ISOLATION AND CHARACTERIZATION OF RTCS, A MAIZE MUTANT DEFICIENT IN THE FORMATION OF NODAL ROOTS

The root system of maize consists of the primary root and a variable n umber of lateral seminal-, crown- and brace roots. Except for the prim ary root and some minor roots forming at the mesocotyl, all other root s grow out of nodal regions, namely, the embryogenic scutellar node an d the underground-as well as the lower aboveground stem nodes. Besides their role in water and nutrient uptake, some of these roots (crown- and brace roots) are essential for the lodging resistance of the plant s. This property of the crown roots has now been successfully used for screening a segregating F-2 population of a cross between a flint inb red line and an En transposon line. Two allelic root-deficient mutants have been isolated and have been designated rtcs-1 and rtcs-2 for the ir complete lack of formation of crown- and lateral seminal roots. The y survive by the ability of the primary root to support the growth of the developing plant. The monogenic and recessive mutants appear to be affected in an early root-forming function since no primordia are for med either in the case of embryo-borne lateral seminal or stem-derived crown roots. The Rtcs locus could be mapped to the short arm of chrom osome 1 with the help of a co-segregating RAPD marker. The effect of t he mutation seems to be highly specific since no pleiotropic effects o n other parts of the plants have been observed. The formation of adven titious roots can, however, still be induced in the mesocotyl region o f the mutant.