7895: Quantitative role of seed-borne inoculum for barley net blotch epidemics

Pinnschmidt, Hans O. (2006) Quantitative role of seed-borne inoculum for barley net blotch epidemics. [preprint]

Summary

This work aimed at quantifying the relationships among epidemiologically relevant life cycle variables of seed-borne barley net blotch: seed infection incidence, primary disease incidence on seedlings and disease severity on the foliage at various crop growth stages, i.e. at the beginning of stem elongation (gs 30) and at the beginning of grain filling (gs 70). Field trials were conducted in three years in which spring barley varieties varying in net blotch resistance were sown, employing seed lots with various known levels of net blotch infection. Seed- and seedling disease incidence and disease severity at gs 30 and gs 70 were highly positively inter-correlated. Seedling disease incidence represented only about 5% to 20% of the seed infection incidence. Disease severity at gs 70 was up to several hundred times higher than the disease severity at gs 30. Variety- and/or environment-specific effects were apparent when estimating dis-ease severity at gs 30 or gs 70 based on seed- or seedling infection incidence or when estimating disease severity at gs 70 based on disease severity at gs 30. Results of gen-eralised linear model analyses explained between about 80% and 86% of the variation of the dependent variables. The results imply that the effect of infected seed with re-spect to triggering net blotch epidemics depends on the environmental conditions (year and/or bloc) and on the resistance level of the variety. Resistant varieties appear to remain relatively healthy even at higher seed infection levels, compared to suscep-tible varieties. Resistant varieties should therefore preferably be used to prevent the build-up of seed-borne net blotch over growing cycles and seed infection thresholds should consider varietal resistance levels. For highly resistant varieties, no seed infec-tion thresholds may be required while for highly susceptible varieties, current thresh-old levels may even need to be lowered to avoid net blotch outbreaks in net blotch-prone years. Such flexible thresholds may be advantageous especially for organic seed production where efficient chemical seed treatment options are unavailable.

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