Analysis of genetic diversity and host preference in Colletotrichum gloeosporioides

Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. is known to infect a wide variety of crop species including mango avocado, almond, strawberry and papaya, and they cause significant economic damage to crops worldwide. To investigate genetic variation among these fungal isolates from different hosts, we developed a genotyping method based on inter-simple sequence repeat (ISSR), and used it for the analysis of our fungal isolates. The results obtained by ISSR-PCR indicated that, in most cases, C. gloeosporioides obtained from the same host species displayed similar gel patterns and were grouped in the same cluster by the UPGMA-based cluster analysis. This phenomenon was most predominant for isolates collected from mango; irrespective of the collection time, location, and mango varieties, C. gloeosporioides collected from this host tends to exist in the same cluster. Isolates from papaya, in contrast, were highly diverse in the ISSR patterns, despite that they were collected from the same area. We tried to develop expressed sequence tags-SSR markers, but less polymorphism was observed. Therefore, the EST-SSR markers which we analyzed are not the effective markers. To investigate the pathogenicity of isolates, we conducted inoculation tests of mango, avocado and papaya isolates. The results showed the potential of cross-infection among the C. gloeosporioides isolates from different host. However, isolates showed host preference since they were more pathogenic in their natural hosts (P < 0.05). The mango isolate C157 and MAC060 produced small lesions on avocado and papaya fruit, whereas isolates C442 and C447 produced large lesions. It indicates that even from the same host, isolates showed different pathogenicity.