Characterization of novel inbred lines of white clover (Trifolium repens L.). I. Dynamics of plant growth and nodule development in flowing solution culture

Abstract

Growth, dry matter partitioning between shoots and roots, and extent of nodulation were characterised in four novel self-fertile highly inbred lines (referred to as A, B, C and D) of white clover (Trifolium repens L.) thought to differ fundamentally in their nitrogen relations and therefore regarded as candidate material for genetic mapping. Plants were inoculated with a mixture of three strains of Rhizobium and grown in flowing nutrient solutions without N for 18 d. Half the plants were then supplied with 20 μM NO3 - during a 36 d treatment period, the remaining plants acting as ‘controls’ solely dependent upon N2 fixation for acquisition of N. Total dry matter production and shoot:root ratios were similar in all lines supplied with NO3 - and in control plants 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 attributed to a failure to develop effective N2 fixation capacity after apparently normal infection. Mean nodule size, nodule numbers and nodule d.w. per plant were extremely low in line D compared with the other lines, irrespective of whether NO3 - was supplied. Lines A, B and C differed in the severity with which NO3 - decreased mean d.w. per nodule and total nodule d.w. per plant relative to corresponding control plants, with line C being least sensitive. Nitrate also decreased the total number of nodules per plant relative to control plants after day 14 in all lines except C, and most severely in line B.