Influence of irrigation regime on productive and qualitative traits of kale (Brassica oleracea var. acephala DC) under organic farming system

Brassica oleracea crops, such as kale, are well known for their health value and their secondary metabolites like glucosinolates and polyphenols, activate antioxidant and chemo-preventive activities against several chronic degenerative diseases. As part of the European H2020 BRESOV project “Breeding for Resilient, Efficient and Sustainable Organic Vegetable Production”, the possibility of selecting water stress resistant materials genotypes was explored. To select germplasm for organic farming, yield, and healthy characteristics of six accessions of kale of the core collection (CC) of the BRESOV project, subjected to 35 and 100% of crop evapotranspiration (ETc) irrigation regimes have been evaluated. Trials were performed in an organic certified greenhouse from December 2018 to July 2019. At harvest, the bio-agronomic characterization of the plant (height, diameter, leaf number and area, stem diameter, and root weight) and the chemical composition of the leaves (total polyphenols and their profile) were analysed. Over the six accessions studied, all the biometric and productive characteristics were affected by the irrigation regime, and in particular: the height of the plant was 26.1 vs. 73.4 cm, the basal diameter 18.4 vs. 26.4 mm, the stem diameter 29.6 vs. 35.3 mm, the number of leaves 22 vs. 34, respectively at 35 and 100% of the ETc, with an overall biomass production of 651 vs. 1864 g plant-1. Plants in sub optimal conditions have addressed biomass production more towards root growth with an average incidence of 9% on the total biomass vs. 7% registered at 100% of the ETc. The total phenol content was 90.42 vs. 898.59 mg g-1 of gallic acid equivalents, and it was significantly influenced both by the genotype and by the irrigation regime. On average of the two irrigation regimes. The accessions ‘BH 50’ (Di3A germplasm bank of the University of Catania) and ‘HRIGRU7546’ (bank germplasm of Warwick, UK) were the most productive and the more resistant to water stress with satisfactory production of edible parts and a high content of phenolic compounds.