ARTIFICIAL HYBRIDIZATIONS IN THE SUBTRIBE PERITYLANAE (COMPOSITAE–HELENIEAE)

Artificial hybridizations were conducted with 37 species of four genera of the subtribe Peritylanae (Compositae). Crossability, pollen stainability, and meiotic behavior were examined for most of the resulting 61 F₁ hybrid combinations. Intergeneric hybrids involving Amauria, Eutetras, Pericome, and Perityle, and infrageneric hybrids involving Perityle were readily obtained. Lower crossability and hybrid fertility were displayed by intergeneric crosses. The infrageneric crosses of Perityle were organized into two categories, intersectional and infrasectional, based upon the taxonomic sections that are recognized for the genus; sect. Pappothrix, sect. Laphamia, and sect. Perityle. In general, the crossability and hybrid fertility of intersectional crosses was markedly higher than that of intergeneric crosses. The results suggest a closer relationship between the three taxonomic sections of Perityle than between Perityle and other genera of the subtribe.     

THE PROBLEM OF PLOIDY IN ECHEVERIA (CRASSULACEAE) II. TETRAPLOIDY IN E. SECUNDA

Every chromosome number from n = 12 to n =34 and also many higher numbers are known in one or more of the 130+ species of Echeveria, and the numerical boundary between diploids and tetraploids is not immediately apparent. Echeveria also is extraordinary for the number and diversity of hybrids that it can produce in cultivation, both within the genus and with species of several related genera. In 42 collections studied, the morphologically and cytologically variable E. secunda of central Mexico has n = 30-32, often with one or more B-chromosomes, and some quadrivalents are formed at meiosis in nearly every cell. Twenty-four hybrids of E. secunda, with 22 species or cytotypes considered diploids, resemble the former much more closely in appearance, and at meiosis 15-16 paired elements (bivalents and multivalents) are formed, never more, regardless of the number of chromosomes, 12 to 34, that were received from the other parent. It is concluded that the 15-16 paired elements in these hybrids are formed by the 30-32 chromosomes received from E. secunda, and that most chromosomes from the other parents occur as univalents, although usually a few associate with pairs from E. secunda to produce multivalents. Hybrids of E. secunda with 11 definitely tetraploid species having n = 34 to n = 68 are nicely intermediate in morphology between their parents, form mostly or entirely bivalents at meiosis, and most, probably all, including five intergeneric hybrids, are fertile. These observations are all consistent with the conclusion that E. secunda is an autotetraploid, even though no plants of the species having n = 15 or 16 have been found, and even though some other species of Echeveria having as many as 34 gametic chromosomes appear to be effectively diploid. Observations on pollen stainability and on second-generation hybrids are all compatible with this conclusion. The high chromosome numbers in many Mexican Crassulaceae that are now effectively diploid may have originated as polyploids that have become diploidized by mutation, loss, or suppression of duplicated chromosomes, segments, and genes. Hybrids of E. secunda, with three other species that appear to be tetraploids, have less regular meiosis, apparently because all of the chromosomes from the other parents do not regularly form pairs in the hybrids. These three species may represent intermediate stages in the processes of diploidization.     

Expression of unilateral incompatibility in pollen of Lycopersicon pennellii is determined by major loci on chromosomes 1, 6 and 10

