CYTOGENETICS OF GALINSOGA PARVIFLORA CAV. AND G. CILIATA (RAF.) BLAKE, AND THEIR NATURAL HYBRIDS (ASTERACEAE)

Abstract

The somatic and meiotic chromosomes of four natural populations of Galinsoga Ruiz & Pav. ‐ Population I (G. parviflora Cav.), Population II [G. ciliata (Raf.) Blake], Population III and Population IV have been analyzed. Our studies show that G. parviflora is a diploid (2n= 16); G. ciliata is a segmental allotetraploid (2n= 32); Population III is a triploid natural hybrid between G. parviflora and G. ciliata (3n= 24); and population IV is a putative introgressant between G. parviflora and the natural triploid hybrid (2n= 16). The meiotic chromosomes form eight bivalents and do not reveal any irregularities in G. parviflora which shows 100% pollen viability. During the meiosis of G. ciliata, however, 16 bivalents with occasional quadrivalents, anaphasic bridges and laggards are noticed, and pollen viability varies from 90 to 100%. In the triploid hybrids all the 24 chromosomes form univalents which are grouped into an unanalyzable chromosomal entanglement at metaphase I; consequently the per cent pollen viability is 0. The meiotic behaviour of chromosomes in introgressant is similar to that of G. parviflora, except for the high frequency of quadrivalents and laggards, and lesser pollen viability. The presence of inversion loops in G. ciliata and in Population IV imply that the parental species differ in chromosomal rearrangements. Copyright © 1982, Wiley Blackwell. All rights reserved