Relationships among Colletotrichum Isolates from Fruit-Rots Assessed Using rDNA Sequences

Abstract

Isolates of Colletotrichum associated with fruit rots in New Zealand were used to test the applicability of morphological, cultural, and rDNA sequence data to clarify relationships within this genus. Morphological and cultural features were used to recognize 16 distinct groups among the New Zealand fruit-rotting isolates. These included the currently accepted species C. coccodes, C. musae, C. orbiculare, and Glomerella miyabeana as well as 3 C. acutatum like groups and 9 C. gloeosporioides-like groups. Analysis of rDNA sequences from the D2 region allowed the isolates to be separated into 4 broad groups (the relationships of C. coccodes remaining unresolved), the various morphological/cultural groups clustering as subgroups among the rDNA sequence groups. The same 4 groups were recognized when rDNA sequences from the New Zealand isolates were compared with those from Colletotrichum isolates from other hosts and other countries. Taxonomic treatment of the molecular and morphological/cultural data is discussed. A trinomial group-species concept may provide the best approach to subgeneric classification within Colletotrichum. The species name (based on rDNA sequence similarity and supporting morphological and cultural features) indicates the broad group within Colletotrichum to which the isolate belongs; the subspecific name provides additional information on host specialisation, morphological variation, etc. However, before the utility of this concept can be properly assessed, the evolutionary and genetic relationships between the various morphological and sequence-defined groups need to be better understood. If such a scheme is shown to be practical in a biological sense then a number of taxonomic and nomenclatural problems will need to be resolved before it could be adopted.