Summary We have previously described gene introgression from the wild nightshade Solanum lycopersicoides into tomato (Lycopersicon esculentum) through the use of either diploid or sesquidiploid hybrids (the latter consisting of two genomes of L. esculentum and one genome of S. lycopersicoides). Both types of intergeneric hybrids display pollen sterility, but workable ovule fertility. Unilateral incompatibility prevents their direct hybridization with staminate L. esculentum. Pollen of a self-compattible form of the related wild species L. pennellii is compatible with pistils of L. esculentum x S. lycopersicoides hybrids. This trait was backcrossed from L. pennellii to L. esculentum in order to develop bridging lines that could be used to obtain progeny from the intergeneric hybrids and to study the inheritance of bridging ability. In progeny of L. esculentum x S. lycopersicoides hybrids pollinated with L. pennellii-derived bridging lines, preferential transmission of L. pennellii alleles was observed for certain isozyme and RFLP markers on chromosomes 1, 6 and 10. The skewed segregations suggest linkage to three major pollen-expressed compatibility loci. This was confirmed by observations of pollen tube growth, which indicated that compatibility with pistils of the diploid intergeneric hybrid occurred only in bridging lines at least heterozygous for the L. pennellii markers on chromosomes 1, 6 and 10. Compatibility with the sesquidiploid hybrid required only the chromosome 1 and 6 loci, indicating an apparent effect of gene dosage on expression of incompatibility in the pistil. In an F₂ L. esculentum x L. pennellii population, preferential transmission of L. pennellii alleles was observed for the same markers on chromosomes 1 and 10, as well as other markers on chromosomes 3, 11, and 12, but not 6. The chromosome 1 pollen compatibility locus maps to or near the S-locus, which determines S-allele specificity. The results are discussed in relation to existing genetic models for unilateral incompatibility, including the possible involvement of the S-locus.     

Lipochaeta and Melanthera (Asteraceae: Heliantheae subtribe Ecliptinae): establishing their natural limits and a synopsis

We restrict the genusLipochaeta to the allopolyploid species of the typical section.Lipochaeta s.str. is interpreted to be the result of an intergeneric hybridization betweenMelanthera and a presently unknown taxon, perhaps of the genusWedelia. Lipochaeta is characterized, in addition to its allopolyploidy (n=26), by having both flavonols and flavones, disk corollas with 4 lobes, achenes tuberculate at maturity, the disk achenes flattened to slightly biconvex, and ray achenes obcompressed.Lipochaeta sect.Aphanopappus andWollastonia are here reduced to synonymy underMelanthera. We transfer 14 HawaiianLipochaeta and one New Caledonian species as well as the AsianWedelia prostrata toMelanthera. These transfers, along with the species in Africa and North America, bring the number of species in the genus to 35.Melanthera is delimited by an abruptly narrowed to truncate and flattened top of the achene, (0−)1–15(−20) often unequal, ciliate or barbellate, caducous pappus bristles immediately surrounding the corolla, involucral bracts and receptacular paleae with many veins forming longitudinal striations, and n=15. The florets are 5-merous, the corollas are yellow or white, and rays are absent (in white-flowered species) or present and neutral or fertile. In dealing with species formerly placed inLipochaeta, the GalapagosL. laricifolia is here transferred from the illegitimate generic nameMacraea toTrigonopterum and the BrazilianL. goyazensis is transferred toAngelphytum. We maintain the earlier reduction ofEchinocephalum underMelanthera and reduce all three taxa originally described in it to one,M. latifolia.     

STERILITY BARRIERS OF SOME ARTIFICIAL F1 ORCHID HYBRIDS: MALE STERILITY. I. MICROSPOROGENESIS AND POLLEN GERMINATION

Microsporogenesis, pollen germination and fertility of males gametes were studied in 24 artificial intergeneric and interspecific F₁ hybrids of orchids. Although parental species had the same chromosome number (2n = 40), microsporogenesis of the hybrids was irregular due to the lack of homology of the chromosomes of the parental species. This led to formation of tetrads of microspores without micronuclei, tetrads with 1–8 micronuclei, triads, dyads with and without micronuclei, and monads. Chromosomes numbers found in haploid microsporocytes ranged from 7 to 40; in micronuclei the chromosome number varied between 1 and 5. In terms of pollen germination, three situations were observed: 1) hybrids whose pollen grains did not germinate in the stigma; 2) hybrids in which the pollen tubes grew down in the style, but did not penetrate into the ovary; 3) hybrids in which the pollen tubes grew down normally through the ovary, reaching the ovules. When the pollen tubes did not penetrate the ovary no fruit was formed. Therefore germination tests carried out in vitro may not indicate pollen fertility, because pollen tube growth in the style of the flower may be insufficient to induce fruit formation or to accomplish fertilization.     

