GENETIC-CONTROL OF A LONG-JUVENILE TRAIT IN SOYBEAN

The long-juvenile (LJ) trait in soybean [Glycine mar (L.) Merr.] has been defined as delayed flowering under short-day conditions. The genetic control of this trait remains ambiguous in the literature, and this study was undertaken to determine the genetic control of the LJ trait. Three field experiments were conducted between 1984 and 1998. In the first experiment, segregation patterns of the LJ trait were examined in six F-2 populations from crosses between conventional juvenile (CJ) lines and PI 159925 (source of the LJ trait). Results indicated that the LJ trait is controlled by a single recessive gene influenced by the genetic background in which it occurs. In the second experiment, the confounding effect of other genes segregating for flowering was eliminated by studying F-2 populations from crosses between members of four pairs of near isogenic Lines primarily differing in the presence of the LJ trait. A total of 1954 F-2 plants were observed from eight crosses. Within all F-2 populations, the segregation patterns for the LJ trait had a good fit to a 3:1 ratio of CJ/LJ expected for a single recessive gene. The dominance relationship of the alleles was examined in the third experiment using F-5 and F-6 families developed from seven different crosses. Results indicated that the J allele, which conditions the CJ phenotype, is nearly completely dominant. Our results indicated that the LJ trait is controlled by a single recessive gene and the symbol J/j has been assigned for the alleles conditioning the flowering response (J-, CJ and jj, LJ).