Eleusine indica is one of the most common weed species found in agricultural land worldwide. Although herbicide-glyphosate provides good control of the weed, its frequent uses has led to abundant reported cases of resistance. Hence, the development of genetic markers for quick detection of glyphosate-resistance in E. indica population is imperative for the control and management of the weed. In this study, a total of 14 specific random amplified polymorphic DNA (RAPD) markers were identified and two of the markers, namely S4R727 and S26R6976 were further sequence characterized. Sequence alignment revealed that marker S4R727 showing a 12-bp nucleotides deletion in resistant biotypes, while marker S26R6976 contained a 167-bp nucleotides insertion in the resistant biotypes. Based on these sequence differences, three pairs of new sequence characterized amplified region (SCAR) primers were developed. The specificity of these primer pairs were further validated with genomic DNA extracted from ten individual plants of one glyphosate-susceptible and five glyphosate-resistant (R2, R4, R6, R8 and R11) populations. The resulting RAPD-SCAR markers provided the basis for assessing genetic diversity between glyphosate-susceptible and -resistant E. indica biotypes, as well for the identification of genetic locus link to glyphosate-resistance event in the species.
Herbicide resistance is a worldwide problem in weed control. This prompts researchers to look for new modes of action to slow down the evolution of herbicide-resistant weeds. This research aims to determine the herbicidal action of thiazolo[3,2-a]pyrimidines derivatives, which are well known as antihypertensive drugs. The phytotoxic effects of ten compounds were investigated using leaf disc discoloration test and seed germination bioassay. At concentrations of 125 to 250 mg/L, the 5-(3-Fluoro-phenyl)-7-methyl-5H-thiazolo[3,2-a]pyrimidine-6-carboxylic acid ethyl ester (c) was highly active against Oldenlandia verticillata and Eleusine indica. At application rates of 1.25 to 2.5 kg ai/ha, formulated c demonstrated selective post-emergence and pre-emergence herbicidal activity against O. verticillata, E. indica and Cyperus iria. In the crop tolerance test, formulated c outperformed the commercial herbicide diuron, with aerobic Oryza sativa being the most tolerant, followed by Zea mays, and Brassica rapa. The addition of calcium chloride partially nullified compound c's inhibitory effects on weed shoot growth, indicating that it has potential as a calcium channel blocker. Compound c acted by triggering electrolyte leakage without affecting photosystem II. These findings imply that c could be explored further as a template for developing new herbicides with novel modes of action.
Eleusine indica (goosegrass) populations resistant to fluazifop, an acetyl-CoA carboxylase (ACCase: EC6.4.1.2)-inhibiting herbicide, were found in several states in Malaysia. Dose-response assay indicated a resistance factor of 87.5, 62.5 and 150 for biotypes P2, P3 and P4, respectively. DNA sequencing and allele-specific PCR revealed that both biotypes P2 and P3 exhibit a single non-synonymous point mutation from TGG to TGC that leads to a well known Trp-2027-Cys mutation. Interestingly, the highly resistant biotype, P4, did not contain any of the known mutation except the newly discovered target point Asn-2097-Asp, which resulted from a nucleotide change in the codon AAT to GAT. ACCase gene expression was found differentially regulated in the susceptible biotype (P1) and highly resistant biotype P4 from 24 to 72h after treatment (HAT) when being treated with the recommended field rate (198gha(-1)) of fluazifop. However, the small and erratic differences of ACCase gene expression between biotype P1 and P4 does not support the 150-fold resistance in biotype P4. Therefore, the involvement of the target point Asn-2097-Asp and other non-target-site-based resistance mechanisms in the biotype P4 could not be ruled out.