A Quantitative Indoor Test to Identify and Select Oat Lines
that Perform Well Under Barley Yellow Dwarf (BYD) Disease Pressure
         Steve Haber, Scott Duguid and Brian O. Gillis
   Cereal Research Centre, Agriculture and Agri-food Canada,
               195 Dafoe Rd., Winnipeg MB R3T 2M9
The difficulty of reliably obtaining clear, quantitative results currently limits the usefulness of small-scale, indoor tests for identifying and exploiting oat germplasm that performs well under BYD disease pressure.  We optimized virus inoculation protocols and seedling rearing conditions to reduce inter-plant variability. Objective, quantitative parameters that had been identified in earlier experiments with quantitiative indoor BYD assays (QIA) with spring wheat were adapted for use with oat.  The parameters that accounted the best for loss of seed yield in BYDV-infected oats compared to non-infected controls of the same line were loss of height and delay of panicle emergence.  Virus titres as determined by ELISA, by contrast, were not a reliable guide to predicting performance under pressure from seedling infection with BYDV.  We are now applying the BYD Oat-QIA to successive early generations (F2 to F5) of the progeny of crosses made between oat parents chosen for the diversity of their genetic backgrounds as well as their superior agronomic and quality traits.

The essential aspect of our optimized virus inoculation protocols is that they "simplify and exaggerate" the effects of BYD on oat plants grown under controlled conditions.  To "simplify", variability among seedlings is reduced by using seed as uniform as experimental design allows, and by maintaining relatively cool conditions (10 - 13 C) from seeding to the 1-2 leaf stage.  Variablity in virus infection is reduced by applying abundant viruliferous aphid inoculum to uncaged 1-2 leaf stage
seedlings and maintaining at 10 C for 10 days; non-inoculated control seedlings are maintained in a separate growth cabinet under identical conditions.  After the 10 d inoculation access period, aphids are killed with insecticide and the temperature raised and maintained at 20 C.

The high levels of inoculum per early stage seedling and prolonged inoculation access combined with intense lighting over the entire plant growing period serve to "exaggerate" the BYDV infection.  To "simplify" the effect of BYD infection, tillers are trimmed during the elongation phase concentrating seed yield in a single panicle per plant.  The parameters that identify the individual plants with the best performance under BYD disease pressure are height and seed yield (or panicle mass).

An example of QIA applied to the selection of F2 plants with superior BYD tolerance is shown in the figures.  For both parental checks, height and panicle mass were reduced compared to non-inoculated controls.  Among the 83 F2 plants under BYD disease pressure, there were several that performed better than any individual plant of the parental lines subjected to similar disease pressure.  The F3 seed of these best-performing F2 plants will be grown out, subjected to QIA and the cycle repeated.



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