Powdery Scab - Strains and Conducive Conditions

Research Review

J. Brierley & A. Lees SCRI

S. Wale SAC

A review of literature and other sources of information

2008

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CONTENTS

CONTENTS ...... 3

1 Industry Summary ...... 5

Life Cycle...... 5 Inoculum ...... 5 Conducive Conditions...... 6 Soil Moisture...... 6 Temperature ...... 6 Weather and Powdery Scab ...... 7 Soil pH ...... 7 Soil Type...... 7 Host Resistance...... 7 Strains of Powdery Scab ...... 8 Practical Steps for Current Production Methodology...... 8 Inoculum - assess level of powdery scab on seed and in soil ...... 8 Conducive Conditions - reduce the risk of powdery scab developing in your field...... 9 Carry Out Specific Control Measures...... 9

2 Introduction ...... 11

Information on the Disease ...... 11 The Pathogen...... 12 Life Cycle...... 13 Geographical Occurrence...... 13 Disease Management ...... 14 Host Resistance...... 16

3. Conducive Conditions...... 18

Soil Moisture...... 18 Temperature ...... 20 Seasonal Variation - weather ...... 21 Soil pH ...... 23 Soil Type...... 24 Inoculum ...... 25 Spore ball survival and germination ...... 27 Determining Levels of Soil Inoculum...... 29

4 Strains...... 30

Significance of variation or ‘strains’ of Spongospora subterranea...... 30 Variation in Spongospora subterranea f.sp. subterranea: methods and evidence...... 30

5 Overall summary...... 34

Research Review: Powdery Scab - Strains and Conducive Conditions Areas which require future research efforts...... 34 Cultivar resistance...... 34 Biological control (impact of soil microbiology on pathogen/disease) ...... 34 Risk assessment and decision support software...... 34

6 References...... 35

Cited literature...... 35

Research Review: Powdery Scab - Strains and Conducive Conditions

1 Industry Summary

Powdery scab has become a persistent problem for potato growers since the late 1980’s. It has been recorded throughout GB since disease intelligence records began. However, whilst severe powdery scab can occur anywhere in GB, it is not perceived as a major issue in either the processing or table sectors of the ware market. There is a perception in the industry that the disease is more of a problem in northern Britain and that the seed industry is worst affected. Seed quality is critically examined when seed is purchased and powdery scab is high on a list of exclusion priorities for many domestic and export markets. Seed-borne inoculum is a major impediment to opening up new markets or expanding existing markets. The recent discovery that powdery scab may be carried on seed as latent infections adds another dimension to r