ROOT-GROWTH DYNAMICS OF BRUSSELS-SPROUTS (BRASSICA-OLEARACEA VAR GEMMIFERA) AND LEEKS (ALLIUM-PORRUM L) AS REFLECTED BY ROOT LENGTH, ROOT COLOR AND UV FLUORESCENCE

Minirhizotron observations of roots of leeks and Brussels sprouts grow n in the Wageningen Rhizolab were used to study the dynamics of root l ength. Day of appearance and the time of decay were assessed for indiv idual root segments visible on the minirhizotron surface. A Brussels s prouts crop produced much more root length than leeks, but the average longevity of these roots was about half that of leek roots. To invest igate whether root colour or UV fluorescence could be used as a quanti tative index of root functionality or root age, changes in root ''colo ur'' (on a scale of greys) over time were measured with interactive im age analysis. In both crops a gradual change towards black was found w ith ageing. Measurements of the intensity of the UV fluorescence showe d that leek roots fluoresced more than Brussels sprouts roots. Over ti me, UV fluorescence decreased in Brussels sprouts roots but increased in leek roots. It is concluded that UV fluorescence cannot be used as a universal indicator of root age or root functionality, but in some p lant species it may be used to separate (transparent) roots from the b ackground with image analysis techniques.