Abstract
Estimating maturity in pome fruits is a critical task that directs virtually all postharvest supply chain decisions. This is especially important for European pear (Pyrus communis) cultivars because losses due to spoilage and senescence must be minimized while ensuring proper ripening capacity is achieved (in part by satisfying a fruit chilling requirement). Reliable methods are lacking for accurate estimation of pear fruit maturity, and because ripening is maturity dependent it makes predicting ripening capacity a challenge. In this study of the European pear cultivar ‘d’Anjou’, we sorted fruit at harvest based upon on-tree fruit position to build contrasts of maturity. Our sorting scheme showed clear contrasts of maturity between canopy positions, yet there was substantial overlap in the distribution of values for the index of absorbance difference (IAD), a non-destructive spectroscopic measurement that has been used as a proxy for pome fruit maturity. This presented an opportunity to explore a contrast of maturity that was more subtle than IAD could differentiate, and thus guided our subsequent transcriptome analysis of tissue samples taken at harvest and during storage. Using a novel approach that tests for condition-specific differences of co-expressed genes, we discovered genes with a phased character that mirrored our sorting scheme. The expression patterns of these genes are associated with fruit quality and ripening differences across the experiment. Functional profiles of these co-expressed genes are concordant with previous findings, and also offer new clues, and thus hypotheses, about genes involved in pear fruit quality, maturity, and ripening. This work may lead to new tools for enhanced postharvest management based on activity of gene co-expression modules, rather than individual genes. Further, our results indicate that modules may have utility within specific windows of time during postharvest management of ‘d’Anjou’ pear.
Highlights
Pome fruit ripening is a coordinated process that includes peel color change, softening, and acid loss
Pears picked from internal and external canopy positions showed an overlapping distribution of index of absorbance difference (IAD) and were sorted into 5 classes to afford finer-grained comparisons (Figure 1)
The comparison between pears harvested from external and internal tree canopy positions belonging to IAD class C at each postharvest time point revealed some significant differences in terms of color and appearance
Summary
Pome fruit ripening is a coordinated process that includes peel color change, softening, and acid loss. Fruit quality and ripening of European pear (Pyrus communis) is very complex and strongly dependent on various aspects of the orchard environment This includes fruit position in the canopy and tree architecture (Layne and Quamme, 1975; Faragher and Brohier, 1984; Palmer et al, 1997; Fideghelli, 2007; Serra et al, 2016; Wu et al, 2018). Harvest time is a critically important factor when targeting the final fruit quality necessary to satisfy consumer expectations (Predieri et al, 2005; Vanoli and Buccheri, 2012; Blanckenberg et al, 2016) This all-together can lead to heterogeneous ripening among lots of fruit (Jajo et al, 2014), due in large part to variability in fruit maturity.
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