Ascospore Infection and Colletotrichum Species Causing Glomerella Leaf Spot of Apple in Uruguay.

Glomerella leaf spot (GLS) caused by Colletotrichum spp. is a destructive disease of apple restricted to a few regions worldwide. The distribution and evolution of GLS symptoms were observed for two years in Uruguay. The recurrent ascopore production on leaves and the widespread randomized distribution of symptoms throughout trees and orchard, suggest that ascospores play an important role in the disease dispersion. The ability of ascospores to produce typical GLS symptom was demonstrated by artificial inoculation. Colletotrichum strains causing GLS did not result in rot development, despite remaining alive in fruit lesions. Based on phylogenetic analysis of actin, ß-tubulin and glyceraldehyde-3-phosphate dehydrogenase gene regions of 46 isolates, 25 from fruits and 21 from leaves, C. karstii was identified for the first time causing GLS in Uruguay and C. fructicola was found to be the most frequent (89%) and aggressive species. The higher aggressiveness of C. fructicola and its ability on to produce abundant fertile perithecia could help to explain the predominance of this species in the field.

Extracellular enzymes of Colletotrichum fructicola isolates associated to Apple bitter rot and Glomerella leaf spot.

Colletotrichum fructicola causes two important diseases on apple in Southern Brazil, bitter rot (ABR) and Glomerella leaf spot (GLS). In this pathosystem, the Colletotrichum ability to cause different symptoms could be related to differences of extracellular enzymes produced by the fungi. Thus, the objectives of this study were to compare the production of these enzymes between ABR- and GLS-isolate in vitro and to evaluate their involvement on infected apple leaves with C. fructicola. In agar plate enzymatic assay, ABR- showed significantly higher amylolytic and pectolytic activity than GLS-isolate. In contrast, for lipolytic and proteolytic no significant differences were observed between isolates. In culture broth, ABR-isolate also had higher activity of pectin lyase (PNL), polygalacturonase (PG) and laccase (LAC). Notably, LAC was significantly five-fold higher in ABR- than GLS-isolate. On the other hand, in infected apple leaves no significant difference was observed between isolates for PNL, PG and LAC. Although differences in extracellular enzymes of ABR- and GLS-isolate have not been observed in vivo, these results contributed to highlight the importance to investigate such enzymes in depth.