Inheritance o f B chromosomes in garden roses*

P. Lata Department of Plant Biology and Microbiology, Queen Mary College, London, England

Abstract

Transmission of B chromosomes in tetraploid (2n = 28) garden roses was studied. A total of I 304 seeds were used in the experiment which were obtained from various crossings and selfings made between two ) B and four 0B parents. B chromosomes were inherited in only 51 plants out of a progeny of 143. In the progeny IB was more common in occurrence than 2Bs. About 17% of the plants were aneuploids. In general, the B chromosomes adversely affected survival, vigour and pollen fertility of the progeny plants.

Introduction

B chromosomes are of rare occurrence in roses (Jones, 1975). Until recently (kata, t980) their behaviour during male meiosis was not understood. In roses, the B chromosomes can be readily trans- mitted to successive populations by vegetative propagat ion methods, but their inheritance through gametes was not studied. It was therefore found necessary to carry out a breeding experiment where either the male or the female, or both parents possessed B chromosomes and the inheritance of B chromosomes was traced in the offspring. Certain progeny plants were studied in greater detail in order to determine the behaviour of B chromosomes at male meiosis.

Material and methods

Plants of six rose cultivars were obtained from the Warley Roses Ltd, Essex and Peter Beales Roses, Norwich. Seeds produced from the various

* This work is a part of a Ph.D. thesis of the University of London (1980).

Genetica 58, 51--54 (1982). 0016 6707:'82,.581 0051,'$0.80. © Dr W. Junk Publishers, The Hague. Printed in The Netherlands.

combinations (Table 1) were sown in the month of January using the method described earlier (Lata, 1971). Data on germination and chromosome number determinations of the offspring were presented in Table I.

Results

One B chromosome, which is about one fourth of the size of the longest chromosome of the comple- ment (Figs. 2 and 4), was found in 51 out of 143 progeny plants examined (Table I). Two Bs were found in only four offspring and were associated either with 28 or 30 chromosomes (Fig. 5). The remaining 92 plants failed to inherit B chromo- somes. No relationship was found between the B chromosomes and the flower colour of the progeny plants.

Self pollinations in 1B cultivars Aunty Dora and Dearest (Figs. 2, 3 and 5) resulted in a high (17%) proport ion of seedlings with more than 28 chromo- somes (Table 1). Similar pollinations in 0B cultivars (Fig. 1) resulted in only 6% cases with 29 chromo- somes.

A range f rom 28-30 chromosomes was exhibited

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Table 1. Inheritance of B chromosomes in the offspring of cultivated tctraploid roses and their chromosome numbers.

Sample Number of Chromosome numbers 2n= seeds germinated plants 28 28 + I B 28 + 2B 28-30 sown studied

29 2 9 + 1 B 30 3 0 + 2 B

IB X IB Selfed Aunty Dora 392 73 54 29 16 I 2 3 0 2 1 Selfed Dearest 8 5 4 1 0 0 2 0 0 0 I Aunty l)ora X Dearest 14 4 3 0 0 0 0 1 1 1 0 Dearest X Aunty Dora 26 4 3 1 1 0 0 1 0 0 0

IBXOB Aunty Dora X Baronesse E. de Rothschild 22 2 2 1 0 0 0 1 0 0 0 Aunty Dora X Lilac Charm 91 2 2 1 0 0 0 I 0 0 0 Aunty Dora X Papa Meilland 8 5 4 2 2 0 0 0 0 0 0 Dearest X Lilac Charm 25 2 2 0 0 0 0 1 1 0 0 Dearest X Orangeade 10 6 6 2 2 0 1 0 1 0 0

0BX IB Lilac Charm X Aunty Dora 8 2 2 I 1 0 0 0 0 0 0 Orangeade X Aunty Dora I00 13 9 5 3 0 0 1 0 0 0

1B X open pollination Aunty Dora 300 86 38 22 13 1 0 2 0 0 0 Dearest 300 34 14 8 6 0 0 0 0 0 0

by the different cells of certain offspring. These did not carry a B chromosome and were less vigorous than those having a constant number in their complement. On the other hand, the progeny with 30 or 2B chromosomes were less vigorous than those with lower number of chromosomes or with only 1B chromosome.

