Onion bacteriosis

Article

August 12, 2022

Bacteriosis of onion (sour skin of onion) - bacterial disease of onion (Allium cepa).

Occurrence and harm

It is a disease from the group of wet rot. It occurs in all onion growing regions in the world, but in different climatic zones, and depending on the agrotechnics used there, it is caused by different species of bacteria. In Poland, it is caused by the bacteria Pectobacterium carotovorum subsp. carotovorum, Burkholderia gladioli var. alliicola, Burkholderia cepacia and Pantoea allii. Research conducted by scientists in 2004–2009 in Poland showed the presence of other bacteria in rotting bulbs: Pseudomonas marginalis var. marginalis, Pseudomonas viridiflava, Pseudomonas fluorescens, Pseudomonas aeruginosa, Enterobacter cloacae, Serratia plymuthica and Pantoea ananatis. The disease has a varied aetiology and its symptoms depend on the species of bacteria that cause it. The harmfulness of the disease is mainly due to the rotting of the bulbs during their transport, storage and in stores.

Symptoms

Onion bacteriosis caused by Burkholderia cepacia (sour skin of onion) is manifested by rot and a specific, sour, vinegar smell. It causes wrinkling of the outer fleshy scales of the onion and turning the scales yellow. The outer, wrinkled scales are easily removed, revealing rotting yellow and slimy scales. Their color comes from microscopic yellow granules formed as a result of tissue decomposition. Only the outer scales are rotting, while the inner scales remain healthy together with the buds at the base. Burkholderia galdioli var. alliicola attacks plants already in the field. On the onion leaves, small black necrotic spots appear, which, however, do not affect the growth of the onion. On the cross-section of the bulbs, however, some of the bulbs' skins appear water-soaked. They rot over time, turning dark brown.

Epidemiology

Onion-infecting bacteria live in the soil on the rhizosphere of crops and weeds, and on plant debris. They can attack the onion while it is growing in the field. The condition for them to penetrate inside are injuries and the presence of water. This is most often done when the onion is harvested and the leaves are cut. Not drying the bulbs after harvesting makes it easier for bacteria to penetrate them through the wounds.

Protection

Chemical protection is not used. The greatest importance is the correct agrotechnics and the selection of the right soil for growing onions. It should have regulated water conditions and be weeded. Weeding is of particular importance during the maturation period of the bulbs, as the presence of weeds at this time extends the drying time of the onion necks, which extends the time of infection for the bacteria and thus the severity of the disease. The harvest time is also important; this should be done in dry weather. The collected onions must be dried.

Footnotes