B Carrier Genome in Soybean (Glycine max)

Abstract

SummaryHere we report the presence of 2B-chromosomes in Glycine max, which has yet not been reported. These chromosomes were observed in the natural population in 6 out of 85 plants tested in the variety JS90-41. In our case the B's however did not affect the morphology of the plant but had random meiotic behaviour. These chromosomes were smaller than the A-chromosomes and did not pair with them. The pollen fertility in the carrier and non-carrier plants was almost similar. About the possible origin of B-chromosomes in Glycine, it can be assumed that the B's observed in our case might have originated in the course of evolution to discard the inert heterochromatic part from the main nucleus.Key words Glycine max, B-chromosomes, Meiosis, Pollen fertility.B-chromosomes or supernumerary chromosomes are extra chromosomes present in some individuals of many eukaryotic species and are generally considered to be dispensable for normal development, since they have no apparent function (Jones and Rees 1982). B-chromosomes have been found in approximately 15% of living species (Beukeboom 1994). B-chromosomes are non-vital (occurring in only some individuals within a species) and typically have accumulation mechanisms that increase their transmission prior, during, or following gametogenesis (Nur 1962). As a rule, carriers of these chromosomes are phenotypically indistinguishable from those individuals without them (Clark and Wall 1996). In most of the cases, B chromosomes behave as genome parasites that are maintained in natural populations because of specific accumulation mechanisms, despite being detrimental to the host. The B's having no similarity to the autosomes, are inherited according to a non-Mendelian pattern and occur as univalents at meiosis Rees 1982, Green 2004).There are a number of plants species like Plantago, rye, Trigonella, maize, Haplopapus etc. where B-chromosomes have been reported but so far reports on the presence of B's in Glycine max have been encountered. Here we report the occurrence of '2B-chromosomes' in the natural population of Glycine max. Possible behaviour of B's during meiosis and their prospects have been investigated in Glycine max. Materials and methodsSeeds of variety JS 90-41 were obtained from National Research Center for Soybean, Indore, India. Seeds were sown in soil standard management and fertilization recommendations were followed at weekly intervals. At the time of flowering, young floral buds were fixed in 1 : 3 acetic alcohol solution for 24 h, after which they were transferred to 70% alcohol and stored at 4°C. Slides were prepared using anther smear technique with 2% acetocarmine. Approximately 85 plants were analyzed cytologically. Pollen fertility was calculated in them using acetocarmine glycerine stain-