There are 4 types of botrytis bacteria, which is a fungal disease. The one most important to onion crops is botrytis allii. (ie. Neck Rot).

There is much scientific evidence available to indicate that botrytis allii free seed is the beginning of control of this disease in onion crops. 

 MKS has developed crop management strategies to permit the production of certified botrytis allii free seed. Certification is carried out by an independent laboratory. 

There is increasing demand for botrytis allii free seed where the disease is a major problem, particularly in cooler climates. When onion crops have been damaged by other factors for example hail, excessive heat or mechanical damage they will also become prone to botrytis allii as a second infection. The provision of botrytis allii free seed is a major step forward in seed quality and is recommended as an integral part of a quality control program. 

It is recommended that a combination of certified botrytis allii free seed and fungicide film coating be used in the initial control of this disease.

The following notes relate to the role of seed infection in the incidence of Neck Rot in onions :

‘Onion seed can be infected and play an important role in transmission’

There are 2 stages in disease development - 

a)  The transfer of the pathogen from seed to seedlings, and
b)  The subsequent spread of the fungus through the crop.

Two factors which effect the amount of disease in a crop are - 

a)  the percentage of infected seeds planted, and
b)  Weather conditions during crop growth.

10% of seed infection results in Neck Rot losses of commercial significance BOTH in wet and dry years; 1% of seed infection causes losses in wet summers particularly.

‘Disease can be introduced to the crop by the use of infected seed. Botrytis Allii grows from the seed coat into the tip of the flag leaf, from which it can grow down the flag leaf without producing symptoms of infection. From the flag leaf, Botrytis Allii, can infect the base of the first true leaf unnoticed, and remain in the plant undetected.

It is recommended that planting seed with Botrytis Allii infection be avoided. This becomes even more important as the threat of resistance to chemicals increases.’

Ref. Metcalf D. Plant Pathologist - Tasmanian institute of Agricultural Research, Devonport.