Optimization of culture conditions for improved plant regeneration efficiency from wheat microspore culture

The production of haploid plants through microspore culture is a very important tool for plant breeding. However, progress in microspore culture for many species has been hampered by a number of factors that have resulted in low recovery of regenerated green plants. In this study, a series of experiments were conducted to increase the regeneration of haploid green plants from isolated wheat microspores. The use of different basal media and variations in media components resulted in the increased recovery (approximately double) of regenerated haploid wheat plants. Our findings demonstrate that CHB medium, in combination with 2,4-d, was a better medium for embryoids induction and plant regeneration than medium MC17 with either 2,4-d or PAA growth hormones. Wheat microspores cultured without ovary co-cultivation did not respond. Furthermore, high efficiency of microspore derived embryoids (up to 296 MDEs per 100 anthers) and green plant regeneration (up to 71 green plants per 100 anthers) were achieved by the use of gelrite instead of agarose as a gelling agent, and by the addition of media additives such as spent medium or MET.     

High frequency spontaneous production of doubled haploid plants in microspore cultures of Brassica rapa ssp. chinensis

Brassica rapa (syn. Brassica campestris) ssp. chinensis is an important vegetable crop, but it is relatively recalcitrant to microspore culture. One genotype each of B. rapa ssp. chinensis var. communisand var. utilis were used formicrospore culture. Embryo production of3.8–42.4 embryos/bud was obtained. A high rate of plant regeneration directly from microspore-derived embryos without subculture was achieved by an improved protocol involving replacement of culture media and reduction of sucrose concentrations after 48 h of induction,among other modifications. More than 70%of regenerated plants were spontaneous diploids. Some spontaneous tetraploid plants were also obtained from isolated microspores of both genotypes tested. These tetraploids may be directly exploited a snew varieties in a Brassica rapabreeding programme. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of different genotypes of Brassica carinata to microspore culture

Sixteen lines of Brassica carinata were evaluated for microspore culture and plant regeneration. The highest values of cell division and embryo yield resulted from buds between 2.5 and 3.5 mm long with 3 days of pretreatment at 32°C and plating densities of 100 000-150 000 microspores/ml. Ten out of 16 lines tested (63%) responded positively to microspore culture. In all breeding and F₁ lines, both cell division and embryo yield varied over a wide range, but embryogenic response was higher in F₁ lines than in the breeding lines.     

Efficient Production of Doubled Haploid Plants through Chromosome Doubling of Isolated Microspores in Brassica napus

Three methods of chromosome doubling to produce doubled haploid plants from microspore cultures of Brassica napus were compared: colchicine treatment of microspore-derived plants, microspore-derived embryos, and isolated microspores. In the whole plant treatment, 53% of the treated plants set seed, but the treatment delayed plant growth and reduced seed set. When microspore-derived embryos were treated with colchicine, the doubling frequency was 32% (compared to 15% for spontaneous doubling). Direct colchicine treatment of isolated microspores resulted in a doubling efficiency of 70 % of the whole plants. This treatment also stimulated embryogenesis in microspore culture, leading to increased plant regeneration. Thus, direct chromosome doubling of isolated microspores is efficient and more than 10 000 doubled haploid plants have been produced in this manner in the past three years in order to accelerate the plant-breeding process.     

