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

Abstract

SummaryThe growth and composition of satsuma mandarin fruit from trees which had been 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 each stage temperature was identified as the key factor influencing fruit development and changes to fruit were generally maintained when trees were returned 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 accumulation of sugars throughout their development. Titratable acidity levels were also increased and quinate levels decreased when trees were warmed during stage one, but these differences did not persist until harvest. Fruit grown under elevated temperatures during stage one had larger pedicels and dorsal vascular bundles, which suggests that temperatures during early fruit development determine the fruits' subsequent ability to import and unload 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 maintained until harvest. Fruit from trees grown in a tunnel house all season and those from control trees were supplied with photosynthate synthesized from 14CO2 or injected with 14C sucrose during either stage one or stage two of fruit development. During stage one, warmed fruit incorporated less 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 division phase. During stage two, less radioactivity was incorporated into acids and more into sugars in warmed fruit.