Nuclear Fusion during Early Stage of Microspore Embryogenesis Indicates Chromosome Doubling in Wheat (Triticum aestivum)

Studies of barley and maize indicate that chromosome doubling occurs via nuclear fusion during an early stage of microspore embryogenesis, but the time and mechanism by which chromosome doubling occurs in bread wheat (Triticum aestivum) remains undetermined. The purpose of this study was to determine the relative time during induction culture when chromosome doubling may occur in wheat, and to identify early indicators for doubled haploid microspores. Microspore nuclei were stained with 4’,6-diamidino-2-phenylindole (DAPI) and observed under a fluorescent microscope on the day of isolation, three days after isolation, and six days after isolation. The change in the percentage of microspores containing a single small nucleus, two small nuclei, a single enlarged nucleus, and three or more nuclei was then tracked throughout the six-day period. Ploidy levels were estimated by determining the cross-sectional area and number of nucleoli in microspores containing small and large nuclei then comparing the results of each respective cell-type. The percentage of microspores containing enlarged nuclei increased throughout the six-day test period, and the percentage of binucleated microspores containing small nuclei decreased. Comparison of the changes in average percentage of microspores containing a single small nucleus, binucleated microspores, microspores containing a single large nucleus, and multinucleate microspores on days 0, 3, and 6 indicates that nuclei classified as “small” are likely haploids and nuclei classified as “large” are doubled haploids. The percentage of microspores with enlarged nucleus (nuclei) during the first six days of induction culture could be used as an early indicator for the frequency of chromosome doubling in wheat microspore culture.

Study on Pollen Chromosome Doubling in Zenjimaru Persimmon

The factors influencing pollen chromosome doubling in Zenjimaru persimmon were studied, based on the knowledge of meiosis process of pollen mother cells. The results showed: (1) the suitable concentration of colchicine was 0.3-0. 5%; (2) the best doubling effect could be obtained during the period from the diplotene stage to the diakinasis stage, and the highest proportion was up to 40.6%; (3) considering giant pollen ratio and proportion of staminate-flower collection, the better treating frequency was 3 times; (4) giant pollen, which formed mainly from dyad and had bigger cell nucleus volume, was unreduced and hexaploid.

Doubling Efficiency of Maize Haploids Treated with Different Methods

Haploid seedlings were inducted from different maize materials.At 2-3-leaf stage,maize haploids were treated with 0.06% colchicine and 2.0% dimethyl sulfoxide（DMSO） by dipping root,dripping heart leaf and acupuncturing growing point,respectively.The doubling rate and mortality rate in different treatments were analyzed by variance analysis and multiple comparisons.The result showed that growing point acupuncturing method exhibited the highest doubling efficiency with an average doubling rate of 23%,seed-setting rate of 21.4%,and mortality rate of 16.3%.Composed with other two chemical doubling methods,growing point acupuncturing method significantly improved the doubling rate of maize haploids with a lower application dose of colchicine.This study laid the foundation for industrial application of haploid breeding techniques.

Assembly Line Balancing Based on Double Chromosome Genetic Algorithm

Aiming at assembly line balancing problem,a double chromosome genetic algorithm(DCGA)is proposed to avoid trapping in local optimum,which is a disadvantage of standard genetic algorithm(SGA).In this algorithm,there are two chromosomes of each individual,and the better one,regarded as dominant chromosome,determines the fitness.Dominant chromosome keeps excellent gene segments to speed up the convergence,and recessive chromosome maintains population diversity to get better global search ability to avoid local optimal solution.When the amounts of chromosomes are equal,the population size of DCGA is half that of SGA,which significantly reduces evolutionary time.Finally,the effectiveness is verified by experiments.

Genetical study on the parthenogenesis in Laminaria japonica

The parthenogenesis and natural doubling of chromosomes in wild type female gametophytes of Laminaria japonica were studied. The results indicate that not all the female gametophytes from the wild type hybrid parent can propagate through parthenogenesis. Most parthenosporophytes can mature, their spores germinate into gametophytes, the latter then developed into female sporophytes. To form these parthenosporophytes the natural doubling of chromosomes occurred mainly at the first and second cell divisions of the spores. It is thus considered that the parthenogenesis of L. japonica is inheritable and the relative genes link closely with the genes controlling the natural doubling of chromosomes and the female determination.

