Shoot clump cultures of Narcissus cultivars St. Keverne and Hawera were used to investigate the effects of culture medium carbon supply, type of carbohydrate and osmolarity on in vitro bulblet development. Increasing the medium osmolarity using mannitol or sorbitol, which did not act as substrates for growth, failed to stimulate bulblet formation with either cultivar. An exception to this was a relatively small increase in total bulblet dry weight per culture, in the cultivar Hawera only, caused by adding 30 g l )1 sorbitol in combination with 30 g l )1 sucrose. Simultaneously increasing the medium osmolarity and carbon supply using the metabolisable carbohydrate sources, sucrose, glucose, fructose or an equimolar mixture of glucose and fructose stimulated bulblet production, total dry matter accumulation and partitioning into bulblets. At comparable levels of carbon supply up to 19.0 g l )1 , bulblet development of both cultivars was similar with monosaccharide and sucrose media. This indicates that substrate supply is more important for bulblet development than osmolarity of the culture medium. The cultivar Hawera also showed similar responses to monosaccharide and sucrose media supplying 37.9 g C l )1 , despite the high osmolarity of monosaccharide media (c. 650 m Osm kg )1 , equivalent to )1.6 MPa, compared to 380 m Osm kg )1 for sucrose medium). However in St. Keverne total dry matter accumulation and dry weight per bulblet were further stimulated only by increasing the sucrose supply from 19.0 to 37.9 g C l )1 , not by increasing the monosaccharide supply. Implications of the findings for Narcissus micropropagation are discussed.
SUM M.A RYBulbil formation in vitro by single leaf explants from shoot clump cultures was investi^iiied for Sarctssus cultivars ftt Kfverne and Ilaweva. Smgie leaf explants (30 50 mm leaf with attached basal plate tissue) formed bulbils very mfrequently unless cultured on media containing both auxin and a high concentration of sucrose wbereas auxin was not necessary for bulbil formation by sboot clump cultures. As well as showing mucb stronger stimulation by auxin, bulbil initiation and development were more stronglv inhibited by BA in single leaf cultures than in shoot clump cultures. Partitioning of dry matter into bulbils was generally lower in single leaf cultures tban in shoot clump cultures but was more sensitive to growth regulators.Optimal sucrose and auxin concentrations for bulbil development b> single leaf cultures were investigated. Bulbil formation in the presence of NAA was strongly stimulated bv 176 mM sucrose for both cultivars but ibere w^ere genotypic differences m auxin responses. St Keverne showing good bulbil dex elopment witb 054 //M NAA, 5-4//M IAA and 5-4 ^/M lBA and Hawera responding only to 27/'M IA.A.It is concluded tbat single leaf cuhures could provide a simple system for investigation of the regulation i>f Narcissus bulb initiation and development.
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