A and B chromosomes do not pair with each other(Figs. 5-7). At diakinesis univalents, bivalents and polyvalents are formed in different frequencies. In the majori ty of cases B chromosomes lag at anaphase I and divide into chromatids (Figs. 8 11). In the rest of PMCs they are lost. All the progeny plants exhibit cytological irregularities at anaphase, such as laggards, bridges and unequal segregations. At second anaphase the daughter Bs either reach a pole or lag and get eliminated from the tetrad (Figs. 12 and 13), resulting in a low proport ion of pollen grains with B chromosomes. The high inci- dence of cytological irregularities in the progeny leads to high pollen sterility.

Discussion

The B chromosomes in roses did not show the heterochromatic type of staining found in about half of the B-possessing plants(Jones, 1975). The B

chromosome in the progeny follows the same pattern of behaviour irrespective of its occurrence in single or double dose. Erlanson (1933) found pairing in two single 'fragments ' in B chromosomes of Rosa pyrifera; these sometimes pair with A chromosomes. In the present studies the two Bs sometimes lie close together but pairing was not found.

The transmission ofa B chromosome in Solanum viarum was found in all plants when 1B plants were selfed and in only about 13% of the progeny when they were crossed with 0B plants (Dnyansagar & Pingle, 1979). In roses the situation was in marked contrast, as only one third of the progeny inherited the B chromosome irrespective of its occurrence in one or both parents.

In PMC and EMC meiosis the inheritance of B can occur with equal frequency (Dnyansagar & Pingle, 1979) or a more preferential accumulation can take place in the egg cells (Parker, 1976). It appears that in roses, the accumulation of chromo- somes was similar in both pollen and egg cells since reciprocal crosses between 0B and 1B both gave rise to almost equal proportions of progeny with Bs.

Adverse effects of B chromosomes on pollen fertility and vigour are reported in many plants (Jones, 1975) and there is some evidence for this from the present work on roses.

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Figs. 1-13. Inheri tance and behaviour of B ch romosomes in offspring of cultivated roses: ( I ) Selfed Lilac Charm, 2n = 28; (2) Selfed Aun ty Dora, 2n = 28 + 1 B;. (3) same, 2n = 29; - (4) Aunty Dora X Dearest , 2n = 29 -- I B; (5-13) Selfed Dearest , (5) diakinesis, 21 + 1411 + 2B. (6) 1211 + 1 IV + I B, diakinesis, (7) rnctaphase 1, A and B chromosomes , (8) anaphase I, B ch romosomes lagging and dividing, (9) 14-14, B c h r o m o s o m e divided into chromat ids . (10) 15-13, two B ch romosomes divided into ehromat ids , (l l) 15-13, - one chromat id at each pole, (12) anaphase 1I, both chromat ids lagging, (13) late anaphase II, two chromat ids f rom B and thrcc A ch romosomes lagging. Bar: 10 ~m. Arrowheads indicate B chromosomes.

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References

Dnyansagar , V. R. & Pingle, A. R., 1979. Effects of fragments and probable origin of B-chromosomes in Solanum viarum Dunal. Cytologia 44:561 569.

Erlanson. E. W., 1933. Chromosome pairing, structural hybridity and fragments in Rosa. Bot. Gaz. 94: 551-566.

Jones, R. N., 1975. B-chromosome systems in flowering plants and animal species. Int. Rev. Cytol. 40: 1-100.

Lata, P., 1971. Hybridization in modern roses. Curr. Sci. 40: 4-6.

Parker, J. S., 1976. The B-chromosome system of Hypochoeris maculata 1. B-distribution, meiotic behaviour and inheri- tance. Chromosoma 59: 167-177.

Received 2.3.1981 Accepted 1.10.1981.