Optimum temperatures for colour development in apples

[摘要] ENGLISH ABSTRACT: Peel colour is an important quality factor in the production of bi-coloured apple fruit. Most markets set minimum requirements for red colour coverage. Fruit that do not meet these requirements are downgraded and has a major impact on the profitability of apple productionin South Africa. South African apple production areas are amongst the warmest in the world.Since anthocyanin accumulation requires induction at low temperature and synthesis requiremild temperatures, experiments were conducted to investigate optimum day and night temperatures for red colour development throughout fruit development for red and bi-coloured apple cultivars grown in South Africa. We found that redder strains of bi-coloured apple cultivars did not appear to owe their enhanced pigmentation to higher temperature optima for anthocyanin synthesis. The optimum day temperatures for red colour development in thedifferent cultivars seemed to differ between seasons, but not between production areas. Ingeneral, red colour in the cultivars evaluated developed maximally between 17 ºC and 25 ºC.The optimum day temperature for red colour development remained constant throughout fruitdevelopment for most cultivars, but increased roughly from 14 ºC to 22 ºC in 'Cripps' Pink'between January and April. The extent of red colour development increased during fruit development in all the cultivars assessed. We were unable to determine optimum induction temperatures for red colour development. 'Royal Gala' from Ceres seemed to benefit frominduction at 4 ºC while red colour in 'Fuji' decreased with decreasing temperature.To explain the presence of anthocyanins in immature apple fruit, we tested the hypothesisthat anthocyanins protect the peel from photoinhibition and photooxidative damage duringconditions of increased light stress. First we established that the rate of colour change inresponse to a passing cold front appears to be sufficient to provide photoprotection during acold snap. Also in agreement with the hypothesis, 'Cripps Pink' peel incurred significantlymore photoinhibition at low temperature (16 ºC) compared to mild (24 and 32 ºC) and high (40ºC) temperature under high irradiance with visible light. Recovery rate was temperaturedependent,being the slowest at low temperature and increasing with temperature. The photoapparatus in 'Cripps Pink' peel appears to be particularly sensitive to light stress at low temperature throughout the season, with significant photoinhibition occurring even atmoderate temperature (24 ºC). The sensitivity of the apple peel to photoinhibition increased throughout the season at lower irradiance levels, but remained the same at higher irradiance.In our final experiment, fruit were exposed to high irradiance at low and mild temperature before exposure to high temperature in combination with high irradiance. This was done to test the hypothesis that photoinhibition incurred during cold snaps predisposes peel to photothermal damage when temperature increases again after the cold snap. Unfortunately, due to the severity of the stress incurred in response to high temperature treatment, theresults were inconclusive.

[发布机构] Stellenbosch University