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202303 Fresh Quarterly Issue 20 03 Case Study Plant Improvement Web
Issue TwentyMarch 2023

Case study: effective plant improvement

The Netherlands is a small country that packs a powerful horticultural punch —can the South African pome- and stone-fruit industries up their game by studying Dutch plant-improvement practices? By Anna Mouton.

Article summary

The Dutch plant certification system at a glance Horticultural legislation in the Netherlands falls under the Ministry of Agriculture, Nature and Food Quality. Registration with an inspection service is compulsory for companies that trade plant-propagation material.

The government has authorised Naktuinbouw to perform mandatory inspections for health status and varietal characteristics. Naktuinbouw also provides laboratory testing, inspects imported material, offers post-entry quarantine, and performs optional plant-quality inspections.

Naktuinbouw can inspect and sample plant material at nurseries at any time without warning. Certified and uncertified nursery material is inspected, and selling unapproved plant material is illegal.

Pre-basic material — the Dutch equivalent of nucleus material — is maintained by Clean Fruit Plants.

Vermeerderingstuinen is the sole supplier of fruit-tree bud- and graftwood in the Netherlands. Vermeerderingstuinen grafts basic material — the Dutch equivalent of foundation material — from pre-basic material provided by Clean Fruit Plants.

Vermeerderingstuinen sells certified bud- and graftwood from certified mother trees, but rootstocks are certified at the nursery level. Specialised rootstock nurseries use basic material from Vermeerderingstuinen to establish stool-beds.

Naktuinbouw, Clean Fruit Plants, and Vermeerderingstuinen are all privately owned, self-funded foundations.

A commitment to plant improvement in all crops is one reason why the Netherlands is worth examining. Fresh Quarterly contacted leading horticultural figures to find out how the Dutch are getting plant improvement right.

The European context

Horticultural legislation in the Netherlands falls under the Ministry of Agriculture, Nature and Food Quality. Their agency responsible for plant health is the Netherlands Food and Consumer Product Safety Authority. It contains the National Plant Protection Organization, which focuses on international aspects of phytosanitary risk such as representing the Netherlands in negotiating phytosanitary regulations within the European Union and import requirements of non-European Union countries.

The Netherlands is a member of the European Union so their legislation and standards must be harmonised with the relevant European Union directives. Plants — including vegetative propagation material of pome- and stone-fruit trees — that are traded or moved within the European Union require documentation of quality and a phytosanitary plant passport.

Plant passports provide traceability and evidence of compliance with plant-health requirements such as freedom of regulated pests and diseases. Passports are issued by an official body of the member state — the Netherlands Ministry delegates this function to one of four non-governmental inspection services. The inspection service that deals with horticultural crops, including fruit trees, is called Naktuinbouw.

The name Naktuinbouw translates roughly as the Netherlands Inspection Service for Horticulture. They deal with seeds and vegetative propagation material of trees, vegetables, and ornamental plants, except flower bulbs, which fall under the Flower Bulb Inspection Service. Field crops such as potatoes, cereals, and pasture grasses fall under the Dutch General Inspection Service. Once agricultural products are sold as food, they are inspected by the Quality Control Bureau.


Naktuinbouw is an independent foundation created in 2000 from the merger of three general inspection services: the Netherlands General Inspection Services for Arboricultural Crops, Floricultural Crops, and Vegetable and Flower Seeds.

These three bodies were established in 1941–1947 but Dutch inspection services are much older — the first field inspections of propagation material occurred as far back as 1888, and the first inspection body for trees dates from 1895.

“In the Netherlands, growers themselves organised an inspection service before there was even legislation,” says Naktuinbouw director John van Ruiten.

Eventually the government passed the Dutch Seeds and Planting Materials Act 1967 and the Netherlands also helped found the European Economic Community, which became the European Union in 1993. This led to a proliferation of new rules and regulations for the marketing of seeds and plant material.

“Our government decided to use the already existing non-governmental institutions as inspection bodies,” says Van Ruiten. “Naktuinbouw is privately organised, but we carry out official functions, a structure which is quite normal in the Netherlands, not only in agriculture, but also in other fields.”

