Abstract
Decrease of yield from synthetic 1 to synthetic 2 is undesirable feature in synthetic variety method. The optimum number of composite clone or inbred in synthetic varieties among species or materials. A breeder needs the information about the optimum number. This report exemplify an optimum number of composite clone in alfalfa synthetic. Sixty four plants were selected on the basis of disease resistance, plant type and fall vigor from the 5, 300 individuals which were introduced in 1967 and 1968 from over seas. The selected individuals were propagated into 10 to 12 propagules in 1970 and these clones were evaluated in 1971 and 1972. Based on the clonal evaluations, 35 clones were selected and transplanted into polycross field in 1972 with 10 replications. The polycross seeds were harvested in 1973 and polycross progeny test were carried out from 1974 to 1976. Two-clone synthetic, 4-clone synthetic, 8-clone synthetic and 16-clone synthetic were composed of high yielding 2-, 4-, 8- and 16- clones, respectively based on polycross progeny test. The seeds of synthetic 1 (Syn-1, afterwards) were harvested in the glass house in the spring of 1976 by using alfalfa leaf cutter bees. The seeds of synthetic 2 (Syn-2, afterwards) were harvested in the isolation fields in 1978. Syn-1 and Syn-2 seeds of 2-, 4-, 8- and 16-clone synthetics were sown in 1978 and yielding performance and changes of characteristics were observed from 1978 to 1980. The results were as follows ; 1. The yields of the synthetics were the most in the second year and the least in the first year. The ratio of the yield of the lowest clone to the highest clone in 2-, 4-, 8- and 16-clone synthetics were 98.0, 91.4, 86.7 and 85.6%, respectively, in the polycross progeny test. 2. The observed yields of 2-, 4-, 8- and 16-clone Syn-1 were close to the estimated yields. The yield of 8-clone Syn-2 was the highest and followed by 16-clone Syn-2. On the other hand, the yields of 2-clone Syn-2 and 4-clone Syn-2 were low. The yields of 8-clone and 16-clone Syn-2 were more or less higher than those of Syn-1. On the other hand, the yields of 2-clone and 4-clone Syn-2 were much lower than those of Syn-1. 3. Plant heights in the third year of 2-clone and 4-clone Syn-2 were significantly lower than those of the Syn-1. Stem number of 2-clone Syn-2 was less than that of Syn-1. The proportion of plants with variegated flower color in 4-clone Syn-2 was higher than that of Syn-1. These changes of the characteristics in 2-clone and 4-clone synthetics seem to be the factors of yield decrease in Syn-2. From the above results, 8-clone synthetic seems to be the best in terms of high yielding ability and least yield decrease in the advanced generation in alfalfa.
