Potential improvement in rice seedling establishment and weed suppression in reduced-input systems using osmotically pre-conditioned seed

Authors: Gealy, David; McClung, Anna

Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: 1/28/2013
Publication Date: 1/28/2013
Citation: Gealy, D.R., Mcclung, A.M. 2013. Potential improvement in rice seedling establishment and weed suppression in reduced-input systems using osmotically pre-conditioned seed. Proceedings of Southern Weed Science Society. 66:273.

Interpretive Summary:

Technical Abstract: Asian indica rice cultivars have exhibited suppression potential against barnyardgrass (Echinochloa crus-galli) in drill-seeded, flood-irrigated production systems in the U.S. However, the degree of weed suppression has been inconsistent, and is dependent on environmental and production factors which vary from year to year. Weed-suppressive cultivars could improve the efficacy of low-input/ organic rice systems. In earlier research, increased seedling emergence rates of rice have resulted in improved weed suppression and yield performance in drill-seeded rice systems. Exposing rice seeds to brief, pre-plant soaking in water or aqueous solutions under reduced osmotic potential followed by drying, has been shown to improve the rates and maximum levels of seedling emergence, which resulted in increased grain yield. Our objective was to determine the efficacy of pre-plant seed soaking/drying treatment of diverse rice germplasm to improve yield and suppression of weeds under low input systems. In order to address these objectives, a split-plot experiment was conducted in the field at Stuttgart, AR in 2012. Main plots were a factorial combination of nine cultivars or germplasm lines and three seed treatments. Sub-plots were two levels of barnyardgrass infestation (weedy or weed-free). Rice cultivars consisted of commercial standards (long-grain cultivars, ‘Cocodrie’,’Katy’, ‘Sierra’, and ‘Lemont’, and medium-grain, ‘Bengal’); and indica (or indica-derived) germplasm putatively suited to low-input/organic systems (‘Rondo’, ‘PI 312777’, ‘PI 338046’, and ‘STG06L-35-061’). Rondo and Sierra are being grown in commercial organic systems in the southern U.S. PI 312777 and PI 338046 have been demonstrated to be allelopathic against barnyardgrass, and were among the parental lines used to develop STG06L-35-061. Rice seed treatments were 1) dry (i.e. conventional); 2) two sequential cycles of 24-h soaking/ 24-h drying at 27C in distilled water (DW) followed by chilling at 4 C for 48 h prior to drill-seeding; and 3) a procedure identical to treatment #2 except that the seeds were soaked in a solution of 0.2M CaCl2 ('s =~ -1.25 Mpa). The soaking/drying treatments serve to initiate key seed germination processes which are then arrested before germination can be completed. Herbicides were applied to control weeds in the weed-free plots. The time to 50% of maximum emergence for the dry seed treatment ranged from 190 hours after planting (HAP) for PI 338046 to 380 HAP for Lemont. Both CaCl2 and DW treatments increased emergence rates of Rondo. For most rice cultivars, however, the DW treatment reduced emergence, and CaCl2 had minimal effect. These results suggest that the soaking treatments may have degraded the vigor of seeds. The DW treatment inhibited emergence of Katy, Lemont, and STG06L-35-061 by more than 50%, but did not affect Bengal. However, a severe drought, which extended through the planting and emergence period, resulted in substantial moisture stress that may have interacted with the seed soaking treatments to reduce seedling emergence of some rice cultivars. In weed-infested plots, PI 338046, PI 312777, and Rondo produced the greatest suppression of weeds and highest grain yields among the rice cultivars tested. Bengal was the most weed-suppressive and highest yielding among the non-indica cultivars. Although atypical environmental stresses occurred during the planting/emergence period in 2012, clear differences in emergence response to the seed treatments were observed among some cultivars, suggesting that further studies conducted under additional (preferably less extreme) environmental conditions are warranted.