Growth and productivity of cut rose as related to the rootstock

Keywords : Rosa, rose, rootstock, rootstock vigour, carbohydrate, respiration, photosynthesis, pruning, shoot regeneration, water content, water potential, water conductivity, Natal Briar.This research examines various rose rootstock effects and the relationships between them, particularly between the effect on flower productivity (defined as rootstock vigour) and the effects on other growing aspects. 5 to 8 rootstocks, both weak and invigorating, were investigated in a series of related experiments. The rootstocks affected flower production mainly by affecting the number of budbreaks in each flush cycle rather than the duration of cycle. The rootstocks also significantly affected flower qualities. Flower shoots were generally shorter and lighter on weak rootstocks than those on significantly more invigorating rootstocks. However, this observation did not apply to the invigorating rootstocks that have little differences in vigour. This is because that the stem density, which was significantly higher on invigorating rootstocks, has a strong impact on flower qualities, resulting in the relationship between the production (in number of flowers) and the quality parameters to be reversed.The rootstock effects on shoot regeneration in darkness with respect to both the dry weight and the lifespan of the regenerated shoots, though very significant, were not correlated with rootstock vigour. The rootstocks affected the capacity of photoassimilation mainly through leaf area. The same was true for respiration. When the size effect is eliminated, neither photoassimilation nor respiration is (closely) correlated with rootstock vigour. There were little differences between the rootstocks in the concentrations of carbohydrates except for starch (at the marketable flower stage of the primary shoots). The rootstocks showed stronger effects on sucrose and starch than on glucose and fructose. In roots, sucrose and starch were generally lower in weak rootstocks than in invigorating ones. In basal stems, however, the situation is reversed. Rootstocks had significant effects on plant water relations. Shoot water content as well as leaf water potential of invigorating rootstocks was higher than those of weak rootstocks. This is corresponding to a higher water conductivity of the root system. The importance of the rootstock effect on water status in relation to rootstock vigour is addressed and discussed.