XVI International Botanical Congess

To define the genetics of host specificity,176 non-pathogenic gene-disruption mutants were isolated by REMI transformation (Tx) from the cucurbit pathogen Colletotrichum magna. The mutants retained the ability to colonize plants and expressed three symbiotic lifestyles based on protecting plants against virulent fungi: A mutualistic (80-100% protection), B undefined (20-65% protection), and C commensalistic (0% protection). The Tx vector and flanking DNA from REMI A and C mutants were recovered and designated pFSLm and pFSLc, respectively. pFSLm and pFSLc were used to disrupt homologous sequences in pathogenic wild types and generated the respective phenotypes. Changing the symbiotic lifestyle of C. magna by gene disruption resulted in an expansion of host specificity. Analysis with other Colletotrichum species revealed that host range consists of both disease hosts and non-disease hosts, and the host directly influences fungal symbiotic lifestyle expressed.