Margaret Y. Menzel

Genetic relationships in hibiscus sect. Furcaria

The eighteen species studied form an allopolyploid series (x=18). The morphology, crossing behavior, and geographical distribution of 6 diploid, 9 tetraploid, 2 octoploid, and 1 decaploid species were studied. From over 26,500 crosses, 19 hybrid combinations and several derived allopolyploids and three-species hybrids were obtained. Chromosome pairing in the hybrids showed that a minimum of 6 and a maximum of 14 well-differentiated genome groups exist in sect. Furcaia, at least two of which appear to be confined to the Old World. No evidence was found that New World genomes are represented in the Old World. The primary radiation of the diploid genomes probably occurred at about the same time as that of the diploid genomes of Gossypium, whereas the tetraploids and one of the octoploid species (H. furcatus Roxb., non Willd.) seem to be of later origin (late Pleistocene or Recent). Octoploid H. diversifolius Jacq., a circumtropical species, may be a relict of a much earlier round of polyploid evolution.

The Tolerance of Gossypium hirsutum for Deficiencies and Duplications

Exposure of germinating seeds of G. hirsutum to 1200r of X-rays was effective in producing chromosome aberrations. Ten lines having 12 different translocation complexes were recovered, involving a minimum of 29 breaks and rearrangements. At least ten, and probably all twelve, of these complexes gave one or more viable and fertile deficiency-duplication genotypes when outcrossed. Several of the complexes differed in the size of the chromosomes and length of the interchanged arms in such a way as to permit identification of the heterozygote and some or all of the deficiency-duplications by the configurations formed at metaphase I. In three lines, deficiency-duplications for segments carrying marker genes were recovered. It is concluded that the recovery of viable, fertile deficiency-duplications from translocations is the rule rather than the exception in this amphidiploid species.

Relationships among New World species of Hibiscus section furcaria (Malvaceae)

Seventeen species ofHibiscus sectionFurcaria are native to the New World, of which 12 (one diploid, nine tetraploids, one octoploid and one decaploid) have been studied cytotaxonomically. New chromosome counts (2n=4x=72) are reported forH. cucurbitaceus, H. flagelliformis, H. kitaibelifolius, andH. laxiflorus. Seventeen types of tetraploid interspecific hybrids (seven new to this study) all showed complete meiotic chromosome homology (genome formulaGGPP) and normal floral development. That all hybrids were nevertheless almost completely sterile suggests a cytoplasmic component to the genetic differentiation of the species. The diversification of the tetraploid species in habits, habitats and geographical ranges is considerable, despite their similar genome constitutions. A key to 17 native and four introduced African species is presented.Hibiscus cerradoensis sp. nov. is described.

Chromosomes in parthenogenetic miracidia and embryonic cercariae of Schistosomatium douthitti.

Abstract Chromosomes of Schistosomatium douthitti have been studied in miracidial embryos derived from (1) unfertilized eggs in unisexual female mammalian infections and (2) eggs in bisexual mammalian infections. Chromosomes have also been analyzed in cercarial embryos derived from parthenogenetic miracidia. In 168 parthenogenetic miracidial embryos from unisexual mammalian infections, a haploid X set of chromosomes occurred in 160 and a diploid XX set in three; an additional five were probably diploids, although the exact chromosome constitution could not be determined. In 153 miracidial embryos from bisexual mammalian infections the following chromosome constitutions occurred: haploid X in four embryos, diploid XX in 69, diploid XY in 78, triploid XXY in one and triploid XYY in one. Chromosome analyses of cercarial embryos derived from parthenogenetic miracidia gave the following results: of 10 male infections, three were haploid X, six were normal diploid XX, and in embryos from one snail both haploid X and diploid XX cells were observed. All seven female infections were XY diploids and possessed the normal female constitution except for one which was trisomic for the smallest (7) chromosome. It is believed that haploid individuals developed from reduced eggs, and the absence of the haploid Y constitution indicates that the X chromosome is necessary for viability. Possible methods of origin of XX and XY constitutions from parthenogenetic eggs are considered briefly and it is suggested that such diploids arose as a result of meiotic irregularities.

Genetic affinities of the North American species of Hibiscus sect. Trionum

Study of herbarium specimens, crossing behavior, chromosome conjugation, and live populations has shown that the endemic North American species ofHibiscus sect.Trionum comprise two distinct genetic groups.Hibiscus militaris Cav. andH. coccineus Walt, crossed readily and yielded fertile Fi’s. Also,H. incanus Wendl.,H. moscheutos L., andH. lasiocarpos Cav. crossed freelyinter se, and the hybrids were all vigorous and fertile. However, crosses of these three forms with eitherH. militaris orH. coccineus gave lethal hybrids. Preliminary evidence suggests thatH. palustris L. is similar toH. moscheutos, H. incanus, andH. lasiocarpos in crossing behavior. These four forms were found to occur in distinct geographical areas. They may be considered as ecotypes of a single ecospecies.H. grandiflorus Michx. is morphologically related to this alliance, but yielded a viable fertile hybrid when crossed withH. coccineus. Further study of the affinities ofH. grandiflorus andH. palustris is in progress.