Root Traits of a Soybean (Glycine max) Recombinant Inbred Population Segregating for Flooding Tolerance.

Soybeans (Glycine max) are known to be sensitive to flooding stress. Flooding at the reproductive stage can reduce soybean yield by 50%. However, recent screening efforts have resulted in the identification of genotypes differing in susceptibility to flooding. The flooding tolerant genotype PI 408105A showed only 32.1% reduction in yield compared to 81.2% reduction in the flooding sensitive breeding line S99-2281.  A recombinant inbred population (RIP) that segregates for flooding tolerance was developed from a cross of PI 408105A x S99-2281. To investigate the segregation of the RIP for root traits, 200 recombinant inbred lines (RILs) were grown in polyethylene cones (8 cm in diameter x 30 cm length) containing 25% Metro-Mix 350 and 75% Promix PGX at one plant per cone in the greenhouse. Flooding treatment was applied at the early vegetative stage by placing the cones in 50 L plastic tubs. Water was added to the tubs to a level of 3 cm above the soil surface. Ten days after the onset of flooding, the water was drained and plants were rated for adventitious root formation using a scale from 1 to 3; with 1 = less than two adventitious roots and 3 = more than five adventitious roots. The roots were transferred to nail boards to preserve the root architect during root washing. Root photos were taken and the roots and shoots were dried for biomass determination. Maximum and total root length and root distribution were determined using the WinRhizo software. The experiment was repeated four times.  The PI 408105A plants produced 32% more adventitious roots and had a 74% greater root biomass than the S99-2281 plants. Transgressive segregation was detected for both root traits among the RILs. The correlation between the root traits and seed yield reduction due to field flooding stress will be presented.