In the past the use of rootstocks represented an important step in the fight against soil-borne diseases. But rootstocks offer many more possibilities: Improved vigour, setting, flower and fruit quality. And more resistance to stress or low temperatures. With respect to saving energy, the latter is an interesting option and is faster to achieve than by breeding.
Grafting allows you to combine the desired properties of the rootstock with those of the graft. When growing in soil, resistance to soil-borne diseases is an important reason to choose a rootstock. As growers have switched to substrates this argument no longer holds true for many crops and the use of grafted plants has decreased. However, time has shown that substrates are not as sterile as at first thought and that persistent soil-borne diseases can occur here too. Therefore resistance to microbial diseases remains a reason to choose a rootstock. Over the course of the time many other reasons have been added.
10% increase in production
Rootstocks are back on the agenda again, first and foremost to boost production. This, for example, is an important reason to seriously consider using a rootstock for roses grown on a substrate. In this case production can rise by some ten per cent. The grafting of tomatoes offers better resistance to different diseases and thus greater security over production. In addition, these grafted plants yield more.
But rootstocks offer many more possibilities. Production at a lower temperature, improved fruit quality, and improved resistance to heat and drought stress. Nevertheless, they are still used very little; the emphasis remains – also in research – on improving yield. But this is changing: The last few years have seen plenty of developments. In an international context, research is being carried out into the mechanisms whereby the rootstock influences the processes that take place above ground and how the genetic mechanisms function.
Greater tolerance to cold
Greater tolerance by fruit vegetables to lower temperatures would be very attractive. It would also allow further energy savings to be made and increase the crop’s resilience. Now, for example, a tomato crop that has encountered a temperature that is far too low (under 12ºC) for some time hardly recovers.
The roots, however, appear to play an important role in tolerance to lower temperatures. Photosynthesis continues as usual when it's cold, but the development of the leaves deteriorates. This is due to the poor absorption of water and nutrients and a disturbed hormone balance. So it makes sense to select species with a root system that functions better under cold conditions. For this it is often necessary to return to the wild varieties. Grafting tomatoes onto Solanum habrochaites is a way to achieve better growth under cold conditions. In cucumbers the fig-leaf gourd (Cucurbita ficifolia) is a good example.
Larger root system
The types of rootstock that are best suited to achieving tolerance to low temperatures appear to have a number of features in common. Quite simply, when it becomes cold they produce a larger root system than rootstocks that are more sensitive. Also, research on the fig leaf gourd shows that uptake of nutrients is better. And, the uptake of phosphate by tomatoes drops considerably at low temperatures but this is not a problem in wild varieties, according to trials.
If a crop of fruit vegetables has had far too much cold the leaves wilt. This clearly points to a water absorption or transport problem. This problem is much less apparent with cold tolerant rootstocks, due primarily to the more extensive root system and the longer roots. In addition, they are more capable of suppressing the formation of free radicals (which affect the cell membranes) during cold stress. Finally, the hormone production is also different. Cold tolerant roots, for example, produce more cytokinins. These hormones stimulate the root meristem and ensure that sufficient assimilates are drawn to the roots.
On the other hand, theoretically, the rootstock should also play a role in the crop’s resistance to heat stress. The formation of the hormone ethylene is partly causing the lagging root growth when it is hot, as well as damage by free radicals. There are undoubtedly differences in ethylene production and free radical formation between the different rootstocks, but research findings so far offer little perspective. However, it has been possible to increase eggplant production by 10% under hot conditions by grafting onto a heat tolerant rootstock.
Fruit quality can also be influenced by the choice of rootstock. This includes appearance, firmness, taste and healthy ingredients such as vitamins. In general, the external fruit quality (size, colour, shape) improves with greater vigour as a result of the chosen rootstock, so you don't have to select specifically for this.
Firmness is a property that is more complicated. This depends on the shape of the cells, cell turgor, composition of the cell wall and its chemical properties. All these features are influenced by the hormone systems, water and nutrient uptake. Trials have shown that grafting has a positive influence on the firmness of watermelons and cucumbers while courgettes grown on rootstocks were actually softer.
