PREFACE

I heartily congratulate the Research Station and all workers of this station on its 75th anniversary and I hope this Acta Horticulturae number 75 will be good and long-lasting symbol for all the work done on fruit-growing during these 75 years.

Personnally I am very attached to the Research Station at Wilhelminadorp In fact when I started my career, which lasted in the province of Zeelannd from 1941 till 1948, one of my duties was supervision of ther named - Trial Garden Zeeland-, also located at Wilhelminadorp. I followed with interest the work on this Station. In those years the circumstances were very difficult , butreminiscing, I have very good memories of work and workers in that period.

Regarding tha actual situation I like to express words of thanks to the organizers of the Symposium and comlpiment them with great success of the meeting and excursions.

May the future have development and progress in store for this thriving Research Station, also based on international collaboration in fruit culture

Dr. G. de Bakker
Secretary General - Treasurer
of ISHS


OPENING ADDRESS

Mr. Chairman, ladies and gentlemen,

It is a great pleasure to me to have the opportunity to speak a few words to you at the beginning of this symposium and to welcome you in our country on behalf of the Ministry of Agriculture and Fisheries in The Hague.

I bring you the greetings of Dr. W.F. Walker from Australia, President of the International Society for Horticultural Science. We are very honoured with his visit to our country.

The ISHS is a living and active organisation which is clearly demonstrated by its many international working groups and their activities with regard to congresses, symposia and publications. It has greatly increased international contacts and the exchange of results of horiticultural research, it stimulates adjustments to and revisious of research programmes and also promotes the applications of results into practice. The next International Horticultural Congress, the XXth, will be held in Australia. We hope that many research workers all over the world will find the opportunity to attend this congress in faraway Australia.

In the meantime we appreciate the fact that the ISHS has organized this symposium in the Netherlands as a scientific contribution to the celebration of the 75th anniversary of the Research Station for Fruit Production at Wilhelminadorp.

Because of the many congratulations and reflections on fruit production already expressed at the beginning of the festivities on friday last week, I shall now only dedicate a few words to the anniversary of our Fruit Research Station.

Seventyfive years is quite a respectable age for a research station, though age itself is not a merit to be proud of. The merits of "Wilhelminadorp", however, consists of its contribution to the development of the fruit growing industry in the Netherlands and especially of the good initiatives it has taken in order to overcome the various crisis situations the industry had to deal with in the past.

We can say that the Research Station at Wilhelminadorp, in good cooperation with other research institutes, experimental gardens and with the Advisory Service, has played an important part in the many changes which have been introduced in Dutch fruit culture during this century. The Station has solved many practical problems by own research and invention and also knew how to utilize new possibilities, created by science and technology.

I express the wish and confidence that the Research Station at Wilhelminadorp will proceed in this way and that it will complete the first century of its existence successfully.

Mr. chairman, ladies and gentlemen, the subject of your symposium, "Clonal variation in apple and pear", is a topic of research which in many countries, including ours, has received considerable attention in the past few years. The priority given to this research project is due to favourable prospects for increasing productivity and fruit quality. At first glance "clonal selection" in apple and pear varieties seems somewhat odd, as each variety is a clone as such, created by vegetative propagation of one original seedling. However, it is known for quite a while that eventually within a variety distinct variations have occurred, expressing themselves e.g. in changes of productivity, fruit characteristics and at times also in clear morphological changes in the tree.

The results by clonal selection achieved in the past, meaning the selection of trees for budwood on fertility and fruit quality, will have to be attributed mainly to the selection on the absence of viruses. Considerable results along this line have been achieved with the variety Cox's Orange Pippin e.g.

Furthermore over the years spontaneous mutations have clearly appeared within a variety, both directly visible ones (colour mutations), and not directly visible mutants, which after a while may show considerable differences in productivity.

Thirdly mutations can be stimulated by irradiation, whereby next to mostly negative effects also more favourable characteristics might appear, for instance concerning productivity, vigour and suitability for small types of trees, fruit quality, etc.

There are even indications that by irradiation mutants can be developed which are self fertile and others less susceptible to certain diseases. No doubt the possibilities and prospects of irradiation will be important topics of discussion for your symposium.

Eventually a fourth plea for clonal selection is the recent experience achieved with virus free propagation material of apple and pear varieties and rootstocks.

Knowledge of virus diseases of fruit crops and methods to free fruit varieties and rootstocks of viruses, including checks on success, have increased a great deal lately. It appears that the virus free material from one and the same variety obtained by heat therapy still demonstrates a clear diversity. Whether this diversity within a variety is the result of mutations induced by heat therapy or possibly of a not genetic origin, may also be an unsolved question for you.

Whatever it may be, research has proved that it is absolutely necessary to check the virus free propagation material obtained by heat therapy on vigour, productivity and fruit quality. The same holds for virus free material obtained by bud initiation, according to the experience with various other crops, such as lilies.

A matter I want to draw your special attention to is supplying the nurseries, and through them, the fruit growers with high quality plantmaterial. The point is, as you know, that the results of your investigations are put into practice as adequate and complete as possible.

Research supplies us the knowledge concerning virus diseases and techniques to free plant material from viruses. In our country this knowledge is mainly produced by the Research Institute for Plant Protection (IPO). The Plant Protection Service (PD) applies this knowledge and actually makes the basic materials of fruit varieties and rootstocks virus free and maintains them as such. The Research Station for Fruit Production at Wilhelminadorp is engaged on evaluating the various clones of this material on productivity, fruit quality, etc. The high quality basic material thus obtained is planted out by the Dutch General Inspection Service for Nursery stocks (NAK-B) to such an extent that nurseries can be supplied with sufficient labelled budwood and rootstock material each year.

Thanks to a smooth organization, good cooperation and coordination among the participating institutes and services the Dutch nurseries and the Dutch fruit growers are now already for a high percentage supplied with this outstanding plant material.

Mr. chairman, ladies and gentlemen, I wish you all a fruitful symposium.

I sincerely hope that the exchange of knowledge and experience, and the personal relations that will be made at your symposium, will contribute to a better cooperation between nations in the field of scientific research, which, to my opinion, is progressing too slowly when regarding the growing scarcity of funds and resources. I finally hope that you'll have the opportunity to see something of the Dutch fruit industry (it has been raining badly lately) and that you'll also get a good impression of the beautiful old towns and country side in this part of the Netherlands.

ir. W. van Soest
Director of Horticulture and Arable crops,
Ministry of Agriculture and Fisheries,
The Hague