A number of redroot pigweed and Powell amaranth populations from various locations in Ontario, Canada, have distinct patterns of resistance to the acetolactate synthase–inhibiting herbicides imazethapyr and thifensulfuron. This suggested the presence of diverse ALS gene mutations among these populations. Seven polymerase chain reaction primer pairs were used to amplify the gene to obtain full sequence information and to determine the identity of resistance-conferring mutations. There was a high degree of similarity in the ALS gene of the two species with only five nucleotides and one amino acid differing. A total of four herbicide resistance-conferring mutations were identified in the two species. The Ala122Thr, Ala205Val, and Trp574Leu amino acid substitutions were found in redroot pigweed whereas Ala122Thr, Trp574Leu, and Ser653Thr were detected in Powell amaranth. The pattern of resistance known to be conferred by the mutations concurred with the resistance level observed at the whole plant level. Distinct mutations being found in geographically separated populations suggest that selection for resistance occurred simultaneously in different locations. It reinforces the fact that resistance to ALS inhibitors is easily selected and that growers need to take this into account when formulating weed management strategies.

The objective of this study was to improve induction of embryogenesis in wheat microspore culture in order to obtain a high number of regenerable embryos. The arabinogalactan (AG) Larcoll and the arabinogalactan-protein (AGP) from gum arabic were tested on two spring genotypes to see if they could increase microspore viability and induce embryogenesis in the microspore culture. Adding Larcoll significantly decreased microspore mortality in both genotypes regardless of the presence or absence of ovaries in the culture. Similarly, gum arabic had a strong effect on the number of embryos produced and regenerated green plants. In fact, by using only gum arabic we were able to obtain green plants from wheat microspore cultures without the presence of ovaries. In addition to preventing a high mortality rate of the cells, our results show that the induction of embryogenesis in wheat microspore cultures is strongly affected by the use of both AG or AGP.

Plant Cell Reports (2006) 24: 691-698In Material and methods, the subsections "Microspore induction culture" and "Plant differentiation and regeneration" contain errors. Please find the correct sentences below. Microspore induction cultureThe induction medium, MMS4, (Kasha et al. 2003a, b) was modified MS medium (Murashige and Skoog 1962) containing 2 mgl −1 PAA, 0.5 mgl −1 kinetin, 90 gl −1 maltose, 355 mgl −1 U2.5 amino acid mix (Comeau et al. 1992), and 975 mgl −1 glutamine. Plant differentiation and regenerationOnce ELS reached a size of about 2 mm, they were transferred onto differentiation medium: MMS5 (Kasha et al. 2003a, b) containing 0.5 mgl −1 PAA, 0.2 mgl −1 kinetin, 0.5 mgl −1 GA 3 , 30 gl −1 maltose, 355 mgl −1 Sigma U2.5 amino acid mix, 10 µM CuSO 4 at 22 • C during a 16 h light period.The online version of the original article can be found at http://dx.

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A Powell amaranth population suspected to be resistant (R) to linuron was discovered in a carrot field in Keswick, Ontario, Canada, in 1999. Dose–response analysis with different herbicides and DNA sequencing of thepsbAgene encoding the D1 protein of photosystem II were done to confirm the resistance and identify its basis. A calculated resistance factor indicated a 12-fold increased resistance when linuron was applied to an R population compared with a susceptible (S) population. Moreover, the R population showed 6.4- and 3.1-fold greater resistance to two other phenylurea herbicides (diuron and monolinuron), 1.8- and 1.4-fold greater resistance to two triazine herbicides (metribuzin and prometryn), and 2.6-fold greater resistance to the triazinone metribuzin. R population was also cross-resistant to bentazon and bromoxynil when compared with S population, with a calculated resistance factor of 1.4 and 2.2, respectively. The partial nucleotide sequence of thepsbAgene of R populations differed at two locations when compared with S populations. The first mutation coded for a Val219Ile substitution in the deduced amino acid sequence of the D1 protein, and the second mutation was silent and encoded for a proline at position 279 in both R and S populations. The Val219Ile substitution in thepsbAgene is most likely the cause of this Powell amaranth population resistance to linuron and other PSII inhibitors. This is the first recorded instance of a Val219Ile substitution in anAmaranthusspecies.