Embryogenesis and plant regeneration of pakchoi (Brassica rapa L. ssp. chinensis) via in vitro isolated microspore culture

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.

Quantitative Trait Loci (QTLs) Associated with Microspore Culture in Raphanus sativus L. (Radish)

The radish is a highly self-incompatible plant, and consequently it is difficult to produce homozygous lines. Bud pollination in cross-fertilization plants should be done by opening immature pollen and attaching pollen to mature flowers. It accordingly takes a lot of time and effort to develop lines with fixed alleles. In the current study, a haploid breeding method has been applied to obtain homozygous plants in a short period of time by doubling chromosomes through the induction of a plant body in the haploid cells, in order to shorten the time to breed inbred lines. We constructed genetic maps with an F1 population derived by crossing parents that show a superior and inferior ability to regenerate microspores, respectively. Genetic maps were constructed from the maternal and parental maps, separately, using the two-way pseudo-testcross model. The phenotype of the regeneration rate was examined by microspore cultures and a quantitative trait loci (QTL) analysis was performed based on the regeneration rate. From the results of the culture of microspores in the F1 population, more than half of the group did not regenerate, and only a few showed a high regeneration rate. A total of five significant QTLs were detected in the F1 population, and five candidate genes were found based on the results. These candidate genes are divided into two classes, and appear to be related to either PRC2 subunits or auxin synthesis.

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.

Culture and fusion of pollen protoplasts of Brassica oleracea L. var. italica with haploid mesophyll protoplasts of B. rapa L. ssp. pekinensis

Hybrid callus was formed from the successful protoplast fusion between pollen protoplasts of Brassica oleracea var. italica and haploid mesophyll protoplasts of Brassica rapa. The pollen protoplast isolation frequency in broccoli was highly related to the ratio of trinucleate pollens in the male gametophyte population. Large quantities of pollen protoplasts with high vigor could be isolated, and the isolation frequency reached up to 90% in 6.0-7.0 mm long flower buds with about 94.7% trinucleate-stage pollens. Pollen protoplasts could be collected and purified by discontinuous gradient centrifugation. In 1% Na-alginate embedding culture, cell divisions were observed but no further development was found. The haploid mesophyll protoplasts were isolated from in vitro haploid plants of B. rapa. Results strongly showed the variability in culturability of mesophyll protoplasts from different haploid lines. Both pollen protoplasts and haploid mesophyll protoplasts retained a stable round shape in the designed prefusion solution with an osmotic pressure of 0.74 osmol/kg. Polyethylene glycol was used for the protoplast fusion, and 40% polyethylene glycol 4000 enabled the highest fusion frequency of about 20%. Some postfusion protoplasts showed cell divisions up to callus proliferation. Calli were screened by random amplified polymorphic DNA analysis for their hybrid character. Results revealed the existence of the hybrid calli. Some of the hybrid calli grew well with green color and shoot primordia. According to our knowledge, this is the first report about a hybrid formation between two haploid protoplasts. Potential comprehensive applications, as well as problems of this technique, are discussed.