Gamma Radiation Induced In-Vitro Mutagenesis and Isolation of Mutants for Early Flowering and Phytomorphological Variations in Dendrobium 'Emma White'.

In vitro mutagenesis offers a feasible approach for developing new orchid cultivars through genetic manipulation. In the present study, protocorm-like bodies (PLBs) were exposed to gamma rays (10, 20, 40, 60, 80 Gy) to study in vitro growth responses and induction of mutants in Dendrobium 'Emma White'. Both proliferation and regeneration of PLBs decreased progressively with increasing doses, except for a significantly enhanced growth response at 10 Gy. The optimal dose of gamma radiation for mutagenesis was found in the range 10 to 25 Gy based on the growth reduction curve. Analysis using a high-throughput cell analyzer revealed a significant reduction in nuclear DNA content at > 40 Gy doses. At 10 Gy treatment, the growth attributes, such as root length, plant height and leaf number, were significantly increased by 36%, 26% and 20%, respectively, compared to the control. This increase was significant over other tested doses as well. Testing of random amplified polymorphic DNA markers revealed the presence of detectable polymorphism among gamma mutant plantlets with a polymorphism information content value at 0.41. The gamma-ray-induced earliness in flower development was observed within 294 days post ex vitro growth of 10 Gy mutant compared to the control plants flowered after 959 days. Our results highlight the significance of gamma radiation in inducing enhanced growth, morphological variations and early floral initiation in Dendrobium, providing a basic framework for mutation breeding and improvement of orchids.

First De novo whole genome sequencing and assembly of mutant Dendrobium hybrid cultivar 'Emma White'.

The Dendrobium hybrid cultivar 'Emma White' is an ornamental, successfully commercialised orchid. We used a gamma ray-induced early flowering mutant and the Illumina HiSeqX10 sequencing platform to generate the first draft de novo whole genome sequence and assembly. The draft sequence was 678,650,699 bp in length, comprising 447,500 contigs with an N50 of 1423 and 33.48% GC content. Comparing 95,529 predicted genes against the Uniprot database revealed 60,741 potential genes governing molecular functions, biological processes and cellular components. We identified 216,232 simple sequence repeats and 138,856 microsatellite markers. Chromosome-level genome assembly of Dendrobium huoshanense was used to RagTag-scaffold available contigs of the mutant, revealing a total length of 687,254,899 bp with an N50 of 2096. The longest final contiguous length was 18,000,059 bp from 30,571 bp. BUSCO genome completeness was 93.6%. This study is valuable for investigating the mechanisms of mutation, and developing Dendrobium hybrid cultivars using mutation breeding.

Genetic analyses for deciphering the status and role of photoperiodic and maturity genes in major Indian soybean cultivars.

Allelic combinations of major photoperiodic (E1, E3, E4) and maturity (E2) genes have extended the adaptation of quantitative photoperiod sensitive soybean crop from its origin (China ∼35◦N latitude) to both north (up to ∼50◦N) and south (up to 40◦S) latitudes, but their allelic status and role in India (6-35◦N) are unknown. Loss of function and hypoactive alleles of these genes are known to confer photoinsensitivity to long days and early maturity. Early maturity has helped to adapt soybean to short growing season of India. We had earlier found that all the Indian cultivars are sensitive to incandescent long day (ILD) and could identify six insensitive accessions through screening 2071 accessions under ILD. Available models for ILD insensitivity suggested that identified insensitive genotypes should be either e3/e4 or e1 (e1-nl or e1-fs) with either e3 or e4. We found that one of the insensitive accessions (EC 390977) was of e3/e4 genotype and hybridized it with four ILD sensitive cultivars JS 335, JS 95-60, JS 93-05, NRC 37 and an accession EC 538828. Inheritance studies and marker-based cosegregation analyses confirmed the segregation of E3 and E4 genes and identified JS 93-05 and NRC 37 as E3E3E4E4 and EC 538828 as e3e3E4E4. Further, genotyping through sequencing, derived cleaved amplified polymorphic sequences (dCAPS) and cleaved amplified polymorphic sequences (CAPS) markers identified JS 95-60 with hypoactive e1-as and JS 335 with loss of function e3-fs alleles. Presence of photoperiodic recessive alleles in these two most popular Indian cultivars suggested for their role in conferring early flowering and maturity. This observation could be confirmed in F2 population derived from the cross JS 95-60 × EC 390977, where individuals with e1-as e1-as and e4e4 genotypes could flower 7 and 2.4 days earlier, respectively. Possibility of identification of new alleles ormechanism for ILD insensitivity and use of photoinsensitivity in Indian conditions have been discussed.