Studies in organ culture and the development of organogenic potential in Alnus, Sorbus and Prunus
Micropropagation was investigated in order to develop protocols for rapid mass production of shoots ofSorbus aucuparia and Alnus glutinosa. Removal of apical dominance either physically by pruning the plantlets or chemically by using anti-auxins TIB A (2,3,5-triiodobenzoic acid) and NPA (1-naphthylphthalamic acid) was investigated. There was a 6-fold increase in the number of rooting-ready shoots of S. aucuparia produced by the pruning of plantlets grown in vitro. A. glutinosa however, needed more drastic measures to remove apical dominance and block the endogenous auxin transport. Incorporation of TIBA (3 μm) in the medium produced an initial 8- fold increase in the number of shoots. However, repeated subculture of shoots of Alnus on TIBA containing medium proved detrimental to shoot multiplication. There was 100% rooting of shoots of S. aucuparia on agar solidified medium. The auxin: cytokinin ratio of the multiplication medium played an important role in the rooting ability of shoots. A. glutinosa also had 100% rooting on agar solidified medium. Plants were acclimatised in Baumgartner vessels before transferring to soil. There was 100% rooting and survival of the shoots of A. glutinosa both after transfer to Baumgartner vessels and subsequent transfer to soil. In S. aucuparia the survival rates in Baumgartner vessels was 70% and after transfer to soil was 65%. Direct somatic embryogenesis from zygotic tissue of both S. aucuparia and A. glutinosa was achieved. Embryos of S. aucuparia were produced on medium containing MS salts and vitamins supplemented with 1 μM BAP, 1 μM kinetin, 0.5 μM NAA, 250 mg/L L-glutamine and 500 mg/L casein hydrolysate. A. glutinosa embryos were obtained on medium containing salts and vitamins of Driver and Kuniyuki (1984) supplemented with 3 μM BAP. No auxin was required. Adventitous shoot regeneration from leaves of S.aucuparia was also achieved at a frequency of 40% on medium containing MS salts and vitamins supplemented with 10 μM TDZ and 1 μM NAA. A method for chromosome doubling of S. aucuparia using 15 uM pronamide to treat shoot tips immersed in a semi-solid medium was developed. After 14 days of treatment, 86.5% treated shoots survived and there was 44.5% chromosome doubling of the survivors. The tetraploid shoot had a higher rate of multiplication than the diploid shoots. The involvement of extracellular proteins in direct somatic embryogenesis of Prunus 'Colt' was studied. Changes in the expression of proteins were observed from the first day of transferring the tissue to embryo induction medium. Most changes were seen on the days 28 and 35 when the embryos became visible.