Modeling the Effects of Elevated Temperature and Weed Interference on Rice Grain Yield.

A 3-year phytotron study was conducted in Suwon (37.27°N, 126.99°E), Korea, to evaluate and model the effects of elevated temperature on rice-weed competition. The dry weight and the number of panicles in rice were the most susceptible components to weed interference during the early growth of rice, regardless of weed species, while other yield components, including the number of grains, % ripened grain, and 1000-grain weight, were more susceptible to elevated temperature. A rectangular hyperbolic model well demonstrated that rice grain yield was affected by weed interference under elevated temperature, showing that the competitiveness of late watergrass (Echinochloa oryzicola) and water chestnut (Eleocharis kuroguwai) increased under elevated temperature conditions. Quadratic and linear models well described the effects of elevated temperature on the weed-free rice grain yield and weed competitiveness values of the rectangular hyperbolic model for the two weed species, respectively. Thus, a combined rectangular hyperbolic model incorporated with the quadratic and linear models well demonstrated the effects of elevated temperature and weed interference on rice grain yield across years. Using the combined model and estimated parameters, the rice grain yields were estimated to be 58.9, 48.5, 41.3, and 35.9% of the yields under weed-free conditions for 80 plants m-2 of late watergrass and 86.8, 64.3, 51.1, and 42.3% of the yields under weed-free conditions for 80 plants m-2 of water chestnut at 1,300, 1,500, 1,700, and 1,900°C·days of accumulated growing degree days (GDD; from transplanting to flowering, 89 days), respectively. The combined model developed in this study can provide an empirical description of both the elevated temperature and weed interference effects on rice yield and can be used for predicting rice grain yields due to weed interference under future elevated temperature conditions.

Baseline Sensitivity of Echinochloa crus-gall and E. oryzicola to Florpyrauxifen-Benzyl, a New Synthetic Auxin Herbicide, in Korea.

Echinochloa species is one of the most problematic weed species due to its high competitiveness and increasing herbicide resistance. Florpyrauxifen-benzyl, a new auxin herbicide, was recently introduced for Echinochloa management; however, the potential risk for the development of herbicide resistance in Echinochloa species has not been well-investigated. Thus, this study was conducted to evaluate the baseline sensitivity of Echinochloa species to florpyrauxifen-benzyl to estimate the risk of future resistance development. A total of 70 and 71 accessions of Echinochloa crus-galli and Echinochloa oryzicola were collected from paddy fields in Korea, respectively. These two Echinochloa species were grown in plastic pots up to the 5-leaf stage, and treated with florpyrauxifen-benzyl at a range of doses from 2.2 g to 70.0 g a.i. ha-1. Nonlinear regression analyses revealed that GR50 values for E. oryzicola ranged from 4.54 g to 29.66 g a.i. ha-1, giving a baseline sensitivity index (BSI) of 6.53, while those for E. crus-galli ranged from 6.15 g to 16.06 g a.i. ha-1, giving a BSI of 2.61. Our findings suggest that E. oryzicola has a greater potential risk than E. crus-galli for the development of metabolism-based resistance to florpyrauxifen-benzyl.

Environmental risk assessment of glufosinate-resistant soybean by pollen-mediated gene flow under field conditions in the region of the genetic origin.

Pollen-mediated gene flow of genetically modified crops to their wild relatives can facilitate the spread of transgenes into the ecosystem and alter the fitness of the consequential progeny. A two-year field study was conducted to quantify the gene flow from glufosinate-ammonium resistant (GR) soybean (Glycinemax) to its wild relative, wild soybean (G. soja), and assess the potential weed risk of hybrids resulting from the gene flow during their entire life cycle under field conditions in Korea, where wild soybean is the natural inhabitant. Pollen-mediated gene flow from GR soybeans to wild soybeans ranged from 0.292% (mixed planting) to 0.027% at 8 m distance. The log-logistic model described the gene flow rate with increasing distance from GR soybean to wild soybean; the estimated effective isolation distance for 0.01% gene flow between GR and wild soybeans was 37.7 m. The F1 and F2 hybrids exhibited the intermediate characteristics of their parental soybeans in their vegetative and reproductive stages. Canopy height and stem length of hybrids were close to those of wild soybean, which shows an indeterminate growth; the numbers of flowers, pods, and seeds per hybrid plant were close to those of wild soybean and significantly higher than those of GR soybean. Seed longevity of F2 hybrid plants was also intermediate but significantly greater than that of GR soybean due to high seed dormancy. Our results suggest that transgenes of the GR soybean might disperse into wild populations and persist in the agroecosystem of the genetic origin regions due to the pollen-mediated gene flow and the relatively high fitness of the hybrid progeny.

Assessment of potential environmental risks of transgene flow in smallholder farming systems in Asia: Brassica napus as a case study in Korea.