CYTOGENETICS OF HYBRIDS OF CARTHAMUS SPECIES (COMPOSITAE) WITH TEN PAIRS OF CHROMOSOMES

Plants thought to be typical of 7 species were chosen to represent the various taxa of Carthamus species with 10 pairs of chromosomes. These entities were crossed in all possible combinations and 20 of the possible 21 interspecific hybrids were obtained after 3 seasons of crosses. Analyses of the hybrids included studies of microsporocytes, pollen stainability, achene fertility, rudimentary ovaries, and other morphological characteristics. Pairing of chromosomes at metaphase I indicated no translocations were present in hybrids between C. tenuis from Israel, C. alexandrinus from Egypt, C. glaucus from northern Israel, and C. syriacus from Jordan. Members of this group are assigned the standard arrangement. Hybrids of C. glaucus from Iran, C. glaucus from Syria, and C. dentatus from Turkey always showed a translocation or chromosomal interchange when crossed with any member having the “standard” arrangement. The last 3 species are considered to have the “non-standard” chromosomal arrangement. The parental species used in this study can be regarded as a set of testers which will allow identification of chromosomal differentiation in additional Carthamus materials as they are collected.     

POLYPLOIDY,DYSPLOIDY, AND CHROMOSOME PAIRING IN ECHEVERIA (CRASSULACEAE) AND ITS HYBRIDS

The 140+ species of Echeveria have more than 50 gametic chromosome numbers, including every number from 12 through 34 and polyploids to n = ca. 260. With related genera, they comprise an immense comparium of 200+ species that have been interconnected in cultivation by hybrids. Some species with as many as 34 gametic chromosomes include none that can pair with each other, indicating that they are effectively diploid, but other species with fewer chromosomes test as tetraploids. Most diploid hybrids form multivalents, indicating that many translocations have rearranged segments of the chromosomes. Small, nonessential chromosomal remnants can be lost, lowering the number and suggesting that higher diploid numbers (n = 30–34) in the long dysploid series are older. These same numbers are basic to most other genera in the comparium (Pachyphytum, Graptopetalum, Sedum section Pachysedum), and many diploid intergeneric hybrids show very substantial chromosome pairing. Most polyploid hybrids here are fertile, even where the parents belong to different genera and have very different chromosome numbers. This seems possible only if corresponding chromosomes from a polyploid parent pair with each other preferentially, strong evidence for autopolyploidy. High diploid numbers here may represent old polyploids that have become diploidized by loss, mutation, or suppression of duplicate genes, but other evidence for this is lacking. Most species occur as small populations in unstable habitats in an area with a history of many rapid climatic and geological changes, presenting a model for rapid evolution.     

CYTOLOGICAL ANALYSIS OF ANTHURIUM ANDRAEANUM (ARACEAE), ITS RELATED TAXA AND THEIR HYBRIDS

Karyotypes and meiotic configurations of Anthurium andraeanum and closely related taxa were analyzed. The karyotypes of A. andraeanum, A. caperatum, A. formosum, A. kamemotoanum, A. lindenianum, A. roseospadix, A. cf. sanctifidense, A. subsignatum, A. garagaranum, and an unidentified Anthurium sp. commonly consisted of four large metacentric or submetacentric chromosomes, two fairly large acrocentric chromosomes, two satellite chromosomes, and 22 smaller chromosomes. Variation in the karyotypes of A. nymphaeifolium and A. ochranthum suggested chromosomal rearrangement in the genus. All taxa showed 15 pairs of chromosomes at prometaphase I of meiosis in pollen mother cells. Four large chromosomes appeared as ring bivalents, and the rest of the chromosomes appeared as either ring or rod bivalents. Regular bivalent formation at prometaphase I of meiosis in pollen mother cells of species hybrids suggested close genomic relationships among parental taxa. On the other hand, reduction of pollen fertility estimated by pollen stainability in those hybrids suggested genetic divergence of species.     

