The morphological characteristics and reproductive potential of a haploid plant obtained from the cross between `Banpeiyu' pummelo (Citrus grandis) and `Ruby Red' grapefruit (C. paradisi Macf.) were investigated. The haploid was confirmed to be derived from female gamete of `Banpeiyu' pummelo by isozyme and random amplified polymorphic DNA (RAPD) analysis. Flow cytometry analysis revealed that the haploidy was maintained in several tissues and organs of this plant. It also had the typical morphology of a haploid, such as small leaves and flowers, and had slightly fertile pollen grains. Furthermore, diploid progenies were obtained from the cross between `Kiyomi' tangor and the haploid. The hybridity of these seedlings was confirmed by assessment of the leaf characteristics and RAPD analysis. These results suggest that this haploid produced fertile unreduced pollen grains (n = 9).
Intergeneric somatic hybrids between embryogenic callus-derived protoplasts of round kumquat (Fortunella japonica Swingle) and 'Morita navel' orange (Citrus sinensis Osbeck) were produced by electrofusion. Among the eight different fusion strains obtained, six showed normal morphology, whereas the remaining two showed malformation. All the regenerated plants were intermediate in leaf morphology and had thick and round leaves, which are typical characteristics of polyploids. Ploidy analyses by flow cytometry and chromosome counting in root-tip cells revealed that these plants are amphidiploid (2n=4x=36). Hybridity of the fusion products was confirmed by random amplified polymorphic DNA and cleaved amplified polymorphic sequence (CAPS) analyses. Furthermore, analyses of chloroplast (cp) and mitochondrial (mt) DNA by CAPS showed that these somatic hybrids contained cp- and mt-DNA of round kumquat without recombination in the regions analyzed.
Somatic hybrids were produced hetween embryogenic callus protoplasts of 'Shogun' mandarin (Citrus reticulata Blanco, 2n = 2x = 1 8) and leaf protoplasts of grapefruit (C. paradisi Macf., 2n = 2x =18) by electrofusion. Hybridity of the two regenerated plants was confirmed by leaf characteristics and nuclear genorne analysis using RAPD and PCR RFLP. Flow cytometry and root tip cell count of the two hybrids revealed a chromosome number of 27. These triploid somatic hybrids on transfer to field showed norma] morphology and vigorous growth. Field performances as well as disease resistance are under investigation.
Embryogenic protoplasts of 'Shogun' mandarin (Citrus reticulata Blanco) were electrically fused with mesophyll protoplasts from Citropsis gabunensis Swing. & M. Kell, and two green embryoids were regenerated after 3 months of culture. Two months after transfer to the regeneration medium, numerous plantlets were obtained from the embryoids. These plants grew vigorously, had well-developed root systems, and exhibited leaf characteristics intermediate to those of the parents. The absolute nuclear genome size of the regenerated plant SH2 (1.75 pg/4C) was the sum of those of the 'Shogun' mandarin (0.75 pg/2C) and C. gabunensis (0.97 pg/2C). The chromosome counts of the young leaves revealed that they were tetraploids (2n=4x=36). Random amplified polymorphic DNA (RAPD) analysis of the two lines (SH1 and SH2) verified their hybridity. Cytoplasmic genome analysis using universal primers reveal that their chloroplast (cp) DNA banding pattern is identical to that of C. gabunensis, while the banding pattern of the mitochondrial (mt) DNA is identical to that of the 'Shogun' mandarin. These somatic hybrids are important materials for investigating the phylogenetic relationships between these two genera in the subfamily Aurantioideae.
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