Why are my onions rotting in storage? What causes neck rot in onions? How to get rid of onion neck rot? How to prevent onion neck rot? Let’s find out about neck rot of onion symptoms and control guidelines!
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Neck Rot of Onion Definition
Neck rot of onion meaning – What is neck rot of onion?
Neck rot is mostly a problem for allium crops when they are stored. For many years, the disease cost the UK bulb onion industry a lot of money until better ways to harvest and store onions were found. However, even without modern drying facilities, producers still lose much money. Neck rot can happen to garlic, leeks, shallots, and multiplier onions, but it is most damaging to bulb onions, where losses can be as high as 50%.
Neck Rot of Onion Causes
What causes neck rot of onion? What is the most common cause of neck rot in an onion?
Botrytis allii, which is the same as Botrytis aclada, is the cause of neck rot. This fungus makes spores that are 7–11 x 5–6 μm, which are smaller than those made by most other Botrytis species that grow on alliums. The conidia of B. allii can be made easily in a lab. On the other hand, the Botrytis leaf blight pathogen B. squamosa does not easily make spores in culture and has much bigger conidia (14–24 x 9–18 μm). B. porri is an important Botrytis pathogen on garlic and leeks. Botrytis byssoidea is another type of organism that can cause onion neck rot. This pathogen is not the same as B. allii. It causes gray mold neck rot, which is a disease.
Neck Rot of Onion Symptoms
Signs and symptoms of neck rot of onion – What are some symptoms of neck rot of onion?
Usually, the neck of a stored bulb onion will be water-soaked or light brown. Around the neck and between the scales of the bulb, dense gray mycelia grow. On the shoulders of the bulb, many black sclerotia are about 5 mm in diameter.
This mold growth doesn’t show up until after a few weeks of storage. Then, the disease spreads from the neck until most of the bulb is soft and rotten. In the field, a brown rot can happen on the fleshy scales of a bulb onion that is getting ready to mature. This is usually caused by splitting or damage to the bulb.
The disease-causing agent can affect any bulb part, not just the neck. Therefore, before crops are harvested, it is possible to find B. allii sporulating on old leaves.
Neck Rot of Onion Disease Cycle
The pathogen is spread by onion and shallot seeds and sets. If the seed is stored in a cool enough place, the fungus may be able to live on it for more than three years.
The disease spreads from the seed coat to the seedling leaves, which stay attached to the cotyledon. These leaves are infected by B. allii, which makes spores when the tissue dies.
Symptoms may only show up on the leaves during the growing season. But right before the bulb onions are picked, the leaves are topped or bent, making cuts that can be infected.
While the neck tissue keeps water, the pathogen grows down to the bulb, where it causes scale rot. Inoculum can also come from sclerotia in the soil, which grow into conidia when they germinate. Sclerotia can live underground for two years.
Neck Rot of Onion Control Management Guidelines
Control of neck rot of onion – What is the best treatment for neck rot?
Use seed that does not have a lot of the pathogen. Use sets that haven’t been infected with the disease and were grown from such seeds. A 1% seed infection is seen as an economic threshold.
The treatment for seed-borne B. allii has been very effective. Use heat treatments to stop the pathogen in sets. Plant-resistant kinds or cultivars of alliums.
When you harvest onions, leave a neck about 10 cm long so that it can be thoroughly dried before the fungus spreads down the neck and into the bulb. Bulb necks can be dried by forced air drying or harvesting onions and letting them dry in a warm, dry field. After drying, keep things in storage below 75% relative humidity and at 0–1º.
C. Fungicides used during the growing season may help stop neck rot somewhat. Rotate with non-hosts to reduce the number of B. allii soil-based sclerotia.
I hope you understand about neck rot of onion symptoms and control guidelines.