Optimisation of Transplant Age in Combination with Dark-chilling to Enhance the Biological Quality of Broccoli Cultivated in Summer

Abstract

Under field conditions, crops are exposed simultaneously to more than one environmental stress factor. Controlled abiotic stress applied at the transplant stage can be used as a tool for inducing stress memory, improving stress tolerance after transplanting, and enhancing the nutraceutical value of the yield. The aim of present study was to determine the effect of dark-chilling at 2 °C for 1 and 2 weeks on the tolerance of broccoli seedlings of various ages against adverse conditions in the field and the chemical composition of the inflorescences. Two separate planting programmes were undertaken in the summer. In general, planting delay by about 1 month resulted in an increase in dry weight of about 3%, ascorbic acid (38%), soluble sugars (18%), K (14%), P (13%), Zn (12%), Fe (8%), and Mn (9%) in broccoli inflorescences. Planting of young, 4-week-old seedlings resulted in higher ascorbic acid content in broccoli inflorescences of about 15%, soluble sugars (7%), K (5%), P (6%), Mg (4%), Na (11%), and Zn (3%) in broccoli inflorescences as compared to 10-week-old ones. Chilling of seedlings for two weeks caused an increase in dry weight in broccoli inflorescences of about 6%, ascorbic acid (15%), soluble sugars (12%), K (2%), P (2%), Mg (5%), Zn (3%), Fe (4%), and Mn (6%) as compared to the non-chilled control. The results indicated that the age of the seedlings and dark-chilling influenced the level of chemicals related to taste and biological value of broccoli inflorescences in a complex way. There was no general superiority or interaction of any of the experimental factors affecting all health-related compounds. Dark-chilling can be considered as a practice of broccoli seedling management before transplanting, positively affecting some yield parameters through stress memory induction.