Project Detail
Project Number
SW1A
Project Leader
S. J. E. Wand
Institution
Stellenbosch University
Team Members
-
Student(s)
-
Date Started
January, 2001
Date Completed
December, 2006
The influence of climate stress and source/sink manipulations on gas exchange, size and colour development of bi-colour apples
Executive Summary
- Environmental and endogenous influences on carbohydrate assimilation and allocation of apple trees: Fruit size of some apple cultivars in the Western Cape is not satisfactory. Various tree manipulations, namely scoring, fruit thinning and the application of a chemical growth regulator, were used to improve the balance between fruit and vegetative growth, and to study the underlying effects on photosynthesis and carbohydrate allocation. Results show that the correct use of these source/sink manipulations within the first six weeks of fruit development leads to significant improvements in fruit size and flower bud initiation. However, high temperatures during this period reduce the growth potential. Recommendations were made to the industry w.r.t. tree and crop management which should lead to improvements in Class 1 packouts. Mr Mias Pretorius was awarded a PhDAgric for this work.
- Climate-ameliorating technologies: Field trials were performed over six years to evaluate the use of evaporative cooling, shade netting, SurroundÒ (reflective kaolin) and RAYNOXÒ (wax) to reduce sunburn on apples. Shade netting is most effective but has negative effects on red colour. EC is also effective but is not recommended due to high water useage. SurroundÒ and RAYNOXÒ reduce sunburn to some degree with no negative effects on quality, and are also most affordable. Sunburn control technologies are particularly effective for the two most susceptible cultivars ‘Fuji’ and ‘Granny Smith’, and it is debatable whether interventions are economically beneficial for other cultivars.
- Climate change: Significant warming trends across the Western Cape (1967-2004) were statistically identified. Trends were variable between stations and between seasons, but showed generally increasing temperatures in spring, mid- to late summer, and autumn. Chill units showed marked reductions in May.
For Final Report, please contact:
anita@hortgro.co.za