Production of 27-, 28-, and 56-chromosome apomictic hybrid derivatives between pearl millet (2n=14) and Pennisetum squamulatum (2n=54)

Summary An interspecific hybridization program designed to transfer gene(s) controlling apomixis from Pennisetum squamulatum Fresen. (2n=6x=54) to induced tetraploid (2n=4x=28) cultivated pearl millet, Pennisetum americanum (L.) Leeke resulted in four offtype plants, two with 27 chromosomes and two with 28 chromosomes. These plants were found among 217 spaced plants established from open-pollinated seed of an apomictic 21-chromosome polyhaploid (2n=21) plant derived from an apomictic interspecific hybrid (2n=41) between tetraploid pearl millet and Pennisetum squamulatum. It appeared that a 21- (or 20-) chromosome unreduced egg from the apomictic polyhaploid united with a 7-chromosome pearl millet (2n=2x=14) gamete to produce a 28- (or 27-) chromosome offspring. Meiotic chromosome behavior was irregular averaging from 3.60 to 4.05 bivalents per microsporocyte in the 27- and 28-chromosome hybrids. The 27- or 28-chromosome hybrids, like the 21-chromosome female parent, shed no pollen, but set from 1.8 to 28 seed per panicle when allowed to outcross with pearl millet. Progeny of the 28-chromosome hybrids were uniform and identical to their respective female parents, indicating that apomixis had been effectively transferred through the egg. In addition, a 56-chromosome plant resulting from chromosome doubling of a 28-chromosome hybrid was identified. Pollen was 68 per cent stainable and the plant averaged 2.3 selfed seeds per panicle. Chromosomes of the 56-chromosome plant paired as bivalents (x=10.67) or associated in multivalents. Three to nine chromosomes remained unpaired at metaphase I. Multiple four-nucleate embryo sacs indicated the 56-chromosome hybrid was an obligate apomict. The production of 27-, 28-, and 56-chromosome hybrid derivatives were the results of interspecific hybridization, haploidization, fertilization of unreduced apomictic eggs, and spontaneous chromosome doubling. These mechanisms resulted in new unique genome combinations between x=7 and x=9 Pennisetum species.     

Genetic diversity revealed in the apomictic fruit species Garcinia mangostana L. (mangosteen)

The novel molecular marker technique Randomly Amplified DNA Fingerprinting (RAF)was used to survey genetic relationships between 37 accessions of the tropical fruit G. mangostana (mangosteen) and among 11 accessions from eight other Garcinia species. Although mangosteen is believed to reproduce exclusively through apomixis, our results show that considerable genetic diversity exists within G. mangostana and between other Garcinia species. Among the 37G. mangostana accessions examined, nine different genotypes were identified which clustered into three distinct groups based on correspondence analysis(reciprocal averaging). For 26 (70%) of the accessions no marker variation was detected over 530 loci screened. A further eight (22%) accessions exhibited very low levels of variation (0.2–1%) suggesting at least one well conserved mangosteen genotype. The remaining three accessions (8%) showed extensive variation (22–31%)compared with the majority of accessions. The three mangosteen groups were 63–70% dissimilar to the other Garciniaspecies investigated. The genetic diversity identified in this research will assist in the conservation of Garciniagermplasm and provides a valuable framework for the genetic improvement of mangosteen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Powdery mildew resistance in Kentucky bluegrass genotypes regenerated from excised seed pieces

Summary Severity of powdery mildew was assessed on seven cultivars and lines of Kentucky bluegrass propagated by seed and tissue culture. Tissue culture plants were started from embryo axes cultured on Murashige and Skoog medium containing different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BAP), and incubated (1 to 4 weeks) or not incubated in the dark prior to transfer to a lighted culture room. There were significant differences in disease severity (DS) among seed propagated and tissue culture regenerated plants. DS ranged from highly susceptible (100% of leaf covered by mildew) (DS=9) to resistant (DS=3.0). In some tissue culture regenerants the disease severity was significantly affected by the tissue culture process. Ten clones expressing resistance were selected, and plants propagated vegetatively. In six clones, disease resistance was sustainable in subsequent vegetatively propagated plants, while resistance was lost in four of the selected clones. Results are discussed with a view to using tissue culture to produce Kentucky bluegrass genotypes with resistance to powedery mildew.Abbreviations BAP benylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - DS disease severity - MS Murashige & Skoog - SDW sterile distilled water     

Seed of Ullucus tuberosus—An apomict or not

Summary The paper deals with variations in enzyme pattern in the seeds of ulluco, Ullucus tuberosus. Six seeds per clone, four clones and three enzyme systems (malate dehydrogenase, glutamate oxaloacetate transaminase and 6-fosfoglucose dehydrogenase) were examined. There was variation in enzyme pattern between the seeds of a single clone. It is concluded that ulluco is not an apomictic species but a truly sexual one. Consequences of these findings for breeding programmes of ulluco are pointed out.     

水稻多胚苗的初步研究 Ⅰ.胚胎学的观察

对3份水稻多胚材料的胚囊观察表明,水稻多胚来源有5条途径:(1)合子胚原体裂生形成2个胚;(2)合子与助细胞受精同时发育成胚;(3)反足细胞多次分裂形成类似胚状的“拟胚”;(4)珠心细胞进入胚囊发育形成胚原体;(5)胚乳发育形成胚状体.其中第(1),(2)条途径能形成多胚苗.由反足细胞形成的‘拟胚”一般只能发育到几十个细胞就停止了.珠心细胞形成的胚原体,由于发育时间较迟,只有合子胚败育后,才能得到进一步的发育.     

水稻无融合生殖材料PDER选育的初步研究

通过离子注入Ｆ１代杂交种子，从后代中选育出２个早发生胚水稻品系，开花前１～２ｄ，未经授粉受精，卵细胞能自行分裂成多细胞原胚，发生频率高达２６．８％，用显性紫色稻作父本测交，Ｆ１代出现一定比例母本类型植株。经细胞胚胎学观察，已证实该材料存在二倍体孢子生殖（Ｄｉｐｌｏｓｐｏｒｙ）和无孢子生殖（Ａｐｏｓｐｏｒｙ），同时还存在未受精极核分裂成初生胚乳核的现象。     

水稻多胚苗的初步研究Ⅲ.来源与频率

选用水稻多胚材料 PM_1,通过胚胎学的观察,证实了多胚苗的形成途径有多条.将水稻多胚苗的形成途径归纳为4类10种。即(1)裂生多胚苗,包括合子胚和助细胞胚裂生;(2)增生多胚苗,包括合子胚、助细胞胚和不定胚增生;(3)混生多胚苗,包括合子胚+助细胞胚、合子胚+不定胚、助细胞胚+不定胚和合子胚+助细胞胚十不定胚混生:(4)双生多胚苗,即1个胚囊内同时具有2个不定胚.其中由合子胚增生、裂生或合子胚+助细胞胚是多胚苗形成的主要途径.在多胚苗组成中,二胚苗和三胚苗占绝大多数.     

缘管浒苔的单性生殖

发现缘管浒苔生活史中，配子体进行单性生殖有两种方式：一种是配子体放散的配子不经结合，固着后直接发育成新个体，完成单性生殖；另一种是配子体配子囊中最后一个或几个配子不放散直接在原藻体上发育成新个体。放散出去的配子进行单性生殖时，第一次分裂分别产生顶端细胞和基部细胞，其发育呈顶基极性。两个细胞分别成为叶片和假根的祖细胞。末放散的配子在原藻体上进行单性生殖发育成叶状体，形成的新个体可聚生成簇。后一种单性生殖发育方式为首次报道。