Impact and interactions of Ramularia collo-cygni and oxidative stress in barley

Summary

Sector:
Cereals & Oilseeds
Project code:
PR431
Date:
01 July 2004 - 31 March 2008
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£125,225 From HGCA (Project No. 3024)
Project leader:
SJP Oxley1 , ND Havis1 , JKM Brown2 , JC Makepeace2 , J Fountaine1 1 SAC, West Mains Road, Edinburgh EH9 3JG 2 John Innes Centre Colney Lane, Norwich, NR4 7UH

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About this project

Abstract

Ramularia leaf spot, caused by the fungus Ramularia collo-cygni, has become an established disease in the north of the UK. This research shows the average yield loss associated with ramularia in spring barley ranged from 0.2 - 0.6 t/ha. The estimated cost to the malting barley industry was £10.68m at a grain price of £125/tonne.

The research shows that Recommended List (RL) varieties differ in susceptibility. In winter barley differences in leaf spot levels were not significant and no variety had effective resistance. In spring barley, Quench, Decanter, Oxbridge, Riviera, Rebecca and Jolika showed lowest disease levels. Cocktail, Doyen, Publican and Belgravia exhibited more symptoms, but all RL varieties showed better resistance compared to older varieties Pewter and Prestige. The greatest benefit to fungicide control of ramularia (1.3 t/ha) was with the susceptible spring barley variety Cocktail whilst there was no response with the resistant variety Decanter.

Airborne spores were released two days after a period of leaf wetness. Spore release from winter barley occurred too late to have a major impact on spring barley in the two high disease pressure years, 2005 and 2007. Seed infection and weather conditions played a greater role in the disease epidemic than airborne spores, which potentially play a role in seed infection late in the season.

  • Quinone outside Inhibitor (QoI or strobilurin) fungicides no longer achieved control of ramularia and only contributed to 0.1 t/ha in yield with no benefits in green leaf area retention. This resistance mutation first occurred in the UK around 2001-2002, corresponding to the decline in field performance since then.
  • Prothioconazole achieved effective control and the best yield response. Chlorothalonil achieved good control of symptoms, but no yield response and may have a role in situations where infection is predominately systemic.
  • Morpholine fungicides showed no activity against ramularia. Yield losses from using this type of fungicide seen in 2002 were not observed in 2005-07.

The role of mlo mildew resistance gene on varietal susceptibility to ramularia is complex. Presence of mlo5 increases the susceptibility of the variety to ramularia particularly where the variety is stressed by light. Breeding for resistance should be an important aim for plant breeders if reliance on fungicides is to be reduced.

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