Update:
Preliminary results:
1) Root cells of soybean did not develop HR (localized cell necrosis) at or near the site of RN infections. Note that a) a number of studies have speculated that soybean and plant roots activate HR upon PPN infections, which is considered as the most eminent and effective immune machinery of plants against pathogens, and b) our concomitant experiments with cotton roots further supported that HR is not a part of plant defense mechanisms against PPN.
In particular, HR was not detectable until RN grew up to reach the pregnant stage. Considering that pregnancy takes a few days from the infection (J2) stage, this result clearly concludes that soybean roots are incapable of activate HR against PPN.
2) Root growth and shapes (preformed immunity) are correlated with plant tolerance against PPN attacks. In the concurrent studies with cotton roots, we noticed that PPN tolerant germplasm (Barbaren- 713) produces a larger number of root hairs than susceptible germplasms (Lonren-1, and Sure- Grow-714), suggesting the potential importance or roles of root morphology in plants’ tolerance against PPN infections.