Naktuinbouw is a foundation — a non-profit organisation — governed by a board of representatives from the horticultural industry. The chair is appointed by the Minister of Agriculture, Nature and Food Quality. Three sector councils — floristry, vegetable, and tree nursery — and several advisory committees support the board and management.

All funding comes from service delivery. “So if you are a fruit-tree nursery, you will be billed for the inspector who visits your company, the certificates that we issue, and the laboratory tests that we do, and you pay a registration fee related to the size of your company,” explains Van Ruiten. “We do not get any government subsidies for inspection and testing work.”

Certification starts with inspection

In the Netherlands, registration with an inspection service is compulsory for companies that trade plant-propagation material. About 3 800 breeders, propagators, processors, and traders are registered with Naktuinbouw. Of these, approximately 2 400 are involved in production of trees for everything from fruit orchards to forest plantations.

The legally required inspections that Naktuinbouw is authorised by the government to perform aim to determine health status and assess varietal characteristics. Naktuinbouw also provides optional inspections for plant quality.

“All the legal standards that we work with are set by the European Union,” says Van Ruiten. These include conditions for CAC material — propagation material with confirmed varietal identity, adequate varietal purity, and acceptable health status. For example, European Union directives specify pests and diseases that must be absent for a plant passport to be issued.

“The end result of an inspection is that material is either approved or not. If it is not approved, you can grow the material yourself or you can try to resolve the problem, and have the material re-inspected,” says Van Ruiten. “But legally you are not allowed to market it.”

Illegal marketing of plant material carries financial and other penalties. The identities of companies that commit fraud are published — a potent deterrent.

The voluntary certification scheme for fruit trees and soft-fruit plants is called Naktuinbouw Elite. “The European Union standards are the minimum levels, and we have growers that want material with more guarantees than the minimum standards,” says Van Ruiten. He adds that Naktuinbouw Elite can help companies to market to non-European Union countries that have additional phytosanitary requirements.

Plant material imported to the European Union must meet certain phytosanitary requirements that may include post-entry quarantine and testing. Naktuinbouw inspectors check plant material imported from outside the European Union and Naktuinbouw also offers a post-entry quarantine service for breeders all over the world who want to access European Union markets.

Quality is confirmed by testing

Naktuinbouw offers comprehensive laboratory testing, including culture, bioassays, ELISA, and PCR for disease-causing microbes and nematodes. Most of the testing is performed for certification purposes but Naktuinbouw also does diagnostic testing on diseased material submitted directly by companies.

Besides genetic testing on disease-causing organisms, Naktuinbouw can run forensic genetic tests on plant material, for example to investigate an infringement of plant breeders’ rights. More recently, Naktuinbouw has developed isotope-based tests to verify the origin of plant material.

Although Naktuinbouw is an inspection body, not a research institute, ongoing research and development is a key activity, according to Van Ruiten. “We want to ensure that we apply internationally accepted, validated, test methodologies. Every year we develop new detection protocols that can be applied not only by our inspectors, but also by other companies.”

Varietal testing for registration and plant breeder’s rights is another function delegated to Naktuinbouw in the Netherlands, but they specialise in varietal testing of ornamental plants, vegetables, and potatoes — most tree-fruit varietal testing is done in Germany.

When asked why propagation material matters, Van Ruiten has a clear answer. “The success of a grower starts with good plant material. They must be very sure that they get the right variety — and properly selected material of that variety — on the correct rootstock. And the material must be free not only of quarantine pathogens, but also free of viruses and internal diseases that will harm fruit yields and quality.”


The initiative for Vermeerderingstuinen came around 1960 from Dutch fruit growers and tree nurseries who wanted a reliable production system for propagation material. They approached the Netherlands General Inspection Services for Arboricultural Crops — a forerunner of Naktuinbouw — for assistance.

“We were part of Naktuinbouw, or its predecessor, in the beginning, but in the year 2000 we became an independent organisation,” says Vermeerderingstuinen chief executive Gerard Jongedijk.

Initially, Vermeerderingstuinen was a foundation — a non-profit company — like Naktuinbouw but they subsequently became a private limited company — the South African equivalent is a property limited company — owned by a foundation.

“We chose this legal form because we operate all over the world, and the foundation was not accepted as a business partner in many of the countries where we sell material,” explains Jongedijk.

