Breeding of Some Amphidiploid Dendrobium

Abstract

Floral characters, meiotic behavior at Metaphase I and sporad formation were compared in three diploid species hybrids and their tetraploid or amphidiploid counterparts. The flowers of the tetraploids were larger than those of diploids. There was also less curling and reflexing of the petals in the tetraploids. The meiotic behavior of the diploids was highly variable with mean configurations ranging from 14.32 bivalents and 9.36 univalents to 18.9 bivalents and 0.16 univalents. Bivalents were almost exclusively observed in the tetraploids. Sporad formation also varied in the diploids with the formation of 36-70% tetrads. The derived tetraploids produced between 97-100% tetrads which reflected the high degree of fertility indicated by the seed set seen in these plants during hybridization. Preferential pairing and small chromosome size appeared to restrict the amphidiploids to bivalent pairing. Selfed progenies of Dendrobium Neo Hawaii Y972-4N, and D. Jaquelyn Thomas 0580-3-4N and 0580-8-4N were found to have relatively small amounts of variation for both inflorescence and floral characters, reflecting the preferential pairing within genomes. Multivalent formation was observed at diakinesis in pollen mother cells in one offspring of 0580-3-4N indicating the possibility of either a reciprocal translocation or intergenomal pairing. The observance of multivalents and small cunounts of variation observed could result from the occasional intergenomal pairing of chromosomes. Sixteen amphidiploid progenies were compared to determine whether existing cultivars could be improved by the use of selected inbreds (S1-S3) in various outcrosses. The progenies included three groups; D. Jaq-Hawaii 'Uniwai Pearl' and related hybrids, D. Jaquelyn Thomas 'Uniwai Supreme' and related hybrids, and other hybrids involving D. Jaquelyn Thomas 66302-2, D. Jaquelyn Thomas 0580-8-4N, and D. Jaquelyn Concert K327-16. Very few differences were observed among the progenies involving inbred selections. Pseudobulb height was tallest in the progeny with the least inbred parent. A progeny involving an S3 had the shortest mean pseudobulb height while exhibiting other similar characters. Overall the inbred selections did not produce progenies superior to 'Uniwai Supreme' and 'Uniwai Pearl'. The unrelated amphidiploids each contributed different characteristics to their offspring. D. Jaquelyn Thomas 66302-2 transmitted the characteristics of long inflorescences with a larger number of smaller flowers. D. Jaquelyn Thomas 0580-8-4N transmitted long pedicel length, which was undesirable. D. Jaquelyn Concert K327-16 contributed low yield and shorter pseudobulbs. Offspring with fused leaf blades were also produced in hybrids with K327-16. None of these cultivars appeared to be superior to 'Uniwai Supreme' and 'Uniwai Pearl'. Discriminant and Principal Component analyses were performed on the 16 progenies. The progenies were generally found to separate into 16 classes. Principal Component 1 reflected overall inflorescence characters. Principal Component 2 had positive loadings for inflorescence characters and negative loadings for floral characters. The analyses were found to have the potential for evaluating and comparing progenies. Three plantings of dendrobiums were compared to determine the effects of age of plants in relation to yield and seasonality. The production of racemes increased each year during the first three years indicating that maturity had not been reached until at least the third year. Peaks were observed to occur in the spring and fall but there were no consistent patterns of seasonal yields in relation to age of plants.