Induced mutations for varietal improvement in soybean

Since soybean necrotic virus (SMV-N), which was identified as a strain of soybean mosaic virus (SMV), has severe effects on such leading varieties as Kwangkyo and Kangrim, mutation studies were aimed at obtaining mutants resistant to SMV-N, without causing drastic changes in other agronomic characters, from these varieties. Prior to mutation induction, inheritance of resistance was determined and it was found that resistance was conditioned by a single recessive gene. With this information, soybean seeds were irradiated with 15 and 25 kR of gamma rays. The mutants were screened for SMV-N resistance, both under natural infection pressure and artificial inoculation. Through the selections, five lines were selected as desirable mutants and, according to the objective of this study, these mutants were stocked in a gene pool. Meanwhile, another mutation was induced to obtain a small seeded mutant with higher yield potential from the exotic variety CB-27. Through the usual selections, one mutant was registered as a new leading variety for soybean sprouts and named Bangsa-kong. Apart from that, attempts were made to determine the mutation frequency and mutation sector in soybean. Plant height and the number of seeds in M1 plants were closely related to the mutation frequency of visible characters. The mutation sector of the irradiated seeds was not apparent in M2 plants regardless of radiation dose. It was found that all seeds harvested from SMV infected plants did not produce mottled seeds and all of the mottled seeds did not contain the virus. The soybean necrotic virus was not transmitted through the seeds of the variety Kwangkyo. (author). 7 refs, 2 figs, 9 tabs