Batia Pazy

Chromosome divergence in the genus Cuscuta and its systematic implications

SUMMARYCuscuta L. plants are holoparasites with high chromosome divergence. Species representing the three subgenera of the genus were checked for their chromosome number, length and behaviour. Chromosome numbers range between 2n = 8 and 2n = 60, and their size, although roughly uniform within species, varies between 1–23μm. On the whole, size or number of Cuscuta chromosomes cannot be used as diagnostic criteria, except for very few species with unique numbers or sizes. Some associations between certain systematic entities and chromosome characters can be inferred. Species of the Old World of subgenus Cuscuta Engelm. are characterized by inverted meiosis and apparently by holocentric chromosomes, whereas species of the two other subgenera, subgenus Motiogyna Engelm. and subgenus Grammica Yuncker, undergo the regular process of meiosis and have monocentric chromosomes. The presence of holocentric chromosomes does not seem to be associated with their number.

Holocentric chromosome behaviour inCuscuta (Cuscutaceae)

The present study demonstrates thatCuscuta babylonicaChoisy has holocentric chromosomes. Evidence for this phenomenon comes from three different observations. (1) Mitosis: During metaphase and anaphase the sister-chromatids are situated parallel to the equatorial plane with no sign of localized kinetochore activity. (2) Inverted meiosis in microsporocytes. (3) X-rayed microsporocytes, in which the numerous chromosome fragments do not show any lagging or formation of micronuclei. We assume that only one out of the three subgenera inCuscuta, namely subg.Cuscuta, has holocentric chromosomes, while the two other subgenera have monocentric chromosomes.

Insect Induced Self-Pollination

Significant increase of pod production occurs inLupinus palaestinusBoiss. andL. pilosusMurr. following insect visits. The cause of this increase is investigated through (1) examination of the biology of pollination, (2) examination of pod production under various pollination conditions, (3) examination of cross pollination by genetical markers. All data strongly suggest that “Insect Induced Self Pollination” is the main factor in the increase of pod production of these species in nature.

Genetic relationships betweenLupinus pilosus andL. palaestinus (Fabaceae)

Lupinus pilosusMurr. andL. palaestinusBoiss., are both East Mediterranean annuals, greatly resemble each other in morphology, and have the same chromosome number (2n = 42). Some fertile hybrids can be formed by artificial hybridization or under unusual habitat conditions. Isolation in nature between the species is, however, maintained by prevalent selfing, partial reproductive barriers and genic imbalance, together with differences in ecological requirements. It is suggested that this speciation pattern which includes little morphological and hardly any chromosomal divergence might have occurred in other cases of edaphic vicariants too.

Asynapsis inCistanche tubulosa (Orobanchaceae)

Asynapsis, i.e., lack of chromosome pairing in meiosis, is reported and documented for the first time in the holoparasitic plantCistanche tubulosa in a natural population.

The annual species ofAdonis (Ranunculaceae)—a polyploid complex

The five annual species ofAdonis L., sect.Adonis, growing in Israel, form a series of diploid, tetraploid and hexaploid species. Their somatic chromosome numbers are 2n = 16 inA. annua L.,A. dentataDel. andA. palaestinaBoiss., 2n = 32 inA. microcarpa DC., 2n = 48 inA. aestivalis L.; counts forA. dentata, A. palaestina andA. microcarpa are new records. There are indications that alloploidization may have been involved in the process of speciation in sect.Adonis. A taxonomic survey of the 8 species of the section reveals that a higher ploidy level is usually combined with a larger distribution area.