Characterization of Colletotrichum fructicola, a new causal agent of leaf black spot disease of sandy pear (Pyrus pyrifolia)

In recent years, a devastating fungal disease characterized by small black spots (<1 mm) on sandy pear (Pyrus pyrifolia Nakai) leaves has occurred in sudden outbreaks in southern China, resulting in severe defoliation and a loss of fruit quality and yield. To identify the etiology of the disease, 147 fungal isolates from sandy pear leaves showing typical black spots were collected from 30 orchards; 10 fungal species were included among the isolates, and the prevailing 124 Colletotrichum isolates were subjected to morphological and molecular characterization. Based on differences in colony morphology, the isolates were separated into five groups (I to V); the groups were specifically separated according to a combination of colony color, pigment, sporulation, perfect stage, and spore size. In addition to their morphological features, the five groups were assessed for their molecular and taxon statuses based on ITS sequences, multilocus regions (ITS, ACT, TUB, CHS-1, GAPDH), and the Apn2/MAT locus, which provided molecular proof for the identification of these isolates as Colletotrichum fructicola Prihastuti. The result also indicated different resolution of the three loci in delimiting the species. Koch’s postulates were fulfilled by inoculating conidium suspensions of the representative isolates on attached and detached leaves of sandy pear cvs. Cuiguan, Xueqing and Huali No. 2 with analogous conditions (under saturated humidity and with tiny wounds) to those that appeared in the field, and similar symptoms were elicited by the isolates, suggesting that C. fructicola was causing the disease. To our knowledge, this is the first report of C. fructicola causing leaf black spot of pear. The etiological clarification and characterization of the C. fructicola isolates provide useful information to aid in the understanding of leaf black spot disease in pears and for designing management strategies to control this economically significant disease.