Moderators note:
The following excellent information is an excerpt from an article published in Publication 520, Acta Horticulturae 189, 1986 Roses. Only the ABSTRACT, INTRODUCTION and DISCUSSION are posted here.

H. W. M. Fuchs
Agricultural University, Department of Horticulture
The Netherlands

ABSTRACT

Root regeneration of rose plants was promoted by application of auxin in all experiments. Indolebutyric-acid (IBA) applied to root segments of Rosa multiflora 'Kanagawa' increased number of regenerated roots as well as root length. The best results were obtained with the highest concentrations 11 000 ppm). Addition of sucrose 5% to the solution enhanced the results.

IBA applied to roots of dormant 'Motrea' on rootstock R. canine 'Inermis' promoted root regeneration, while Indole acetic acid (IAA) showed no promoting effect. Most effective was IBA in a concentration of 500 ppm.

The promoting effect of IBA on root regenerating of dormant 'Sonia' on rootstock R. canine 'Inermis' was observed in a range of temperatures from 5 to 25EC. Optimum concentration depended on temperature: at the lowest temperature the highest IBA concentration was the most effective; at the higher temperature it was the lower concentration.

INTRODUCTION

A rose crop in the Netherlands often starts with transplanting dormant material. Survival and good growth of these transplants is only possible when during the first weeks after transplanting the temperature can be maintained at about 5EC. This is only possible in a small period in winter. Problems with survival and bush development may be due to bad root regrowth (root regeneration). Any treatment that would decrease the time to new root initiation and increase the number of roots or the elongation rate of the roots should increase the chances of successful establishment and early productivity of rose plants. Regrowth of roots is generally known as root-regenerating potential (RRP) which is defined as the capacity of roots to elongate or initiate and elongate new lateral roots (Stone et al., 1962). In woody ornamentals the RRP varies with the species (Struve et al., 1984b), with scion variety in roses (Lee et al., 1978) and with physiological stages of the shoot system (Stone et al., 1959; Lathrop et al., 1971; Lee et al., 1976). Several researchers showed that stimulation of RRP is possible by auxin treatments (Looney et al., 1968; Lee et al., 1976; Kelly et al., 1983; Struve et al., 1984b). A review of species studied, method of application, types and concentration of auxin was recently made by Struve et al. (1984b). This study was undertaken to determine the effects of types of auxin, auxin concentration and their interaction with temperature on root regeneration of rose plants.

DISCUSSION

Auxin enhanced root regeneration in dormant rose roots as was observed ln several other woody plants (Looney et al., 1968. Lee et al., 1976; Kelly et al., 1983; Struve et al., 1984b). The best root regeneration in dormant rose plants occurred after application of IBA, rather than IAA or NAA. This was also observed in scarlet oak seedlings (Struve et al., 1984a). IAA seemed to be less effective and NAA only initiated a large number of roots, but these did not elongate in the same way as those caused by IBA. A similar effect was observed in seedlings on other plants (Kelly et al., 1983; Struve et al., 1984a) and also in cuttings with high concentrations of IBA (Hartmann et al., 1975).

The promoting effect of auxins on dormant rose roots was partly due to an increased number of newly initiated roots and partly to elongation of these roots, while in oak seedlings the promoting effect was due primarily to increased number of regenerated roots rather than to elongation (Struve et al., 1984a). In other species it varied with the season, in autumn almost exclusively from elongation of roots, whereas , in spring regeneration results from both initiation and elongation (Struve et al., 1984a, b). The promoting effect of sucrose on root regeneration was due partly to an increase of number and elongation of new roots, but it seemed that especially elongation is promoted. The reason for this could be the limitation of available carbohydrates. The need for reserve material for good root growth and regeneration has been reported for several species (Richardson, 1958a and 1958b; Blakeley et al., 1972; Rogers et al., 1968; Lathrop et al., 1971). Another possible mode of action can be the increase of auxin efficiency (Nanda et al., 1968). Auxin affected root regeneration in the whole range of temperatures from 5 to 25EC, but optimum concentration of IBA changed with temperature. The lower the temperature, the higher the concentration of optimum IBA, hence at high temperatures the optimum concentration for good root regeneration is lower. This can be due to the generally known fact that a concentration range of auxin yields an optimum response curve which changes with temperature. Although according to the literature cold storage before treatment should unify both root and shoot growth under forcing conditions (Webb, 1977; Farmer, 1979) in the present experiment only uniform root development was observed. An explanation could be that the selection criterion was the root rather than the shoot system. The application of auxin could have contributed also to this lack of uniformity because auxin prohibits bud release. Perhaps this prohibition is for some reason not the same for each plant, however the treatment without auxin also showed this lack of uniformity. Another possibility is that the chilling required for good uniformity is different for the root and the shoot (Lathrop et al., 1971). It should be kept in mind that shoots and roots in these roses are even genetically different. It can be concluded that stimulation of root regeneration of dormant rose plants is possible but further work has to be done on its after-effects on shoot growth and bush development (cut flower production, renewal canes). Other fields of study are the different methods of application and the effect of auxin application on other rose plants that are not dormant (e.g. regeneration of roots after harvest of the flowers).

[Other Technical Articles]