Haploidy in tomato (Lycopersicon esculentum Mill.): a critical review

Results on the induction of haploidy in tomato via both gynogenesis and microspore embryogenesis in vitro are far from satisfactory. The number of reports available on the gynogenic induction via in vitro non-fertilized ovary culture, wide hybridization and the use of irradiated pollen are limited. The main reason for this may be the difficulty experienced in working with this species. Therefore, many failed attempts have not been reported. Non-fertilized ovary culture and wide hybridization using Solanum sisymbriifolium Lam. as the male parent seem to be promising (Bal and Abak, Pak J Biol Sci 6:745–749, 2003a, b). Further efforts in this line may improve results obtained earlier. Several reports (Gresshoff and Doy, Planta 107:161–170, 1972; Sharp et al., Planta 104:357–361, 1972; Zamir et al., Plant Sci Lett 17:353–361, 1980; Chlyah and Taarji, Proc. Int. Symp. Plant tissue and cell culture application to crop improvement. 24–29 Sept. 1984; Jaramillo and Summers, J Amer Soc Hort Sci 115:1047–1050, 1990, HortScience 26:915–916, 1991; Summers et al., HortScience 27:838–840, 1992) are available on anther culture of tomato but a working protocol is yet to be developed. For the induction of anther callus, anthers carrying microspores at the meiotic stages appear to be the most responsive. However, the callus and the regenerants obtained were mainly of somatic origin. Somatic tissues of tomato anthers carrying the meiotic stages are highly responsive to tissue culture manipulations in comparison to anther tissues of the later stages. Therefore, reports on the induction of callus from anthers carrying early microspore stages should be met with caution. If culturing young anthers is of any help then it may be that the anther tissues are nursing the microspores and bringing them to the responsive uninucleate stage. Following the first report by Sharp et al. (Planta 104:357–361, 1972) on the induction of microspore embryogenesis, using a modified version of the microspore culture, reports concentrated only on anther culture (reviewed by Chlyah et al., Haploids in crop improvement I. Biotechnology in agriculture and forestry 12. Springer-Verlag, Berlin, 1990). Based on findings reported by Yinnan et al. (J Agric Biotechnol, , 1999) and Bal and Abak (Biotechnol Biotechnol Equip 19:35–42, 2005) on the induction of symmetrical division of microspore nuclei from uninucleate microspores, the formation of multicellular structures and globular embryos, it is likely that the future of tomato haploidy lies in the technique of isolated microspore culture.     

Somatic in vitro culture response of Lolium perenne L.: genetic effects and correlations with anther culture

Summary Genotypic effects on callus induction and plant regeneration in callus, suspension and protoplast culture, and their correlations with both phenotypic and GCA-values for anther culture response, were studied using 21 genotypes of perennial ryegrass. Differences between genotypes accounted for approximately 40% of the total variation for callus induction and initial callus growth, and 59 and 83% of the variation in callus culture for regeneration percentage and percentage of green plants. Effects of genotypes were less pronounced in suspension culture, where suspensions from the same genotype often behaved differently. Some suspension cultures retained their capacity for green plant regeneration for almost two years, repeatedly producing 80–100% green regenerants during this period. Genotypes with high regeneration percentage and a large proportion of green plants from callus culture were also superior in suspension culture for both regeneration performance and longevity. Regeneration percentage and percentage of green plants were uncorrelated, and probably under different genetic control. While capacity for green plant formation from the different genotypes showed no correlation between anther culture and somatic in vitro culture, a positive correlation was observed between the regeneration percentages in somatic in vitro culture and anther culture (r=0.44^*–0.85^***), suggesting some common genetic control of the two systems.     

Increasing embryogenesis and doubling efficiency by immediate colchicine treatment of isolated microspores in spring Brassica napus

The effect of colchicine on induction of embryogenesis andchromosome doubling during microspore culture was evaluated in twoF₁ hybrids of spring oilseed rape (Brassica napus L.). Immediatecolchicine treatment of isolated microspores with the concentrations 50 and500 mg/L for 15 h stimulated embryogenesis and produced largeamounts of healthy-looking embryos. These normal embryos germinatedwell at 24 ^°C after being transferred to solid regeneration mediumand an initial period of low temperature (2 ^°C) for 10 days, andcould directly and rapidly regenerate vigorous plants. A high doublingefficiency of 83–91% was obtained from 500 mg/L colchicinetreatment for 15 h with low frequency of polyploid and chimeric plants.The present experiment showed that a treatment duration of 30 h revealedless positive effects on embryogenesis and doubling efficiency, especially athigher colchicine concentration (1000 mg/L). Poor embryogenesis andembryo germination were observed from ordinary microspore culturewithout change of induction medium and colchicine treatment, and severalsubcultures were required for induction of secondary embryogenesis andplant regeneration.     

