The effects of simulated daylight and shade-light on vegetative and reproductive growth in kiwifruit and grapevine

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Abstract
Summary Plants of kiwifruit, female cv Hayward and male cv Matua, and grapevine cv Muller Thurgau were grown in controlled environments, which simulated the daylength and temperature of a typical New Zealand fruit production region, for the whole of one growing season to study the influence of light environment on vegetative growth and reproductive development. The controlled environments differed in the distribution of their short-wave radiation: comparisons were made between high and low photosynthetic photon flux density (PPFD) and high and low red:far-red ratios. The red:far-red ratio did not have a large effect on either vegetative or fruit growth during the first season or on flowering in the following season. Elongation of some organs was increased with low red:far-red ratio which simulated the radiation quality of shade-light. In contrast, low PPFD reduced specific leaf area and pruning weight, although it did not have a large effect on other apsects of vegetative growth, and severely decreased fruit growth while the plants were in the treatments. In the season following the treatments, low PPFD reduced both bud break and flowering. Transferring grapevines between the radiation treatments suggested that, in this case, the decrease in flower numbers following growth at low PPFD was an effect on primordia differentiation, not on induction. It is suggested that flowering on vines in orchards will be markedly reduced if the daily integral of PPFD to a shoot is a third or less of the incident radiation.