Abstract
Genotypes of Lolium perenne were grown in soil of low phosphorus status, with and without additional phosphorus. Lack of phosphorus resulted in a great reduction in the number of main roots and in an increase in the length of each individual root. The number of tillers was also reduced, but to a lesser extent than the number of main roots. The dry weight of the root and shoot system was reduced to a lesser extent than the numbers of roots and tillers. The effect on root relative to shoot growth varied with the genotype.