Cauliflower Plant Organ Water Status and Nitrogen Translocation From Leaf–Stem Sources to Head Sinks in Its Three Hybrid Cultivars

Abstract

Cauliflower's (Brassica oleracea var. botrytis L.) fresh appearance and high nutritional values may be related to plant organ water holding and nitrogen (N) translocation from leaf–stem sources to head sinks. Cauliflower plant water and N nutrition relations were examined in a two-site field study in Nova Scotia. The objectives of this study were to assess cauliflower plant organ water and N translocation efficiency and to quantify the correlations between cauliflower plant organ water status, N translocation, head size, and fresh yield under various N treatments applied at shoot–tip-straightened stage. The experimental treatments consisted of three cauliflower hybrid cultivars (cvs. Minuteman, Sevilla, and Whistler) and three N combinations (105 + 30 + 0, 105 + 30 + 45, and 105 + 30 + 90 kg·ha−1) supplied at transplanting, seedling standing, and shoot straightened stage, respectively. The N treatments were arranged with four replicates in a split-block design in the two fields. Results showed that cauliflower plant N temporal storage in leaves and stems (source N) peaked (10.6 g/plant) at curd initiation. Plant water index was positively correlated with solar irradiance but negatively correlated with normalized difference vegetative index (NDVI). Nitrogen translocation from leaves and stems to heads was only 5% of total N uptake within the first week of the heading process, but the sink N reached 22.3%–24.9% (or 2.28–2.81 g/plant) of whole plant total N uptake within 15 days at head maturity. Mean N concentrations were significantly higher in heads (5.66%) than in leaves and stems (4.97%) at harvest (P < 0.05). The sink/source N ratios varied between 0.29 and 0.35 and head organ water holding (29 ± 12%) was significantly associated with whole plant water holding (R 2 = 0.62, P < 0.01). Cauliflower marketable head size (CHS) increased quadratically with head N accumulation (Nhead, sink N) and whole plant water holding (PW; CHS = −0.5065Nhead 2 + 5.4427Nhead + 5.5946, R 2 = 0.71, P < 0.01; CHS = −0.000002PW2 + 0.0137PW − 2.1501, R 2 = 0.50, P < 0.05). It was suggested that increasing N and water temporal storage in leaf and stem sources could stimulate cauliflower head development.