Shoot architecture, growth and development dynamics of Vitis vinifera cv. Semillon vines grown in an irrigated vineyard with and without shade covering

Covering vines with shade cloth has been proposed as a means of reducing canopy temperatures to reduce heat impacts. Because shade cloth concomitantly reduces irradiance, the objective of the study was to assess the effects of shade covering on growth and development of Semillon (Vitis vinifera L.) vines in vineyard conditions over three growing seasons. Air and canopy temperatures were measured throughout. Stem extension and leaf areas were measured on selected shoots throughout the season and at harvest, all shoots were destructively harvested and internode lengths, leaf areas and stem lengths were measured and leaves, stems and bunches dried to the determine the dry matter of each shoot. Results showed shoot growth, architecture and development were all affected by the shade. Total shoot biomass was reduced by 20%, although shoot biomass allocation was not affected. The distribution of different shoot types, based on numbers of nodes and stem lengths, was shifted in favour of medium length shoots at the expense of long shoots under the shade, consistent with decreased apical meristem activity in shade conditions. Shade also caused a major impediment to leaf development, with individual leaves delayed in expansion by 10-25 days compared with leaves on exposed vines at comparable stages of development. However, the delay in development was offset by expansion; shaded leaves expanding to a larger size than for exposed leaves. The difference in leaf size may be a strategy to compensate for the slower development in the shade conditions.