Development of colchicine‐induced tetraploid St. Augustinegrass (Stenotaphrum secundatum) lines

St. Augustinegrass is well suited for lawns and commercial landscapes. While many genotypes are cross‐fertile, all cultivars are propagated vegetatively in sod production. To ensure varietal purity, development of sterile triploid hybrids by crossing tetraploid and diploid genotypes has been successfully used in other warm‐season turfgrasses. Applying this model in St. Augustinegrass would be beneficial to sod producers and turf managers who require purity for certification and uniformity for performance, respectively. This study was conducted to develop colchicine‐induced tetraploid lines of St. Augustinegrass. Seeds of cultivar ‘Raleigh’ were treated with four colchicine concentrations at four exposure times. A non‐treated control was included among the treatments. Seedlings that germinated were screened for genome size changes using flow cytometry. Line DSA 13005 and two progeny lines derived through selfing, DSA 16001 and DSA 16016, were corroborated as tetraploids (2n = 4x = 36) through chromosome counts. These lines will be used in future breeding efforts to attempt development of sterile triploid cultivars of St. Augustinegrass.     

欠发达地区农村“收入倍增计划”实践路径浅析

"收入倍增计划"是党的"十八大"所提出的目标,即"到2020年实现国内生产总值和城乡居民人均收入比2010年翻一番"的宏伟目标。作为欠发达的农村地区,怎样实现"收入倍增计划"这一目标是一项艰巨而重大的历史课题。文章以"立足基层、用活政策、激发活力、服务农民"为宗旨,研究其经济现状和发展潜力,探析未来发展新路径,在找准难题中破解难题,为欠发达地区农村实现"收入倍增计划"目标提供理论和实践参考,具有重大的社会价值和现实意义。     

Natural hybridization between wheat (Triticum aestivum L.) and its wild relatives Aegilops geniculata Roth and Aegilops triuncialis L.

BACKGROUND

Cultivated bread wheat (Triticum aestivum L.) spontaneously hybridizes with wild/weedy related Aegilops populations, but little is known about the actual rates at which this hybridization occurs under field conditions. It is very important to provide reliable empirical data on this phenomenon in order to assess the potential crop–wild introgression, especially in the context of conducting risk assessments for the commercialization of genetically modified (GM) wheat, as gene flow from wheat to Aegilops species could transfer into the wild species genes coding for traits such as resistance to herbicides, insects, diseases or environmental stresses.

RESULTS

The spontaneous hybridization rates between wheat and A. geniculata and A. triuncialis, which are very abundant in the Mediterranean area, have been estimated for the first time in the northern part of the Meseta Central, the great central plateau which includes the largest area of wheat cultivation in Spain. Hybridization rates averaged 0.12% and 0.008% for A. geniculata and A. triuncialis, respectively. Hybrids were found in 26% of A. geniculata and 5% of A. triuncialis populations, at rates that can be ≤3.6% for A. geniculata and 0.24% for A. triuncialis.

CONCLUSION

The detection of Aegilops spp.–wheat hybrids in Aegilops populations indicates that gene flow can occur, although wheat is considered a crop with a low-to-medium risk for transgene escape. These data on field hybridization rates are essential for GM wheat risk assessment purposes. © 2023 Society of Chemical Industry.     

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.     

Oryzalin as an Efficient Agent for Chromosome Doubling of Haploid Apple Shoots in vitro

In an outbreeding species such as apple, haploid plants may be especially useful in breeding programmes for the production of homozygous material. However, methods must be available to induce chromosome doubling in the haploid plants. Two antimitotic agents, colchicine and oryzalin, were compared as regards their efficiency in inducing chromosome doubling of in vitro haploid apple shoots. Three colchicine levels (0.025, 0.25 and 1.25 mM) and three oryzalin levels (5, 15 and 30 μM) were evaluated. Three techniques were also used and compared. Survival rate and chromosome counts were determined. Differences were observed between the two antimitotic agents and between the three techniques. This study demonstrates that oryzalin could be a better choice than colchicine for chromosome doubling on haploid apple shoots in vitro.     

