Identification and characterization of Colletotrichum fructicola causing black spots on young fruits related to bitter rot of pear (Pyrus bretschneideri Rehd.) in China

In recent years, Pyrus bretschneideri Rehd. var. 'Suli' has been damaged by a disease characterized by the presence of black spots on young fruit in China, which was always followed by severe bitter rot on matured fruits. The etiology of these symptoms and their relationship with the bitter rot was unknown. A colony was routinely isolated from young and matured 'Suli' pear fruits showing black spots and rot symptoms, respectively. This fungal colony was identified as Colletotrichum fructicola based on morphological characteristics and DNA sequence data of 7 regions. C fructicola was confirmed to be capable of eliciting both black spots and bitter rot symptoms by completion of Koch's Postulates. The results suggested that the disease characterized by the presence of black spots on young fruits is indeed an early stage of the bitter rot observed on matured fruits of 'Suli' pear. Variety resistance analysis indicated an obvious resistance variation possessed by the pear varieties generally cultured in China, with black spots only occurring on some pear varieties. Our results also indicated that wounding can break the quiescent infections, enhance the infectivity of C. fructicola, and lead to more rapid rot of young and matured fruits. These results provided a clear clue that C fructicola can invade some varieties of P. bretschneideri Rehd. directly without entry via wounds, but subsequently turned into quiescent infection and causing black spots on the fruit surface. The quiescent infection acts as a pathogenic factor responsible for bitter rot of matured fruits. The influence of temperature and pH conditions for growth and colony morphology of C fructicola were also evaluated. The characterization of C fructicola causing bitter rot of pear (P. bretschneideri) is expected to provide useful information for controlling this economically important disease. (C) 2014 Elsevier Ltd. All rights reserved.