NATURAL HYBRIDS BETWEEN ORYZOPSIS AND STIPA. II. ORYZOPSIS HYMENOIDES x STIPA NEVADENSIS

Johnson , B. Lennart . (U. California, Los Angeles.) Natural hybrids between Oryzopsis and Stipa. II. Oryzopsis hymenoides X Stipa nevadensis. Amer. Jour. Bot. 49(5): 540–546. Illus. 1962.—The amphiploid Stipa nevadensis and one of its parents, S. elmeri, cross with Oryzopsis hymenoides to give nearly identical sterile hybrids heretofore referred to O. bloomeri. Tenuous differences between them proved reliable when verified cytologically. They were distinguished by chromosome counts of 2n = 58 for O. hymenoides X S. nevadensis and 2n = 42 for O. hymenoides X S. elmeri, which counts were expected on the basis of 2n = 68 for S. nevadensis, 2n = 36 for S. elmeri and 2n = 48 for O. hymenoides The parents showed regular bivalent formation and the hybrids mostly univalents. A suggestion that bivalent formation in polyploid species of Stipa may be genically controlled is based on the assumption of homology between different genomes of the amphiploid, S. nevadensis.     

GENOME RELATIONSHIPS IN INTERSPECIFIC AND INTERGENERIC HYBRIDS OF RENANTHERA

Kamemoto , H., and K. Shindo . (U. Hawaii, Honolulu.) Genome relationships in interspecific and intergeneric hybrids of Renanthera. Amer. Jour. Bot. 49(7): 737–748. Illus. 1962.—Chromosome numbers and meiotic behavior of species and hybrids of Renanthera (Orchidaceae) were investigated. Renanthera elongata, R. histrionica, R. matutina, R. monachica, and R. storiei were diploid (2n = 38). The race of R. coccinea commonly grown in Hawaii was found to be hexaploid (2n = 114), while a recently introduced clone from Thailand was diploid (2n = 38). Diploid interspecific hybrids formed about 18 bivalents at M-I, indicating a relatively strong homology of parental chromosomes. The tetraploid hybrid of diploid R. monachica and hexaploid R. coccinea showed predominantly 37 or 38 bivalents, indicating good homology of genomes of the 2 parental species, and autosyndetic pairing in the 2 additional genomes of R. coccinea. Intergeneric hybrids involving Renanthera spp. could be classified into 2 distinct groups: those with 14–11 bivalents that are generally oriented at the metaphase plate and eventually lead to a preponderance of tetrads or tetrads with microcytes, and those with fewer bivalents (9–5) many of which are unoriented pseudobivalents and which ultimately give rise to dyads and dyads with microcytes. Relationships of parental species on a taxonomic basis are closer in the former than the latter group.     

MEIOTIC IRREGULARITY IN SPECIES AND INTERSPECIFIC HYBRIDS OF PINUS

This paper describes a comparative analysis of meiotic conditions in 61 individual trees representing 21 species and 22 interspecific hybrid combinations of the genus Pinus. Material was collected during three successive growing seasons at the Eddy Arboretum of the Institute of Forest Genetics at Placerville, California. Meiotic irregularity occurred in all species and hybrids examined; mean irregularity frequencies of individual trees ranged from 0 to 47.2 percent. Abnormalities in chromosome movement and their consequences, (1) precocious disjunction associated with the occurrence of univalents and (2) the failure of chiasma terminalization leading to lagging chromosomes and to chromosome breakage and fragments, account for most of the observed irregularity. The same kinds of irregularity occur both in the species and in the hybrids, but they were considerably more frequent in certain of the hybrids than in the related species. These abnormalities in chromosome movement seem to be characteristic of Pinus and are attributed primarily to rrechanical difficulties which attend the large pine chromosomes in meiosis. The most spectacular meiotic irregularities were the characteristic bridge-fragment configurations considered to be the result of crossing-over in heterozygous paracentric inversions. Inversion bridges were observed in 59 of the 61 trees and were as frequent in the species as in the hybrids. They apparently do not result from interspecific differentiation in chromosome structure but from spontaneous intra-specific rearrangements. The literature and work now in progress provide increasing evidence that introgression has been an important factor in the evolution of pine populations. The cytological study of pine chromosomes has failed to produce qualitative evidence of introgression, but the quantitative measurement of meiotic irregularity may serve as a useful criterion for recognizing the results of past hybridization.     

INTERSPECIFIC INCOMPATIBILITY IN GOSSYPIUM. II. LIGHT AND ELECTRON MICROSCOPE STUDIES OF CELL NECROSIS AND TUMORIGENESIS IN HYBRIDS OF G. KLOTZSCHIANUM

Many Gossypium interspecific hybrids that involve G. klotzschianum result in either embryo or seedling lethals. Histologically, lethal symptoms are characterized by necrotic cells and tumors that appear 10–15 days after fertilization in the embryo lethals and at the first true-leaf stage in the seedling lethals. Ultrastructural studies of cell necrosis in seedling lethals show that the first subcellular abnormality is the degeneration of the inner membrane and cristae of the mitochondria. Mitochondrial degeneration is essentially complete before other organelles show evidence of structural aberrations.     

