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This study was conducted to evaluate the cross‐resistance of acetolactate synthase (ALS) inhibitors with different chemistries, specifically azimsulfuron (sulfonylurea), penoxsulam (triazolopyrimidine sulfonanilide) and bispyribac‐sodium (pyrimidinyl thio benzoate), in Echinochloa oryzicola and Echinochloa crus‐galli that had been collected in South Korea and to investigate their herbicide resistance mechanism. Both Echinochloa spp. showed cross‐resistance to the ALS inhibitors belonging to the above three different chemistries. In a whole plant assay with herbicides alone, the resistant/susceptible ratios for azimsulfuron, penoxsulam and bispyribac‐sodium were 12.6, 28.1 and 1.9 in E. oryzicola and 21.1, 13.7 and 1.8 in E. crus‐galli, respectively. An in vitro ALS enzyme assay with herbicides showed that the I 50‐values of the resistant accessions were approximately two‐to‐three times higher than the susceptible accessions, with no statistical difference, suggesting that the difference in ALS sensitivity cannot explain ALS inhibitor resistance in Echinochloa spp. for azimsulfuron, penoxsulam and bispyribac‐sodium. A whole plant assay with fenitrothion showed that the GR 50‐values significantly decreased in both the resistant E. oryzicola and E. crus‐galli accessions when azimsulfuron, penoxsulam and bispyribac‐sodium were applied with the P450 inhibitor, while no significant decrease was observed in the susceptible accessions when the P450 inhibitor was used. Thus, these results suggest that ALS inhibitor cross‐resistance for azimsulfuron, penoxsulam and bispyribac‐sodium is related to enhanced herbicide metabolism.

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.

1181Á1192. The aim of the presented study was to develop a bioassay for rapid diagnosis of herbicide doseÁresponse and resistance in Echinochloa. Pre-germinated seeds of Echinochloa spp. were incubated in growth pouches (18 cm )16.5 cm) containing herbicide solutions in a range of concentrations. Shoot and root lengths were measured after 6 d of incubation. DoseÁresponses estimated by measuring root lengths in the growth pouches were well-described by the log-logistic doseÁ response model and similar to those estimated by a whole-plant assay. Accurate doseÁresponse curves were successfully generated for several herbicides with different modes of action, suggesting that the growth pouch method can be used for herbicide bioassays. The suitability of the growth pouch method for rapid diagnosis of acetyl coenzyme-A carboxylase (ACCase) and acetolactate synthase (ALS) inhibitor resistance in Echinochloa spp. was also tested. For cyhalofop-butyl, resistant and susceptible biotypes were discriminated at 180Á300 mg a.i. L (1 and 80Á120 mg a.i. L (1 for barnyardgrass (E. crusgalli) and late watergrass (E. oryzicola), respectively. For penoxsulam, the discriminatory dosage was 350Á500 mg a.i. L (1 for barnyardgrass and 650Á1000 mg a.i. L (1 for late watergrass. The method was further used to identify late watergrass biotypes resistant and susceptible to two other ALS inhibitors, azimsulfuron and bispyribac-sodium. Our results show that the growth pouch method can be reliably used in herbicide doseÁresponse studies and to diagnose herbicide resistance in Echinochloa spp., with significant time and cost savings compared with conventional whole-plant assays. Le mode`le logarithmique-logistique de la doseÁre´ponse de´crit bien l'estimation de la doseÁre´ponse d'apre`s la longueur des racines dans les sacs de croissance, et les re´sultats sont similaires a`ceux obtenus avec les e´preuves portant sur la plante entie`re. Les auteurs ont produit des courbes doseÁre´ponse exactes pour plusieurs herbicides au mode d'action diffe´rent, signe que la technique du sac de croissance pourrait servir aux essais biologiques sur les herbicides. Les auteurs ont e´galement ve´rifie´si cette me´thode pourrait servir a`diagnostiquer rapidement la re´sistance aux inhibiteurs de l'ACCase et de l'ALS chez Echinochloa sp. Les biotypes re´sistants et sensibles au cyhalofop-butyle ont e´te´diffe´rencie´s a`la concentration de 180Á300 mg de matie`re active par litre et de 80Á120 mg de matie`re active par litre, respectivement, chez le panic pied-de-coq (E. crus-galli) et l'e´chinochloe´phyllopogon tardif (E. oryzicola). Avec le penoxsulam, la dose permettant d'e´tablir une discrimination correspond a`350Á500 mg de matie`re active par litre pour le panic pied-de-coq et a`650Á1 000 mg de matie`re active par litre pour l'e´chinochloe´phyllopogon tardif (E. oryzicola). Cette me´thode a e´galement permis d'identifier les biotypes d'e´chinochloeṕ hyllopogon tardif re´sistants et sensibles a`deux autres inhibiteurs de l'ALS, l'azimsulfuron et le bispyribac-s...