Harvest and post-harvest performance of autumn-winter butterhead lettuce as affected by nitrogen and azoxystrobin application

An autumn-winter trial was carried out in Southern Italy in open-field conditions on butterhead lettuce to investigate the effect of the nitrogen (N) fertilizer rate (0, 50, and 100 kg ha(-1), N0, N50, N100) and the application of the azoxystrobin, sprayed twice in an earlier vs. a later application scheme, specifically at 65/85 or 65/100 days after transplantation. An untreated control was also included. The evaluation of the product quality was conducted on fresh and stored shredded leaves. The N50 was a suitable rate for autumn-winter butterhead lettuce, but it does not guarantee the color appearance of the fresh leaves (lowest h degrees, highest L*). Concerning post-harvest changes, the N50- and N100-product were less suitable for storage, accounting for higher decay of visual quality (h degrees) and physiological senescence (EL) indices. Irrespective of N rate and application time, azoxystrobin improved growth and yield (+16%), visual (lower L*, higher h degrees, and chlorophylls), and nutritional (higher carotenoids and antioxidant capacity) quality of the fresh leaves. The application of azoxystrobin improved the shelf-life of butterhead lettuce leaves, by keeping higher turgidity (RWC), lower color decay (CHLs, h degrees), and higher nutritional value (carotenoids), and by limiting the browning spreading in shredded leaves.