Aspergillus niger, Botrytis aclada and Fusarium oxysporum f. sp. cepae are relevant seed-borne fungi of onion (Allium cepa L.) and are known as causal agents of black mould, neck rot and basal rot diseases, respectively. These pathogens can be transmitted from infected seeds to seedlings, sets or bulbs. They eventually kill the entire plant through degradation of the tissues. Different principles are suggested for their control. Botrytis squamosa, Cladosporium alliicepae and Stemphylium vesicarium, which cause several lesion on the onion leaves, can also occur on seeds but they are not able to demonstrate disease transmission to the plant parts. The role of other seed-borne fungi (namely, Alternaria alternata,