Early- and mid-season temperature effects on the growth and composition ofsatsuma mandarins

The growth and composition of satsuma mandarin fruit from trees which had b een covered by a tunnel house during either stage one (the first ten weeks after anthesis), stage two (10-20 weeks after anthesis) or throughout fruit growth, were compared with those grown under ambient conditions. During ea ch stage temperature was identified as the key factor influencing fruit dev elopment and changes to fruit were generally maintained when trees were ret urned to ambient conditions. Raising maximum air temperatures in the canopy of trees by 2.4 K during stage one increased both fruit growth rates and a ccumulation of sugars throughout their development. Titratable acidity leve ls were also increased and quinate levels decreased when trees were warmed during stage one, but these differences did not persist until harvest. Frui t grown under elevated temperatures during stage one had larger pedicels an d dorsal vascular bundles, which suggests that temperatures during early fr uit development determine the fruits' subsequent ability to import and unlo ad carbohydrate. Raising canopy air temperatures during the second stage of fruit growth lowered tritratable acidity, total acids, citrate and malate levels compared with those in control fruit, and these lower levels were ma intained until harvest. Fruit from trees own in a tunnel house all season a nd those from control trees were supplied with photosynthate synthesized fr om (CO2)-C-14 or injected with C-14 sucrose during either stage one or stag e rao of fruit development. During stage one, warmed fruit incorporated les s radioactivity into structural components and quinate, and more into other soluble components in juice sacs. This suggests that elevated temperatures advanced early fruit development and shortened the duration of the cell di vision phase. During stage two, less radioactivity was incorporated into ac ids and more into sugars in warmed fruit.