ADAPTIVE RADIATION IN THE HAWAIIAN SILVERSWORD ALLIANCE (COMPOSITAE-MADIINAE). II. CYTOGENETICS OF ARTIFICIAL AND NATURAL HYBRIDS

The Hawaiian silversword alliance of Argyroxiphium, Dubautia, and Wilkesia, in spite of exhibiting spectacular morphological, ecological, physiological, and chromosomal diversity, is remarkably cohesive, genetically. This is attested to by the ease of production of artificial hybrids and by the high frequency of spontaneous hybridization among such life forms as mat-forming subshrub, monocarpic rosette shrub, polycarpic shrub, cushion plant, tree, and vine. Even the least fertile of these hybrids is capable of producing backcross progeny. Moreover, first generation interspecific and intergeneric hybrids have been successfully used to produce trispecific hybrids in a number of instances. In general, the widest hybrid combinations have been as readily produced as crosses within a species. At present eight genomes or chromosome races distinguished by reciprocal translocations are recognized on the basis of meiotic analysis of artificial and spontaneous hybrids. Seven of these races are found among those species with 14 pairs of chromosomes. The eighth genome very likely characterizes all nine species of this alliance that have 13 pairs of chromosomes. The cytogenetic data indicate that redundancy of translocations involving the same chromosomes has been a recurrent theme in the chromosomal differentiation of these taxa. There appears to be little, if any, correlation between chromosomal evolution and adaptive radiation as assessed by gross habital differentiation in this group. However, within Dubautia, a novel ecophysiological trait associated with colonization of xeric habitats is restricted to species with n = 13. In contrast to the bulk of the Hawaiian flora, which is characterized by self-compatibility and chromosomal stability, it is suggested that the occurrence of self-incompatibility in the Hawaiian Madiinae may have favored selection of supergenes via chromosomal repatterning, and this may account for the diversity of chromosome structure seen in this group.     

ORGANOGENESIS FROM HELIANTHUS ANNUUS INBREDS AND HYBRIDS FROM THE COTYLEDONS OF ZYGOTIC EMBRYOS

Dormant mature and immature zygotic embryos of sunflower (Helianthus annuus L.) inbreds and hybrids were dissected and cultured on modified Murashige and Skoog's medium supplemented with 0.1 mg/l benzyl adenine (BA), 0.5 mg/l naphthalene acetic acid (NAA), adenine sulfate, and casamino acids. For certain inbreds and hybrids, adventitious shoot formation occurred from callused cotyledonary tissue, particularly along the cut edges. The developmental stage of the zygotic embryo was critical. Eighty percent of immature H. annuus ‘Mammoth Russian’ embryos produced adventitious shoots from cotyledons, while mature embryos did not. The organogenic potential of mature cotyledons diminished as soon as one day after germination was initiated. Different forms of regeneration were observed in two inbred lines, and when these were crossed, both forms of regeneration were observed at a lower frequency from the immature embryos of the hybrid. Rooted shoots were successfully grown to maturity in a greenhouse.     

小麦与黑麦属间杂种的染色体自然加倍的研究

分别以小麦属６个种的变种或品种共９个供试材料为母本,２个黑麦种为父本进行杂交,只有Ｓｔｅｗａｒｔｄｕｒｕｍ小麦与２个黑麦种杂交后,才得到Ｆ１种子,说明染色体的自然加倍需要一定的遗传背景,对这２个Ｆ１代花粉母细胞减数发裂所形成配子的观察表明,配子形成途径的不同,使Ｆ２出现了双二倍体和部分双二倍体的差异。     

STEM ANATOMY OF PARTHENIUM ARGENTATUM,P. INCANUM AND THEIR NATURAL HYBRIDS

Guayule (Parthenium argentatum Gray) contains rubber in the parenchymatous cells of stems and roots. Stem anatomy of P. argentatum is described along with that of P. incanum H.B.K. (mariola). Anatomy of these species differs significantly. Phloem rays in both species increase in width by cell division and expansion; however, the increase observed in mariola is less as compared to that in guayule. Axial xylem parenchyma in guayule is generally a two-cell strand as compared to the fusiform axial xylem parenchyma observed in mariola. Vascular ray cells and cells of the pith region of guayule are parenchymatous, whereas those of mariola are sclerenchymatous. As a result of introgression between guayule and mariola, three forms of guayule exist in the native stands of Mexico. Morphological differences between these guayule plants have been described previously. The stem anatomy of these three groups of plants differ importantly. Group I guayule plants, least introgressed by mariola, have taller rays with the cells of pith region and vascular rays parenchymatous. Group III plants, highly introgressed by mariola, have a few to many cells of vascular rays and pith with lignified secondary walls and shorter rays. Many of the anatomical characteristics of group II plants, somewhat introgressed by mariola, are intermediate between group I and III plants.     