Cytogenetic analysis of Lycopersicon esculentum (+) Solanum etuberosum somatic hybrids and their androgenetic regenerants

The aim of the study was to characterize genomic relationships among cultivated tomato (Lycopersicon esculentum Mill.) (2n=2x=24) and diploid (2n=2x=24) non-tuberous wild Solanum species (S. etuberosum Lindl.). Using genomic in situ hybridization (GISH) of mitotic and meiotic chromosomes, we analyzed intergeneric somatic hybrids between tomato and S. etuberosum. Of the five somatic hybrids, two plants were amphidiploids (2n=4x=48) mostly forming intragenomic bivalents in their microsporocytes, with a very low frequency of multivalents involving the chromosomes of tomato and S. etuberosum (less than 0.2 per meiocyte). Tomato chromosomes showed preferential elimination during subsequent meiotic divisions of the amphidiploids. Transmission of the parental chromosomes into microspores was also evaluated by GISH analysis of androgenic plants produced by direct embryogenesis from the amphidiploid somatic hybrids. Of the four androgenic regenerants, three were diploids (2n=2x=24 or 2n=2x+1=25) derived from reduced male gametes of the somatic hybrids, and one plant was a hypertetraploid (2n=4x+4=52). GISH revealed that each anther-derived plant had a unique chromosome composition. The prospects for introgression of desirable traits from S. etuberosum into the gene pool of cultivated tomato are discussed. Received: 2 August 2000 / Accepted: 4 December 2000     

THE RELATIONSHIPS BETWEEN MALE AND FEMALE FERTILITY AND AMONG TAXA IN DIPLOID WHEATS

Pollen stainability appears to be a reliable indication of the ultimate seed set in diploid interspecific hybrid and backcross populations in Triticum L. The correlation between percent pollen stained and number of seeds set is positive and highly significant (r = 0.92). Estimates of male and female fertility in the hybrids and backcrosses are interpreted to indicate that the domesticated diploid Triticum monococcum L. and wild diploid T. boeoticum Boiss. em. Schiem, are one and the same species, and that T. urartu Tum. is not a variety of monococcum or boeoticum, but rather a separate species. The F₁ hybrids and backcrosses between monococcum and boeoticum are normally male and female fertile. The F₁ hybrids between monococcum and urartu are completely sterile and complete to partial sterility exists in backcrosses.     

Hybrids and backcross progenies between wheat (Triticum aestivum L.) and apomictic Australian wheatgrass [Elymus rectisetus (Nees in Lehm.) A. Löve & Connor]: karyotypic and genomic analyses

Wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) florets were emasculated and pollinated using two apomictic wheatgrass [Elymus rectisetus (Nees in Lehm.) A. Love & Connor, 2n = 6x = 42, SSYYWW] accessions, one of which produces 2n pollen. A 2n = 42 (B_II) hybrid and four 2n = 63 (B _III) hybrids were obtained. The spike morphology of the B _II hybrid was intermediate to that of its parents. The pollen mother cells (PMCs) of this hybrid contained on average 38.361 and 1.62 II, which was consistent with its disparate genome composition (ABDSYW). Its pollen failed to stain and no BC₁ progeny was obtained. The B _III hybrids (reduced egg fertilized with unreduced sperm) were grasslike and had a full complement of E. rectisetus chromosomes, the synapsis of which was slightly impaired by wheat haplome and/or cytoplasm. Their PMCs contained on average 16.30 II, 25.72 I, and 1.54 multivalents (III plus IV). Pollen stainability in these hybrids was low (<1%), and when they were used as females, one 54- and 60-chromosome BC₁ were obtained. A mean of 13.25 II was observed in PMCs of the 54-chromosome BC₁ and pollen stainability was 10%. Pollen stainability in the 60-chromosome BC₁ was only 5%. The use of 2n-pollen-producing E. rectisetus accession accelerated hybrid and BC₁ formation and may accelerate the ultimate transfer of apomixis to wheat.     

Karyotypes,nucleoli, and amphiplasty in hybrids between Hordeum vulgare L. and H. bulbosum L.

