The effects of B-chromosomes on vigour and fertility in Dactylis hybrids

Abstract

SUMMARYB-chromosomes ranging in number from one to 12 had a deleterious effect on the vigour and fertility of a population of tetraploid hybrids between:(Natural 4x) Dactylis glomerata ssp. glomera/a and (Induced 4x) Dactylis glomera/a ssp. lusitanicll. Similar trends in vigour and seed set were shown by the original diploid D. glomerata ssp. lusitanica lines, but pollen fertility appeared to be enhanced by low numbers of B-chromosomes.With increasing B-chromosome number induced tetraploid D. glomerata ssp. lusitanicll showed a reduction in the total seed set within each cross.

Transmission of B-Chromosomes in Dactylis

“…In addition to routine chromosome counting, cytological studies of microsporcyte meiosis and first pollen mitosis were made on plants of the following types: Williams and Barclay (1968). (Six p!ants with 1, 2, 3, 4, or 8 B-chromosomes.…”

“…The chromosome squash technique described by Williams and Barclay (1968) was modified as follows for counts on F2 allotetraploid seed-ings: seeds on moist filter p:tper in petri plates were held at a temperature of 5°c for 4 days. and then transferred to 20·c until germination.…”

“…On the female side, transmission of B-chromosomes is normal. INTRODUCTION A reduction of vigour and fertility associated with the presence of B-chromosomes was reported for tetraploid DactyUs hybrids by Williams and Barclay (1968). During routine chromosome counting of hybrid progenies, evidence emerged for the existence of a mechanism which increased the numbers of B-chromosomes transmitted by male gametophytes.…”

Chromosomal stability in natural and induced tetraploid Dactylis

“…(2n=28) and natural tetraploid D. glomerata ssp. glomerata Hayek (2n = 28), has been described by Williams and Barclay (1968). These allotetraploids had varying numbers of Bchromosomes which were associated with deleterious effects on vigor and fertility (Williams and Barclay, 1968), and which were increased in male transmission by non-disjunction and preferential segregation at first pollen mitosis (Williams and Barclay, 1972).…”

“…Among a sample of 170 FJ allotetraploids surveyed for chromosome number by the method described in Williams and Barclay (1968).30% were aneuploids with 27, 29, or 30 normal chromosomes. The frequency of aneuploidy among progeny derived from crosses D. glomerata ssp.…”