Flowering Time Response of Long Juvenile Soybean under Extreme Photoperiods.

The long juvenile (LJ) trait results in delayed soybean [Glycine max (L.) Merr.] flowering under short days.  The J and E6 locus control LJ flowering responses.  Most work with J and E6 has been undertaken in 13 to 14 photoperiods.  This work was carried out to characterize LJ line responses to a greater range of photoperiods, and to characterize the genetic control of LJ.  A comparison of Parana (E6) and its spontaneous mutant LJ isoline Paranagoiana (e6) showed similar flowering times at both 4 and 16 h photoperiods, while differences were maximized under 8 to 12 h photoperiods.  Both LJ genotypes, e6e6 and jj, flowered similarly under 6 and 12 h photoperiods.  During introgression of the LJ trait from Paranagoiana to a MG 0 Harosoy isoline, late maturity was confirmed to be a recessive trait and seemed to be controlled by two genes.  The BC1- and BC2-F2 populations were shifted toward early flowering while maintaining some lines flowering 18 d later than the recurrent parent under a 12 h photoperiod.