria parasitica (Polashock and Hillman, 1994;Polashock et al, 1997), Ophiostoma novo-ulmi (Brasier, 1983;Rogers et al, 1987), Sclerotina homoeocarpa (Deng et al, 2003;Deng and Boland, 2004), Helicobasidium mompa (Osaki et al, 2005), Chalara elegans (Park et al, 2006) and Botrytis cinerea (Castro et al, 2003;Wu et al, 2007). In most cases, the presence of mitoviruses is associated with reduction of fungal pathogenicity (Ghabrial and Suzuki, 2009;Wu et al, 2010).…”

Detection of isometric, dsRNA-containing viral particles in Colletotrichum gloeosporioides isolated from cashew tree

“…Therefore, transcription factors regulated by protein G are downregulated, including CpST12, which is necessary for fungal virulence and expression of genes that respond to hypovirulence (Deng et al, 2007). Hypovirulent strains of phytopathogenic fungi have been reported in several species such as Fusarium oxysporum (Kilic & Griffin, 1998), Rhizoctonia solani (Liu et al, 2003a;Cardinale et al, 2006) Sclerotinia sclerotiorum (Li et al, 2003), Helicobasidium mompa (Osaki et al, 2006), Botrytis cinerea (Wu et al, 2007), and Fusarium graminearum (Kwon et al, 2009). The best examples have been described in Cryphonectria parasitica, the causal agent of chestnut blight, a devastating disease of the American chestnut tree (Castanea dentata [Marsh] Borkh) (Anagnostakis & Day, 1979;Rae et al, 1989;Liu et al, 2003b;Lin et al, 2007;Turchetti et al, 2008).…”