Efficient production of doubled haploid wheat plants by in vitro treatment of microspores with trifluralin or APM

Isolated microspore cultures from two doubled haploid (DH) lines of wheat, Triticum aestivum L., were used to develop an in vitro chromosome-doubling protocol. During the initial 24 h or 48 h of culture the microspores were treated with either of the two antimicrotubule herbicides trifluralin or amiprophos-methyl (APM) in concentrations ranging from 0.1 μM to 10μM. Untreated control cultures yielded 209 embryos per 100000 microspores, which is the equivalent of one spike. Among the regenerated plantlets 67% were green, and 15% of the flowering plants were spontaneously chromosome doubled. Treatments with both the herbicides had a significant effect on chromosome doubling, measured as the percentage of fertile regenerants. With the best combination of treatment duration (48 h) and herbicide concentration (10/μM) the percentage of fertile plants among regenerants could be increased up to 74% with APM and up to 65% with trifluralin. The largest numbers of DH plants per spike could be obtained with herbicide concentrations at 1–3 μM. Treatments with either herbicide at these concentrations resulted in an estimated average between the two genotypes of 27 DH plants per 100 000 microspores. These results demonstrate the high potential of APM and trifluralin as chromosome-doubling agents in isolated microspore cultures. The in vitro treatment integrated into tissue culture procedures will constitute an efficient method for chromosome doubling in future wheat breeding     

Somatic embryogenesis and plant regeneration of Tripsacum dactyloides L.

Summary This article reports the culture and plant regeneration of Tripsacum dactyloides. Mature embryos of Tripsacum dactyloides dactyloides were used to obtain embryogenic callus cultures. Currently, 180 normal plants have been regenerated from these cultures. Callus was initiated on MS medium supplemented with dicamba (10 mol or 20 mol) and sucrose (3% or 6%), and plants were regenerated on hormone free MS medium containing 2% sucrose. No significant differences were found in callus initiation frequency or in embryogenic response of cultures on the four combinations of sucrose and dicamba tested. The embryogenic cultures have been maintained for 9 months (12 subcultures) and have retained regeneration capacity. Plants regenerated from tissue culture of maize-by-Tripsacum hybrids could be useful in maize improvement.     

Effect of donor plant age and inflorescence age on microspore culture of Brassica napus L.

Summary Effect of age of donor plants and age of inflorescence on embryogenesis in microspore culture of B. napus was examined. Microspores isolated from buds of older plants had a higher embryo yield than those of younger ones. The effect of the age of inflorescence showed a different pattern. In older plants, a higher embryogenesis response was observed in microspores isolated from buds of new inflorescences, while in young plants, microspores isolated from buds of old inflorescences showed high embryo yield. These different responses were considered to be attributable to a difference in the developmental stage of pollen at the time of microspore isolation. Our results indicated that microspores collected from older inflorescences and older plants have sufficient embryogenic potential when the optimum developmental stage of pollen was used. Frequency of embryo to plant conversion was influenced by the size of embryos subcultured, but not by donor plant age or the age of the inflorescence.     

Functional genomics of microspore embryogenesis

Isolated plant microspores, when stressed and cultured in vitro, can be diverted from their normal gametophytic pathway towards sporophytic development, with the formation of haploid embryos and ultimately doubled-haploid plants. This process is called androgenesis or microspore embryogenesis, and is widely used in plant breeding programmes to generate homozygous lines for breeding purposes. Protocols for the induction of microspore embryogenesis and the subsequent regeneration of doubled haploid (DH) plants have been successfully developed for more than 200 species. These practical advances stand in stark contrast to our knowledge of the underlying molecular genetic mechanism controlling this process. The majority of information regarding the genetic and molecular control of the developmental switch from gametophytic to sporophytic development has been garnered from four intensely studied (crop) plants comprising two dicotyledonous species, rapeseed (Brassica napus) and tobacco (Nicotiana tabacum), and two monocotyledonous species, wheat (Triticum aestivum) and barley (Hordeum vulgare). In these species the efficiency of microspore embryogenesis is very high and reproducible, making them suitable models for molecular studies. In the past, molecular studies on microspore embryogenesis have focussed mainly on the identification of genes that are differentially expressed during this developmental transition and/or early in embryo development, and have identified a number of genes whose expression marks or predicts the developmental fate of stressed microspores. More recently, functional genomics approaches have been used to obtain a broad overview of the molecular processes that take place during the establishment of microspore embryogenesis. In this review we summarise accumulated molecular data obtained in rapeseed, tobacco, wheat and barley on embryogenic induction of microspores and define common aspects involved in the androgenic switch.     

