Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 1/29/2018
Publication Date: N/A
Technical Abstract: ndica rice genotypes with enhanced weed suppression traits have been previously identified as potentially useful in supplementing weed control efforts in drill-seeded systems in the southern USA. A particularly weed-suppressive indica genotype (PI 312777) that was also high tillering and high yielding was crossed with a non-weed-suppressive tropical japonica genotype (Katy) to produce a mapping population of ~330 recombinant inbred lines (RILs). In 2016, the two parents and 27 F9 RILs with diverse growth traits were selected from the full population of 330 RILs, and evaluated in the field. In 2017 an additional ~21 F10 RILs were evaluated for a total of 48 RILs. Crop growth, yield, and weed suppression were evaluated, with the objective of identifying RILs possessing both yield and weed suppression potential that meet or exceed those of the parents (particularly the tropical japonica). The experiment was designed as a split plot with four replications, and main plots as rice genotypes, and subplots as weed control (weedy or weed-free). Rice seed was planted 2 cm-deep in plots 3-m-long with 6, 18-cm-wide rows on May 9-13, and emerged on May 23-24 in both years. Weeds in weed-free plots were controlled using commercially-recommended rates of pre-emergence (clomazone plus quinclorac) or postemergence (fenoxaprop) herbicides. Propanil was applied postemergence to weedy plots at the 1/2X use rate in late June as needed (2016 only) to mildly suppress barnyardgrass. Plots were fertilized with 110 kg/ha N as urea and flooded on June 21-27, and harvested Oct. 3-26 in both years. Agronomic traits, including rice tiller number, biomass, plant height, yield, and weed suppression, were recorded. In 2016 yield averaged over all genotypes was ~50% lower in weedy compared with weed-free plots. Several RILs, however, maintained relatively greater yields under weed pressure. These included RIL90, RIL122, RIL274, RIL144, and RIL100 (2017 yield data not yet available). Averaged over all genotypes in 2016 and 2017, respectively, heights were 11% and 8% lower, tiller numbers were 25% and 22% lower, and midseason rice biomass was 33% and 30% lower in weedy compared with weed-free plots. RILs that were among the most weed-suppressive in both years based on visual control ratings and weed biomass reduction included RIL392, RIL90, RIL244, RIL122, RIL404, RIL291, RIL274, and RIL33. Among the RILs that were evaluated for the first time in 2017, RIL109, RIL394, RIL306, and RIL44 also exhibited high levels of weed suppression. Various RIL traits appeared to be associated with weed suppression in these studies. RIL90 is very tall and was shown to maintain yields well under ‘alternating wetting and drying’ (AWD) moisture stress in previous research. RIL122, RIL291, and RIL244 are high tillering lines (similar to PI 312777). RIL274 is also very tall and was shown to produce high root mass in previous research. Thus, many of the promising RILs appeared to benefit from advantageous traits such as tall plant height, high tillering, high root mass, high seedling emergence rates, and tolerance to AWD moisture stress as determined in these or in previous studies, and might be using several strategies to reduce the impacts of weeds. Overall, RIL90 and RIL122 appear to have an excellent combination of high yield and weed suppression ability that equals or exceeds that of the parents, and may be potential candidates for release as improved germplasm.