HYBRIDS AND GENOME RELATIONS OF HIBISCUS SABDARIFFA,H. MEEUSEI,H. RADIATUS AND H. ACETOSELLA

Chromosome pairing was studied in the following hybrids: Hibiscus radiatus-meeusei (tetraploid F₁), H. sabdariffa-meeusei (tetraploid F₁ and spontaneous allooctoploid F₂), and hexaploid H. acetosella-(sabdariffa-meeusei). Genome constitutions of the species adduced from these data are symbolized as follows: H. radiatus and H. acetosella, AABB; H. meeusei, AAXX; H.sabdariffa, XXYY or AAYY.     

HYBRIDS AND INDUCED AMPHIPLOIDS OF ELYMUS CANADENSIS X AGROPYRON LIBANOTICUM

North American Elymus canadensis L., 2n = 28, and Asian Agropyron libanoticum Hack., 2n = 14, crossed with ease and yielded vigorous but sterile F₁ hybrids, 2n = 21. Chromosome pairing in the hybrids averaged 9.47^I, 5.38^II, and 0.26^III in 150 metaphase-I cells. One genome of E. canadensis is more or less homologous with the A. libanoticum genome. Treatment of the F₁ hybrids with colchicine produced 42-chromosome amphiploids, C₀, which were advanced through two seed generations, C₁ and C₂. More than half of the metaphase-I cells in the C₀ amphiploids contained 21^II; and average associations were 1.09^I, 20.16^II, 0.07^III, and 0.09^IV in 116 cells. Meiosis became increasingly irregular beyond metaphase-I; nevertheless, the C₀ amphiploids produced 68% stainable pollen and averaged 0.75 seed per spikelet. Multivalent frequencies increased in advanced generations, and the C₂ amphiploids averaged 1.11^I, 19.00^II, 0.23^III, and 0.55^IV in 100 metaphase-I cells. Meiosis was essentially regular in the C₁ and C₂ amphiploids beyond metaphase I, and the C₂ amphiploids averaged 73% stainable pollen and 2.28 seeds per spikelet. The amphiploids have an excellent chance of developing into a meiotically stable, fertile, new species. Forage characteristics of the amphiploids indicate that they have considerable economic potential as a forage grass.     

分布于日本和中国的鹅观草及其杂种的形态学和细胞学研究

本文对分布于日本的Agropyron tsukushiense (Honda) Ohwi var. transiense (Hack.) Ohwi (2n=6x=42)和分布于中国的Roegneria kamoji Ohwi (2n=6x=42)及其杂种F_1(2n=6x=42)进行了形态学及细胞学的研究,并同时探讨了亲本种的亲缘关系。总体来看,亲本材料之间在形态上虽有差异但并不十分显著。杂种F_1的形态特征介于其父、母本之间。在减数分裂过程中,亲本种和杂种F_1的染色体配对行为均十分正常。但在检查了大量的成熟花粉和穗状花序之后,发现杂种F_1有部份不育现象。上述研究结果表明A. tsukushiense var. transiens的三个染色体组与R. kamoji的三个染色体组同源。结合形态学和育性等方面的研究资料,作者认为上述两个材料仍应属于同一分类等级。但必须指出,由于长期的地理隔离,他们之间产生了一定的形态变异和生殖障碍。按照国际植物命名法规(ICBN)上述两个材料应组合为:Roegneria tsukushiensis (Honda) B. R. Lu, Yen et J. L. Yang及其变种var. transiens (Hack.) B. R. Lu, Yen et J. L. Yang comb. nov.     

MORPHOLOGY AND CYTOLOGY OF SYNTHETIC HYBRIDS OF AGROPYRON TRICHOPHORUM X AGROPYRON CRISTATUM

Dewey, Douglas R. (Utah State U., Logan.) Morphology and (cytology of synthetic hybrids of Agropyron trichophorum X Agropyron cristatum. Amer. Jour. Bot. 50(10): 1028–1034. Illus 1963.—Three hybrids were obtained from controlled crosses of pubescent wheatgrass, A. trichophorum (2n = 42), and hexaploid crested wheatgrass, A. cristatum (211 = 42). The hybrids were intermediate between the parent plants for all vegetative and spike characteristics observed. Under open pollination, 2 of the hybrids set 2 seeds each, and the other hybrid produced 60 seeds. Meiosis in the parent plants was basically regular. Average motaphase-I chromosome associations were 0.09 I, 20.56 II, 0.05 III, and 0.16 IV per cell in the A. trichophorum parent, which was described as a segmental autoallohexaploid. The hexaploid A. cristatum parent averaged 0.18 I, 7.44 II, 0.81 III, 2.86 IV, 0.08 V, and 2.11 VI per cell at diakinesis and was described as an autohexaploid. Chromosome pairing in the hexaploid hybrid averaged 5.08 I, 8.94 II, 4.33 III, 1.11 IV, 0.27 V, and 0.05 VI per cell. On the basis of chromosome pairing in the parent species and their hybrids, it was concluded that 1 of the A. trichophorum genomes was partially homologous with the 3 genomes of hexaploid A. cristatum. Genome formulae for hexaploid A. cristatum, A. trichophorum, and their hybrids were represented as AAAAAA, A₁A₁B₁B₁B₂B₂, and AAAA₁B₁B₂ respectively.