The plant age influences eggplant fruit growth, metabolic activity, texture and shelf-life
Graphical Abstract
Introduction
Vegetable quality is determined by the interaction several of concurring preharvest factors that can affect development at any time, from ovary fertilization to harvest (Caruso et al., 2017). In tree fruit crops large differences in chemical, physical and physiological attributes have been reported along the production cycle (Khalid et al., 2012). For instance, early harvested apples are more susceptible to some disorders such as watercore than late season fruit (Yamada et al., 2005a, b). Second crop Mediterranean figs tend to be richer in phenolics than early picked fruit (Veberic et al., 2008). In the case of vegetable crops, the information available the quality modifications occurring along the production season is far more limited. Early season tomato fruit are more prone to zippering and blossom end rot than those harvested in mid season (Olle and Williams, 2016; Vicente et al., 2019). Mid-summer fruit showed lowest lycopene levels when compared to early or late season fruit the season (Raffo et al., 2006). Most of such quality changes have been so far attributed to variations in the prevailing environmental conditions.
In perennial tree crops, in which fruit production may last decades, it is well established that also the “mother” plant age could deeply influence fruit quality (Khalid et al., 2012). Contrariwise, this effect has been barely evaluated in annual species. Eggplant has become in the last decade a highly popular and worldwide-grown annual vegetable (Niño-Medina et al., 2017). Seedlings are normally initiated in late winter, when the risk of freezing damages decreases and normally transplanted in spring (Uzun, 2007). Fruits are normally picked based on size, when reaching 13−20 cm long, and before excessive seed growth and bitter compound accumulation (Mohammed, 2002; Concellón et al., 2007), though in the last decade, baby eggplants (5−10 cm long) have become increasingly marketed, along with a rising demand for specialty vegetables (Zaro et al., 2015). In a recent study, we found that the wide quality variation in eggplant during the harvest season leads to large changes in tissue microstructure. These include differences in cell epidermal and parenchyma cell packing and size and cuticle thickness (Valerga et al., 2019). The aim of this work was to evaluate if the plant age at harvest has an impact in eggplant fruit composition at harvest and postharvest performance besides the well studied preharvest environmental effects.
Section snippets
Plant material and growing conditions
The experiment was carried out in La Plata, Argentina (Latitude: 34°59′18″ S, Longitude: 57°56′17″ W) in an arch-type greenhouse (2.5 m height ×10 m width × 40 m length), covered with low-density polyethylene (150 μm thick). Ventilation was provided by opening greenhouse laterals when the air temperature exceeded 25 °C (Fig. S1). Light was provided only by natural solar radiation. Seeds of dark-purple eggplant (Solanum melongena L.) cv. Monarca were germinated in vermiculite during winter
Seed and fruit growth weight and firmness
The number of seeds on the evaluated eggplant equatorial slices ranged between 60 and 75 and was similar in fruit harvested from both 4- or 9-month plants (Fig. 2A and B). Seed growth occurred mostly between the Baby and Large-CM, without significant changes in mean seed area afterwards (Fig. 2C and D). Most importantly, and alike for total seed number, the mother plant's age did not affect seed growth. In contrast, it clearly modulated fruit pericarp elongation. Both 4- and 9-month plants
Discussion
The plant's age did not affect fruit seed number, size or fruit antioxidant content. Instead, it clearly modulated fruit pericarp elongation. Eggplant from young plants grew faster and reached commercial length earlier than fruit from 9-month plants. Moreover the eggplants picked in 4-month plants were significantly softer and accumulated at the large-CM stage higher levels of sugars. One of them most direct explanations behind these effects is that young 4-month plants, having a greater area
Conclusion
Eggplants picked from 4-month plants grew faster, showed higher respiration rate and accumulated higher sugar content upon commercial maturity than fruit from 9-month plants. Instead the plant age did not affect fruit seed number and size, color or antioxidant contents. Commercially mature eggplants harvested in 4-month plants also showed better shelf-life than fruits from 9-month plants, as evidenced by a lower visual deterioration index, weight loss and softening. Results demonstrate that
CRediT authorship contribution statement
Lucía Valerga: Formal analysis, Investigation, Writing - original draft, Writing - review & editing. Magalí Darré: Investigation, Writing - original draft. María José Zaro: Investigation. Ariel Roberto Vicente: Conceptualization, Writing - original draft, Writing - review & editing. María Laura Lemoine: Conceptualization, Supervision. Analía Concellón: Conceptualization, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank to the Agencia Nacional de PromociónCientífica y Tecnológica (PICT 2015-3690) for financial support. LV and MD are fellows of CONICET. MJZ, ARV, MLL and AC are research members of CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), Argentina.
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