Optimization of chromosome doubling treatment for efficient in vivo doubled haploid production in maize

An investigation to optimize the protocol for application of colchicine for enhancing the doubled haploid production in maize was done. 106 maize genotypes were used as maternal parents, whereas, pollen source involved tropically adopted haploid inducer (TAIL P1 and TAIL hybrid). After the elimination of chromosomes of inducer lines, haploid seeds were obtained from the crosses. Haploid seedlings were treated with three different doses, such as 0.04, 0.06 and 0.08 per cent of colchicines for different durations (8, 12 and 15 hours). The response of various colchicine concentrations applied for different time durations revealed significant differences at P ≤ 0.05 for various parameters viz., per cent plants survivability, stalk colour, the fertility of tassel, silk present/absent, pollen viability, seed set and per cent doubled haploid formation. In maize, colchicine doses of 0.04 per cent for 12 hours and 0.06 per cent for 8 hours, respectively were established as optimum for enhanced doubled haploid production. But among these two, 0.04 per cent for 12 hours was observed to be best dose for doubled haploid production in maize.

Development of late temperate in vivo haploid inducers

In vivo doubled haploid technique has been widely used in advanced maize breeding programs due to cost, labor and time advantages and increase in efficiency. However, the number of available inducer lines in the world is sufficient. Six BC1 breeding populations including RWS and RWK-76 haploid inducer lines and late temperate ADK-451, ADK-737 and ADK-455 lines were developed by Sakarya Maize Research Institute (MRI) in Turkey. The RWS and RWK-76 haploid inducer lines were used as donors. Pedigree method was employed to develop the inducer lines. Anthocyanin coloration of plant, tassel length, branch number of tassel, plant height, days to flowering, embryo-endosperm colorfulness and haploid induction rate (HIR) were determined. The genotypes with the best characteristics were selected. The families from BC1F3 to BC1F7 were hybridized to liguleless line to determine the HIR and families with HIR over 8% were selected from BC1 populations. The HIR, plant height and days to tassel flowering values of in-1021 and in-1076 candidate haploid inducer lines were 10.5 and 12.3%, 195 and 200 cm, and 69 and 68 days, respectively. The HIR value of RWS donor haploid inducer ranged from 8.9 to 11.3% and for RWK-76 from 7.3 to 9.8%. Simple Sequence Repeats (SSRs) markers were used to identify genetic similarity between late temperate haploid inducer lines and donors. The similarity rates of in-1021 and in-1076 inducer lines to the RWS donor were 38 and 15%, and to the RWK-76 donor were 23 and 27%. The similarity rate between the two candidate inducer lines was 30%. The results indicated that the late temperate haploid inducer lines developed will increase the efficiency of maize breeding.

Rare instances of haploid inducer DNA in potato dihaploids and ploidy-dependent genome instability

In cultivated tetraploid potato, reduction to diploidy (dihaploidy) allows hybridization to diploid germplasm, introgression breeding, and may facilitate the production of inbreds. Pollination with haploid inducers yields maternal dihaploids, as well as triploid and tetraploid hybrids. It is not known if dihaploids result from parthenogenesis, entailing development of embryos from unfertilized eggs, or genome elimination, entailing missegregation and loss of paternal chromosomes. A sign of genome elimination is the occasional persistence of haploid inducer DNA in some of the dihaploids. We characterized the genomes of 1,001 putative dihaploids and 134 hybrids produced by pollinating tetraploid clones with three haploid inducers, IVP35, IVP101, and PL4. We detected inheritance of full or partial chromosomes from the haploid inducer parent in 0.87% of the overall dihaploid progeny, irrespective of the combination of parental genotypes. Chromosomal breaks commonly affected the paternal genome in the dihaploid and tetraploid progeny, but not in the triploid progeny. Residual haploid inducer DNA is consistent with genome elimination as the mechanism of haploid induction. Further, the fact that paternal chromosome breaks are specific to dihaploids and tetraploid progeny suggests that they may be specific to 2x sperms, and supports the hypothesis that 2x sperms facilitate genome elimination.

Doubled haploid production in maize under Sub-montane Himalayan conditions using R1-nj-based haploid inducer TAILP1

The use of in vivo haploid induction system makes the doubled haploid (DH) technology easier to adopt for the conventional maize breeders. However, despite having played an important role in the initial developmental phases of DH technology, Indian maize research has yet to harvest its benefits. Haploid Inducer Lines (HILs) developed by CIMMYT are being widely used in maize breeding programmes in many countries including India. There, however, is no published information on the efficiency of DH line production using CIMMYT HILs in Indian maize breeding programmes. In the present study, the efficiency of DH production using CIMMYT’s tropically adapted inducer line TAILP1 was investigated with eight source populations including two of sweet corn. The average haploid induction rate (HIR) of TAILP1 was 5.48% with a range of 2.01 to 10.03%. Efficiency of DH production ranged from 0.14 to 1.87% for different source populations with an average of 1.07%. The information generated will be useful for maize breeders intending to use DH technology for accelerated development of completely homozygous lines.