Methods are described for the detection of latent infection byErwinia carotovorassp.atroseptica(blackleg and soft rot),Corynebacterium sepedonicum(ring rot) andPhoma exiguavat.foveata(gangrene) which are regarded as the most important tuber‐borne pathogens of potato. The methods comprise selective media forE. carotovorassp.atrosepticaandP. exiguavar.foveata, indirect fluorescence antibody staining forE. carotovorassp.atrosepticaandC. sepedonicum, and the eggplant test forC. sepedonicumandP. exiguavar.foveata.These are used in Northern Ireland to detect pathogen contamination in nuclear stock mother tubers prior to micropropagation. Marked reductions in disease levels of blackleg have been observed in present pre‐basic stocks raised by micropropagation compared with those previously propagated from stem cuttings. It was found thatPseudomonas stutzeri, a saprophytic contaminant bacterium, can pass through the micropropagation process in a latent f