Colchicine-induced chromosome doubling in Platanus acerifolia and its effect on plant morphology

We report the production of tetraploid plants of Platanus acerifolia, with the ultimate aim of improving the ornamental qualities of this important urban landscaping tree. Chromosome doubling was achieved by the application of colchicine to either pre-soaked seed or to the apical meristems of young seedlings. Treatment of the ungerminated seed was the more efficient method in terms of numbers of tetraploid seedlings (up to 40%, as determined by chromosome counting of the root-tip nuclei) but this method produced no mature tetraploid plants due to the deleterious effect of colchicine on subsequent root growth. When colchicine was applied directly to the apical growing tip of cotyledon-stage seedlings, leaf and stem growth was temporarily affected but the plants eventually recovered. We conducted a preliminary screen for putative tetraploids based on the observation in other plant species of a correlation of stomatal size and distribution with ploidy. Plants containing significantly larger stomata and at a lower density across the lower leaf epidermis, were selected for further analysis by flow cytometry and chromosome counting. These techniques confirmed that, of the 12 putative polyploids, four were tetraploid, five were mixoploid and three were, in fact, diploid. Morphological differences of the tetraploids included a more compact growth habit and broader, thicker leaves. These plants are being grown to full maturity in order to test their potential for use in a breeding programme aimed at producing sterile triploid lines.     

The effect of colchicine on triticale anther-derived plants: Microspore pre-treatment and haploid-plant treatment using a hydroponic recovery system

In cereals, chromosome doubling of microspore-derived haploid plants is a critical step in producing doubled haploid plants. This investigation was undertaken to study the effect of incorporation of colchicine in the induction medium for anther culture, and the effect of colchicine on anther culture-derived plants of triticale grown under controlled greenhouse conditions. In the latter case, chromosome doubling of adult sterile plants derived from anther culture of fourteen triticale populations was attempted, where androgenetic plants with non-dehiscent anthers were cloned and subjected to the colchicine treatment, and then grown with the aid of hydroponics. The hydroponic system provided optimal conditions for recovery of the affected haploids from the toxic effects of colchicine treatment and all colchicine-treated plants survived. A topcross-F₁ (TC₁F₁) population with timopheevii cytoplasm produced the highest percentage of plants with seed-set either due to chromosome doubling by colchicine (98%) or spontaneous doubling of chromosome number (15%). Colchicine-treated anthers performed inferior than control in both induction and regeneration phases. One of the key observation of this study was the reversal from reproductive stage back to the vegetative stage which in turn enabled further cloning of haploid plants under hydroponic conditions once they were identified as sterile. The one hundred percent survival rate of in vitro-derived plants, 100% survival rate of colchicine treated haploid plants and the high chromosome doubling success rate (X = 82.3) observed in this study imply that a temperature-controlled greenhouse with an hydroponic system provides an efficient environment for inducing chromosome doubling of haploid plants in cereals. This revised version was published online in August 2006 with corrections to the Cover Date.     

Doubled Haploids of Cocoa (Theobroma cacao L.) 1. Observations of Fertility

Ovule and pollen fertility have been studied in doubled haploids of cocoa derived from spontaneous haploids, doubled by colchicine treatment. The two measures of fertility were very variable; occasionally, the levels were as high as those of the parent plant, but most were lower. The low fertility was not improved either by changing pollinators or after grafting. Pollen fertility also varied seasonally more in doubled haploids than in their parents. The lack of differentiation of embryo sacs seemed to be the cause of low values of ovule fertility. Both of these unfavourable characteristics were not observed in the progeny of doubled haploids, The low fertility is described in terms of homozygote depression, forced, on normally allogamous plants, its consequences for the use of doubled haploids in the production of hybrid seeds are discussed.