Anther culture response of wild Oryza species

Thirteen different wild species of the genus Oryza were investigated for their response to anther culture and plant regeneration. Callus induction from microspores of anthers was found to be strongly dependent on the species. Although large numbers of anthers from wild Oryza species, including O. barthii, O. latifolia, O. australiensis, O. minuta, O. nivara, O. paraguagensis and O. eichingeri, were cultured, no calli could be obtained. However, calli were produced from anthers of O. punctata, O. perennis, O. alta, O. ridleyi and O. rufipogon, although the frequency of callus induction was different. Similar species-dependence was observed in plant regeneration from microspore-derived calli. In total, 62 plants were derived from anther culture, including 47 albino and 15 green plants (of which 26.7% were haploids) from O. perennis; for the first time, six albino plants were obtained from O. ridleyi. Phytohormone combinations in the callus induction medium were found to influence callus induction and different wild Oryza species exhibited their own preferred phytohormone combinations for anther culture. In general, NK medium containing suitable concentrations of auxin and cytokinin may be successfully applied for anther culture of selected wild Oryza species.     

小麦游离小孢子培养的研究

在游离小孢子培养过程中认为子房共培养可显著地提高游离小孢子胚状体愈伤率和再生率 ,子房共培养以 2 0个子房为宜。低温子房共培养胚状体发生和愈伤率低 ,但绿苗分化率较高 ,施加PAA、谷氨酰胺对游离小孢子形成的胚状体有促进作用。麦芽糖是游离小孢子培养最好的碳源 ,以蔗糖、葡萄糖以及葡萄糖和果糖搭配作碳源均未获得胚状体。检查培养 3d后的小孢子活力发现 ,唯有麦芽糖作碳源培养的小孢子有活力 ;认为高浓度的蔗糖、葡萄糖以及葡萄糖加果糖对小孢子有毒害作用。当葡萄糖浓度达到 2 0mmol/L时就对小孢子有毒害作用且致死。当在麦芽糖培养基中培养 1d后加入高浓度的葡萄糖发现小孢子存有活力 ,而且随着起始培养天数的增加活力也增加。对Y77品系来讲 ,适宜小孢子培养的麦芽糖浓度为 0 12mol/L。饥饿和热激 (33℃ )预处理对游离小孢子培养有促进胚状体和愈伤形成的作用     

Callus induction and plant regeneration from anther and inflorescence culture of Sorghum

