Production of haploids of neem (Azadirachta indica A. Juss.) by anther culture

In vitro production of doubled haploid plants in Camellia spp. and assessment of homozygosity using microsatellite markers

In this report, in vitro doubled haploid (DH) plants were established in two tea (Camellia spp) cultivars, TV21 (Assam Type) and TV19 (Cambod Type). Androgenic globular stage haploid embryos, obtained via callusing from microspores at an early-to-late uninucleate stage in anther cultures, were diploidized by colchicine treatments at varying concentrations and durations under dark incubation at 25 ± 2 °C temperature. Thereafter, treated embryos were transferred to development medium, Murashige and Skoog (MS) medium supplemented with 6-benzylaminopurine (BAP; 1 μM) + gibberellic acid (GA₃; 0.3 μM) + L-glutamine (80 mg l^-1) + L-serine (20 mg l^-1) and incubated in diffused light. Ploidy of germinating embryos was evaluated by flow-cytometry and cytological squash preparation. High chromosome doubling, 76.89% and 67.34%, was obtained in embryos of TV21 and TV19, respectively, at 0.2% colchicine treatment for 24 h. The DH plants were further multiplied via axillary-bud proliferation on multiplication medium, MS + glucose (30 g l^-1) + BAP (5 μM) + GA₃ (0.5 μM) + IBA (0.5 μM) + L- glutamine (80 mg l^-1) + L-serine (20 mg l^-1). Rooting of shoots was achieved on ⅓ MS basal medium within 50 days of inoculation when shoots were pre-treated with IBA (175 μM) for ten days. The rooted plants were acclimatized in field. Homozygosity in diploidized plants was validated by SSR marker.

Generation of doubled haploids in cauliflower

Hybrids of cauliflower are in high demand world over due to their high yield potential, earliness, better quality, better resistance to biotic and abiotic stresses. Conventionally, hybrids are developed from the intercrossing of two diverse inbred parental lines which are developed through continuous inbreeding for 8-10 generations and still don't attain complete homozygosity. Doubled haploid technology on the other hand generate completely homozygous inbred lines in a single step. Therefore, a study was undertaken at Punjab Agricultural University, Ludhiana, to develop a protocol for the development of doubled haploid lines in cauliflower. The anthers were excised from the flower buds of different genotypes viz. Jyoti, Pusa Sharad, Kartiki, CAUMH-2, CAUMH-10, LS-2, LS-3, and LS-5 followed by their culture on five different callus induction media compositions. Genotypes differed significantly in the ability to induce callus which was maximum in Jyoti followed by LS-2. Different media compositions also varied significantly in callus induction efficiency which was maximum on MS media+1.5 mg/L 2,4-D +1.0 mg/L NAA. Maximum shoot regeneration was recorded in genotype Kartiki followed by LS-2 when cultured on MS media+3.0 mg/L BAP+2.0 mg/L Kin. The regenerated shoots thus obtained were rooted on ½ MS media +1.0 mg/L IBA. Ploidy analysis of root tips revealed that 22.2% of the regenerated plantlets were haploids, 27.8% were spontaneous doubled haploids, 16.7% were tetraploids and remaining 33.3% were mixoploids.

Species with Haploid or Doubled Haploid Protocols

In this chapter, we present a list of species (and few interspecific hybrids) where haploids and/or doubled haploids have been published, including the method by which they were obtained and the corresponding references. This list is an update of the compilation work of Maluszynski et al. published in 2003, including new species for which protocols were not available at that time, and also novel methodologies developed during these years. The list includes 383 different backgrounds. In this book, we present full protocols to produce DHs in 43 of the species included in this list. In addition, this book includes a chapter for one species not included in the list. This makes a total of 384 species where haploids and/or DHs have been reported up to date.

Enhancement of androgenesis by abiotic stress and other pretreatments in major crop species

Rapid production of doubled haploids (DHs) through androgenesis is an important and promising method for genetic improvement of crop plants. Through androgenesis complete homozygous plants can be produced within a year compared to long inbreeding methods that may take several years and costly. Significant advantage of androgenesis is that it not only speeds up the process to achieve homozygosity, but also increases the selection efficiency. Though success in androgenesis has been achieved in many crop plants, yet there are certain limitations especially, low frequency of embryogenesis and regeneration in few species. In fact in many cereals, induction of embryos and regeneration of green plants is still a hurdle that one needs to overcome to improve the efficiency of androgenesis. Efficient androgenesis is usually induced by the successful application of different stress pretreatment. Since so many stress factors can trigger the reprogramming of microspores and that have been co-related to change the ultrastuctural changes of cells to embryos and finally haploid plants. It has been shown that certain pretreatment such as (i) physical stresses as cold, heat shock, starvation, drought stress, osmotic pressure, gamma irradiation, oxidative stress, reduced atmospheric pressure, and (ii) chemical treatments such as colchicine, heavy metal, ABA, CGA, AEC, Azetidine, 2-NHA, either individual or combined effect of more than one stress factors may positively influence androgenetic efficiency. This review highlights the recent and past work on uses of various abiotic stresses and pretreatments and their impact on enhancing the efficiency of androgenesis on some major crop species for the development of doubled haploid plants.

Increased production of azadirachtin from an improved method of androgenic cultures of a medicinal tree Azadirachta indica A. Juss

Present report is the first direct evidence of azadirachtin production in androgenic haploid cultures of Azadirachta indica, a woody medicinal tree. Anther cultures at early-late-uninucleate stage of microspores were established on MS medium with BAP (5 μM), 2,4-D (1 μM) and NAA (1 μM) containing 12% sucrose. The calli, induced, were further multiplied on 2,4-D and Kinetin media. Shoots, differentiated on BAP (2.2 μM) + NAA (0.05 μM) medium, were elongated on MS + BAP (0.5 μM) and multiplied on MS + BAP (1 μM) + CH (250 mg/l). Thereafter, the shoots were rooted on ¼ MS + IBA (0.5 μM). Cytological analysis of the calli and regenerants have confirmed their haploid status with the chromosome number as 2n = x = 12. The haploid cell lines and leaves from in vitro grown plantlets were analyzed for azadirachtin by RP-HPLC and mass spectroscopy. Maximum azadirachtin (728.41 μg/g DW) was detected in calli supporting best shoot proliferation while least (49 μg/g DW) was observed in an undifferentiated line from maintenance medium. This study has brought us a step closer to develop genetically pure lines that could serve as new and attractive alternative ways of homogeneous controlled production of high value compounds, round the year, independent of geographical and climatic barrier.

In vitro androgenesis in tree species: an update and prospect for further research

Most, if not all, trees are outbreeding, highly heterozygous and undergo a long developmental period before reaching their reproductive stage. Classical breeding and cross-pollinating procedures are both unpredictable and time-consuming. In vitro androgenesis is, thus, the most prolific and desirable approach of haploid production. But various attempts to induce androgenic potential in the trees have met with rather limited success, as they ought to be extremely recalcitrant in culture. The success rate in this case is nowhere close to that achieved for some model species like Brassica and Nicotiana. Our review article intends to focus on the overview of androgenic process and all the major contributions till date on tree species with regard to this aspect. We wish to bring together in one place all the important variables used by different workers, that influence androgenic potential immensely like, stage of anther or microspore at culture, media composition, combinations and concentrations of growth regulators, and additives. This will prove to be a worthy guide to all the prospective workers in this area and in designing their experiments further.