新疆甘草属的种间杂交

试验以居群为单位的新疆甘草属７个种进行种间人工杂交。通过对种间杂交结实量（ＲＳ）和亲本种平均结实量（ＲＳｍ和ＲＳｆ）的分析比较,测出相应的杂交结实指数（ＩＳ）、初步了解种间杂交亲和性的大小,为甘草属植物系统与演化的研究提供参考依据。     

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability. The hybrids do not have meristic counts intermediate to the counts of the parental species. The hybrids usually have counts as high as the species with the higher count for those characters that differ between the parental species and often have higher counts for those characters that do not differ between the parental species. We suggest that the tendency for interspecific hybrids to have high meristic counts may be related to differences between the species in the length and timing of the developmental periods during which the counts of the characters are determined.     

猕猴桃属种间体细胞杂种

利用PEG融合方法,分别进行了中华猕猴桃(Actinidia chinensis var.chinensis)(2n=2x=58)子叶愈伤组织来源的原生质体与美味猕猴桃(A.deliciosa var.deiciosa)(2n=6x=174)子叶愈伤组织原生质体、以及狗枣猕猴桃(A.kolomikta)(2n=2x=58)叶肉原生质体种间原生质体融合。结果表明:中华猕猴桃与美味猕猴桃融合的1个克隆和中华猕猴桃与狗枣猕猴桃融合的4个克隆的RAPD谱带分别具有双亲特异的DNA谱带;经流式细胞仪分析,前者细胞核倍性推测为8倍体,后者细胞核为3倍体、4倍体和5倍体。初步鉴定这5个克隆是猕猴桃属种间体细胞杂种。     

杂交在进化中的作用及杂种的识别和分类处理

所谓杂交和杂种,可以有不同的概念。从最广义的角度来理解,凡基因型不同的个体之间的交配都叫杂交。基因杂合状态是自然界正常的现象。互交繁育的生物体,在正常情况下,在许多位点上都是不同等位基因的杂合体,也就是杂种,它们在自交和杂合时都产生有变异和分离的子代。但杂交最常用的含义是指已有生殖隔离的异种个体或甚至异     

CHROMATOGRAPHIC DOCUMENTATION OF INTERSPECIFIC HYBRIDIZATION IN VERNONIA: COMPOSITAE

Chromatographic analysis of the flavonoid compounds in leaf extracts support field and morphological studies which lead to the interpretation of Vernonia guadalupensis Heller as a natural hybrid between V. lindheimeri Engelm. and Gray and V. interior Small. Of 16 major flavonoids found in leaf extracts of the parental species, 8 were found only in V. lindheimeri, 3 were found only in V. interior; 5 were common to both. All 16 were found in leaf extracts of V. guadalupensis.     

B-CHROMOSOMES,THEIR ORIGIN AND RELATION TO MEIOSIS IN INTERSPECIFIC LOLIUM HYBRIDS

The following Lolium species were shown to have 14 chromosomes: L. canariensis Steud. (= L. gracile Parl.), L. loliaceum (Bory and Chaub.) Hand.-Mazz., L. multiflorum Lam., L. perenne L., and L. temulentum L. B-chromosomes in addition to the normal complement were observed during metaphase I and anaphase I for L. persicum Boiss. and Hohen., L. remotum Schrank, L. rigidum Gaud., L. strictum Presl. (= L. rigidum?), and for several synthesized interspecific hybrids. General absence of B-chromosomes in diakinesis suggested that they originated by misdivision of A-chromosomes during prometaphase I. The B-chromosomes reached a maximum of eight but the number varied for microsporocytes of the same plant. B-chromosomes appeared spontaneously in progenies from sibbing of hybrid plants without supernumeraries but were also eliminated in the F₂ from other sibbings. Degree of chromosome pairing during meiosis was unrelated to the subsequent presence of B-chromosomes. Normal pairing of seven bivalents was typical for L. perenne × L. multiflorum, L. perenne × L. rigidum, L. multiflorum × L. loliaceum, and L. rigidum × L. loliaceum. Between five and seven bivalents were recorded for L. multiflorum × L. persicum, L. multflorum × L. remotum, L. multiflorum × L. strictum, L. rigidum × L. persicum, L. rigidum × L. remotum, L. rigidum × L. strictum, and L. rigidum × L. temulentum. The results indicated that these Lolium species have a common and generally undifferentiated genome suggesting relatively recent speciation.     

