TRANSGENIC CUCUMBER PLANTS HARBORING A RICE CHITINASE GENE EXHIBIT ENHANCED RESISTANCE TO GRAY MOLD (BOTRYTIS-CINEREA)

A rice chitinase cDNA (RCC2) driven by the CaMV 35S promoter was intro duced into cucumber (Cucumis sativus L.) through Agrobacterium mediati on. More than 200 putative transgenic shoots were regenerated and grow n on MS medium supplemented with 100 mg/l kanamycin. Sixty elongated s hoots were examined for the presence of the integrated RCC2 gene and s ubsequently confirmed to have it. Of these, 20 were tested for resista nce against gray mold (Botrytis cinerea) by infection with the conidia : 15 strains out of the 20 independent shoots exhibited a higher resis tance than the control (non-transgenic plants). Three transgenic cucum ber strains (designated CR29, CR32 and CR33) showed the highest resist ance against B. cinerea: the spread of disease was inhibited completel y in these strains. Chitinase gene expression in highly resistant tran sgenic strains (CR32 and CR33) was compared to that of a susceptible t ransgenic strain (CR20) and a control. Different responses for disease resistance were observed among the highly resistant strains. CR33 inh ibited appressoria formation and penetration of hyphae. Although CR32 permitted penetration of hyphae, invasion of the infection hyphae was restricted. Furthermore, progenies of CR32 showed a segregation ratio of 3:1 (resistant:susceptible). As the disease resistance against gray mold was confirmed to be inheritable, these highly resistant transgen ic cucumber strains would serve as good breeding materials for disease resistance.