Dissection of genetic and environmental factors involved in tomato organoleptic quality

Abstract

Background: One of the main tomato breeding objectives is to improve fruit organoleptic quality. However, this task is made somewhat challenging by the complex nature of sensory traits and the lack of efficient selection criteria. Sensory quality depends on numerous factors, including fruit colour, texture, aroma, and composition in primary and secondary metabolites. It is also influenced by genotypic differences, the nutritional regime of plants, stage of ripening at harvest and environmental conditions. In this study, agronomic, biochemical and sensory characterization was performed on six Italian heirlooms grown in different environmental conditions.

Result: We identified a number of links among traits contributing to fruit organoleptic quality and to the perception of sensory attributes. PCA analysis was used to highlight some biochemical, sensory and agronomic discriminating traits: this statistical test allowed us to identify which sensory attributes are more closely linked to environmental conditions and those, instead, linked to the genetic constitution of tomato. Sweetness, sourness, saltiness and tomato flavour are not only grouped in the same PCA factor, but also result in a clear discrimination of tomato ecotypes in the three different fields. The three different traditional varieties cluster on the basis of attributes like juiciness, granulosity, hardness and equatorial diameter, and are therefore more closely related to the genetic background of the cultivar.

Conclusion: This finding suggests that a different method should be undertaken to improve sensory traits related to taste perception and texture. Our results might be used to ascertain in what direction to steer breeding in order to improve the flavour characteristics of tomato ecotypes.

Figure 1

A, B, C, Box plots of the agronomic data of fruit from six tomato ecotypes grown in three different fields, showing variation within single fields. A, diagram of commercial yield, expressed as kg per plant, of six tomato ecotypes clustered into three different fields. B, diagram of commercial fruit expressed as no. of fruit per plant of six tomato ecotypes clustered into three different fields. C, ratio of polar and equatorial diameter of fruit per plant of six tomato ecotypes clustered into three different fields.

Figure 2

Quantitative descriptive analysis of sensory attributes of the six tomato ecotypes grown in three different fields. Individual attributes are positioned like the spokes of a wheel around a centre (zero, or not detected) point, with the spokes representing attribute intensity scales, with higher (more intense) values radiating outward. Legend: red is used for the tomato ecotypes grown in the Sarno field; green, the tomato ecotypes grown in Ercolano; blue, the tomato ecotypes grown in Sorrento.

Figure 3

Heat map showing correlation analysis among physicochemical, biochemical, sensory and agronomic traits in six tomato ecotypes grown in three different fields. Regions in red and blue indicate negative or positive correlations among the traits, respectively. Abbreviations: His, Histidine; Lys, Lysine; Arg, Arginine; Gln, Glutamine; Asn, Asparagine; Ser, Serine; Glu, Glutamic acid; Thr, Threonine; pH, pH, SS., Soluble solid; Ash, Ash; DM., Dry Matter; Mal, Malic acid; Asc, Ascorbic acid; Citr, Citric acid; Fum, Fumaric acid; Smell, Tomato smell; Hard, Hardness; Juic, Juiciness; Gran, Granulosity; Res, Skin resistance; Swe, Sweetness; Sal, Saltiness Sou, Sourness; Flav, Tomato flavour; Pleas, Pleasantness; Yield, Commercial yield; n, Number of commercial fruits; Pol, Polar diameter; Len, Equatorial diameter.

Figure 4

Principal component analysis of the physicochemical and biochemical compounds, agronomic traits and sensory attributes, in tomato ecotypes harvested in three different fields. Axes of two-dimensional plots are derived from (A) PC-1 and PC-2, (B) PC-1 and PC-3. These factors were chosen for the best visualization of field and genotype separation and include 50% of the total information content. Plotted points represent individual samples. In scatter plot A different coloured points were used to indicate samples belonging to a same field. In scatter plot B different coloured points were used to indicate samples belonging to the same tomato type.