Aneusomaty inOrobanche gracilis

Abstract

InOrobanche gracilis Sm. (collected in Vienna, Lower Austria, and N. Italy) the somatic chromosome numbers were found to be inter-and intra-individually variable. Most plants yielded counts of around the tetraploid level (2n = 73−91), a few of around the hexaploid level (2n = 112−116). Only 36% of the plants were eusomatic, only 24% eutetraploid (2n = 76). Depending on the variable somatic chromosome number, gametophytic numbers are also variable. Univalents, multivalents, and anaphase anomalies were of regular occurrence during meiosis of plants with more than 2n = 76 chromosomes.

This is the first report of variable polyploid chromosome numbers (4x = 76, 6x = 114) inOrobanche sect.Orobanche. Aneusomaty is due to a constitutional tendency to nondisjunction during mitosis. The supernumerary chromosomes are considered to represent A- (= normal) rather than B-chromosomes. A possible causality between the chromosomal and the morphological variation, and the adaptive significance of this phenomenon are discussed.