Shoot type and light exposure influence carbon partitioning in peach cv. elegant lady

Carbon partitioning and translocation in one year old fruiting limbs of 'Elegant Lady' peach (Prunus persica L. (Batsch)) was studied, as affected by source (leaves on actively growing extension shoots (EXT), leaves on lateral shoots at nodes carrying (F) or not carrying (NF) fruit), and by light regime (full sun or 5 d 70% shade conditioning), five times during the season (2, 4, 7, 11, 17 weeks after full bloom (WAFB)). Growing shoot apices were the strongest sinks early in the season (2 WAFB), with the EXT apices capable of attracting more carbon (C) and over longer distances, than the NF or F ones. The major source of newly synthesized carbohydrates for fruit growth 2 WAFB was the F lateral shoot, i.e. the most important C contributor for fruit growth well into stage II (11 WAFB in this study). EXT shoots began contributing to fruit growth before the NF shoots: 4 WAFB on, they exported to the fruits in amounts similar to the F shoots. This contribution was even larger 17 WAFB, when the F shoots retained more C than the other two shoot types. The NF shoots exported to growing apices 2 WAFB, but export decreased 4, 7, and 11 WAFB, compared with the other treatments. NF shoots contributed to fruit growth in the same amounts as the EXT shoots 17 WAFB, and more than the F shoots. Shade did not consistently affect patterns of carbon partitioning within limb components, except for the F treatment, where it diminished C export to the fruit in the first four treatment dates. Partitioning within fruit components (mesocarp, endocarp and seed) followed the fruit growth curve, with more C allocated to endocarp tissues at 11 WAFB (stage II). Results are in agreement with, and substantiate, earlier findings concerning the effects of fruit position on the limb, and competition for carbon with active vegetative sinks on fruit development.