Mapping resistant QTLs for rice sheath blight disease with a doubled haploid population

Sheath blight（SB） disease,caused by Rhizoctonia solani Kuhn,is one of the most serious diseases causing rice（Oryza sativa L.） yield loss worldwide.A doubled haploid（DH） population was constructed from a cross between a japonica variety CJ06 and an indica variety TN1,and to analyze the quantitative trait loci（QTLs） for SB resistance under three different environments（environments 1-3）.Two traits were recorded to evaluate the SB resistance,namely lesion height（LH） and disease rating（DR）.Based on field evaluation of SB resistance and a genetic map constructed with 214 markers,a total of eight QTLs were identified for LH and eight QTLs for DR under three environments,respectively.The QTLs for LH were anchored on chromosomes 1,3,4,5,6,and 8,and explained 4.35-17.53%of the phenotypic variation.The SB resistance allele of qHNLH4 from TN1 decreased LH by 3.08 cm,and contributed to 17.53%of the variation at environment 1.The QTL for LH（qHZaLH8） detected on chromosome 8 in environment 2 explained 16.71%of the variation,and the resistance allele from CJ06 reduced LH by 4.4 cm.Eight QTLs for DR were identified on chromosomes 1,5,6,8,9,11,and 12 under three conditions with the explained variation from 2.0 to 11.27%.The QTL for DR（qHZaDR8）,which explained variation of 11.27%,was located in the same interval as that of qHZaLH8,both QTLs were detected in environment 2.A total of six pairs of digenic epistatic loci for DR were detected in three conditions,but no epistatic locus was observed for LH.In addition,we detected 12 QTLs for plant height（PH） in three environments.None of the PH-QTLs were co-located with the SB-QTLs.The results facilitate our understanding of the genetic basis for SB resistance in rice.

Induction of Tetraploid Male Sterile Tagetes erecta by Colchicine Treatment and Its Application for Interspecific Hybridization

Tagetes erecta is an annual multifunctional plant which can be cultivated under a broad range of climatic conditions. Polyploidization and interspecific hybridization are applied to facilitate breeding cultivars of T. erecta with improved ornamental qualities. Colchicine treatment to the germinating seeds was proved to be a useful tool for chromosome doubling of the male sterile two-type line ‘M525AB', with the resulting frequency of polyploid seedlings ranging from 88.89%(following 0.05% w/v colchicine applied for a 3–6 h exposure period) to a maximum of100.00%(following 0.1% for 3–6 h, or 0.2% for 3 h). Morphological observation, stomatal size and density analysis, flow cytometric analysis and chromosome counting were conducted to identify the tetraploid plants. Distinctive morphological changes were observed in a notable proportion of polyploid plants. The colchicine-treated polyploid T. erecta plants showed dwarfed and more robust growth, thicker, larger and greener leaves, larger inflorescences and florets. The mutant plants identified through morphological observation all aligned as polyploid plants, thus morphological observation could be an effective method for the detection of polyploidy. The polyploid plants had significant larger stomata size over the abaxial leaf surface, whereas the density of stomata distribution was remarkably reduced. The survival rate of tetraploid cuttings(i.e. 38%)was greatly reduced compared to that of diploid plants. The fertility of tetraploid plants was also decreased, as shown by cross-pollination yields.Interspecific hybridizations between colchicine-induced tetraploid plants of a male sterile T. erecta line and the naturally tetraploid fully fertile Tagetes patula species resulted in hybrid progeny. Most of these hybrids displayed the dwarfed growth stature and compact, larger-flower morphology which is the typical ideotype of herbaceous flowers. Thus, polyploidization may be employed effectively as a means to facilitate interspecific hybridization, thereby contributing significantly to the improvement of quantitative traits of Tagetes spp.