Cell nuclei were isolated from leaf tissues of wild banana (Musa balbisiana, M. acuminata ssp, banksii and M. acuminata ssp. errans) and of the two vegetative clones of diploid cultivar "Pisang Mas". Relative fluorescence intensity was measured on propidiurn iodide-stained nuclei by flow cytometry. Nuclei isolated from Glycine max with known nuclear genome size were used as internal standard to determine nuclear DNA content of Musa in absolute units. The results of the study showed that the size of nuclear genome of Musa is smaller than previously estimated. In general, it is smaller in comparison with many other angiosperms. Furthermore, it was found that nuclear DNA content of M. balbisiana (genome BB) is significantly lower than that ofM. acuminata subspecies and cultivars (genome AA). This finding should permit estimation of genome composition in Iriploid Musa clones with expected hybrid composition. Flow cytometry is proposed as a useful technique with potential applications in taxonomy, breeding and biotechnology of Musa.

Nuclear DNA content and genomic distributions of 5S and 45S rDNA were examined in nineteen diploid accessions of the genus Musa representing its four sections Eumusa, Rhodochlamys, Callimusa and Australimusa, and in Ensete gilletii, which was the outgroup in this study. In the Eumusa (x = 11), 2C DNA content ranged from 1.130 to 1.377 pg, M. balbisiana having the lowest DNA content of all sections. M. beccarii (x = 9), a representative of Callimusa, had the highest 2C nuclear DNA content (1.561 pg). Species belonging to Rhodochlamys (x = 11) and Australimusa (x = 10) had 2C DNA contents ranging from 1.191 to 1.299 pg and from 1.435 to 1.547 pg, respectively. E. gilletii (x = 9) had 2C DNA content of 1.210 pg. The number of 5S rDNA loci in Musa varied from 4 to 8 per diploid cell. While different numbers of 5S rDNA loci were observed within Eumusa and Rhodochlamys, four 5S rDNA loci were observed in all accessions of Australimusa. M. beccarii (Callimusa) and E. gilletii contained 5S rRNA gene clusters on five and six chromosomes, respectively. The number of 45S rDNA loci was conserved within individual sections. Hierarchical cluster analysis of genome size, number of chromosomes and 45S rDNA sites suggested a close relationship between Rhodochlamys and Eumusa; Australimusa was clearly separated as were M. beccarii and E. gilletii. Within the Eumusa-Rhodochlamys group, M. balbisiana, M. schizocarpa and M. ornata formed distinct subgroups, clearly separated from the accessions of M. acuminata, M. mannii, M. laterita and M. velutina, which formed a tight subgroup. The results expand the knowledge of genome size and genomic distribution of ribosomal DNA in Musa and Ensete. They aid in clarification of the taxonomical classification of Musa and show a need to supplement the analyses on the DNA sequence level with cytogenetic studies.

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Sixteen inbred lines and one hybrid of maize were tested for their capability of somatic embr) ogenesis, and fully developed plants could be regenerated from ten inbred lines. The highest frequency of plant regeneration was expressed in the inbred line CHI 31, and when this line was crossed with a recalcitrant, non-regenerating line, the Fi and BC hybrids were regenerable. The results of reciprocal crosses demonstrated that dominant nuclear genes and cytoplasmic factors are primarily responsible for the heritable determination of embryogenic callus proliferation and in vitro regeneration of maize plants.Somaclonal and radiation-induced variability was studied in maize to assess their nature and potential contribution to plant breeding. The inbred line GHI 31 possessing a high in vitro capacity of somatic embry'O formation was used as experimental material. CHI 3! plants were seifed, and twelve-day old zygotic embryos irradiated with '"Co gamma radiation in situ. Mature caryopses were han-ested and assigned as M, material, in another series, immature z)-gotic embryos (size 1.2-1.5 mm) wtrt cultured in Vttro on K-6 medium supplemented with 2,4-D (2.5 uM), and somatic embr)'os regenerated into plants i these were transplanted into soil and selfpollinated. Regenerants from non-irradiated cultures were grown as Rj generation, while regenerants from irradiated explants were considered as M|R] generation.The genetic variability was evaluated in the M2, R2 and M2R2 generations, respectively, and compared with a non-treated seed control. Irradiation induced a variety of chlorophyll and morphological variants segregating in the M; generation; however, the frequency of deviant types obtained in the R; generation (somaclonal variation) was significantly exceeding the one derived from the Mi populations. The combination of explant irradiation and in vitro regeneration was most effective for the manifestation of chlorophyll and morphological offtypes in the JV12RT generation, and increased drasticalh' the frequenc)' of early flowering ^'ariants. Differences in the segregation patterns of mutant phenotypes among sister somaclones in the R., and M;R> generations indicate a different genetic basis of plants originating from the same explant. This phenomenon suggests a mutational sectoring of the callus during culture. Radiation induced and somaclonal variation exerted a similar spectrum of chlorophyll and morphological deviants.Kev words: Zea ma-i^s -in vitro plant regeneration -somaclonal variation -induced mutations

Although the nuclear genome of banana (Musa spp.) is relatively small (1C ∼ 610 Mbp for M. acuminata), the results obtained from other sequenced genomes suggest that more than half of the banana genome may be composed of repetitive and non-coding DNA sequences. Knowledge of repetitive DNA can facilitate mapping of important traits, phylogenetic studies, BAC-based physical mapping, and genome sequencing/annotation. However, only a few repetitive DNA sequences have been characterized in banana. In this work, we used DNA reassociation kinetics to isolate the highly repeated fraction of the banana genome (M. acuminata ‘Calcutta 4’). Two libraries, one prepared from Cot ≤0.05 DNA (2,688 clones) and one from Cot ≤0.1 sequences (4,608 clones), were constructed, and 614 DNA clones were chosen randomly for sequencing and further characterization. Dot-plot analysis revealed that 14% of the sequenced clones contained various semi-tandem and palindromic repeated sequences. ‘BLAST’ homology searches showed that, in addition to tandem repeats, the Cot libraries were composed mainly of different types of retrotransposons, the most frequent being the Ty3/gypsy type monkey retrotransposon. Selected sequences displaying tandem organization properties were mapped by PRimed IN Situ DNA labeling (PRINS) to the secondary constriction on metaphase chromosomes of M. acuminata ‘Calcutta 4’. Southern hybridization with selected BAC clones carrying 45S rDNA confirmed the presence of the tandem repeats in the 45S rDNA unit. This work significantly expands the knowledge of the repetitive fraction of the Musa genome and organization of its chromosomes.