Chromosome measurements were carried out in Hordeum vulgare, H. bulbosum, and their diploid, triploid, and tetraploid hybrids. The chromosomes were classified by using relative values, and thus karyotypes were established. For comparison of these karyotypes both relative and absolute values were used. It was concluded that differential amphiplasty occurred, whereas neutral amphiplasty could not be demonstrated. In the hybrids the relative length of the parts of the chromosomes (long arm, short arm, satellite) was not changed in comparison with these lengths in the pure species. The karyotypes of both species had considerable similarities. From comparing the mean absolute genome lengths, it was, however, concluded that in the pure species, as well as in all hybrid types, the chromosomes of H. vulgare were longer than those of H. bulbosum. In the diploid and tetraploid hybrids the mean genome lengths were shorter than those in the pure species and the triploid hybrids. The differential amphiplasty was such that the secondary constriction of chromosome 6 of H. bulbosum, did not show up in the hybrids. This could be related to the suppression of nucleolar formation in the genome of H. bulbosum, because the maximum number of nucleoli in root tip cells equalled the number of satellite chromosomes. Finally it was found that the pattern of nucleolar fusion in diploid and triploid hybrids deviated from the expectation. The results were discussed in relation to chromosomal disturbances that occurred in the hybrid tissues and that resulted in elimination of chromosomes and other effects.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

EXPERIMENTAL HYBRIDIZATION,CHROMOSOMAL DIVERSITY,AND PHYLOGENY WITHIN GAURA (ONAGRACEAE)

Patterns of interfertility for intersectional hybridizations in Gaura are generally consistent with current taxonomic hypotheses regarding the sectional division of the genus. Crossability is generally lower for intersectional crosses than for intrasectional, interspecific crosses. Average intersectional cross-success ranged from 0–14% among the eight sections, and a total of 54 intersectional hybrids were produced from 1,872 intersectional pollinations. Low rates of capsule-set and no intersectional hybrids were produced by G. mutabilis (section Gauridium), an early offshoot of a primitive ancestor of Gaura. Two species of section Xerogaura that are regarded as relicts of the primitive ancestor of all other Gaura showed low averages for cross-success, but did produce hybrids in combination with three relatively advanced sections (Campogaura, Stipogaura, Pterogaura). Low capsule-set and no intersectional hybrids were produced by G. parviflora (section Schizocarya). Extreme morphological specialization for autogamous reproduction has been accompanied by reproductive isolation of G. parviflora. Only three hybrids resulted from crosses using G. coccinea (section Campogaura), a polyploid complex. Each successful cross paired G. coccinea with a putative progenitor, either a species of section Xerogaura or G. villosa of section Stipogaura. Hybrids of G. coccinea with odd ploidy number showed reduced pollen staining. Species of Stipogaura produced only three hybrids, one each in combination with species of sections Xerogaura, Campogaura, and Pterogaura. Gaura drummondii (section Xenogaura) registered the highest average cross-success despite being a tetraploid. All 25 hybrids of G. drummondii resulted from crosses with G. suffulta, and were triploids that showed reduced pollen staining. Intersectional crosses fail to support the hypothesized relationships of G. drummondii either to G. coccinea or to species of section Stipogaura. Section Gaura produced moderate averages of cross-success, but all 20 hybrids resulted from crosses with G. suffulta. Fifty of the 54 intersectional hybrids were descended from a species of section Pterogaura. Crosses that used G. suffulta as one parent produced 49 of these hybrids. Four hybrids were from crosses with G. macrocarpa (section Xerogaura), and the remaining 45 were due to the recurrent success of crosses that paired G. suffulta as maternal parent with either G. drummondii or a species of section Gaura.     

Factors affecting the induction of pollen plants of intergeneric hybrids of Triticum aestivum X Triticum-Agropyron

Summary Experimental results showed that the use of potato extract as a basic component of culture medium had a promoting effect on producing calli in anther culture of the intergeneric hybrids of Triticum aestivum × Triticum-Agropyron (intermediate type). The induction frequencies of pollen callus on the Potato-II medium containing potato extract as the main component was much higher than that found on N₆ and W₅ media. The induction frequencies of pollen callus and green plantlets in four intergeneric hybrid material inoculated at the late-uninucleate pollen stage were all higher than those inoculated at the mid-uninucleate stage. Appropriate increases in culture temperature significantly increased pollen callus induction frequencies of the intergeneric hybrids. The genotype and physiological state of anther donor plants also influenced pollen callus and green plantlet induction frequencies.     

