The decrease in dry matter production in guineagrass by the use of a mechanical harvesting system was investigated in terms of treading resistance. It was revealed that treading treatment of stubbles led to a serious decrease in dry matter production while shading of stubbles by foliage did not result in an appreciable decrease in dry matter production. A cultivar resistant to treading was found to show more stems at the time of cutting and better tiller regeneration after harvest. Most of the tillers trodden using a tractor regenerated from the nodes near the ground level, whereas cultivars with a low treading resistance regenerated new tillers from the higher nodes, suggesting the presence of a strong apical dominance. Analysis of varietal differences in the treading resistance indicated that the tiller number and apical dominance could become morphological and physiological selection criteria for the treading resistance, respectively. Based on this assumption, 3,541 plants consisting of 318 accessions of genetic resources were evaluated for their morphological traits and apical dominance over a period of 7 years. Several candidate strains were then investigated for their treading resistance, and one strain with a strong treading resistance and suitability for rollbale harvest was eventually selected, and released as a new cultivar named Natsukomaki in 1999. Natsukomaki belongs to the slender guinea grass group characterized by fine stems, small leaves and a short plant height. Drying rate and flexibility of stems and leaves were outstanding in Natsukomaki. Hay from Natsukomaki contained a higher TDN content, and showed a good digestibility and high palatability.