Seed should always be tested for germination, pests and diseases. Growers are advised to request the germination level on certified seed and have homesaved seed tested by a reputable laboratory, so that the results can be used – together
with seed size or TGW – for calculating sowing rate.
Modern UK varieties have good Ascochyta resistance, but seed with over 1% infection should not be used. In addition, seed shown to have any infection of stem nematode should not be drilled.
Imported varieties must have their health status checked, as neither Ascochyta nor stem nematode are likely to be tested for in France or any other bean-producing country.
Seed quality and testing
Beans are often sown during late autumn into cold, wet soils. They are extremely sensitive to compaction and waterlogging which reduce root growth and can therefore influence water uptake in drought conditions. In poor soil conditions, seed quality is of great importance, allowing good emergence and establishment in often difficult conditions.
Bean seed is easily damaged during harvesting, drying and handling so it is important to ensure that the seed sown is of the best quality. Work at Nottingham University showed a 50% reduction in establishment in the spring of combine damaged seed compared with undamaged seed of the same seed lot.
Seed harvesting and drying
Seed drying at too high a temperature can cause damage to the seed and reduce the quality. Guidelines for seed drying are outlined below:
Maintenance of quality during seed drying
Equilibrium moisture contents of bean seeds at different values of relative humidity at 25oC
Germination and vigour seed tests
Germination measurements often bear little relation to field emergence since damaged seed which germinates well in the lab is prone to damping off diseases in cold, wet soils. Seed conductivity measures seed damage and is better related to field emergence. Conductivity measurements below 16 indicate healthy undamaged seed that should establish well in the field.
1. Conductivity test
Conductivity measurements are not a standard for beans although the test is routinely done on peas, requiring 100 g sample and taking 1 to 3 days to complete. Conductivity measurements will be conducted by NIAB although this is not a standard test and no interpretation of the results is offered. Research in Scotland, suggests that conductivity measurements below 16 indicate healthy undamaged seed that should establish well in the field, whereas seed with higher conductivity scores are more prone to damage from seed borne diseases and should not be sown into poor, wet seedbeds.
2. Tetrazolium test
The tetrazolium test is a rapid test used as a vigour score. It was designed for use on green beans and is currently also used on field beans. It involves soaking the seed in tetrazolium chloride, which stains the living areas of the seed red. It denotes area of mechanical damage or areas of the seed that may have been damaged by disease.
The test takes 1 to 3 days to complete and requires 150 g sample
Disease and pest testing
Standard seed tests for field beans include Ascochyta leaf and pod spot and stem nematode. Seed treatments are available for Ascochyta. Stem nematode results are indicated as either present or absent although more detailed scoring is available from PGRO and NIAB. Uninfected land should not be planted with seed at any level of infection. Where infection has been present in the past, low scores can be planted whilst moderate scores are fine if pulses or oats will not be planted in the same field for four years. High counts (equivalent to 1% in the PGRO test) should not be planted.