First Attempts of Linking Modelling , Postharvest Behaviour and Melon Genetics

The onset of climacteric is associated with the end of melon fruit shelf-life. The aim of this research was to develop practical and applicable models of fruit ripening changes (hardness, moisture loss) also able to discriminate between climacteric and non-climacteric behaviour. The decrease in firmness was measured non-destructively by flat-plate compression; moisture loss was measured by weight loss. A set of 13-15 near-isogenic lines (NILs) derived from the climacteric line SC3-5 was used to verify the relationship among the climacteric behaviour and ripening related changes (weight loss, softening and color) during two consecutive seasons. The biological variance models for moisture loss and firmness followed a simple exponential behaviour that explained more than 90% of the total variance. Results of the analyses using these models could not be linked to properties of near-isogenic lines like climacteric behaviour, ethylene production or skin thickness. The results suggest that the phenotype is more important than genotype, when considering mean values. These results seem to suggest that relations may exist between the different processes and properties of NILs on an individual basis, not on mean values. INTRODUCTION Eduardo et al. (2005) developed a collection of near-isogenic lines (NILs) (Eduardo et al. 2005). The parental lines used to generate the NILs produced melons with non-climacteric behaviour. In contrast, SC3-5 and other NILs with shorter introgression in LG III showed climacteric behaviour during melon ripening (Moreno et al., in press). In this paper this variability is used to model the behaviour of melon firmness and weight loss during postharvest ripening, to understand the variation in firmness behaviour and to gain insights for the evaluation of genotypes with regard to their postharvest behaviour. MATERIAL AND METHODS Near-isogenic lines (NILs) of melons (Cucumis melo L.) were produced in two seasons (2005 and 2006) containing introgressions of different extent from the Korean accession ‘Shongwan Charmi’ PI161375 (SC) on the linkage group III into the ‘Piel de Sapo’ (PS) (Eduardo et al., 2005). Some lines (Eduardo et al., 2005) contained introgressions of SC into PS in linkage groups X and VII, respectively. A large range of weight, colour, shape and firmness was present in the NILs in both seasons. Lines were coded as 5Mx or 6Mx in 2005 and 2006 seasons, but the x codes were only common in some NILs (Table 2). 5-6 fruit per line chosen at random from the replicates (about 20 plants), were stored covered by plastic liners at 21 °C at a relative humidity of 66 % (2005) or 73 % Proc. IVth IS on Model-IT Eds.: P. Barreiro et al. Acta Hort. 802, ISHS 2008 402 (2006). Fruit firmness was measured as the maximum force in a flat plate compression at the equator of the fruits (indicated spot) until a predefined compression distance of 2 mm (2.2 mm in 2006). Water loss was determined by weighing the same fruit during storage. Statistical analysis of the data was conducted using non linear mixed effects regression using the procedure nlme of the free package R (www.R-project.org).