Temperature influences growth and maturation of fruit on 'Hayward' kiwifruit vines

The responses of fruit and shoot growth of ‘Hayward’ kiwifruit vines to changes of temperature were determined during spring, summer or autumn. Mature vines were warmed 2–5°C above ambient temperatures by enclosing them in temperature-controlled tunnel houses for 34–89 d. Increasing temperature during spring advanced the date of flowering by 17 d and increased the rate of shoot elongation by 6 mm d–1 °C–1. The fruit on these early-flowering vines were larger and had a higher dry matter concentration than control fruit during the first part of the season. Increasing temperature during summer increased the rate of shoot elongation but reduced fruit growth, accumulation of dry matter in fruit and fruit firmness. In contrast, increasing temperature during late autumn increased fruit growth but reduced the soluble solids concentration (SSC) of fruit and thus, delayed commercial maturity. When fruit growth data for summer and autumn were combined the variation in fruit growth with temperature could be described by a single quadratic curve. Maximum fruit growth occurred at 17°C and temperatures above or below this optimum reduced fruit growth. Consequently, during summer when ambient temperatures averaged 17°C, warming vines decreased fruit growth, while during late autumn, when ambient temperatures had fallen to 13°C, warming vines increased fruit growth. Warming vines during summer reduced both the SSC of ripe fruit and the vitamin C concentration. Warming vines during autumn increased SSC but reduced the vitamin C concentration.