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  • Author or Editor: Atilla Eris x
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A stock plant etiolation treatment was tested to improve rooting of the important cherry rootstock Gisela-5. To create the etiolation effect, at the beginning of the growing season, banding (blanching) was initiated on stock plants by placing black plastic tape at the base of new shoots for 6 or 10 weeks. Cuttings were excised so that the banded area was at the cutting base. IBA was applied at two concentrations (5 and 10 mm) to the cutting base following wounding and cuttings were placed in perlite (100%) rooting medium under mist. The rooting percentage, number of roots per cutting and root length were measured 4 weeks after planting. Banding and duration significantly stimulated rooting of leafy softwood cuttings. The highest rooting percentage (80.0%) was obtained on cuttings banded for 6 weeks and treated with 5 mm IBA.

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The influence of photoperiod and temperature on the seasonal (fall to winter) cold acclimation and accumulation of a 25 kDa dehydrin in Rhododendron `Chionoides' was studied by exposing two groups of plants each in the greenhouse or outdoors to either a natural photoperiod (or short days) or an extended photoperiod (or long days) regime. Results suggest that the shortening daylength alone is sufficient to trigger both the first stage of cold acclimation and concomitant 25 kDa dehydrin induction. Exposure of the plants to natural photoperiod and temperatures induced the greatest cold hardiness and 25 kDa accumulation, while exposure to extended photoperiods (long days) and warmer temperatures (in the greenhouse) failed to induce any significant freezing tolerance in leaves. Whereas short days trigger the cold acclimation process initially, low inductive temperatures can eventually replace the photoperiod stimulus. Seasonal accumulation of 25 kDa dehydrin, on the other hand, appears to be predominantly effected by short photoperiods. Data indicated that the leaf water content of outdoor plants maintained under natural photoperiod was lower than that of plants grown under extended photoperiod. This was also true for the greenhouse plants at the first (September) and the last (January) sampling. It is hypothesized that early 25 kDa dehydrin accumulation may be due to short-day-induced cellular dehydration. Accumulation of two other dehydrins of 26 kDa and 32 kDa molecular masses does not appear to be associated with short day (SD)-induced first stage of cold acclimation. Results show that their accumulation may be regulated by low, subfreezing temperatures and may be associated with the second and/or third stage of cold acclimation of `Chionoides' rhododendron leaves.

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