Changes in the Activities of Protective Enzymes Induced by Mepiquat Chloride (DPC) in Cotton to Defend Against Aphids

Background: Mepiquat chloride (DPC) enhances the resistance of cotton plants, and it is widely used as a growth regulator. DPC can stimulate photosynthesis, stabilize the structure of cotton leaves, and affect population reproduction and energy substances in cotton aphids, but interactions between DPC and cotton aphids remain unclear. In this study, we analyzed the physiological responses of cotton to DPC, and the toxicity of DPC toward cotton aphids, before and after feeding, to explore the DPC-induced defense mechanism against cotton aphids.Results: Measurements of protective enzyme activity in cotton showed that the soluble protein contents, peroxidase (POD) activity, and catalase (CAT) activity in cotton treated with different concentrations of DPC were higher than in the control. Superoxide dismutase (SOD) activity was higher than that of controls when the concentration of DPC was <0.1 g/L. Under aphid stress, POD activity of cotton treated with a low insect population density was significantly lower than that of controls, but the reverse was true for cotton treated with a high insect population density, and SOD activity was positively correlated with population density. The activities of detoxification enzymes in field and laboratory experiments showed that DPC promoted the specific activity of glutathione S-transferase (GST) in cotton aphids, while the specific activities of carboxylesterase and acetylcholinesterase were decreased.Conclusions: DPC enhanced the resistance of cotton by increasing the activity of protective enzymes. It also had a toxic effect on cotton aphids by increasing GST activity (the main DPC target) and lowering carboxylesterase and acetylcholinesterase activities. DPC increased the soluble protein content and SOD activity in cotton under aphid stress, and thereby enhanced tolerance to cotton aphids.

Impact of Exogenous Plant Growth Regulators on Physiological Traits, Tendril and Flowering in Horsegram (Macrotyloma uniflorum Lam) under Kharif Season

Background: Horsegram is an important pulse crop grown as Rabi crop in Tamil Nadu. Kharif sown crop could not flowers may be because of more number of tendrils produced as compare to Rabi sown crop. Hence, an attempt was made to reduce the number of tendrils and induce flowering in horsegram during Kharif season by plant growth regulators. Methods: A field experiment was conducted to study the impact of plant growth regulators viz., salicylic acid (100 ppm), chlormequat chloride (CCC - 250 ppm), mepiquat chloride (250 ppm), tri iodo benzoic acid (TIBA - 200 ppm) and nitrobenzene (0.2%) on physiological traits and tendril growth associated with flowering in horsegram during Kharif. Different treatments were applied through foliar application at 25 Days after sowing. Result: Among the PGRs, foliar application of TIBA registered the lowest number of tendrils (2.3) followed by CCC (3.0) compared to other treatments. Higher root length of 16.8 cm and RWC of 82.3% was found in CCC treatment. CCC also registered the highest photosynthetic rate (27.15 µmol m-2 s-1), transpiration rate (18.06 mmol m-2 s-1) and lowest leaf temperature (26°C) compared to other treatments. The highest soluble protein content of 13.1 mg g-1 was also estimated in CCC treatment followed by mepiquat chloride (12.51 mg g-1). Sucrose phosphate synthase (SPS) activity did not show any significant difference between the treatments. Number of flowers buds formed per plant was zero and hence the flowering did not take place in any treatments. Among the plant growth regulators used, TIBA and CCC registered its positive action on reduced the number of tendrils and leaf temperature, but not enough to induce flowering under Kharif season.

Effect of Storage Methods, Covering and Spraying Treatments of Sugar Beet Roots During Storage Periods on Quality Characters of Roots

A research experiment was conducted after sugar beet harvesting season of 2018/2019 to study the losses in sugar beet roots quality after harvesting and reducing it by using different storage methods (storage roots in shadow and open air), covering (without, covering with rice straw, sugar beet foliages and net) and spraying treatments (without, spraying with tap water and Mepiquat chloride at the rates of 0.5, 1.0 and 1.5 cm/L) during storage periods (one, two, three and four weeks from beginning the study) under environmental conditions of Dakahlia Governorate, Egypt. The experiment was carried out in factorial experiment in randomized complete blocks design with three replicates. Stored sugar beet roots in piles under shading net conditions indexed the highest sucrose and quality percentages and lowest K, Na and alfa amino nitrogen percentages in roots. The highest sucrose and quality percentages and lowest K, Na and alfa amino nitrogen percentages in roots were obtained by covering sugar beet piles with sugar beet foliages. The highest sucrose and quality percentages and lowest K, Na and alfa amino nitrogen percentages in roots were resulted when spraying piles before storage with Mepiquat chloride at 1.0 cm/L. It can be concluded that stored sugar beet roots after harvesting directly in piles under shading and covering with beet foliages and spraying piles with Mepiquat chloride at 1.0 cm/L to reduce losses in sugar beet roots quality after harvesting and during storage and achieve high quality characters of roots under the environmental conditions of Dakahlia Governorate, Egypt.

