NON-GENETIC VARIATION IN NITRATE CONTENT OF RADISH

As part of a research project on breeding radishes with a low nitrate content, also non-genetic variation in nitrate content of radish plants was examined. Highest nitrate concentrations were measured in the central parts and in the tops and bottoms of roots. Between halves of the same root sometimes considerable differences in nitrate content were found. With increasing root size nitrate content tended to decrease. Old leaves contained more nitrate than young leaves and cotyledons. When calculated on a fresh-product basis, nitrate content of leaves was higher than or as high as that of roots, but when calculated on a dry-matter basis the reverse was usually the case. In ageing roots nitrate content decreased, but in ageing leaves this was found only on soils poor in nitrogen.

In summer lower nitrate concentrations in roots were found than in winter and spring. The effect of variation in harvesting hour on nitrate content of roots was negligible.

No correlation was found between dry-matter content and nitrate content of the roots, a slight negative correlation was found between root weight and nitrate content, and a clearly significant positive correlation between nitrate content of leaves and that of roots.