WELCOMING ADDRESS

As dean of the Agricultural Faculty of this University I have the honor and the pleasure to say some words of welcome.

I like to note with particular pleasure that this Symposium, held in this Faculty, will confirm and renew his scientific tradition and therefore we like to express to the I.S.H.S. my satisfaction for choosing this Faculty as the place of this meeting.

I am also pleased for the presence at this Symposium of several I.S.H.S. council members who will have their meeting in Florence in the following days. To the president of the ISHS and to the council members I wish a fruitfull working meeting.

This Symposium is dealing with the physiology of flowering seen by the both point of view: theoretical and practical significance. I take the opportunity to formulate my appreciation for this kind of approach to the topic because as Faculty of Agriculture we are very much interested in any technique which allows plant production improvement.

The Symposium you will attend in the next days is planned to give a picture of the most advanced steps now attempted in flower formation. The subject of this symposium is particularly interesting also because you are studing the flower formation in Ornamentals which, as you might kow, are relevant crops in Italy and specially in this area.

For all the reason above expressed it seems worth while to strech our forces to achieve the goal of the symposium. I hope that your staying in Pisa will not be troubled by any organization misfortune and whish you good success and a continuing productive cooperation as well as the best conclusion of the now opened symposium.


OPENING ADDRESS by L. Quagliotti

Magnifico Rettore, Mister President, dear Collegues, ladies and gentlemen,

It is a great honour for the Società Orticola Italiana and in particular for the Sezione Floricoltura, to hold here a meeting of such prestige by virtue both of content and the renown of those taking part in it. It is thus my especial pleasure to extend our Society's welcome to the President of the ISHS and to all the specialists gathered here from so many countries in and outside Europe. I also wish to extent our hearty thanks to Prof. Wellensiek, Prof. Sachs and Prof. Bellini, for having accepted to introduce the basic aspects of the subject of our Symposium in three general surveys. My thanks, too, to Prof. Amedeo Alpi, who has taken over the organizational details with unsparing care and enthusiasm.

The title "Flower formation in ornamentals" may at first sight seem so vast as to be almost bewildering. The fact is that we chose it just because it leaves ample space for various interpretations:

that is, it can include all the theoretical premises (genetic, physiological and agrotechnical) of the production of ornamental flowers.

So this Symposium should offer us an opportunity of getting an up-to-date picture of basic knowledge of the flowering phenomena in ornamental plants and to enrich our informations on clearly specified subjects, through experimental data. And we shall be here considering both the more widespread species (rose, gerbera, chrysanthemum) and others less well-known but no less interesting (Gloriosa, Dicantra, and so on).

Flower formation marks the transition from vegetative to reproductive growth in seed plants. It is thus an essential event in the life-cycle of ornamental plants, because of the special relationship that exists in these plants, between the vegetative and the reproductive development, which is related to the morphological structure of the flower itself.

Flowers are modified shoots, which are produced by modified shoot meristems, the flower primordia. From the cytologic point of wiew, the change in the apical meristem during the transition stage from the vegetative to the flowering condition is a good example of a shift from an elongation - determined to a mitosis - determined situation. This shift is often induced by genes and by gene interactions that control the rate of mitosis; often they do so by regulating the rate of timing for DNA synthesis.

The central problem of the physiology of flower formation is to understand which factores induce the transformation of a shool-meristem in a flower primordium and in what way they bring this about.

Like any other physiological process, flower formation is basically controlled by the genotype of the individual. In a great number of ornamental plants, the genetical feature is the only factor that determines flower initiation; this takes place only if and when the plant has reached a certain, definite stage of development. Environmental conditions merely favour the plant or hinder it in reaching this stage.

In many other ornamentals, on the other hand, flower formation occurs only if there is a precise interaction between the genotype and specific environmental conditions. Such conditions are, as we now know, daylength and a period of low temperature. Most of our information on the physiology of flower initiation in ornamentals is derived from research on this second group of plants, as it is on these that horticultural technics can be most efficacious in modifying our environment.

With regard to the action of light in photoinduction, photoperiodic effects depend, by definition, on alternation of dark and light periods. The first subject of enquiry to be gene into is that which concerns the reciprocal action of these two factors in including a certain effect.

As far as the role of dark periods is concerned, three principal kinds of treatment are used in floriculture: 1) combinations of short and long light and dark periods; 2) light break interval; 3) differential temperatures in light and dark periods.

Since both the dark and the light periods seem to play active roles in photoinduction of flower formation in many ornamentals, it becomes opportune to analyse first of all the function of light which counteracts the effect of the long dark periods; and secondly the function of the light in the light periods of the inductive cycle. Hence in the first place the action spectra for each species must be established; after which we have to identify which pigments can mediate these effects of the light.

The argument here obviously centres on phytocrome as a photoreversible pigment which can exert, basically, two types of action: firstly it has been shown that in short-day-plants there is a requirement for P_fr previous to the dark reaction; when tgis stage is completed a dark reaction induces hormone synthesis and flower formation. The opposite occurs as an effect of the night-break, which, by converting phytocrome to P_fr, inhibits flowering in short-day-plants and promotes it in long-day-plants.

But on this subject, by no means simple, in all its biochemical and physiological implications, we shall be hearing Prof. Bellini, who will be giving us extremely interesting and modern interpretations in his paper.

