Abstract
ABSTRACT Papaya target-spot, caused by fungus Corynespora cassiicola presents a wide geographic distribution, causing leaf spots in several hosts. The aim of this research was to evaluate the behavior of papaya varieties and/or selections to the natural occurrence of target spot, and test the fungi toxic effect of neem, citronella and eucalyptus extracts, and fungi static effects of Bacillus isolates on the fungus C. cassiicola in vitro. To evaluate the natural occurrence of the disease in field, symptoms on leaves of 11 papaya varieties and/or selections have been assessed. The pathogenicity of isolates was verified by inoculation of plants in greenhouse. Neem, citronella and eucalyptus extracts were prepared at concentrations of 10, 15 and 20% and poured into Petri dishes containing C. cassiicola mycelium discs. For , Bacillusnine isolates were used, and the antagonistic potential was evaluated by the pairing of pathogen and isolate colonies by the circle method. Papaya varieties and/or selections presented all leaves with injury, and Canaan Sunrise Solo and Canaan Golden selections showed the greatest number of injuries per leaf, showing that papaya varieties and/or selections respond differently to the phytopathogen. All plant extracts tested showed inhibitory effect on the mycelial growth of C. cassiicola in vitro. Bacillus isolates showed an antagonistic potential on the mycelial growth of the fungus, with B. methylotrophicus (Iso 31 and Iso 41) being the most promising as a biological control agent. The results indicate that forms of alternative control of diseases are promising in the management of papaya target-spot.
Highlights
Papaya target spot or corynespora leaf blight caused by fungus Corynespora cassiicola (Berk & Curt.) Wei. has wide geographical distribution, being reported as causing leaf spot in more than 70 host species (TRAN, et al, 2016; DEÓN, et al, 2014; NGHIA et al, 2008; FARR; ROSSMAN, 2006; SILVA et al, 1997)
In the state of Maranhão, C. cassiicola was found in several hosts, including papaya (Carica papaya L.) and acerola, causing leaf and fruit problems (SILVA et al, 1997; BITU et al, 2016)
Symptoms were initiated by white spots, with yellowish halo, evolving to circular spots of brown coloration. These symptoms coincide with those described in literature on papaya plants (KNAAK et al, 2010; SILVA, 2011; BITU, 2016)
Summary
Corynespora cassiicola in vitro.Papaya target spot or corynespora leaf blight caused by fungus Corynespora cassiicola (Berk & Curt.) Wei. has wide geographical distribution, being reported as causing leaf spot in more than 70 host species (TRAN, et al, 2016; DEÓN, et al, 2014; NGHIA et al, 2008; FARR; ROSSMAN, 2006; SILVA et al, 1997). In the state of Maranhão, C. cassiicola was found in several hosts, including papaya (Carica papaya L.) and acerola, causing leaf and fruit problems (SILVA et al, 1997; BITU et al, 2016) It is mentioned as a pathogen in weeds, such as Commelina benghaleinnsis L.) and Vernonia cinerea (CUTRIM, SILVA, 2003), which are important sources of inoculum, especially under favorable climatic conditions. In papaya, it can affect leaves, stem and fruits, being the symptoms characterized by lesions of pale yellow color ranging from 1 to 2 mm in diameter, reaching up to 10 mm, with necrotic center. Lesions are small and rounded, evolving rapidly, affecting the pulp, making the fruit commercially unfeasible (BITU et al, 2016)
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