Abstract
The present experiments were conducted to clarify firstly whether selection for yielding ability in a space planted condition which was commonly used in crop breeding, was usefull in a sward condition or not, and secondly what were the important traits as selection criteria. The three sets of half-sib families selected at random from the two random mating populations of Italian ryegrass were planted in space planted and sward condition. Data were recorded on forage yield, plant height, leaf width, tiller weight, tiller number and other agronomic traits. The first, second and third experiments were carried out in 1964-'65, 1965-'66 and 1966-'67, respectively. The results were summarized as follows : 1. The heritabilities of forage yield and tiller weight were higher in a sward than a space planted condition. 2. The correlation coefficients between two planting conditions of leaf width and plant height were high in all experiments, but that of forage yield was 0.624 in highest value. 3. In same planting conditions the trait that was most relative to forage yield was plant height, and the next was tiller number. 4. The tendency of correlation between forage yield in a sward and agronomic traits in a spaced planting differed according to the experiments. However, plant height positively correlated to forage yield in every experiments. 5. In a sward condition, the productivity of families was relatively higher when the upper leaf-blades were erect than when they were bent down. 6. Considering above mentioned results, in progeny test a selection for yielding ability is more efficient in sward condition than in a space planted condition, and plant height is the most important trait as a selection criterion in individual selection. In addition plant type and shape of leaves are considerable traits, too.
