Abstract:

Objective: The inflorescences and floral organs of Fargesia yuanjiangensis were studied by morphological and anatomical observations. The inflorescence characteristics, flowering characteristics and seed setting rate of F. yuanjiangensis were analyzed, and the sterility was tried to shift through tissue culture, in order to provide a new theoretical evidence for reproductive biology and breeding of F. yuanjiangensis. Methods: The morphological and anatomical characteristics of floral organs were described by means of anatomical observation. The development process of female and male gametophytes was studied using paraffin sections. The pollen viability was determined using TTC staining. The development of anthers under field and tissue culture conditions was compared and analyzed. Results: The inflorescence of F. yuanjiangensis is terminal or occasionally lateral with phyllomophore, and surrounded by a foliage leaf. The whole inflorescence is uniaxial branched, and the top spikelet develops earlier than the base one, which is finite inflorescence. The base floret of a single spikelet opens first, so it belongs to infinite inflorescence. Each spikelet contains 4-5 small florets and the average length of the florets is 0.9 cm. Each floret is connected by one spikelet, and the tip of the spikelet is swollen with white fluff. There are 2 pieces of glumes at the base of the spikelet. Each floret contains 2 opposite bracts, 3 lodicules, 1 pistil and 3 stamens. The lodicules are located between palea and stamen. When the florets are maturing, lodicules absorb water, yellowish-green or purple anthers are extended outer with four chambers. The immature anther wall consists of four layers:epidermis, endothecium, middle layer and tapetum from outside to inside. The anther develops to the dyad, and the tapetum begin to degenerate, the tapetum cells belong to the glandular type. The mature pollen grains are two-cell type with an average diameter of 43.92 μm. The pollen grains are dyed red by TTC with pollen viability of 54.78%, yet the germination rate is extremely low and even without germination. The pollen sterility can be summarized into four types:tapetum overdevelopment, anther wall shrinkage, pollen grains degradation, empty pollens without nuclei and cytoplasm. The ovary has 2 carpels and unilocular, superior and parietal placentation with dual-integument enclosing the anatropous ovule, and their stigmas have 2 extremely feathery branches, with short column and long stigma, homogamy and herkogamy. Under tissue culture condition, the flower buds can normally develop into spikelets and blossom, the inner and outer lemma and palea open, and the anthers extend out of the spikelet. The fibrous layer of anther wall became thicker and more continuous, but most pollen grains still appear empty shell. Conclusion: F. yuanjiangensis is a mixed inflorescence, uniaxially branched and open wind-borne flower. It is a typical male sterility and cannot form effective pollen, which is the main reason for the low seed setting rate of F. yuanjiangensis. The spikelet of F. yuanjiangensis can continue to bloom under tissue culture and the anthers extend out of spikelets, but the pollen development is still abnormal. The tissue culture techniques cannot change the sterility phenomenon of F. yuanjiangensis, suggesting that the stamen sterility of F. yuanjiangensis may not be caused by nutrient deficiency.

Key words: Fargesia yuanjiangensis, inflorescence, floral organ, pollen viability, tissue culture, sterility