Carbon partitioning in low chill peach cultivars: the impact on yield in summer rainfall areas of South Africa

The objectives of the study were to determine the growth patterns of peach shoots, fruit and roots in relation to one another during the growing season, to assess the influence of spring temperatures on fruit development rates and to assess the impact of treatments influencing sink/source dynamics on fruit growth.

Phenology of peach cultivars was determined from full bloom to 100% leaf drop, in conjunction with measurements of fruit and shoot growth, fruit set and fruit drop and final yield and fruit size. Thinning treatments and estimates of relative growth rates were used to determine sin and source limitations to fruit growth.

Harvest can be predicted reasonably well using the accumulation of growing degree hours 30 days after full bloom. In early maturing cultivars competition between fruit, shoot and root growth is intensified during Stage I of fruit growth. At moderate to high fruit loads, fruit growth is source limited during early fruit growth which is associated with competition limitations.

Fruit growth in medium to low chill cultivars, that are early maturing, are source limited during early fruit growth which is exacerbated by high temperatures during the first 30 days after full bloom

Careful selection of cultivars based on flowering and harvesting dates can ensure that the first 30 days after full bloom take place during a cooler period, which ensures later harvest dates and improved yield and fruit size. This minimizes the risks associated with late cold and hot springs that can negatively impact yield and quality.