Survey of seed-borne pathogens in certified and farm-saved cereal seed in Britain between 1992 and 1994

Abstract

2301 cereal seed samples, drawn from seed stocks of winter wheat and spring and winter barley harvested in England and Scotland in the three years 1992-94, were tested for seed- borne pathogens at the Official Seed Testing Station for Scotland. Samples represented both farm-saved seed and seed intended for certification. Tests were made for:

On winter wheat seed -
Microdochium nivale (Fusarium nivale) (seedling blight)
Septoria nodorum (seedling blight)
Fusarium spp. (seedling blight)
Tilletia caries (bunt)

On spring and winter barley seed -
Microdochium nivale (Fusarium nivale) (seedling blight)
Cochliobolus sativus (seedling blight)
Fusarium spp. (seedling blight)
Drechslera graminea (Pyrenophora graminea) (leaf stripe)
Drechslera teres (Pyrenophora teres) (net blotch)
Ustilago nuda (loose smut)

The incidence of seedling blight pathogens varied between years. M. nivale infection was higher in 1992 and 1993, when more than 40% of certified winter wheat samples had at least 20% of seeds infected, compared to 1994, when only 2% of samples were infected at this level. S. nodorum infection was rare in 1992. It was seen in approximately 40% of winter wheat samples in 1993 and 1994, but only occasional samples had more than 20% of seeds infected.

Bunt spores were recorded in between 20% and 60% of certified and farm-saved seed samples over the three years of the survey but contamination was usually at low levels. Occasional samples had more than five bunt spores per seed. English produced seed was more often contaminated than seed produced in Scotland.

Loose smut infection was higher in winter barley than in spring barley and levels in farm- saved seed were higher than in certified seed. In 1992, 25% of farm-saved winter barley seed samples had more than 0.5% infection. By contrast, in the same year, only 2% of certified spring barley samples were infected at this level.

Leaf stripe was recorded at low levels in both spring and winter barley each year. No more than 2% of samples tested in any year had more than 2% of seeds infected.

The majority of samples tested each year were not infected with seed-borne pathogens at levels that could have been damaging to crop production. Infection at damaging levels could not be determined by visual inspection of the seed and the occasional heavily infected samples could not be predicted by year of production, area of production or category of seed.