In vitro culture of four Rubus species

Meristem tip culture followed by in vitro micropropagation of cultured plants is a valuable technique for producing and mass propagating disease-free select germplasm. This investigation was initiated to determine the nutritional and environmental requirements for the culture of red raspberry (Rubus idaeus L.). A procedure was first developed using black raspberry (R. occidentalis L.), loganberry (R. loganobaccus Bailey), and tayberry, a loganberry-like hybrid. Satisfactory levels of major and minor elements, vitamins, inositol, hormones, carbohydrates, and pH were then established for red raspberry incubation temperature and photoperiod were determined. Some red raspberry plants were given etiolation pre-treatment prior to culture. Some black raspberry, loganberry, and red raspberry plants were given heat-treatment prior to culture. Explant size affected survival, but not rooting in vitro. Apical meristem tips were superior to lateral meristem tips only in some media. Season of excision did not influence survival in culture. Spring-time did appear to increase vigour in cultured plants. Etiolating source plants was not advantageous. The effects of heat-treatment of source plants prior to meristem tip culture varied with the Rubus species. With black raspberry, survival and growth rate were increased, and rooting hastened. Heat-treatment of loganberry source plants had no effect on meristem tips. With red raspberry, survival was only slightly increased; growth rate was not affected. Three media used in succession induced meristem tip development, shoot proliferation, and rooting, respectively. The basal medium used was that of Murashige and Skoog (1962). Effect of diluting macroelements, even by a 1:4 dilution was not dramatic. Inositol at 150 mg/L stimulated axillary bud proliferation. Inositol in the medium inhibited rooting. Effects of the hormones indole butyric acid (IBA) and 6-benzylaminopurine (BAP) were consistent with other reports. Naphthalene acetic acid (NAA) caused callus proliferation and induced adventitious root formation from leaf petioles, leaf lamina, and callused shoot bases. Rooting was normal with IBA. Levels of pH and carbohydrates were critical, and effects were related to concentration of the cytokinin BAP in the medium. Incubation temperature used was 27°C. This temperature may not have been optimum for red raspberry micropropagation, although it was adequate for meristem tip culture. Moderate light intensity, and the use of cool white fluorescent lights were satisfactory. A photoperiod of 16 hours was adequate. All four Rubus species tested had similar culture requirements, and micropropagation potential. Their nutritional requirements are well within the range reported in the literature for Rosaceous plants.Land and Food Systems, Faculty ofGraduat