Cereal Research Centre, Agriculture and Agri-Food Canada, Winnipeg, MB R3T 2M9, Canada

Background and objectives
Since 1994, Fusarium head blight (FHB) has been detected annually in most fields of spring barley in southern Manitoba. Severity levels based on visual symptoms have generally been lower than in wheat; in 1997 these averaged 2.5 and 10% (FHB index) in barley and wheat, respectively. Fusarium graminearum is the principal pathogenic species isolated from infected kernels in both crops, but in barley other Fusarium species may also be involved [1]. An improved understanding of the relationships between FHB levels, Fusarium spp. infestation and mycotoxin levels in barley would facilitate development of disease management protocols and, in particular, breeding for effective resistance.

Materials and methods
Sixteen local cultivars and 16 exotic barley accessions were grown in experimental plots at Carman, MB in 1997. Adapted cultivars included two-row malting barleys (AC Metcalfe, Manley, AC Oxbow, Tankard), six-row malting (Argyle, Stander), two-row feed (Bridge, CDC Guardian), six-row feed (Bedford, Duke, CDC Earl, Heartland, AC Lacombe, AC Rosser) and six-row hulless feed (Falcon, CDC Silky) genotypes. The exotic accessions included barleys reported to have resistance to Fusarium in studies done in Canada, Japan, USA, or by CIMMYT, i.e. Chevron, Fuji Nijo, Gobernadora, Harbin, Korsbyg, Krasnojarskij 1, Maris Mink, Murasaki-mochi, Nepolegajuscij, Seijo II, AC Sterling, Svanhals, Symko, Ussurijskij 8, Zaoshu 3 and Zhedar 1. Infection resulted from field inoculum and no supplemental moisture was applied. At GS 75, when symptoms of FHB were evident as blighted or discoloured spikelets, in contrast to the still green healthy ones, ca 40 heads per plot were sampled randomly and stored in plastic bags at -20C until assessed for disease levels, based on 'FHB index' (percentage incidence x percentage severity/100). A further sampling of heads was made at maturity to evaluate Fusarium spp. kernel infestation, based on 100 random kernels from a hand-threshed sample, and levels of deoxynivalenol (DON), based on a 20-g ground sample, using ELISA.

Results and conclusions
Fusarium head blight levels ranged from 0.1-37.2%. Ten of the 16 exotic accessions had FHB levels of <1%. However, two accessions also had the highest levels measured, 27.6 and 37.2%. The range of FHB among the adapted cultivars was 1.9-12.8%. There was no association between barley type and reaction to FHB. The proportion of kernels from which Fusarium spp. were recovered generally correlated to the levels of visible FHB. As reported by others, Fusarium graminearum was the main species isolated from kernels, but F. poae and F. sporotrichioides also were recovered frequently. Deoxinivalenol levels did not correspond closely to FHB levels, suggesting visual estimation of FHB may not predict DON content in harvested grain. Low levels of FHB sometimes resulted in relatively high levels of DON. However, several barley genotypes with very low levels of FHB also had low levels of DON. These may be useful sources for improving Fusarium resistance in adapted cultivars. As F. graninearum (mainly a DON producer) was not the sole (>95%) pathogenic species isolated from naturally infected barley (as is usually the case in wheat in Manitoba), harvested barley samples probably should be tested for additional trichothecenes, resulting from pathogenesis by F. poae and F. sporotrichioides [2]. Lowering FHB and mycotoxin(s) to negligible levels in barley is imperative to the viability of the malting and feed industries in Manitoba and elsewhere. At present, selection of adapted cultivars least susceptible to FHB, as measured by low disease levels, Fusarium infestation and mycotoxin accumulation, offers the opportunity for reducing damage from FHB.

1. McCallum B, Tekauz A, Gilbert J et al., 1997. Canadian Plant Disease Survey, 77, 53.
2. Wong LSL, Abramson D, Tekauz A et al., 1995. Canadian Journal of Plant Pathology 14, 233-238.