Genetic and phenotypic correlations in plantain-banana euploid hybrids

The objective of this work was to determine intraclass correlations for growth and yield traits, as well as associations between them, in segregating hybrids. Diploid, triploid and tetraploid hybrids were obtained from triploid-diploid crosses between plantains and bananas. These hybrids were evaluated as plants and as ratoon crops on a humid forest site. Significant differences between ploidy within crosses were observed for most traits. The tetraploids were taller, had longer production cycles but a shorter fruit filling time, and heavier bunches than the diploids. There were significant differences between clones of the same ploidy within crosses. Hence, individual selection within ploidy will be effective for the improvement of plantain. Most of the bunch and fruit traits were positively and significantly associated, especially at the tetraploid level. Selection for large fruit at the diploid and tetraploid levels may lead to heavy fruits, thereby resulting in hybrids bearing heavy bunches. Significant and positive correlations between plant height and bunch weight at the tetraploid level suggest that selection of dwarf plantains with heavy bunches may be difficult.     

Meiotic chromosome and pollen morphological studies of polyploid Cucumis species

summary Meiotic chromosome studies of polyploid Cucumis species revealed the presence of bivalent chromosome configurations in the tetraploid C. aculeatus and C. zeyheri and hexaploid C. figarei, while a maximum of ten quadrivalents were observed in pollen mother cells of a tetraploid species, C. heptadactylus.Allotetraploidy was not accompanied by an increase in the number of pores per pollen grain, but the autotetraploid and hexaploid species showed a relatively high percentage of 4-porate pollen. The pollen fertility of the tetraploid species was normal.Contribution from the Department of Horticulture and Department of Agronomy. Supported by the Colorado State University Experiment Station and published as Scientific Series Paper No 2403.Former Graduate Research Assistant, Department of Horticulture (present address, 1030 Sanders St., Auburn, Alabama 36830 USA) and Professor, Department of Agronomy, respectively.     

Occurrence of 2n and jumbo pollen in the Brazilian ginseng (Pfaffia glomerata and P. tuberosa)

An analysis of microsporogenesis was carried out in four populations of Pfaffia tuberosa (2n=4x=68) and in ten populations of P. glomerata(2n=2x=34). Monads, dyads and triads were reported at high frequency in all populations of P. tuberosa. In P. glomerata, on the other hand, only four populations presented monads, and at low frequency. Dyads and triads were observed in both species, albeit at a higher frequency in P. tuberosa populations. Certain abnormalities of spindles in the second division, such as sequential and tripolar spindles, led to triad formation by the rejoining of two chromosome sets. The precise causes of monad and dyad formation have not been found during meiosis, although evidence exists that dyads originated by omission of second meiosis and monads by omission of both meiotic divisions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of epistatic interaction affecting glycoalkaloid content in tubers of tetraploid potato (Solanum tuberosum L.)

Glycoalkaloids are secondary metabolites characterised by an undesirable taste, and known to be toxic when consumed in large quantities. Their content in potato tubers should therefore be selected against and DNA markers can significantly facilitate such a process. This study was designed to describe the genetic control of the total content of glycoalkaloids (TGA) in the potato tuber and to enhance the development of DNA markers. A segregating population was constructed from tetraploid potatoclones, which were characterised by divergent TGA-content. The population had a high-TGA parent, LT7, and a low-TGA parent, NT8. We used 342 Inter-Simple Sequence Repeat (ISSR) single primers or two such primer combinations and 36 Cleaved Amplified Polymorphic Sequence (CAPS)primer pairs, digested with various restriction enzymes, to amplify random PCR products. Parental clones of both populations were used to identify polymorphic PCR products for further linkage analyses with TGA-content. In these analyses, one single ISSR marker was found to be significantly associated with TGA-content. A multiple regression analysis was also carried out using a ‘stepwise’ procedure. In this regression analysis TGA-content was the dependent variable whereas the polymorphic PCR products and all possible two-way interactions among them were the independent variables. The resulting best model consisted of an interaction between two loci in addition to a single locus effect. This interaction suggests that the expression of TGA-content is partially modulated by two interacting loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polyploidy in tulips (Tulipa L.). The occurrence of diploid gametes

Summary From data available in the literature and supplemented by information from private tulip breeders, it appeared that triploid and tetraploid varieties raised in the past, resulted from crosses between diploid tulips and between diploids and tetraploids. This can only be explained by the occurrence of diploid gametes in diploid (2n=24) cultivars. This phenomenon which may affect both female and male gametes, appears to be specific for certain varieties. Consequences for practical breeding are discussed.     

