chlorophyll-a and metribuzin

Herbicide tolerance is an important trait that allows effective weed management in wheat crops. Genetic knowledge of metribuzin tolerance in wheat is needed to develop new cultivars for the industry. Here, we evaluated metribuzin tolerance in a recombinant inbred line (RIL) mapping population derived from Synthetic W7984 and Opata 85 over two consecutive years to identify quantitative trait loci (QTL) contributing to the trait. Herbicide tolerance was measured by two chlorophyll traits, SPAD chlorophyll content index (CCI) and visual senescence score (SNS). The markers associated with major QTL from Synthetic W7984, positively contributing to reduced phytotoxic effects under herbicide treatment were validated in two F. Composite interval mapping (CIM) identified four QTL, two on chromosome 4A and one each on chromosomes 2D and 1A. The chromosomal position of the two QTL mapped on 4A within 10 cM intervals was refined and validated by multiple interval mapping (MIM). The major QTL affecting both measures of tolerance jointly explained 42 and 45% of the phenotypic variation by percentage CCI reduction and SNS, respectively. The identified QTL have a pure additive effect. The metribuzin tolerant allele of markers, Xgwm33 and Xbarc343, conferred lower phytotoxicity and explained the maximum phenotypic variation of 28.8 and 24.5%, respectively. The approximate physical localization of the QTL revealed the presence of five candidate genes (ribulose-bisphosphate carboxylase, oxidoreductase (rbcS), glycosyltransferase, serine/threonine-specific protein kinase and phosphotransferase) with a direct role in photosynthesis and/or metabolic detoxification pathways.. Metribuzin causes photo-inhibition by interrupting electron flow in PSII. Consequently, chlorophyll traits enabled the measure of high proportion of genetic variability in the mapping population. The validated molecular markers associated with metribuzin tolerance mediating QTL may be used in marker-assisted breeding to select metribuzin tolerant lines. Alternatively, validated favourable alleles could be introgressed into elite wheat cultivars to enhance metribuzin tolerance and improve grain yield in dryland farming for sustainable wheat production.

Topics: Cellular Senescence; Chlorophyll; Chromosome Mapping; Chromosomes, Plant; Drug Resistance; Genotype; Herbicides; Phenotype; Photosystem II Protein Complex; Plant Proteins; Polyploidy; Quantitative Trait Loci; Triazines; Triticum

Sugar beet growers in Europe are more often confronted with an unsatisfactory control of Chenopodium album L. (fat-hen), possibly due to the presence of a triazinone resistant biotype. So far, two mutations on the psbA-gene, i.e. Ser264-Gly and Ala251-Val, are known to cause resistance in C. album to the photosystem II-inhibiting triazinones metamitron, a key herbicide in sugar beet, and metribuzin. The Ser264-Gly biotype, cross-resistant to many other photosystem II-inhibitors like the triazines atrazine and terbuthylazine, is most common. The second resistant C. album biotype, recorded in Sweden, is highly resistant to triazinones but only slightly cross-resistant to terbuthylazine. Since farmers should adapt their weed control strategy when a resistant biotype is present, a quick and cheap detection method is needed. Therefore, through trial and error, a protocol for detection with chlorophyll fluorescence measurements was developed and put to the test. First, C. album leaves were incubated in herbicide solution (i.e. 0 microM, 25 microM metribuzin, 200 microM metamitron or 25 microM terbuthylazine) during three hours under natural light. After 30 minutes of dark adaptation, photosynthesis yield was measured with Pocket PEA (Hansatech Instruments). In Leaves from sensitive C. album, herbicide treatment reduces photosynthesis yield due to inhibition of photosynthesis at photosystem II. This results in a difference of photosynthesis yield between the untreated control and herbicide treatment. Based on the relative photosynthesis yield (as a percentage of untreated), a classification rule was formulated: C. album is classified as sensitive when its relative photosynthesis yield is less than 90%, otherwise it is resistant. While metribuzin, and to a lesser extent, metamitron treatment allowed a quick detection of triazinone resistant C. album, terbuthylazine treatment was able to distinguish the Ser264-Gly from the Ala251-Val biotype. As a final test, 265 plants were classified with the protocol. Simultaneously, a CLeaved Amplified Polymorphic Sequence (CAPS)-analysis was conducted on the same plants to verify the presence of the Ser264-Gly mutation. Only one mismatch was found when results of both detection methods were compared. The test results illustrate that this protocol provides a reliable, quick and cheap alternative for DNA-analysis and bio-assays to detect the triazinone resistant C. album biotypes.

Topics: Beta vulgaris; Chenopodium album; Chlorophyll; Fluorescence; Herbicide Resistance; Herbicides; Mutation; Photosynthesis; Photosystem II Protein Complex; Triazines; Weed Control

Recently, fat-hen (Chenopodium album L.) biotypes resistant to metamitron, a key herbicide in sugar beet, were recorded. Pot experiments revealed that these biotypes showed cross-resistance to metribuzin, a triazinone used in potato. Greenhouse and laboratory experiments were performed to develop resistance monitoring tests, so that resistant biotypes can be detected quickly and farmers may adapt their weed management. Resistant and susceptible biotypes were grown in a greenhouse under conditions of natural and artificial light at an intensity of 100 micromol photons m(-2) s(-1). Leaves were collected and, immersed in a solution of 1000 microM metamitron and 500 microM metribuzin, exposed to natural and artificial light (1000, 750 and 100 micromol photons m(-2) s(-1) respectively). After this, chlorophyll fluorescence measurements were carried out. The results revealed that the photosynthetic electron transport of metamitron- and metribuzin-incubated leaves of resistant biotypes decreased less than that of the incubated Leaves of susceptible biotypes. The differences between the metribuzin-incubated leaves of the susceptible and resistant biotypes were larger than those observed with the metamitron-incubated leaves. The aim of the experiments was to optimise the chlorophyll fluorescence test and to find a sufficiently high correlation between the results of the pot experiments and the chlorophyll fluorescence measurements.

Topics: Chenopodium album; Chlorophyll; Fluorescence; Herbicide Resistance; Herbicides; Pest Control; Triazines

While surveying Illinois Amaranthus tuberculatus (Moq) Sauer (tall waterhemp) half-sib populations for herbicide response variability, several were observed to segregate for resistance to atrazine. Studies were conducted on greenhouse-grown A tuberculatus plants to compare atrazine responses among populations that were segregating for resistance (SegR), uniformly sensitive (UniS) or uniformly resistant (UniR). In chlorophyll fluorescence assays, leaves of plants from the SegR and UniS populations displayed changes in fluorescence after treatment with atrazine, indicating that atrazine was inhibiting electron transport of photosystem II in chloroplasts. Sequencing of a fragment of psbA, which encodes the D1 protein, revealed that the SegR population did not contain the amino acid substitution that is typically found in triazine-resistant plants. Whole-plant herbicide dose-response experiments revealed that, relative to the UniS population, atrazine resistances in the UniR and SegR populations were > 770-fold and 16-fold, respectively. The SegR population was also resistant to cyanazine (59-fold), but not to metribuzin, linuron or pyridate. Triazine resistance in the SegR population was shown to be a nuclear inherited trait, unlike maternal inheritance of site-of-action mediated triazine resistance found in the UniR population. Taken collectively, these findings confirm the existence of two distinct triazine resistance mechanisms in A tuberculatus.

Topics: Amaranthus; Amino Acid Substitution; Atrazine; Chlorophyll; Dose-Response Relationship, Drug; Drug Resistance; Electron Transport; Herbicides; Linuron; Photosystem II Protein Complex; Polymorphism, Single Nucleotide; Pyridazines; Triazines