The effect of reducing leaf area on the growth of roots, stems and berries of Gordo grape-vines

To measure the effect of leaf number during berry growth on all organs of the grape vine (Vitis vinifera) a pot experiment was done using Muscat Gordo Blanco plants maintained in the open. Each plant was allowed to develop one fruitful shoot and 4 treatments (12 plants each) were applied following fruit set: (1) control (2) 6 leaves left (3) 3 leaves left (4) 1 leaf left. Leaves left (by tipping the shoot) were primary leaves at and above the first node above the bunch. When primary leaves senesced or were wind damaged a corresponding area of lateral-shoot leaf (125 cm2) was permitted to re>:main. Leaf area measurement of sample plants gave values of 2470 cm2, 850 cm2 , 470 cm2 and 125 cm2 respectively for the 4 treatments. On each shoot there was one bunch limited to 30 berries. Measurements of berry volume and sugar suggested that there was a diphasic growth curve and that wit h fall in leaf number there was a longer lag phase and a shorter second growth phase. Growth rate in the second phase was not greatly affected. Acids fell more slowly where leaf number was less, and the sugar: acid ratio was reduced.From final plant dry weights it was found that the trunk (parent stem) was least affected by leaf reduction, followed in order by shoot, berries and roots. Sugars and starch in trunk and shoot were affected in a way similar to berries. When needs of trunk, shoot and berries were fully met it appeared that cxcess leaf assimilate was channelled into root growth. The minimal leaf area for unimpeded growth of aerial organs was estimated to be 1500 cm2 (12 leaves), but in the field where bunches have more berries a greater leaf area would be required. The data has been interpreted to show that leaf efficiency in terms of carbon fixation, was markedly increased with reduction in leaf number