Euphytica 22 (1973) : 613-614

HAPLOIDY IN BRASSICA NIGRA KoCH

SHYAM PRAKASH

Cummings Laboratory, Indian Agricultural Research Institute, New Delhi, India

Received 22 February 1973

SUMMARY

Meiotic behaviour of haploid plants of Brassica nigra which arose parthenogenetically amongst theprogeny of B. nigra x B. campestris, is described . The presence of two bivalents and s-s associationssuggests the basic chromosome number w as six and the present x = 8 number arose through theduplication of two of the original chromosomes .

INTRODUCTION

The genus Brassica represents an aneuploid series of its elementary species with ga-metic chromosome numbers as 8, 9 and 10 representing A, B and C genomes inaddition to a recently proposed one D (PRAKASH et al ., 1971) . A critical examinationof meiotic behaviour of haploids of these species may be of some importance from theevolutionary point of view as the chromosome behaviour in these may reveal somefacts of the past genetical architecture of the species . RAMANUJAM (1941) was the firstto report haploidy in the genus Brassica for B. campestris . Later it was reported inB. oleracea by THOMPSON (1956). Our investigation records the occurrence of haploidyin B. nigra representing the B genome and the meiotic behaviour is discussed in rela-tion to the evolution of the species .

MATERIAL AND METHODS

B. nigra, a 2n = 16 chromosome species, is a marked cross-fertilizer . The haploidplant (2n = 8) was detected amongst the progeny of B. nigra x B. campestris .Meiosis was studied in acetocarmine squashes of anthers fixed in Carnoys fluid .

RESULTS AND DISCUSSION

The haploid plant was like the mother plant morphologically except that the formerwas slender with small flowers and was completely sterile giving only 0.6 % fertilepollen. Thus it had arisen parthenogenetically .

At meiosis, 83 out of 124 PMC's examined showed the chromosomes as univalentsonly (Fig. IA) at meta-anaphase I. Some chromosomes were seen to undergo pairingalso and a maximum of two bivalents (Fig . 1B) in 17 cells and one bivalent in 24 cellswere observed . In addition to the chiasmate associations, there were two types of uni-valents associations i .e . side-to-side and end-to-end, the former being more frequent .The number of univalents to undergo s-s pairing was restricted to four only . The biva-lents where observed were all rod-shaped monochiasmates .

Chromosome behaviour in haploids of elementary species has earlier been described

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Fig . 1 . Chromosomes at meta-anaphase I . A : 8 univalents . B : 2 bivalents and 4 univalents .

in B. oleracea and B.campestris as pointed out above, having two bivalents in theformer (THOMPSON, 1956) and occasional associations to form a loosely paired bivalentin the latter (RAMANUJAM, 1941) . In the present case, however, the maximum bivalentfrequency was found to be two . This association of chromosomes may be ascribed toresidual homologies in some segments of four chromosomes involved in pairing . Inaddition to chiasmate bivalents, other types of associations of univalents were alsoobserved . As pointed out by RILEY & CHAPMAN (1957) one of such types i .e . s-sdepends on segmental homology of the pairing partners and the same chromosomeswhich undergo chiasmate associations may also form s-s associations . This can beverified from the fact that never more than four chromosomes were found to be in s-sassociations in an sigle cell . Consequently it can be concluded, based on pairing beha-viour, that there are only six types of basic chromosomes and the present X = 8gametic number has arisen through the duplication of two of the six basic chromo-somes which in the course of evolution differentiated from the original ones and nolonger capable of synapse in the diploids while still retaining traces of genetic equiva-lence which cause pairing in the haploid state . A basic genomic number for the Bgenome of six appears probable. Earlier CATCHESIDE (1937), THOMPSON (1956),RoBBELEN (1960), PRAKASH (1969) and NWANKITI (1971) also came to the same con-clusion that the basic genomic number in Brassica is six .

REFERENCESCATCHESIDE, D . G., 1937 . Secondary pairing in Brassica oleracea. Cytologia, Fuji Jub . Vol., 366-378 .NWANKITI, 0 ., 1971 . Cytogenetic and breeding studies with Brassica . I . Cytogenetic experiments

with Brassica napocampestris . Hereditas 66 : 109-126 .PRAKASH, S ., 1969. Production of superior amphidiploids of Brassica juncea Coss from different

20-chromosome species of Brassica and their evaluation to certain fungal diseases . Ph . D . Thesis,Aligarh Muslim Univ ., India.

PRAKASH, S. & A. NARAIN, 1971 . Genomic status of Brassica tournefortii GoUAN. Theor. Appl .Genet . 41 : 203-204 .

RAMANUJAM, S., 1941 . A haploid plant in toria (Brassica campestris L .) . Proc. Ind . Acad . Sci., B,14 : 25 .

RILEY, R. & V. CHAPMAN, 1957. Haploids and polyhaploids in Aegilops and Triticum . Heredity 11 :195-208.

ROBBELEN, G., 1960. Beitrage zur Analyse des Brassica Genomes. Chromosoma 11 : 205-228 .THOMPSON, K . F., 1956 . Production of haploid plants of marrow stem kale . Nature 178 : 748 .

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Euphytica 22 (1973)