Karyological and chemotaxonomical studies of the hybridPelargonium incarnatum ×P. patulum (Geraniaceae) and its parents

Pelargonium incarnatum is a tetraploid species (2n = 40) andP. patulum is diploid (2n = 22). A natural hybrid, collected at the same locality as the parent species, has 2n = 42 chromosomes. The meiosis of the hybrid is practically normal and its pollen fertility corresponds to that ofP. incarnatum. The flavonoid patterns of the parent species and the hybrid are very similar. The origin and phylogenetic implications of this intersectional hybrid are discussed.     

遮荫对南美蟛蜞菊、蟛蜞菊及其自然杂交种叶片显微结构及叶绿体超微结构的影响

利用JSM-6360LV型扫描电镜和JEM-1010型透射电镜,观察了南美蟛蜞菊、蟛蜞菊及其自然杂交种新近成熟和老熟叶片的解剖结构及叶绿体超微结构。结果表明:遮荫后该杂交种与其亲本新近成熟叶片均表现为上下表皮气孔密度、叶片总厚度及上下表皮厚度、栅栏组织、海绵组织厚度减小,叶绿体肿胀变形,基粒片层垛叠程度增加,淀粉粒增多变大;遮荫后杂交种老熟叶片总厚度及上表皮、栅栏组织、海绵组织厚度增加,入侵种的下表皮厚度及本地种的上表皮厚度增加,叶绿体超微结构在遮荫后均出现严重损伤,基粒片层类囊体结构边缘溶解等。说明三种蟛蜞菊属物种及各物种不同叶龄叶片对弱光条件的响应存在差异;杂交种叶片显微及超微结构在不同光照下的变化介于亲本之间,对遮荫环境能较好适应。     

CYTOGENETIC STUDIES OF CARTHAMUS SPECIES (COMPOSITAE) WITH 32 PAIRS OF CHROMOSOMES

Two taxa of Carthamus, each with 32 pairs of chromosomes, merit specific status. C. baeticus (Boiss. & Reut.) Nym. is found on islands of and in countries surrounding the Mediterranean Sea, whereas C. turkestanicus Popov extends from western Turkey to Kashmir. Compared to C. baeticus, C. turkestanicus has wider leaves, wider and less divaricate bracts, larger heads with more florets and achenes, and florets with longer lobes. Their chromosomes differ to the extent that microsporocytes of their F₁ hybrids had a reciprocal translocation in pachytene and a mean of over six, and up to 22, univalents at metaphase I. Pollen stainability and seed fertility were reduced in F₁ hybrids.     

APOMIXIS IN THE POA SECUNDA COMPLEX

Observation of cleared ovules of Poa secunda Presl showed that plants produce aposporous embryo sacs, and emasculation studies showed that they do not set seed without pollen. The ratio of sexual to asexual embryo sacs on a given plant does not correlate with percent stainable pollen, nor does pollen stainability correlate with meiotic regularity or with chromosome number. Percent apomictic ovules, percent pollen stainability, and regularity of meiosis all vary within a given population; they also vary if the same plant is moved from one site to another. Although there is morphological variation in the species, none of the reproductive features correlates with morphology. Pollen from any morph will stimulate seed set in any other morph, and hybrids have been produced in low frequency. Plants will also set seed using their own pollen. In its reproductive biology, P. secunda exhibits many similarities with P. pratensis L.     

Genomic in situ hybridization in Brassica amphidiploids and interspecific hybrids

Genomic in situ hybridization (GISH) methods were used to detect different genome components within Brassica amphidiploid species and to identify donor chromatin in hybrids between Brassica napus and Raphanus sativus. In Brassica juncea and Brassica carinata the respective diploid donor genomes could be reliably distinguished by GISH, as could all R-genome chromosomes in the intergeneric hybrids. The A- and C-genome components in B. napus could not be clearly distinguished from one another using GISH, confirming the considerable homoeology between these genomes. GISH methods will be extremely beneficial for monitoring chromatin transfer and introgression in interspecific Brassica hybrids. Received: 20 May 1997 / Accepted: 28 July 1997