The production of multispecific octoploids from Fragaria species and the cultivated strawberry

Summary A method of incorporating genetic material from five species of Fragaria and the cultivated strawberry into fertile octoploids is described. A synthetic octoploid derived from a hexaploid x diploid hybrid was crossed to octoploid cultivar breeding lines until a BC₂ hybrid was produced. A second synthetic octoploid in which two diploid species and a tetraploid species were combined was crossed to a cultivated strawberry to produce a hybrid breeding clone. The two breeding clones were crossed and 222 seedlings were produced. The seedlings were generally vigorous and fruitful, some having commercial potential.     

毛酸浆浸渍法多倍体诱导技术

以毛酸浆露白种子为试验材料,采用浸渍法进行多倍体诱导,研究了秋水仙素浓度和浸渍时间对后代表型变异率和死亡率的影响,以期筛选适合毛酸浆的多倍体诱导技术体系。结果表明:随着秋水仙素浓度升高和处理时间的延长,毛酸浆下胚轴膨大率升高,但过长的处理时间(36 h)会造成下胚轴膨大率下降。变异株气孔变大、密度变小,染色体数目鉴定结果为正常株2n=2x=24条,变异株2n=4x=48条。不同品种对秋水仙素浓度敏感程度不同,"铁把青"对秋水仙素较敏感,最适宜处理组合为100 mg·L^-1秋水仙素处理12 h,30 d表型变异率可达8.67%;"大黄菇娘果"和"粒粒甜小菇娘"最适宜处理组合为200 mg·L^-1秋水仙素处理12 h,30 d表型变异率分别为6.33%和6.67%。流式细胞仪鉴定发现很多表型变异株是混倍体,流式细胞仪可以在早期对变异株的倍性进行准确鉴定,还可以减少混倍体对育种的影响。     

Potato genetics,genomics, and applications

Potato has a variety of reproductive uniquenesses besides its clonal propagation by tubers. These traits are controlled by a different kind of genetic control. The reproductive information has been applied to enable interspecific hybridization to enhance valuable traits, such as disease and pest resistances, from the tuber-bearing Solanum gene pool. While progress has been made in potato breeding, many resources have been invested due to the requirements of large populations and long time frame. This is not only due to the general pitfalls in plant breeding, but also due to the complexity of polyploid genetics. Tetraploid genetics is the most prominent aspect associated with potato breeding. Genetic maps and markers have contributed to potato breeding, and genome information further elucidates questions in potato evolution and supports comprehensive potato breeding. Challenges yet remain on recognizing intellectual property rights to breeding and germplasm, and also on regulatory aspects to incorporate modern biotechnology for increasing genetic variation in potato breeding.     

Construction of a linkage map based on retrotransposon insertion polymorphisms in sweetpotato via high-throughput sequencing

Sweetpotato (Ipomoea batatas L.) is an outcrossing hexaploid species with a large number of chromosomes (2n = 6x = 90). Although sweetpotato is one of the world’s most important crops, genetic analysis of the species has been hindered by its genetic complexity combined with the lack of a whole genome sequence. In the present study, we constructed a genetic linkage map based on retrotransposon insertion polymorphisms using a mapping population derived from a cross between ‘Purple Sweet Lord’ (PSL) and ‘90IDN-47’ cultivars. High-throughput sequencing and subsequent data analyses identified many Rtsp-1 retrotransposon insertion sites, and their allele dosages (simplex, duplex, triplex, or double-simplex) were determined based on segregation ratios in the mapping population. Using a pseudo-testcross strategy, 43 and 47 linkage groups were generated for PSL and 90IDN-47, respectively. Interestingly, most of these insertions (~90%) were present in a simplex manner, indicating their utility for linkage map construction in polyploid species. Additionally, our approach led to savings of time and labor for genotyping. Although the number of markers herein was insufficient for map-based cloning, our trial analysis exhibited the utility of retrotransposon-based markers for linkage map construction in sweetpotato.     

金银花多倍体诱变及早期形态鉴定

以二倍体金银花(Lonicera japonica Thunb)为材料,采用改良L.D.Cua法对其进行人工诱变,通过对获得的同源四倍体进行植株早期形态鉴定。结果表明,采用改良L.D.Cua法,在药剂浓度0.2%、处理温度20℃、处理时间72 h效果最好,变异率达72.5%;金银花染色体加倍后,获得的M1变异植株生长势强,叶片变大变厚,叶色加深,叶形指数变小。