The genetics of photoperiodic response is also very interesting in floriculture: in plants with a definite photoperiodic sensitivity, the short-day or long-day response is genetically determined: the environmental conditions directly influence the growth of the plant, inducing flower formation on it only if they satisfy the requirements for flowering. However it is the genotype that controls the flowering response, inducing a plant to flower or not in a given environment.

Many varieties of ornamentals have been selected for specific regions because their genotypes results in a photoperiodic response particularly suited to seasonal conditions in the region. The definite photoperiodic requirements of such plants often restrict them to relatively narrow conditions.

With regard to the low-temperature control of flower initiation, the most important topics are the following:

sites of low temperature effect (shoot tip, tissue,….)

character of response

effective temperatures

reversion of the cold effect

stability of the thermoinduced state

biochemical foundations of the process

effects of plant growth hormones in cold requiring plants

The Chrysanthemum represents a typical example of these problems for ornamentals: this species has long been identified as a short-day-plant; only about twenty five years ago, however, it was recognized that its floral differenciation is conditioned by a complex interaction of various factors, among which a vernalizing effect of exposure to low temperature is of very great importance.

Two clearly-defined stages, corresponding to different physiological requirements, have been identified: 1) bud formation, 2) further development of inflorescences. At the second stage, begative effects which cause abortion may easily be met with. The Chrysanthemum morifolium cultivars differ greatly in their environmental requirements: indee, they have been specifically selected so that they shall adapt to different environments and produce flowers at different times.

Some varieties, for instance, have an absolute cold requirement and flower formation failed in both long and short days when kept at continued high temperature. In other varieties normal growth is replaced by a shortening and thickening of the vertical stem or by fasciation; in a few varieties the cold requirement is not absolute.

Experiments on local cooling showed that in the Chrysanthemum the apex alone is the seat of vernalisation. Concerning reversal, the vernalised condition in this species was found to be annulled by exposure to low intensity light which not only prevents the formation of buds, but also induces the creeping habit.

A very important chapter in present-day floricultural technique includes the use of flower regulators to stimulate flower formation.

The growth substances most used have been auxin and, more lately, gibberellin; work with kinetin has been done still more recently. The rationale behind this approach is based on the fact that plant growth hormones are not higly specific in their action and affect a variety of growth and developmental processes in the plant. It is therefore conceivable that they also affect flower formation, both generally and with special respect to photoinduction. It will be very interesting to hear what Prof. Sachs will say about this.

There are a great many growth substances in use today and practical interest in them is progressively increasing, given the successes obtained with them. These products can influence the growth and flowering of ornamentals considerably and often to advantage. The ease with which they can be applied makes it worth while to substitute them for other more complicated and costly means of forcing.

I have touched on a few general ideas on the subject of the symposium, which will be gone into much more deeply by the official Speakers. I have chosen the ideas that seemed to me most important above all from practical point of view. Indeed I should like to emphasize a point that I feel is fundamental, and that is, that when we speak of ornamentals, the real problems are those connected with industrial flower-growing. Theoretical knowledge is therefore so much the more important in so far as it provides operative models at the technical level and certain to be effective for growers. A striking example of this can be found in the now very sophisticated studies on the forcing of bulbous plants. Their primary aim (and it is right that this should be so) is to furnish economically advantageous answers to the requirements of the market. Thus we are dealing with works which must in any case lead to useful results and which cannot but be planned with care and foresight.

These problems are of so great importance that it is really to be hoped too. For floricultural production involves values that go beyond mere economic interests. We all know how much it means to have flower around us, that without them our lives are poorer and somehow deprived. So the work in this field is an essential contribution to improving the quality of life in these hard times.

Some varieties, for instance, have an absolute cold requirement and flower formation failed in both long and short days when kept at continued high temperature. In other varieties normal growth is replaced by a shortening and thickening of the vertical stem or by fasciation; in a few varieties the cold requirement is not absolute.

Experiments on local cooling showed that in the Chrysanthemum the apex alone is the seat of vernalisation. Concerning reversal, the vernalised condition in this species was found to be annulled by exposure to low intensity light which not only prevents the formation of buds, but also induces the creeping habit.

A very important chapter in present-day floricultural technique includes the use of flower regulators to stimulate flower formation.

The growth substances most used have been auxin and, more lately, gibberellin; work with kinetin has been done still more recently. The rationale behind this approach is based on the fact that plant growth hormones are not higly specific in their action and affect a variety of growth and developmental processes in the plant. It is therefore conceivable that they also affect flower formation, both generally and with special respect to photoinduction. It will be very interesting to hear what Prof. Sachs will say about this.

There are a great many growth substances in use today and practical interest in them is progressively increasing, given the successes obtained with them. These products can influence the growth and flowering of ornamentals considerably and often to advantage. The ease with which they can be applied makes it worth while to substitute them for other more complicated and costly means of forcing.

I have touched on a few general ideas on the subject of the symposium, which will be gone into much more deeply by the official Speakers. I have chosen the ideas that seemed to me most important above all from practical point of view. Indeed I should like to emphasize a point that I feel is fundamental, and that is, that when we speak of ornamentals, the real problems are those connected with industrial flower-growing. Theoretical knowledge is therefore so much the more important in so far as it provides operative models at the technical level and certain to be effective for growers. A striking example of this can be found in the now very sophisticated studies on the forcing of bulbous plants.