Vermeerderingstuinen is entirely self-funded. Because it is still owned by a foundation, all income is applied to furthering the aims of the company. Jongedijk points out that no money is paid to investors or shareholders. “If we make a little profit in one year, we keep it in our purse to cover risks for the next two or three years.”

Propagation material basics

In the Netherlands, the production of propagation material starts at the pre-basic stage — pre-basic is similar to South African nucleus material, whereas basic material is similar to South African foundation material.

Naktuinbouw used to maintain pre-basic material, but they transferred this function to Clean Fruit Plants, a new foundation, in March 2022. This prevents potential conflicts of interest arising from Naktuinbouw inspecting and certifying material under their management.

“We use pre-basic material to graft basic material,” says Jongedijk. Basic material is renewed from pre-basic material every three to four years for apples and pears, and even more frequently for some other crops, like cherries and plums.

All multiplication steps between pre-basic and certified are called basic. For bud- and graftwood, two basic steps precede the establishment of certified mother blocks. The first generation of mother trees is allowed to flower and fruit so that their varietal characteristics can be confirmed. “We have a pomological committee under supervision of Naktuinbouw,” says Jongedijk. “They will check the comparison to the official description, and check for mutations.”

Pomological assessment is usually carried out for three years, but could take longer in unstable varieties. “If instability is really a problem, and we can’t get rid of it, we will stop propagation of the variety,” states Jongedijk.

According to Jongedijk, varietal assessments happen in parallel to propagation, to speed up the process. There is a risk that mother trees may be established only to be pulled out when a problem is identified, but the main goal is to supply the demand for propagation material as quickly as possible.

Vermeerderingstuinen sells certified bud- and graftwood from certified mother trees but rootstocks are certified at the nursery level. “We stick to the production of basic plants that are used by specialised rootstock nurseries to establish stool-beds,” says Jongedijk. “So a nurseryman will buy certified graftwood from our company and certified rootstocks from a colleague grower.”

As effectively the sole supplier of fruit-tree bud- and graftwood in the Netherlands, Vermeerderingstuinen takes their responsibilities seriously. “We try to find all the risks — all the mutations and infections — as quickly as we can. The consequence is that, when now and again we find something, we don’t need to be sad,” says Jongedijk. “We’re not happy, of course, but that’s why we are there.”

Multiple sites spread risk

Vermeerderingstuinen has sites in Horst and Zeewolde. Horst is used primarily for bud- and graftwood production whereas Zeewolde focuses on rootstocks. Zeewolde is a polder — reclaimed land — that was created in the 1970s. “We were the first farmers in this area, so it was a kind of virgin soil,” relates Jongedijk. “We couldn’t find a better place for making clean basic rootstock material.”

In Horst, Vermeerderingstuinen has close to 150 hectares spread over about 20 locations. Any given variety is grown at more than one location, says Jongedijk.

“We divide our crops so there is never a risk that we lose a crop for a season. This is not only about disease —phytosanitary issues — but it’s also because hail is an issue in the Netherlands. It’s not profitable to cover the crops in our country, but every 5–8 years there will be big hailstorms and we will lose our crop at one or two production locations.”

Mitigating disease risk by isolating mother trees is challenging in an intensively developed country like the Netherlands. Vermeerderingstuinen works closely with Naktuinbouw and the National Plant Protection Organization to identify and manage the risks specific to each region.

“In our climate, it is about a few diseases that are also a risk in the international market, like fireblight in apples, pear decline in pears, and plum pox virus in plums,” says Jongedijk. Vermeerderingstuinen enlists the inspection and testing services of Naktuinbouw to ensure that problems are detected and resolved promptly.

Strict traceability of all stock and a close relationship with Naktuinbouw make it easier for Vermeerderingstuinen to accommodate changes in European Union legislation. Jongedijk notes that the international stature of Naktuinbouw also helps when obstacles with exports have to be negotiated.

“It’s a little bit like drizzle — internationally there will always be new diseases, new test methods, hiccups. It doesn’t help to complain about drizzle,” reflects Jongedijk. “The only thing that helps is an umbrella, and Naktuinbouw is our umbrella.”