​Defoliants Harvest-aid Chemicals: Cost Effective Technology to Facilitate Synchronized Maturity for Mechanical Harvesting in Cotton: A Review

In the recent years, increasing labour cost and shortage of labour being the major constraints to follow manual harvesting in cotton in staggered manner. Further, it is very expensive and farmers would like to increasingly opt for mechanical harvesting. In this context, it is suggested that research should focus to reduce cost of cultivation substantially by promoting the use of synchronized maturity in cotton and use of defoliants to encourage mechanical harvesting. In agriculture, defoliants are used to eliminate the leaves of a crop plant so that they do not interfere with the harvesting by machinery. Early harvesting with good boll opening can also be achieved by use of defoliants. The use of defoliants also reduces the trash content in picked cotton which will also help in improving the quality of cotton. There is a need to identify suitable defoliant with suitable dose and time of application so as to facilitate mechanical harvesting in rainfed cotton. Some of the successful defoliants for uniform boll bursting and higher yield of cotton such as rthrel, rthepon, mepiquat chloride (MC), sodium salt and DU (Dropp Ultra) are the hormonal defoliants and TDZ thidiazuron butifos, merphos, tribufos and tribufate are the herbicidal defoliants. The best combination of thidiazuron + diuron (DCMU), pyraflufen ethyl, thidiazuron + diuroncellular isozyme, Ethephon + AMADS, ethephon + cyclanilide ethephon + tribufos Mepiquat chloride (MC) + cyclanilide may be recommended to facilitate mechanical harvesting in cotton.

Profiling of MicroRNAs Involved in Mepiquat Chloride-Mediated Inhibition of Internode Elongation in Cotton (Gossypium hirsutum L.) Seedlings

Mepiquat chloride (MC) is the most important plant growth retardant that is widely used in cotton (Gossypium hirsutum L.) production to suppress excessive vegetative growth and improve plant architecture. MicroRNAs (miRNAs) are important gene expression regulators that control plant growth and development. However, miRNA-mediated post-transcriptional regulation in MC-induced growth inhibition remains unclear. In this study, the dynamic expression profiles of miRNAs responsive to MC in cotton internodes were investigated. A total of 508 known miRNAs belonging to 197 families and five novel miRNAs were identified. Among them, 104 miRNAs were differentially expressed at 48, 72, or 96 h post MC treatment compared with the control (0 h); majority of them were highly conserved miRNAs. The number of differentially expressed miRNAs increased with time after treatment. The expression of 14 known miRNAs was continuously suppressed, whereas 12 known miRNAs and one novel miRNA were continuously induced by MC. The expression patterns of the nine differentially expressed miRNAs were verified using qRT-PCR. The targets of the known and novel miRNAs were predicted. Four conserved and six novel targets were validated using the RLM-5′ RACE assay. This study revealed that miRNAs play crucial regulatory roles in the MC-induced inhibition of internode elongation. It can improve our understanding of post-transcriptional gene regulation in MC-mediated growth inhibition and could potentially facilitate the breeding of dwarf cotton.

Global transcriptome changes of elongating internode of sugarcane in response to mepiquat chloride

Background Mepiquat chloride (DPC) is a chemical that is extensively used to control internode growth and create compact canopies in cultured plants. Previous studies have suggested that DPC could also inhibit gibberellin biosynthesis in sugarcane. Unfortunately, the molecular mechanism underlying the suppressive effects of DPC on plant growth is still largely unknown. Results In the present study, we first obtained high-quality long transcripts from the internodes of sugarcane using the PacBio Sequel System. A total of 72,671 isoforms, with N50 at 3073, were generated. These long isoforms were used as a reference for the subsequent RNA-seq. Afterwards, short reads generated from the Illumina HiSeq 4000 platform were used to compare the differentially expressed genes in both the DPC and the control groups. Transcriptome profiling showed that most significant gene changes occurred after six days post DPC treatment. These genes were related to plant hormone signal transduction and biosynthesis of several metabolites, indicating that DPC affected multiple pathways, in addition to suppressing gibberellin biosynthesis. The network of DPC on the key stage was illustrated by weighted gene co-expression network analysis (WGCNA). Among the 36 constructed modules, the top positive correlated module, at the stage of six days post spraying DPC, was sienna3. Notably, Stf0 sulfotransferase, cyclin-like F-box, and HOX12 were the hub genes in sienna3 that had high correlation with other genes in this module. Furthermore, the qPCR validated the high accuracy of the RNA-seq results. Conclusion Taken together, we have demonstrated the key role of these genes in DPC-induced growth inhibition in sugarcane.