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ISHS Acta Horticulturae 430: VII International Symposium on Flowerbulbs

EMBRYOGENESIS AND SEED GERMINATION OF NERINE

Authors:   N.R. Brown, R.K. Crowden, J.R. Gorst
DOI:   10.17660/ActaHortic.1997.430.18
Abstract:
The inflorescence of Nerine is initiated two years prior to anthesis (A-2). In the growing season preceding flowering (A-1) all individual florets have developed, yet megasporogenesis and microsporogenesis do not occur until close to flowering time (A).

Following fertilization a nuclear endosperm develops and embryo growth proceeds slowly. The nucellus appears to remain intact after fertilization and there is a large increase in volume as the seed forms. This increase has also been noted in seeds which do not go on to germinate and in some cases parthenocarpic seeds formed. The seeds are large, globose to ovoid with the epidermis arising from the single integument possessing stomata. They contain a high proportion of water and do not have a dormancy period.

At the time the seed is shed from the parent plant, approximately 5 weeks after pollination (AP), the embryo is undeveloped, globose and approximately 100 μm in diameter. The majority of the development of the embryo takes place after the seed is shed. It becomes polar and undergoes some external differentiation over the next five weeks. Rapid enlargement and elongation of the embryo does not start until 2–3 weeks prior to emergence from the seed, about 13 weeks AP. The embryo remains uncoiled and small relative to seed size occupying no more than 5% of the seed volume.

The germinating embryo is positively geotropic and the tip undergoes swelling to form a pro-bulb from which the contractile root emerges. The cotyledon becomes green but the tip remains inside the seed which does not degenerate until well after the emergence of the first true leaf, approximately 3 weeks after germination and almost five months post anthesis.

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