Characters and floral development of diploid and tetraploid fire lily (Hippeastrum spp.)

Abstract

Commercial varieties of Hippeastrum (fire lily) have currently been in increased demands, thus new varieties via hybridization are unavoidably necessary to replace expensive introduced materials. Attempts have been made on producing hybrids from various Hippeastrum parents of different ploidy levels, in spite of arising obstacles. This research was intended to carry out studies on biological aspects concerning two groups of Hippeastrum, i.e. 1) local and introduced diploids and 2) introduced commercial tetraploid hybrids, to provide informative results applicable in supporting those attempts. The research was organised, in two parts, to examine characteristics and floral development of diploid and tetraploid Hippeastrum. Part I of the studies included investigations on characterization of the plants, capable of determining their ploidy level as well as varietal identity. Such characterizationwas limited to those of pollen morphology, surface anatomy, vascular anatomy and chromosome number. Results showed that Hippeastrum varieties of SP-Pink, SP-Red, Night Star, Tango, Apple Blossom, Lemon Lime and Susan obtained the pollens of similar features, i.e. ellipsoid monad, with the exine of reticulate type but different sculpturing. As for internal structure examined from transverse sections, prepared via paraffin embedding technique, of leaf, petal, peduncle and pedicel of 4 varieties, i.e. diploid SP-Pink and SP-Red and tetraploid Apple Blossom and Susan, it revealed that they all had similar structure of the tissue systems. The dermal tissue of leaf and petal composed of uniseriate upper and lower epidermis. Epidermal cells were parenchyma in type. Stomata were seen distributed in the same level as epidermal cells. The ground tissue also made up of parenchymatous cells with vascular tissue embedded in radius manner. The dermal tissue of peduncle and pedicel expressed the same structure as that of the leaf. Stomata were as well found. The ground tissues of those two organs were composed of loosely arranged parenchymatous cells. Vascular bundles were figured scatteredly in the cortical tissue. In these grounds, sclerenchymatous cells did not exist. Stomata found on the surface of these organs were of anomocytic, having no subsidiary cells. Those distributing on the surfaces of the leaves and petals appeared amphistomatically. Orientation and distribution of stomata on surfaces of various organs were not different, i.e. they appeared in linear order coinciding with lateral venation. The size of stomata distributing in the surfaces of different organs of the same plant and of the same variety were invariable. But, different varieties obtained different stomatal size and stomatal frequencies on the organ surfaces. Chromosome investigations from root tip tissue yielded appropiate technique of tissue preparation as follows: root sampling at 9.30-10.00 a.m., PDB pre-treatment at 10oC for 48 hours, fixing in Carnoy’s solution for 5 minutes, maceration in 1 N HCl for 5 minutes and stained in modified carbol fuchsin for 24 hours. Chromosome counts of the varieties showed 2n = 22 for SP-Pink and SP-Red, 2n = 44 for Apple Blossom and Susan and 2n = 22 and 44 for the hybrids. Investigations in Part II concerned floral developent, especially that occurred the dormant bulbs, microsporogenesis and megasporogenesis and embryo development. Germination capacity of pollens, pollen storage and germination of hybrid seeds were also studied. Results from the 4 varieties showed that the floral buds located at every forth scale axil of individual dormant bulb, with the size and number of the buds correlated with the bulb size. Organogenesis of the floral parts occurred continuously and completed before the opening of the flower. Such floral bud contained fully developed perianth, androecium and gynoeciyum with the anthers full of pollens and the ovary bearing expanded ovules. Germination tests of pollen grains of 7 varieties showed that the pollens collected from the anthers 3 days after blooming stained and germinated well with high germination percentages. Suitable time for germination were 6.00-10.00 a.m. Storage at 5oC can preserve the pollens for longer period and lose germination in 91-120 days while those stored at room temperature (28-33oC) lose germination when kept for 15-45 days. Embryo development of the hybrid seeds was followed. It was found that the embryo embedding inside the endosperm was in cylindrical shape. Its single cotyledon coiled with a plumule enclosed at the base. The radicle was short and tiny. These hybrid seeds could germinate in 14-30 days after pod dishiscence with very high germination percentages, ranging from 62.31 to 98.64%. Results gathered from this research provide specific knowledge and certain information concerning physiological aspects of floral development of Hippeastrumapplicable in breeding programme involving the varieties of different ploidy levels. Such knowledge is useful for practices in parents selecting, appropriate timing of application, particular techniques conveniencing pollination and hybridization. Possible approaches in rescuing immature pods and seedlings obtained from interploidy fertilizations could also be evaluated from the study. On the other hand, varietal identification, necessary in new varietal releasing could also be commenced from the investigation. The above mentioned statement could thus indicate accomplishment of this research at a certain level.