First report ofGuignardia endophyllicolaleaf blight onCymbidium(Orchidaceae) in Brazil

Abstract

Abstract. Leaf blight caused by Guignardia endophyllicola is reported for the first time on Cymbidium (Orchidaceae) in Brazil.Hybrids of Cymbidium are among the most important commercial orchids cultivated in Brazil. In June 2006, leaves of an undetermined Cymbidium hybrid showing severe necrotic symptoms were observed in an orchid nursery in Viçosa (State of Minas Gerais, Brazil). Leaf lesions initially were punctiform abaxially becoming circular, coalescing and leading to extensive necrosis. No fungal structures were found on diseased tissues; however, culturing of surface sterilised fragments of such necrotic tissue in V8 juice agar repeatedly resulted in pure dense blackish fungal cultures. These cultures later sporulated in culture and were further examined.The fungus had the following morphology (VIC 30428): pseudothecia intermixed among pycnidia, unilocular, subglobose, solitary or in groups, black, with a stromatic wall composed of several layers of compressed dark brown cells; asci bitunicate ( Fig. 1), subclavate to cylindrical, eightspored; ascospores biseriate, 13-17 × 3-5 μm, one-celled, fusiform-elliptical, broad in middle, hyaline, with a distinct mucilaginous appendages at both ends; pycnidia intermixed among pseudothecia, variable in shape, black, ostiolate; conidia one-celled, hyaline, obovate to pyriform, 9-14 × 5-7 μm, surrounded by a thick mucilaginous coat, with a hyaline apical appendage, 6-12 μm long. The fungus fitted well within the description of Guignardia endophyllicola, a species previously known only as an endophyte of ericaceous plants (Okane et al. 2001). Nevertheless, its anamorph, Phyllosticta capitalensis, is a well-known fungal pathogen of the family Orchidaceae (Cash and Watson 1955;van der Aa and Vanev 2002). Mendes et al. (1998) did not record the occurrence of P. capitalensis in Brazil. However, in this country, P. capitalensis has been previously reported on the orchid genus Stanhopea, host in which the type species was described (Nag Raj 1993;van der Aa and Vanev 2002).Mycelial plugs containing reproductive structures were taken from a 10-day-old culture growing on V8 juice agar and placed on healthy leaves of hybrid Cymbidium. The inoculated leaves were kept inside moistened plastic bags for 2 days and then in a greenhouse at 25 • C. After 7 days, symptoms similar to those previously observed were detected (Fig. 2) and the fungus was reisolated from infected parts. The control leaves, on which V8 juice agar plugs were deposited, remained healthy.

Endophytic and pathogenic <I>Phyllosticta</I> species, with reference to those associated with Citrus Black Spot

“…Many Phyllosticta species cause leaf blotch, leaf blight and black spots on fruits of various plants (Glienke-Blanco et al 2002, Silva & Pereira 2007). Species of Phyllosticta s.str.…”

“…Phyllosticta species have often been reported as endophytes, plant pathogens or saprobes ( Baayen et al 2002 , Glienke-Blanco et al 2002 , Okane et al 2003 , Silva et al 2008 , Huang et al 2009 , Wulandari et al 2009 ). Many Phyllosticta species cause leaf blotch, leaf blight and black spots on fruits of various plants ( Glienke-Blanco et al 2002 , Silva & Pereira 2007 ). Species of Phyllosticta s.str.…”

Colonization by orchid mycorrhizal fungi primes induced systemic resistance against a necrotrophic pathogen

“…Almost all types pathogens attack orchids, including bacteria (Keith et al ., 2005; Suharjo et al ., 2014; Khamtham and Akarapisan, 2019), fungi (Silva and Pereira, 2007; Lopes et al ., 2009; Srivastava et al ., 2018; Suwannarach et al ., 2018), and viruses (Fogell et al ., 2019; Tsai et al ., 2022). Very little is known about ISR in orchids; to the best of our knowledge, only two studies have reported the occurrence of ISR and its role in alleviating soft rot (Wu et al ., 2011; Ye et al ., 2019).…”

Antimicrobial activity of crude extracts ofPhyllostictaspp.

“…They can cause leaf spot and fruit rots (Glienke-Blanco et al 2002;Silva & Pereira 2007). Its teleomorph state Guignardia is also widely known as a causal pathogen on Citrus and grapevine (Baayen et al 2002;Paul et al 2005).…”