|Moldenhauer, Karen A|
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/10/2010
Publication Date: 10/1/2010
Citation: Gealy, D.R., Moldenhauer, K.K., Mattice, J.D. 2010. Weed control and yield potential for a promising rice line, STG06L-35-061, selected from crosses between weed-suppressive indicas and commercial long-grain rice. Rice Technical Working Group Meeting Proceedings. CDROM - P. 155. Interpretive Summary:
Technical Abstract: Sustainable weed control is an ongoing challenge in rice production. Indica rice lines such as PI 312777 that can suppress Echinochloa crus-galli and other troublesome C4 grass weeds have been evaluated extensively in Arkansas for more than a decade. In an ongoing breeding/selection program, we are combining desirable quality and yield characteristics of southern long grain cultivars with highly weed-suppressive rice lines. In previous findings, both competition and allelopathic components have been implicated in the weed suppressive activity of PI 312777 and other indica lines. The selection RU0701087 (pedigree containing PI 338046, PI 312777, and Katy) produced adequate yield and quality, but provided only marginal weed suppression. STG06L-35-061 (pedigree containing PI 338046, PI 312777, Katy, and Drew) was initially identified in preliminary field trials in 2008 as a highly weed suppressive selection. It was visually distinctive among many other selections and standard cultivars as having relatively few weeds in the midst of a large screening area that was mostly overrun by weeds. Its suppressive activity was subsequently confirmed in several field tests in 2009. STG06L-35-061 and other rice lines of interest were typically evaluated in both weed-free and weed-infested (‘weedy’) drill-seeded plots that were flooded 5 to 6 weeks after planting. Weed-free plots were treated with 4.4 kg/ha propanil to obtain complete control of grass weeds. Weedy plots of the same cultivar were treated with 1.1 kg/ha propanil (¼ of standard use rate) to achieve minimal stunting of weeds. Generally, weed suppression activity of STG06L-35-061 approached that of PI 312777 and other suppressive lines, and was superior to that of Lemont and a number of other commercial tropical japonica cultivars. In weed-free plots in one test, the time from emergence to 50% heading were 87 days and mature plant heights were 109 cm. By comparison, these respective values were 87 days and 111 cm for Drew and 88 days and 97 cm for PI 312777. In other weed-free plots, STG06L-35-061 produced yields similar to those of LaGrue, averaging 8520 kg/ha (169 bu/A), and was not damaged by lodging, which has been a significant problem in its parent, PI 312777. In a bioassay conducted in soil in small cups in a growth chamber, apparent allelopathic activity of STG06L-35-061 roots, as determined by their inhibition of barnyardgrass seedlings, was intermediate between that of known allelopathic cultivars such as PI 312777 and non-allelopathic cultivars such as Katy. STG06L-35-061 appears to be the most promising weed-suppressive selection from our efforts to date. It produces commercially acceptable rough rice yields and its weed control activity, apparently involving an allelopathic component, can be nearly as great as that of its most suppressive parental lines. Natural variation in weed infestation levels and weed suppression activities from experiment to experiment and from year to year suggests that STG06L-35-061 would benefit from supplemental weed control inputs in most situations.