Summary Twenty-five inbred lines, including grain and forage types from the USA and China, two hybrids, one Sorghum almum, and one Parasorghum (S. versicolor) were tested for their response to anther culture. Three nutrient media were effective in inducing anther calli from six cultivars (Xin White, TX 403-TSB, DDY Sommer Milo, TX 2779, Brawley, and Spur Federal) and one was effective for plant regeneration for one cultivar, Xin White. Averaged over media, callus induction frequency (number of calli per 100 anthers) was highest in cultivars Xin White and TX 403-TSB (6.7 and 3.9%, respectively). The means of cultivars for media C17-2 and Ms-t-z-2, 4.3 and 3.2%, respectively, were superior to that for medium 85D3-2 (0.1%). Expressed as an average of the six cultivars and three media the mean calli induction frequency was 2.6%; however, differential responses of genotype and medium were noted. Among the 10 regeneration media tested, medium MS-d-4 containing Murashige and Skoog basal components plus 2.0 mg/l indole-3-acetic acid (IAA) and 2.5 mg/l kinetin was the most effective for plant regeneration. Numbers of albino plants and calli developing only roots increased directly with callus-induction time, whereas the frequency of plant regeneration decreased. Regenerated plants had varied numbers of chromosomes in root tip cells: 10, 15, 20, 40, and 60. The 29 regenerated plants that reached maturity, however, were highly fertile and contained only 10 bivalents in pollen mother cells. Normal chromosome number and behavior for the regenerated plants suggest that induced calli originated from cells other than microspores. However, spontaneous chromosome doubling in microspore-derived haploids may occur. The appearance of albinos also implies that haploids may have been produced from anther culture.Joint contribution of the Dept. of Agronomy and USDA-ARS, Kansas Agricultural Experiment Station, Manhattan, KS 66506-5501, USA. Contribution no. 88-566-J.     

Plant Regeneration Through Anther Culture of Three Wild Species of Hordeum (H. murinum, H. marinum and H. bulbosum)

Plant regeneration was achieved through anther culture of three wild species of Hordeum (H. murinum, H. marinum and H, bulbosum). Calli or embryoids were formed from microspores in anthers cultured on a medium containing 6-benzylammopurine (BAP) and ficoll. These calli or embryoids regenerated green or albino shoots and roots after transfer to regeneration media. Green plantlets which developed on regeneration media were transferred to soil where they showed further growth.     

Genotypic and exogenous factors affecting shoot regeneration from anther callus of linseed (Linum usitatissimum L.)

Summary The objective of this study was to investigate factors affecting the regeneration capacity of linseed anther culture. Four different environmental conditions in a phytotron were tested with regard to their effects on anther donor plants of cv. Hella. Anther response and shoot regeneration from anther callus was maximal when donor plants were grown in a 16 hrs-day at 14°C day/8°C night temperature. Anthers of four linseed genotypes were cultured on different media. Maximum shoot regeneration was achieved when the induced calli were transferred onto a modified N6 medium containing zeatin (1 mg l^-1). Most of the calli regenerated shoots in the second subculture on regeneration media. Shoots were rooted on modified B5 or MS media containing NAA (0.1 mg l^-1). Cytological examinations of incubated anthers and root tips of regenerated plants indicated that the anther calli were derived from microspores.Abbreviations B5 Gamborg's (1975) medium - BAP 6-benzylaminopurine - 2,4D dichlorophenoxyacetic acid - N6 Chu's (1978) medium - NAA -naphthaleneacetic acid - MS Murashige & Skoog's (1962) medium - ZEA zeatin     

Improved plant regeneration and in vitro somatic embryogenesis of St Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze]

St Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is an important warm season turf and pasture grass. In vitro tissue culture of St Augustinegrass could serve as an important mean for its improvement through genetic transformation as well as induced somaclonal variation. To optimize tissue culture conditions for plant regeneration of St Augustinegrass, tissue culture responses of 11 explant tissues and four callus induction/subculture media have been examined. Embryogenic calli with regeneration potential were observed on cultures of early immature embryo [3 days after pollination (DAP)], immature embryo (7–14 DAP), and shoot base of young seedlings. The addition of benzyladenine (BA) in the callus induction/subculture medium enhances callus regeneration ability and does not harm callus induction for immature embryos. The best response came from 7 to 14 DAP immature embryo on MS medium containing 1 mg/l 2,4‐dichlorophenoxyacetic acid and 0.5 mg/l BA. The callus induction and regeneration rates were 97.7% and 47.6% respectively. However, BA supplement reduced callus formation and failed to enhance regeneration for young leaf bases. Scanning electron microscopy revealed that plant regeneration of St Augustinegrass is via somatic embryogenesis.     

Efficient production of callus-derived doubled haploids through isolated microspore culture in eggplant (<Emphasis Type="Italic">Solanum melongena</Emphasis> L.)