INTERSPECIFIC INCOMPATIBILITY IN GOSSYPIUM. IV. TEMPERATURE-CONDITIONAL LETHALITY IN HYBRIDS OF G. KLOTZSCHIANUM

A number of interspecific hybrids involving G. klotzschianum are embryo-lethal or seedling-lethal at temperatures considered optimal for cotton culture (26–32 C). At temperatures between 33–37 C, lethal symptoms (cell-necrosis and vascular plugging) for both stages of lethality are greatly ameliorated and at 40 C lethal symptoms are absent and hybrid ontogeny is normal for embryo- and seedling-lethals. Temperature-repressed lethals revert to type within 12–24 h after being returned to a non-repressive temperature regime.     

INTERSPECIFIC HYBRIDIZATION AND TAXON UNIFORMITY IN ARABIS (CRUCIFERAE)

Intermixed populations of Arabis holboellii Hornem. var. pendulocarpa (A. Nels.) Roll., A. williamsii Roll., and their putative hybrids; and of A. holboellii var. retrofracta (Grah.) Rydb., A. drummondii Gray and A. divaricarpa A. Nels., the latter also considered to be a probable hybrid taxon, were studied in the field in Montana and Wyoming. In spite of the “intermediacy” of the putative hybrids in both cases, hybrid swarms were not found. In each instance, the “intermediate” as well as the taxa regarded as parental were remarkably uniform. The existence of three relatively uniform morphotypes in each of the several populations is contrary to the usual situation involving hybridizing taxa. A possible explanation is that seed production, at least in the “intermediate” morphotype individuals, involves apomixis, thus circumventing the usual sexual process that would result in a hybrid swarm. Amphiploidy as a possible mechanism for producing A. divaricarpa as a stable hybrid was ruled out in one population where the chromosome number 2n = 14 was found in all three taxa present in the population. Arabis divaricarpa, widely distributed in northern North America, often occurs as a uniform morphotype where no other species of Arabis grows. If it is of hybrid origin, as the evidence suggests, a mechanism other than sexual reproduction must be present to keep up uniformity and at the same time perpetuate the taxon. It is suggested that facultative apomixis is involved in the reproductive process and that it controls the genetic variability that would otherwise be present by insuring maternal inheritance in each successive seed crop.     

CHROMOSOME PAIRING AND POLLEN FERTILITY IN INTERSPECIFIC HYBRIDS OF SPECIES OF PARTHENIUM (ASTERACEAE)

Meiotic analyses and pollen viability tests were performed on F, hybrids between diploid guayule (Parthenium argentatum Gray 2n = 36), P. rollinsianum Rzedowski (2n = 36), P. alpinum var. tetraneuris Barneby (2n = 36), and P. alpinum var. alpinum Nutt. (2n = 36). Parthenium chromosomes are small and karyomorphologically similar, and meiotic analysis is difficult because of chromosome clumping. However, cytogenetic studies at metaphase I indicated univalents can be seen in a lateral view of the metaphase plate. Chromosome pairing and the number of univalents varied within and between the interspecific hybrids, with an average univalent number of 1.54 for the P. rollinsianum hybrids, 2.36 for the P. alpinum var. tetraneuris hybrids, and 2.46 for the P. alpinum var. alpinum hybrids. Pollen viability tests for the parental species and the hybrids were conducted by germination of pollen grains on stigmas. The percent of viable pollen recorded for the diploid guayule hybrids with P. rollinsianum, P. alpinum var. tetraneuris, and P. alpinum var. alpinum are 21.94, 13.47, and 11.17, respectively. The degree of chromosome pairing and pollen viability is striking because there are many morphological differences between the parents. The chromosome homology of these species based on their pairing behavior allows for the design of a backcross breeding program that would permit the transfer of the desirable characteristics from these species into diploid guayule.     

INTERSPECIFIC HYBRIDS OF DROSOPHILA HETERONEURA AND D. SILVESTRIS I. COURTSHIP SUCCESS

Drosophila heteroneura and D. silvestris are well-defined, sympatric species of the planitibia subgroup of Hawaiian Drosophila. D. silvestris can be subdivided into two allopatric morphotypes that differ in the number of bristle rows on the front tibia (two rows versus three rows). We measured courtship success of intraspecific and interspecific hybrids as the proportion of females inseminated during a two-week period with a single sib male. Proportions were arcsin-transformed so that the values were asymptotically normal in distribution, and tests of homogeneity and of mean differences were performed. Of key importance is the discovery of genetic variation for the proportion of inseminated females within both D. heteroneura and D. silvestris. The interspecific crosses and the D. silvestris intraspecific crosses also provide evidence for a coadapted gene complex with some dominance or heterosis. This coadapted gene complex correlates with the morphotypes of these flies, rather than with the D. heteroneura/D. silvestris contrasts per se. This observation stresses the importance of recognizing both behavioral and morphological components of the mate-recognition system. The incompatible coadaptation that separates the two-row from the three-row forms also supports recent molecular studies which indicate that the three-row form split from the two-row form prior to the split between D. heteroneura and two-row D. silvestris. The observations of intraspecific variability and coadaptation support the predictions of a genetic-transilience model which explains the origin of a new mate-recognition system in terms of sexual selection in the context of a founder-flush event.