Confirmation of hybridity using GISH and determination of 18S rDNA copy number using FISH in interspecific F1 hybrids of Tecoma (Bignoniaceae)

Interspecific hybridization in Tecoma Juss. was conducted to develop novel forms for the nursery industry. We report fertile hybrids from the cross T. garrocha Hieron. (pistillate parent) × T. stans (L.) Juss. ex Kunth. Leaf morphology of the F1 hybrids of T. garrocha × T. stans was intermediate between the parents. GISH also confirmed hybridity. The F1 hybrids were successfully backcrossed to both parents and self-pollinated to produce BC and F2 progeny. Tecoma garrocha , T. stans, and T. guarume A. DC. ‘Tangelo’ were self-fertile. The F1 hybrids also were crossed with T. capensis (Thunb.) Lindl. and T. guarume ‘Tangelo’, resulting in three-species hybrids. FISH conducted on F1 hybrids identified four copies of the 18S internal transcribed spacer region. Further analysis using FISH has the potential to provide information on the evolution of Bignoniaceae and the potential role of polyploidy.

Reproductive Behavior of Diploid and Allotetraploid Rhododendron L. ‘Fragrant Affinity’

Wide hybridization can lead to recombination of diverse traits and creation of unique phenotypes, but the resultant hybrids are often sterile as is the case with the intersubgeneric hybrid Rhododendron L. ‘Fragrant Affinity’. Sterility in wide hybrids can either be genic or chromosomal; the latter may be overcome by induction of polyploidy, which can restore chromosome homology and fertility. Cytologic studies of ‘Fragrant Affinity’ appear to support the presence of bridges between bivalents in metaphase I and laggard chromosomes in anaphase I. In the current study, an allotetraploid form of R. ‘Fragrant Affinity’ was developed using oryzalin (4-(dipropylamino)-3, 5-dinitro-benzenesulfonamide) as a mitotic inhibitor and chromosomal doubling agent. Genome sizes (2C) were determined using flow cytometry and found to be ≈1.6 and 3.2 pg for the diploid and allotetraploid, respectively. Pollen viability, determined by staining and germination tests, was 4% and 0%, respectively, for the diploid and 68% and 45%, respectively, for the allotetraploid. No seeds were produced when the diploid R. ‘Fragrant Affinity’ was used as a pistillate parent when pollinated with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when pollinated with pollen from either diploid or tetraploid parents, including self-pollination, demonstrating restored male and female fertility.

COCONUT BREEDING: IDENTIFICATION OF PARENTS IN MALAYAN YELLOW DWARF AND TALL CULTIVARS FOR THE PRODUCTION OF PROMISING DWARF FEMALE x TALL MALE HYBRIDS

Results of a study made on the nut and copra characters of Malayan Yellow Dwarf palms and of the local Tall cultivars to select the parents which could combine well, when Malayan yellow Dwarf palms as pistillate parents are crossed with Tall cultivars as pollen parents are presented in this paper. In this study Malayan yellow Dwarf palms were classified into four groups based mainly on nut characters like shell and copra content which are fairly stable characters. The Tall cultivars were classified into five groups based mainly on the copra content per nut. Correlation studies made on the important characters of the nut in the Dwarf and Tall cultivars indicated significant correlations between the stable characters shell, kernel and copra. Based on this relationship it may be possible to identify palms in both which could combine well when Malayan Yellow Dwarf as pistillate parent is crossed with the Tall as pollen parent. The study has indicated that it may be preferable to select Malayan Yellow Dwarf palms which produce nuts which have a low shell content (less than 17 percent of husked nut weight) and yield a copra content of more than 150g per nut as pistillate parent and Tall palms which yield nuts of low husk content (less than 50 percent of the weight of fruit) and a high copra content of 200g or more per nut as pollen parent. The combining ability of the parents could be ascertained form xenia studies before taking up crossing work. Individual palms from both the cultivars which can combine well can be identified and utilized for the production of a large number of hybrid seedlings in a short time.

Origin of B chromosomes in cultivated rye

Cultivated rye (Secale cereale) and its weedy relative (S. segetale) carry B chromosomes. The B chromosomes are known to be morphologically alike at somatic metaphase and they are of the standard type in natural populations. To clarify the cytogenetic relationship between the standard B chromosomes of S. cereale and those of S. segetale, we made four crosses between Afghan S. segetale with two standard B chromosomes as a pistillate parent and Turkish, Iranian, Korean, and Japanese S. cereale, all with two standard B chromosomes as pollen parents. We observed the pairing of B chromosomes at diakinesis in pollen mother cells in all F1 hybrids with four standard B chromosomes, two from each of the pistillate and the pollen parents. The degree of pairing of B chromosomes in all F1 hybrids with four standard B chromosomes was similar to or somewhat lower than, that in parental strains with four standard B chromosomes. These results showed that the standard B chromosomes in S. segetale from Afghanistan are homologous with those in S. cereale from Turkey, Iran, Korea, and Japan. We therefore propose monophyletic origin of the standard B chromosomes in S. segetale and S. cereale.Key words: Secale, B chromosomes, origin, cultivated rye, weedy rye.

Morphology and cytology of the reciprocal hybrids between Elymus trachycaulus and Elymus canadensis

Reciprocal hybrids between Elymus trachycaulus (2n = 4x = 28) and Elymus canadensis (2n = 4x = 28) were generated through emasculation and hand-pollination. All the F1 hybrid plants were tetraploids (2n = 28). The F1 hybrids were readily produced (9 plants from 150 pollinated florets; 6% success) in crosses where E. canadensis was used as the pistillate parent and the hybrid plants were produced directly from the apparently normal hybrid seeds. The percentage of hybrid plants produced was lower (7 plants from 400 pollinated florets; 1.7% success) in crosses where E. trachycaulus was used as the pistillate parent, and embryo culture procedures were necessary to recover plants from the shriveled seeds produced. Distinct morphological as well as cytological differences between the reciprocal hybrids were observed. All the F1 plants from each reciprocal cross more closely resembled their pistillate parent, indicating a strong maternal influence. Chromosome pairing at metaphase I showed a very high frequency of cells with a hexavalent configuration (69–81%) and a low frequency of cells with univalents (15–23%) in hybrids produced from crosses with E. canadensis as the pistillate parent. In all hybrids produced from crosses with E. trachycaulus as the pistillate parent, chromosome pairing showed a relatively low frequency of cells with a hexavalent (12–22%), while the frequency of cells with univalents was high (78–81%). Cytology of these hybrids indicates substantial control by cytoplasmic genes on chromosome pairing behavior. Reciprocal hybridization betwen octaploid E. trachycaulus (8x) and tetraploid E. canadensis (4x) plants yielded three 2n = 42, one 2n = 41, and one 2n = 39 hybrid plants. All plants were weak and sterile and more closely resembled the octaploid parent, although some intermediate characters were apparent.Key words: Elymus, reciprocal hybrids, maternal influence, cytoplasmic genes, chromosome pairing.