Effects of Age and Genotype on Vitamin C (Ascorbic acid) and Fiber Contents in Brassica napus

Rape (Brassica napus) is one of the major vegetables grown in Zambia and is an important source of nutrients in human diet. Vitamin C is an essential antioxidant molecule while fiber on the other hand plays a key role in mitigating constipation. However, the effects of rape genotype and the vegetative maturity (age) on nutrient content on vitamin C and fiber is not clearly understood. The objectives of the study were therefore, to; i) to evaluate the effects of age on vitamin C and fiber nutrient content in rape leaves and ii) evaluate the genotypic effect of rape leaves on vitamin C and fiber contents. The experiment was conducted Munachoonga farm, in Monze district, Zambia (16 o 16’ 45’’ S; 27o 28’25’’ E) during the 2020/ 2021 cropping season. The experiment was laid as a split plot design with three replications. Soil fertilizer amendments were the main plot while variety (genotype) as a subplot. Data was collected at 6 and 10 weeks old after transplanting. However, for each treatment, a representative sample was collected by thoroughly mixing all three associated reps and obtaining a representative leaf sample giving 18 experimental units. The dried samples were taken to the University of Zambia Lab for analysis. The results showed that the mean fiber content was higher at week 10 than week 6 (P< 0.001), while vitamin C was higher at week 6 than week 10 (P= 0.05). Implying that younger leaves are likely to supply a higher content of vitamin C than older leaves. The lesser content of fiber at younger stage of rape explains why most consumers found rape more palatable at a younger stage. It was also revealed that vitamin C and fiber nutrient contents did not depend on the type of genotype. Furthermore, a study to evaluate the precise effects of fertilizer amendment on vitamin C and fiber contents should be undertaken.