Micro-structural and quality changes in growing dark-purple eggplant (solanum melongena L.) as affected by the harvest season

Whereas the production season is accepted to exert profound influence on fruit physiology, micro-structure and quality, very few studies have attempted to find liaisons between these traits. Herein, we determined the micro-structural and quality changes of eggplant fruit produced in Late Spring (mean air temperature 22 degrees C; max. 28 degrees C; min. 16 degrees C), Late Summer (mean air temperature 19 degrees C; max. 25 degrees C; min. 13 degrees C) and Late Fall (mean air temperature 11 degrees C; max. 15 degrees C; min. 6 degrees C), at three growing stages: Baby (S1, 9 cm length), Commercially mature (S2, 17 cm length) and Advanced commercially mature (S3, 21 cm length). We followed fruit elongation and assessed at harvest the size of epidermal and parenchyma cells, cuticle thickness, respiration rate, dry matter, firmness, seed number, seed size and seediness. The time required to reach commercial maturity was 3-4 times shorter in Late Spring than in Late Fall. Micro-structural evaluations showed that Late Spring fruit had epidermal and epicarp cells per unit area than Late Fall eggplants, which in turn presented thinner cuticles and a less compact large-celled central endocarp parenchyma. Commercially mature Late Fall eggplants also lighter color, showed lower respiration and were firmer than fruit growing earlier in the season. For all maturity stages fruit dry matter content was the parameter correlating best with fruit firmness (r = 0.71). Late Summer fruit tended to show intermediate properties, but had higher seed number, size and seediness. Overall, results show the influence that the growing season exerts on eggplant metabolism, micro-structure and quality.