Segregation of 'Hayward' kiwifruit for storage potential : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, New Zealand
This study aimed to develop technologies to segregate 'Hayward' kiwifruit (Actinidia deliciosa (A.Chev) C.F. Liang et A.R. Ferguson) for storage potential. Such segregation will allow the industry to better match market opportunities with the storage potential of particular fruit thereby reducing fruit loss and assuring fruit quality in the market place. The first part of the research rationalised methodologies to study storage potential of kiwifruit. These included firmness measurement, fruit temperature equilibration, calculation of storage life, sample preparation for mineral analysis and the feasibility of using compression force as an alternative to flesh firmness for firmness monitoring. The second part of the research developed a model to segregate kiwifruit on a grower line basis. Based on data collected over 2 years from 108 grower lines, canonical discriminant analysis indicated that the first two canonical functions (CDF1 and CDF2) accounted for 95% variation of four softening-rate groups and correctly classified over 50% of the grower lines to the correct groups compared with a chance criterion of 25%. Grower lines with high CDF1 (characterised by high Ca/N, high Mg, advanced maturity, late harvest and low lightness) softened at low rates and had long storage life. CDF2 discriminated grower lines on prestorage delay. For grower lines with low CDF1, extending prestorage delay improved storage potential. In contrast, extended prestorage delay reduced the storage potential of grower lines with high CDF1. The third part of the research developed a model to segregate kiwifruit on an individual fruit basis. NIR spectra taken at harvest were used to quantify many at-harvest fruit attributes, allowing for prediction of fruit firmness at the end of storage and discriminating disordered fruit from healthy fruit for fruit segregation on an individual fruit basis. Further work is needed to improve prediction and segregation accuracies by selecting appropriate NIR instrument and to incorporate the instrument with grading machines in a way that measurement error can be minimised. Factors affecting NIR measurement and possible improvements were also investigated. The strategic application of segregation technologies and further research directions are discussed for the kiwifruit industry to develop cost-effective procedures to solve problems associated with fruit variation in storage potential.