THE HYPERSENSITIVE REACTION TO BACTERIAL CANKER IN MIRABILIS-JALAPA IS SIMPLY INHERITED

The four o'clock plant (Mirabilis jalapa) displays a hypersensitive re action to the causal agent of bacterial canker, Clavibacter michiganen sis subsp. michiganensis. Two lines of M. jalapa were crossed with one another and a local weed accession not showing the same reaction. All F-1 progeny displayed the hypersensitive reaction within 48 h of inoc ulation with suspensions of Clavibacter michiganensis subsp. michigane nsis. Selfed F-2 progenies of the two hypersensitive parents were show n to be hypersensitive. F-2 populations derived from crosses between e ither hypersensitive parent and the local non-hypersensitive line disp layed Mendelian segregation ratios, 3 hypersensitive: 1 non-hypersensi tive. There were no maternal effects. This demonstrates that the trait is under the control of a single dominant gene. Morphological traits including flower colour and cotyledon colour were under more complex g enetic control.