Boomkwekerij Fleuren

Nurseries are the final link in the plant-improvement chain. Boomkwekerij Fleuren is a respected Dutch nursery that celebrated their centenary in 2022. They produce approximately 1.5 million pome- and stone-fruit trees on about 140 hectares annually.

Owner Han Fleuren is a third-generation nurseryman. He says that Dutch fruit-tree nurseries are used to certification. “For us, it’s as normal as breathing. It has always been there, and it will always be there.”

Fleuren believes that inspection and certification is all about demonstrating trustworthiness. “If you think about it, our clients buy trees from us without leaves, and without apples, so they have to trust us — and since we have been around for 100 years, you can see that we don’t cheat our clients. But although trust is nice, checking is better.”

Boomkwekerij Fleuren orders graftwood from Vermeerderingstuinen. “Naktuinbouw first checks the material at Vermeerderingstuinen, then checks our material — which is the second time they see the material — and they do a final disease check before we deliver material to clients.”

Certified rootstocks are obtained from a specialist rootstock nursery. According to Fleuren, basic material from Vermeerderingstuinen is the obvious choice of starting material for Dutch rootstock producers. “You have to start with the right material, because every year you grow your rootstocks from these mother trees.”

Track and trace

Once plant material is at the nursery, it can be inspected and sampled by Naktuinbouw at any time without warning. “We don’t know when they are coming,” says Fleuren. “They also check if we can prove where we sourced our graftwood, and that the rootstocks came from a certified source.”

All propagation material is identified and traceable by numbers which also link the material to plant labels and certificates. Nurseries record exactly what is planted where, so that Naktuinbouw inspectors can verify the status of each tree. “I think Naktuinbouw knows more about us than the bank does,” jokes Fleuren.

In practice, nurseries sometimes have to be adaptable to accommodate the demands of inspections. For example, when trees come into leaf, the leaves have to remain in place until Naktuinbouw has confirmed the identity of the plants.

“These quality controllers, they do this day in and day out,” says Fleuren. “They know the varieties and they can see whether something is a typical Elstar or Braeburn or whatever. And most of the apple rootstocks in Holland are M.9 — they know exactly what an M.9 leaf looks like.”

Traceability allows problems to be tracked not only to, but also from, source. Should Naktuinbouw find a virus in a nursery tree, for instance, they can identify and eliminate not only infected material at Vermeerderingstuinen, but also determine whether any other nurseries or growers received this material.

“That’s how you clean up,” says Fleuren. “If you have this system, and there is a problem, you can eliminate it. And if you do it right, you do it before the material goes to the grower.”

Certification in practice

Plant improvement initially aimed to benefit Dutch growers but has become increasingly important in securing export markets for nurseries such as Boomkwekerij Fleuren, who sell most of their trees outside the Netherlands. This sometimes entails sacrifices, as Fleuren describes. “In Holland, we are obliged to check the soil for the absence of potato cysts — a nematode disease — before we plant fruit trees.”

Although these nematodes do not affect fruit trees, trees planted on infested sites would not be eligible for certification or export.

Another requirement is to protect trees from severe diseases like fireblight, according to Fleuren. He elaborates that pest-free buffer zones are designated for the production of fire-blight host plants in the Netherlands.

Fleuren is a firm believer in certification, but Boomkwekerij Fleuren also sells uncertified trees. One reason is that not all tissue-cultured material can be certified by Naktuinbouw. When, for example, cherries are grafted on tissue-cultured Gisella rootstocks, the trees are uncertifiable.

A second reason is that waiting for the full certification process to run its course may cost a nursery the opportunity of exploiting a new variety. That these trees are uncertified does not mean they pose high risks to growers — imported material must still be free of quarantine diseases, and the trees are subject to the same checks by Naktuinbouw in the nursery as certified trees.

It goes without saying that certification puts an administrative burden on nurseries and adds to the cost of trees. Nonetheless, Fleuren supports it wholeheartedly.

“Usually, when we speak about good quality, we speak about how the tree looks, but that’s something our clients can check — they cannot check the inside. And it’s the things that you cannot see that you have to trust, that maybe gives a problem in future years. So that’s what Naktuinbouw has to guarantee, and why I think certification is necessary.”

Image: Naktuinbouw test facilities at Horst.

Supplied by Naktuinbouw.

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