5.1.12
THE EFFECT OF INOCULUM PRESSURE, FERTILIZER AND COMPONENT NUMBER ON SEVERITY OF MILDEW AND SCALD, YIELD AND MALTING QUALITY IN MIXTURES OF BARLEY CULTIVARS

AC NEWTON, WTB THOMAS, JS SWANSTON, RP ELLIS, DC GUY and E GACEK

Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK

Background and objectives
Mixtures of species and cultivars have been used worldwide to effectively control disease in practice [1]. In UK agriculture, however, they have been little used due to lack of efficacy against the major pathogens, agronomic problems, or non-acceptance by the end user. Changes in economic pressures and environmental concerns make the use of mixtures more attractive, particularly in cereals. We carried out a series of trials on barley mixtures to determine their main strengths and weaknesses, and whether assumptions that there would be malting quality problems were justified.

Materials and methods
Three-component, equal-proportion mixtures of either Polish or UK spring barley cultivars were grown in replicated trials at IHAR in Bakow, Poland and at SCRI near Dundee, Scotland. Treatments included with and without full fungicide protection, high and low fertilizer treatment, and high and low mildew inoculum pressure, and were applied by surrounding entry plots with either susceptible or resistant cultivars. Mildew infection was assessed up to six times per season, with area under the disease progress curve (AUDPC) calculated, and plot yield recorded. In addition, mixtures of winter barley cultivars containing up to six equal proportion components were grown over 3 years with and without fungicide treatment and assessed for Rhynchosporium secalis infection and yield. Malting quality assessments were made on some mixtures and their components.

Results and discussion
Both Polish and UK spring barley mixtures normally reduced infection of mildew, but few gave significant yield increases compared with the mean of their component monocultures. Higher fertilizer levels increased infection overall but had no effect on mixture efficacy for infection or yield. There was a trend towards a reduced decrease in infection in mixtures under high inoculum pressure. Grain quality characters, e.g. the malting parameters percentage grain less than 2.5 mm, milling energy, dry weight and hot water extract, showed either a small or no reduction in quality.

In winter barley, yield increases were recorded for most mixtures compared with the mean of their monoculture components and there was a significant trend towards greater benefit from an increased number of components [2]. These benefits were partially attributable to a corresponding increase in control of R. secalis in the more complex mixtures. Overall, mixtures reflected the mean of their components for grain and malting quality characteristics, except for percentage grain less than 2.5 mm and homogeneity of cell wall modification, which both decreased. Mixtures of good malting cultivars showed improved malting characteristics compared with their components [3]. Yield benefits were obtained from mixtures when fungicide protected .

By choice of compatible mixture components it should be possible to reduce fungicide inputs and/or increase yield whilst not reducing malting quality in mixtures of barley cultivars. A current trial is being carried out to determine whether preliminary evidence of particular mixtures, which showed enhanced malting quality parameters, can be repeated.

References
1. Newton AC, 1997. In Crute IR, Burdon J, Holub E, eds, The Gene-for-Gene Relationship in Plant Parasite Interactions. CAB International, Wallingford, UK, pp. 65-80.
2. Newton AC, Swanston JS, Guy DC, Ellis RP, 1998. Journal of the Institute of Brewing, in press.
3. Newton AC, Ellis RP, Hackett CA, Guy DC, 1997. Plant Pathology 45, 930-938.