Status of diseases in linseed in the UK

Summary

Linseed is a rapidly expanding crop in the UK, with an area fast approaching 120,000 ha, making the UK the biggest producer of linseed in Europe.

A range of 15 pathogens, with the potential to cause disease problems in the UK, has been selected, their symptoms described, their present status in the UK evaluated and possible control measures outlined.

The most important are believed to be:

(i) Alternaria linicola (seedling disease)

(ii) Fusarium spp. (seedling disease)

(iii) Botrytis cinerea (grey mould)

(iv) Oidium lini (powdery mildew)

The first three are mainly seed-borne and can cause problems with seedling emergence, leading to a poor stand. The level of seed-borne disease varies from year to year, ranging from only 22% of seed infected in 1990 (a dry year) to 98.4% in 1987 (a wet year). A. linicola is by far the most important, followed by F. avenaceum and B. cinerea. Seed-borne diseases can be controlled by seed-treatment, although there have been resistance- problems with some of the fungicides used. Some research has been targeted towards control of seed-borne diseases by application of sprays to the growing crop. Results have been variable, but it appears as if better control is likely to be achieved in the SE of England.

Oidium lini causes powdery mildew and its level also varies from year to year, being worse in dry years. It is also worse in drier parts of the country, such as the SE of England. It can be controlled by resistant cultivars and fungicide sprays.

A number of other pathogens, such as Phoma exigua f.sp. linicola, Sclerotinia sclerotiorum, Fusarium oxysporum F.sp. lini and Verticillium dahliae, have also caused problems from time to time, but so far not on a widespread scale.

Because of the small size of linseed leaves, problems arise with the estimation of various diseases in linseed crops. These are outlined.

The process of seed-certification is described and problems associated with interpretation of the rules are discussed.

Some trials have been undertaken to investigate cultivar effects on disease resistance. Differences between cultivars were observed in responses to A. linicola, B. cinerea, 0. lini and s. sclerotiorum, although it is not always clear how much effect is due to inherent resistance and how much to differences in maturity.

A small section is concerned with the effects of disease on oil quality and quantity. At present there appears little impetus to breed for improvement in these parameters as no minimum standards are laid down by the crushers. This may, however, change in the future. Generally there seems little problem with the quality of linseed oil from UK crops. Seed-producers were asked for their perceptions of disease problems and a summary of these is included. Generally their reports supported research findings in that A. linicola and B. cinerea were considered to be the most important diseases. 0. lini was thought of as a problem in dry years, but it was not clear if it was always economic to use sprays to control it. Surprisingly there was little comment on the Fusarium spp. involved in seedling disease, although this may be because many seed-firms have only become substantially involved with linseed in the last few years; the last year with high levels of Fusarium spp. was 1987.

The Review concludes with recommendations for future research.