Identifying and using tuber characteristics to predict potato keeping quality

[摘要] ENGLISH ABSTRACT: Potato production in South Africa occurs in all nine provinces of South Africa and it isfurther divided into 16 production areas. The trial was undertaken in the Sandveld andCeres production areas, which are characterised by dry and warm weather in summer,which presents obvious challenges to produce high-volume quality potatoes.A macronutrient that is very important for cell wall strength of potato tubers is calcium(Ca). In a previous study, no correlation between keeping quality and tuber Ca contentwas found (Bester, 1993). The reaction of Ca with organic acids might be part of thereason no correlation between keeping quality and tuber Ca could be found (Venter,1989). Calcium oxalate forms when Ca reacts with organic acids and the cells it forms inare referred to as idioblasts. Calcium and magnesium (Mg) are strongly competitive andit seems that the plasma membrane binding site at the root has higher affinity for Ca2+than for the highly hydrated Mg2+ (Marschner, 1995). Calcium has the ability to form ainsoluble complex with pectin due to the free carboxyl groups on the pectin chain(Walter, 2012). Pectin methylesterase (PME) is an enzyme responsible for removing themethoxyl groups and enabling divalent cations Ca2+ and Mg2+ to react with pectin,creating rigid structures with an increase in firmness (Tajner-Czopek, 2003). Due to thehigh immobility of Ca in plants it is sometimes hard to increase the Ca content in tubers.On the other hand, Mg is mobile in the plant and increasing tuber concentrations is notas difficult as Ca, although Mg deficiencies caused by cation competition is a globalphenomenon (Marschner, 2012). A study done in South Africa on several cultivarsshowed that of all the cultivars tested, Sifra had the lowest Mg content and that Fiannahad the highest (Van Niekerk, 2015). Potato is highly susceptible to Mg deficiency,which has been shown to particularly affect the carbon assimilation and thetransformation of energy (Hochmuth, 2007; Barker and Pilbeam, 2015). Considerablefewer studies have been done on Mg to the extent that it is often dubbed the 'orphannutrient compared to Ca (Rosanoff, 2010).When producers export or sell their seed- or ware potatoes it is important for the buyerto know in advance the quality of the product. If the keeping quality can be predicted itwill help both the producer and buyer to know the quality of the product andcompensation can then be arranged more accurately, since good keeping quality potatoes should have higher value than poor keeping quality potatoes. To predict thekeeping quality of seed- and ware potatoes, various quality characteristics must beidentified and used. The main objective for this study was to develop a measuring toolthat can be used to routinely predict the keeping quality of a tuber.Tubers were sampled throughout 2016 season and partially through the 2017 season.Inspection for IBS and hollow heart were assessed to see if any of the qualitycharacteristics could correlate with these disorders. Tubers were stored at 25℃ and 5℃respectively, while mass loss was determined as percentage (%) loss throughout thestorage period. Different quality characteristics were measured to use in a predictionmodel.

[发布机构] Stellenbosch University