Karyotype Variation in Rubus with Particular Reference to R. idaeus L. and R. coreanus Miquel

Abstract

It is generally believed that little chromosome differentiation has occurred in the genus Rubus. But this belief is based largely upon studies in the Eubatus subgenus which contains the blackberries: Heslop-Harrison (1953), for example, reported that the chromosomes of a large number of British blackberry species ranged in size from 1.5 to 2.0 μm and were too small for morphological study. Similarly, Einset (1947) reported that in American blackberries the chromosomes showed little variation, ranging in length from 1.0 to 4.0 μm. These conclusions are supported by meiotic studies, which have led to the idea that chromosome differentiation between Rubus genomes has occurred through minor alterations caused by gene mutations, and by minute structural changes where the rearrangements are so small that the ability of the chromosomes to conjugate has not changed; hence most chromosome combinations are capable of pairing and permitting crossing over, though in allopolyploid hybrids the chromosome differences are frequently sufficient to compel preferential pairing (Gustafsson 1943, Thomas 1940). More recently, Jinno (1958) reported that individual chromosomes of a range of Japanese Rubus species differed in the position of their constrictions, and that species differed in the frequency of chromosomes with median, submedian and sub-terminal constrictions. A greater degree of differentiation was detected by Bammi (1965) for Rubus parvifolius, a Japanese species of the Idaeobatus sub-genus, which contains the raspberries. Bammi used pachytene analyses to identify each of the seven chromosomes, recording their absolute lengths, the ratio of the lengths of the long and short arms and the patten of their chromatic regions. He considered that the chromosomes of this species were unusually easy to spread and that meiotic studies of other Rubus species would be less productive. This paper describes an attempt to detect differences among somatic chromosomes of the Korean species R. coreanus and the raspberry “Glen Clova’, a cultivar of R. idaeus. Both are from the Idaeobatus sub-genus and R. coreanus is used extensively in raspberry breeding as a source of genes for disease resistance (Williams 1950, Keep et al. 1977, Jennings 1978). Four F1 hybrids of the two species were made available from the breeding programme at the Scottish Horticultural Research Institute. © 1981, Japan Mendel Society, International Society of Cytology. All rights reserved.