Response of transgenic cucumber and carrot plants expressing different chitinase enzymes to inoculation with fungal pathogens

Three lines of cucumber cv. Endeavor, each transformed with a chitinase gene originating from petunia (acidic), tobacco (basic), or bean (basic) using Agrobacterium tumefaciens, were compared with nontransgenic plants for response to inoculation with Alternaria cucumerina, Botrytis cinerea, Colletotrichum lagenarium, and Rhizoctonia solani. In both growth chamber studies using whole plants and in vitro inoculations conducted with detached leaves, no differences in disease development (rate and final levels) were detected between transgenic and nontransgenic plants. Carrot cvs. Nanco and Golden State transformed with two chitinase genes (from petunia and tobacco) were also evaluated for response to inoculation with the pathogens Alternaria radicini, B. cinerea, R. solani, Sclerotium rolfsii, and Thielaviopsis basicola. A detached petiole inoculation method was used to compare nontransgenic and transgenic plants. The rate and final extent of lesion development after 7 days were significantly (P = 0.01) lower in the transgenic plants expressing the tobacco (basic) chitinase gene upon inoculation with B. cinerea, R. solani, and S. rolfsii, but not in plants expressing the petunia (acidic) chitinase gene. There were no detectable differences with A. radicini or T. basicola in either group of transgenic plants. These results demonstrate the in planta efficacy of a basic chitinase protein in providing enhanced tolerance of carrot to three fungal pathogens; however, the efficacy of chitinase gene transformation as a strategy for enhancing disease tolerance in plants can be influenced by the plant species used, the type of chitinase protein expressed, and the characteristics of the fungal pathogen.