Colour variation of red kiwifruit and environmental factors affecting its colour expression : a thesis presented in partial fulfilment of the requirements for the degree of Master of AgriScience in Horticulture at Massey University, Palmerston North, New Zealand. EMBARGOED until 10 March 2019
Development of a red kiwifruit cultivar with good size, storage ability, and colour is desirable as the genetic potential exists and it could expand the market for kiwifruit. However, red kiwifruit cultivars, including the subject of this thesis, frequently have inconsistent colour. This thesis aimed to quantify colour variation of this red cultivar and the levels at which this occurred, as well as examining environmental factors (chiefly temperature and light) that may influence colour variation. To achieve this, two harvests were collected in March to May 2014 from eight trial blocks located in five regions around New Zealand (Far North, Western Bay of Plenty, Eastern Bay of Plenty, Gisborne, and Nelson). Orchard information was collected, including within orchard temperature variation via X-Sense temperature loggers, and fruit was assessed for maturity attributes and colour using subjective and objective tests.
It was found that the greatest colour variation was at the orchard and region level, though variation between vines and positions within a vine was also significant. Region was not the largest influence on colour, as out of the three regions with two orchards, two of them had both high and low colour orchards.
Colour was significantly predicted by fruit firmness, estimated light exposure, numbers of leaf layers, and skin colour in a linear mixed effects model. Lower firmness related to higher colour, as did paler, less exposed fruit with a higher number of leaf layers. The effects of light and leafiness may have been mediated by temperature, as carbohydrate supply seemed to be a less important factor for colour. Temperature was not formally identified as a significant factor; however, a relationship between flesh colour and temperature was implied by light exposure data and by scatterplots. These relationships may have implications for canopy management of this variety. Further investigation of the relationship between light exposure, fruit temperature, and colour may be helpful for determining appropriate management practices for this variety. Additionally, further work on temperature may provide a basis for predicting the colour expected in a given season.