Resumen de Light (minimal) pruning enhances expression of higher yield from clones of "Vitis vinifera" L. cv. Sultana following thermotherapy for virus attenuation
Leslie R. Krake, Peter R. Clingeleffer
High-yielding clones of Sultana (syn. Thompson Seedless) were grown in a warm climate under irrigation as either cane-pruned or minimally-pruned field vines. Test material included Sultana clone H5, six heat-treated clones originating from H5, and a heat-treated clone of Thompson Seedless (TS-HT91) sourced from California. Vine performance was measured over 10 seasons (1984-1993). Previous thermotherapy had eliminated leafroll viruses from three of the six selections originating from H5 and from TS-HT91. When cane-pruned, the TS-HT91 clone was 9% more productive than H5 as well as all selections originating from thermotherapy of H5. With minimal pruning all selections free of leafroll viruses had superior performance (approximately 14% increase) compared to those still infected with leafroll viruses. In those clones where thermotherapy had not removed leafroll viruses, yields from two out of three clones (minimally-pruned) were increased relative to H5; one remained lower. Clonal differences in productivity were related to vine growth, particularly above-ground components, but there were no significant clonal effects on berry weight, pH or titratable acidity. While long-term field trials are necessary to clearly demonstrate positive effects from thermotherapy, light pruning can enhance prospects for confirming an improvement in yield. Indeed, severe pruning can even limit expression of yield from putatively superior clones, and thus mask expression of positive outcomes from thermotherapy.
