CHARACTERIZATION OF NOVEL INBRED LINES OF WHITE CLOVER (TRIFOLIUM-REPENS L.) - I - DYNAMICS OF PLANT-GROWTH AND NODULE DEVELOPMENT IN FLOWING SOLUTION CULTURE

Growth, dry matter partitioning between shoots and roots, and extent o f nodulation were characterised in four novel self-fertile highly inbr ed lines (referred to as A, B, C and D) of white clover (Trifolium rep ens L.) thought to differ fundamentally in their nitrogen relations an d therefore regarded as candidate material for genetic mapping. Plants were inoculated with a mixture of three strains of Rhizobium and grow n in flowing nutrient solutions without N for 18 d. Half the plants we re then supplied with 20 mu M NO3- during a 36 d treatment period, the remaining plants acting as 'controls' solely dependent upon N-2 fixat ion for acquisition of N. Total dry matter production and shoot:root r atios were similar in all lines supplied with NO3- and in control plan ts of lines B and C. Growth was severely reduced in control plants of line D and to a lesser extent in control line A. These effects were at tributed to a failure to develop effective N-2 fixation capacity after apparently normal infection. Mean nodule size, nodule numbers and nod ule d.w. per plant were extremely low in line D compared with the Othe r lines, irrespective of whether NO3- was supplied. Lines A, B and C d iffered in the severity with which NO3- decreased mean d.w, per nodule and total nodule d.w. per plant relative to corresponding control pla nts, with line C being least sensitive. Nitrate also decreased the tot al number of nodules per plant relative to control plants after day 14 in all lines except C, and most severely in line B.