Production of doubled haploids (DHs) through androgenesis induction is an important biotechnological tool for plant breeding. In some species, DHs are efficiently obtained through embryogenesis from isolated microspore cultures. In eggplant, however, this process is still at its infancy, despite the economic relevance of this important agricultural crop. To date, only two studies have focused previously on this process, suggesting that in eggplant microspore cultures, the only morphogenic response is callus formation. Given the notable lack of studies on eggplant microspore cultures, in this work we explored this process with different experimental approaches. We studied the response of different cultivars and characterized the development of microspores induced to divide and proliferate. We demonstrated that microspore-derived embryos (MDEs) can be produced in eggplant; however, MDEs stopped at the globular stage, to turn into euploid and principally mixoploid calli. From these calli, 60 % of DH plants could be regenerated. In order to promote microspore induction we evaluated the effect of polyethylene glycol (PEG) and mannitol. PEG, but not mannitol, significantly increased induction of microspore embryogenesis. We also tested the ability of eight different media compositions to promote efficient plant regeneration from calli. In order to test it in a genotype-independent manner, we previously developed a method to generate clonal callus populations derived from single microspore-derived calli. Together, the results presented hereby constitute an efficient way to produce eggplant DHs through microspore culture. In addition, they contribute significant insights into the knowledge of the particularities of androgenesis induction in this species.     

Efficient production of doubled haploid Brassica napus plants by colchicine treatment of microspores

Summary The effect of colchicine on isolated microspore cultures of Brassica napus was evaluated in order to combine a positive effect of colchicine on the induction of embryogenesis with the possibility to induce chromosome doubling at an early developmental stage, thus avoiding the production of haploid or chimeric plants. Colchicine was added to the culture medium immediately after isolation of B. napus microspores. The cultures were incubated from 6 to 72 h with various concentrations of colchicine. Samples were taken from the regenerating embryoids after 6 weeks for ploidy determination by flow-cytometry.The highest diploidization rate was obtained after a 24 h treatment of microspores with 50 mg/l colchicine, leading to 80–90% diploid embroids. A concentration of 100 mg/l colchicine applied for the same duration resulted in a lower diploidization rate (76–80%). Treatment durations of 6 h were not long enough to induce a high rate of diploidization, whereas the application of 10 mg/l for 72 h was also very effective.A sample of the plants regenerated from the colchicine treated microspores was transferred to the greenhouse. The plants looked similar to normal diploid rapeseed plants and showed reasonable pod and seed set. Thus, an additional generation for seed increase in the greenhouse is rendered unnecessary. The advantage of applying a minimum volume of colchicine under controlled in vitro conditions means a considerable saving of time and labour in DH-breeding programs.     

Effect of Cultivar, Incubation Temperature, and Stage of Microspore Development on Anther Culture in Wheat and Triticale

Effects of incubation temperature and developmental stage of microspores on polyhaploid production in three wheat cultivars‘Pavon 76′, ‘Kitt’, and ‘Chris’ and one triticale cultivar, ‘T81′, were studied using a one-step medium. Calli failing to differentiate on the one-step medium were placed on a medium containing 1 mg/l indole-3-acctic acid (IAA) and 2 mg/1 6-furfurylaminopunne (KIN). Anthers containing either early- or late-uninucleate microspores were incubated in dark at 26, 28 or 32°C lor 3 days prior to transfer to 26°C. Averaged over temperatures and microspore stages, frequency of calli and green plantlets were 8.9 % and 3.4 %, respectively, for wheat cultivar‘Pavon 76′, 8.4 % and 1.6 % for cultivar ‘Kitt’, 4.5 % and 0.25 % for cultivar ‘Chris’, and 2.9 % and 0.12 % for the triticale cultivar‘T81′. However, cultivar-by-developmental-stage interaction was significant for frequency of callus induction. Temperature had no significant effects on callus induction and plantlet regeneration. Anthers containing early-unmucleate microspores produced no polyhaploids.