Flower and Microspore Development in ‘Campbell Early’ (Vitis labruscana) and ‘Tamnara’ (V. spp.) Grapes

Abstract

Abstract: The majority of cultivated varieties of grape have perfect flowers that are clustered in an individual inflorescence. Grape flower has a single pistil, five stamens, a protective flower cap (calyptra), and a calyx. After fertilization, an indivi dual flower develops into a single berry. Although there are a number of reported studies focusing on berry formation, berry enlar gement, and sugar accumulation in grape, the morphological studies of flower, including gametophyte morphogenesis and structural chan ge in floral organs, have not yet been studied in detail. In this study, we investigated the flower structure and development char acteristics of grape using microscopy and defined the floral development stages 9 to 13 based on microspore or male gametophyte development stage from tetrad to mature pollen. We used seeded diploid table grapes ‘Campbell Early’ ( Vitis labruscana) and ‘Tamnara’ (V. spp.) as plant materials. At floral development stage 9, pollen mother cells develop to tetrads. During floral development sta ges 10 to 11, unicellular microspore develop to mid bicellular pollen. At the end of floral stage 12, male gametophyte develops to mature tricelluar pollen. In floral stage 13, the flower cap falls off and flower bud opens. During floral development sta ges 9 to 12, there were no major changes in calyx length, whereas the length of the flower cap continuously increased. The flower cap-to-calyx length ratio was 2.0, 3.0, 4.5, and 6.5 at floral stages 9, 10, 11, and 12, respectively. The flower cap-to-calyx length ratio was consistent in the two grape cultivars, suggesting that the ratio is a morphological character representing floral dev elopment stage. This study provides a reference for determining floral development stage of the two grape cultivars. It will be useful for the determination of optimum time for microspore culture needed to generate doubled haploid lines and appropriate gibberellic acid treatment needed to induce parthenocarpic fruit development in ‘Tamnara’ grape.Additional key words: