Inheritance of a long juvenile period under short-day conditions in soybean

The long juvenile period (LJP) characteristic of soybean (Glycine max L. Merrill) cultivars delays flowering under short-day conditions. This trait may be important in increasing the adaptation range of soybean to low latitudes and provides greater flexibility for sowing times within the same latitude. The inheritance of the long juvenile period was studied in the MG/BR22 (Garimpo) soybean cultivar to provide knowledge to support the development of cultivars adapted to short day conditions. Four cultivars ('Parana', 'Bossier', 'Bragg', and 'Davis') were crossed among each other and with MG/BR 22 ('Garimpo'). The study was conducted under short-day conditions (early sowing) in a greenhouse and in the field, in Londrina, Parana, (23degrees22' south latitude). The parents and the F, F, and F, populations were assessed daily for flowering. The genotype ratios of 15:1 (p > 0.95, chi(2) test) and 8:71 (p = 0.193) for the F-2 and F-3 generations, respectively, obtained for the Parana x Bossier cross indicated a case of digenic interaction with a duplicate recessive epistatic effect for the LJP character. Segregation of the F-2 population from the MG/BR 22 (Garimpo) x Parana cross resulted in the expected ratio of 3:1 (p = 0.166, indicating that the MG/BR 22 (Garimpo) and Parana cultivars differed at a single locus. Similarly, in the MG/BR 22 (Garimpo) x Bossier cross, a 3:1 (p = 0.065) segregation indicated that these two cultivars differed at a single locus for number of days to flowering. The Davis cultivar had the same gene for LJP as the Parana cultivar (aa). The F, segregation of the classic flowering Bragg with MG/BR 22 (Garimpo) cross resulted in a 15:1 (p = 0.138) ratio, indicating that these two cultivars differed at two loci for flowering. The genotypes assigned to the cultivars were aaBB for Parana, AAbb for Bossier and aabb for MG/BR 22 (Garimpo). A single locus in recessive homozygosis does not produce LJP.