Latent aluminium toxicity in leafy-green of winter canola (Brassica napus L.)

Species in the Brassica genus representing canola (B. napus and B. rapa) have been classified as phyto-accumulators. Therefore, as consumable green vegetables; excess accumulation of non-essential elements including aluminium (Al), along with essential dietary minerals in edible tissues above the minimum risk level (MRL) could lead to increased bioavailability to consumers. Al in canola leaves and its association with selected essential macro- and micro-nutrients were determined in winter canola cultivars grown in 5.3 soil pH. Leaf tissues from three growth stages were analyzed for calcium (Ca), potassium (K), phosphorus (P), sodium (Na), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), and for Al. Relationships of the essential elements with Al were determined. No significant differences were observed in essential micronutrients (Fe, Cu, and Zn) among the cultivars, however, Mn levels showed significant variations among cultivars. Al ranged between 167 - 243 mg kg(-1) with no significant difference among cultivars. Positive correlations between Al and Fe with r = 0.82710, p< 0.0001; r = 0.66795, p = 0.0013; r = 0.89626, p< 0.0001 exist in all stages of growth, respectively for rosette, bolting and blooming. Highly significant linear association was observed for the model Al = Fe, with an R-2 of 0.91. These results indicate that, production of certain Brassica species in acid soils, whereby soluble Al is available for uptake could facilitate excessive accumulation of Fe, an essential mineral along with non-essential Al to potentially toxic levels. Such outcomes will adversely exacerbate the nutritional value of some leafy-greens among Brassica species.