The cultivation of genetically modified (GM) crops has raised many questions regarding their environmental risks, particularly about their ecological impact on non-target organisms, such as their closely-related relative species. Although evaluations of transgene flow from GM crops to their conventional crops has been conducted under large-scale farming system worldwide, in particular in North America and Australia, few studies have been conducted under smallholder farming systems in Asia with diverse crops in co-existence. A two-year field study was conducted to assess the potential environmental risks of gene flow from glufosinate-ammonium resistant (GR) Brassica napus to its conventional relatives, B. napus, B. juncea, and Raphanus sativus under simulated smallholder field conditions in Korea. Herbicide resistance and simple sequence repeat (SSR) markers were used to identify the hybrids. Hybridization frequency of B. napus × GR B. napus was 2.33% at a 2 m distance, which decreased to 0.007% at 75 m. For B. juncea, it was 0.076% at 2 m and decreased to 0.025% at 16 m. No gene flow was observed to R. sativus. The log-logistic model described hybridization frequency with increasing distance from GR B. napus to B. napus and B. juncea and predicted that the effective isolation distances for 0.01% gene flow from GR B. napus to B. napus and B. juncea were 122.5 and 23.7 m, respectively. Results suggest that long-distance gene flow from GR B. napus to B. napus and B. juncea is unlikely, but gene flow can potentially occur between adjacent fields where the smallholder farming systems exist.

Evaluation of maximum potential gene flow from herbicide resistant Brassica napus to its male sterile relatives under open and wind pollination conditions.

Pollen-mediated gene flow (PMGF) from genetically modified (GM) Brassica napus to its wild relatives by wind and insects is a major ecological concern in agricultural ecosystems. This study conducted is to estimate maximum potential gene flow and differentiate between wind- and bee-mediated gene flows from herbicide resistant (HR) B. napus to its closely-related male sterile (MS) relatives, B. napus, B. juncea and Raphanus sativus. Various markers, including pods formation in MS plants, herbicide resistance, and SSR markers, were used to identify the hybrids. Our results revealed the following: 1) maximum potential gene flow (a maximum % of the progeny of pollen recipient confirmed hybrid) to MS B. napus ranged from 32.48 to 0.30% and from 14.69 to 0.26% at 2-128 m from HR B. napus under open and wind pollination conditions, respectively, and to MS B. juncea ranged from 21.95 to 0.24% and from 6.16 to 0.16%, respectively; 2) estimates of honeybee-mediated gene flow decreased with increasing distance from HR B. napus and ranged from 17.78 to 0.03% at 2-128 m for MS B. napus and from 15.33 to 0.08% for MS B. juncea; 3) a small-scale donor plots would strongly favour insect over wind pollination; 4) no gene flow occurred from HR B. napus to MS R. sativus. Our approach and findings are helpful in understanding the relative contribution of wind and bees to gene flow and useful for estimating maximum potential gene flow and managing environmental risks associated with gene flow.

Complete chloroplast genomes of two Miscanthus species.

The complete chloroplast (cp) genomes of two Miscanthus species, M. sinensis and M. sacchariflorus, were sequenced and investigated for genes, genome size variation, and polymorphisms. There are 170 genes in both cp genomes, consisting of 122 mRNA genes (84 protein-coding genes and 38 hypothetical genes), 40 tRNA genes, and 8 rRNA genes. The cp genome contains two inverted repeat (IR) regions, separated by large single copy (LSC) region and small single copy (SSC) region. Indels were responsible for 40 bp difference in cp genome size in two species. In addition, we established phylogenetic relationship with other monocot cp genomes, and estimated divergence time. The two Miscanthus species clustered together among other C4 monocot species and the divergence time of two Miscanthus species was approximately 0.5 1-0.84 Mya.

Uncovering the differential molecular basis of adaptive diversity in three Echinochloa leaf transcriptomes.

Echinochloa is a major weed that grows almost everywhere in farmed land. This high prevalence results from its high adaptability to various water conditions, including upland and paddy fields, and its ability to grow in a wide range of climates, ranging from tropical to temperate regions. Three Echinochloa crus-galli accessions (EC-SNU1, EC-SNU2, and EC-SNU3) collected in Korea have shown diversity in their responses to flooding, with EC-SNU1 exhibiting the greatest growth among three accessions. In the search for molecular components underlying adaptive diversity among the three Echinochloa crus-galli accessions, we performed de novo assembly of leaf transcriptomes and investigated the pattern of differentially expressed genes (DEGs). Although the overall composition of the three leaf transcriptomes was well-conserved, the gene expression patterns of particular gene ontology (GO) categories were notably different among the three accessions. Under non-submergence growing conditions, five protein categories (serine/threonine kinase, leucine-rich repeat kinase, signaling-related, glycoprotein, and glycosidase) were significantly (FDR, q < 0.05) enriched in up-regulated DEGs from EC-SNU1. These up-regulated DEGs include major components of signal transduction pathways, such as receptor-like kinase (RLK) and calcium-dependent protein kinase (CDPK) genes, as well as previously known abiotic stress-responsive genes. Our results therefore suggest that diversified gene expression regulation of upstream signaling components conferred the molecular basis of adaptive diversity in Echinochloa crus-galli.