Absorption and Translocation of [14c]2,4-Dichlorophenoxyacetic Scid in Herbicide-tolerant Chromosome Substitution Lines of Gossypium Hirsutum L.

Upland cotton is sensitive to 2,4-dichlorophenoxyacetic acid (2,4-D), and the identification of potentially 2,4-D tolerant cotton chromosome substitution (CS) lines and understanding tolerance mechanisms provide a significant step into the development and genetic improvement of upland cotton to reduce yield loss caused by 2,4-D herbicide effects including the drifts. Experiments were conducted to understand the possible mechanism of herbicide tolerance in CS-T04-15, CS-T07, and CS-B15sh, 2,4-D herbicide-tolerant cotton CS lines compared with TM-1, the 2,4-D herbicide susceptible recurrent parent of the CS line as control, using [14C]2,4-D. Percent absorption rate and translocation patterns of the 14C-labeled herbicide application at 5.17 kBq at 6 to 48 hours after treatment (HAT) were determined. The tolerant cotton CS lines showed 15-19% [14C]2,4-D uptake while TM-1 exhibited a reduced uptake of only 1.4% [14C]2,4-D at 24 HAT. Distribution of the absorbed [14C]2,4-D showed that 2-5% was translocated outside the treated leaf. In TM-1, 77% of the herbicide was translocated above and below the treated leaf, contrasting with the reduced translocation of 14C-labeled herbicide observed in the tolerant CS lines. Interestingly, CS-T04-15 showed a restricted movement of 14C below the treated leaf at 6 to 48 HAT, suggesting a novel mechanism of herbicide tolerance. This finding is the first report on upland cotton demonstrating a complex differential uptake and translocation associated with herbicide tolerance for [14C]2,4-D in cotton CS lines.

Induced variation for post-emergence herbicide tolerance in lentil.

Lentil (Lens culinaris L. Medik.) is an important cool-season food legume but is a poor competitor to weeds because of a slow early growth rate. If weeds are left uncontrolled, they can reduce yield by up to 50%. Sensitivity of lentil to post-emergence herbicides warrants development of herbicide-tolerant cultivars. In the absence of natural variability, mutation breeding is a powerful tool to create variability for desired traits. Thus, 1000 seeds of a lentil genotype, LL1203, were exposed to gamma radiation (300 Gy, 60Co) with the objective to induce herbicide tolerance. Seeds of all 530 surviving M1 plants were harvested individually and divided in two parts to raise the M2 generation in two different plots. Each plot was sprayed with imazethapyr (75 g/ha) and metribuzin (250 g/ha) herbicides 50 days after sowing, using water at 375 l/ha. Data on herbicide tolerance for individual M2 plants were recorded after 14 days of herbicide spray on a 1-5 scale, where 1 = highly tolerant (plants free from chlorosis or wilting) and 5 = highly sensitive (leaves and tender branches completely burnt). For herbicide-tolerant M2 plants, data were also recorded for pod and yield per plant. None of the M2 plants showed a high level of tolerance to imazethapyr. However, 14 mutants having higher herbicide tolerance to metribuzin were selected. Two mutants ('LL1203-MM10', 'LL1203-MM7') recorded < 2.0 score, while six mutants recorded < 2.50 score as compared with the 3.13 score of the parent variety. The pods per plant and seed yield per plant of mutants 'LL1203-MM7' (383 and 12.4 g) and 'LL1203-MM10' (347 and 12.1 g) were higher than those of the parent genotype LL1203 (253 and 7.8 g). The study indicated that metribuzin-tolerant mutants have some other desirable traits that can be of use in lentil breeding.

National repository of EMS induced mutants of an upland rice cultivar Nagina 22: progress update on characterization and utilization.

The Indian initiative for creating mutant resources in rice has generated 87,000 mutants in the background of a popular drought- and heat-tolerant upland cultivar, Nagina 22 (N22), through EMS mutagenesis. So far, 541 macro-mutants from this resource have been identified, maintained in the mutant garden and characterized in detail based on 44 descriptors pertaining to distinctness, uniformity and stability (DUS) of rice and other agronomic parameters. The similarity index of the mutants was more than 0.6 for nearly 90% of the mutants with respect to DUS descriptors, further establishing the validity of the mutants. The available high-quality sequence resource of N22 has been improved by reducing the gaps by 0.02% in the coding sequence (CDS) region. This was made possible using the newly synthesized whole-genome data of N22 which helped to remove 9006 'Ns' and replace 12,746 existing nucleotides with the accurate ones. These sequence and morphological details have been updated in the mutant database 'EMSgardeN22'. Further, 1058 mutants have been identified for low-P tolerance, tolerance to sheath blight, blast, drought, heat, higher photosynthetic efficiency and agronomic and root traits from this resource. A novel herbicide-tolerant (imazethapyr) mutant earlier identified and characterized from this resource is now being used in introgressing the herbicide-tolerant trait in eight major rice varieties in India. Further, robust and simpler screening systems have been tested for studying low-P tolerance of the mutants. A grain-size mutant, heat-tolerant mutant, drought-tolerant mutant, stay-green mutant and low-P tolerant and water-use efficient high-root-volume mutants have been characterized at morphological and molecular levels. A brief account of all these mutants, the entire mutant resource and the elaborate trait-based screenings is presented in this chapter.