The taste of a fruit is a combination of acids, sugars, volatile substances and other components. Based on international research it is hard to say to what extent this is dependent on the rootstock. There is a more positive picture for the healthy substances, such as vitamins and lycopene. It appears that in watermelon, cucumber and tomato the levels are indeed sometimes determined by the chosen rootstock. But before a grower can start to steer the crop based on this a lot more research is needed.
The conclusion is that rootstocks certainly offer fruit vegetables perspective in the search for more energy-efficient or cold tolerant production. The impact of rootstocks on fruit quality is still a largely unexplored area.
The ultimate rootstock doesn’t exist
If you inoculate a graft with the best above-ground characteristics onto a rootstock with the best under-the-ground characteristics you’ll have the best plant. Right? Unfortunately it’s not that simple.
It all cases it’s about the combination. Characteristics of the graft and the rootstock can reinforce each other but they can also work against each other. In the worst case they can even be incompatible. (see page 46).
Usually trial and error leads to the best combination. For example, some rose rootstocks produce lots of cytokinin. If you graft onto this a variety that has difficulty developing, it has a positive effect. The graft forms more flowers. But if you graft on a variety that easily develops then you’ll have too many flowers. Sweet peppers that have a problem with setting would very much welcome a good rootstock that encourages setting.
There is renewed interest in rootstocks when growing on substrate, first and foremost to increase production. However, rootstocks offer more possibilities. There certainly provide opportunity to improve cold tolerance and thereby save energy.
Text: Ep Heuvelink (Wageningen University), Dietmar Schwarz (IGZ Grossbeeren) and Tijs Kierkels. Images: Henk Bouwman and Eric van Houten.
Magnesium fulfils many functions within the plant. The element is crucial for the activity of many enzymes. These play a role in photosynthesis, the energy supply, and the formation of the cell organs that produce proteins. Its most visual role is that played in chlorophyll. Without magnesium a plant would not be green.
Chlorophyll is the green ‘colouring’ that plants use to capture light energy. Plants convert this energy into chemical energy and use it for photosynthesis, the process by which the plant converts CO2 and water into sugars and oxygen.
The importance of good health is something I experienced first-hand in January last year, when I slipped a disc. Just as you have to work at keeping your plants healthy, you also have to pay attention to your own vitality to ensure a good “product”. A slipped disc can be a long and painful process and an operation is rare these days. The GP’s solution is to tell you to get as much exercise as possible. It should gradually get better, but the process can be a particularly painful one, as I have discovered.
Interestingly, my GP chose not to examine me but instead to treat me preventively by prescribing heavy-duty chemical painkillers. “If the pain gets worse, take more pills,” was his advice. It reminded me of how less than four years ago we were still routinely “calendar spraying” our bedding plants, as we called it, i.e. spraying a set dose every week, as a way of giving them “medicines”. For years we simply kept on spraying them according to a set regimen to protect them against pests and diseases. Looking back, I would say that for many years, Dutch greenhouse horticulture produced flowers and plants that looked great, but whether they were best for the consumer is another matter entirely.
How things have changed! In recent years we have seen a complete sea change, both in our company and in the ornamentals sector as a whole. We stopped using neonicotinoids some years ago, and last year we started growing all our plants organically or using integrated methods. Growers are constantly looking for ways of making their plants even more resilient by using soil improvers, so that they can reduce the amount of “medicines” they need to use.
My point is that society tends to react very emotionally to the use of “poisons” on plants, and yet no-one says a thing when people are stuffed full of medicines preventively, possibly making them addicted in the process. The medical sector still has a long way to go in this regard and can learn from the horticultural industry. You could even say that the average grower has probably become a better “greenhouse doctor” to their plants than the average GP is to their patients.
Bedding plant grower in the Netherlands
Prof. Dr. Ir. Tiny van Boekel, working in food quality and product design, Lars Charas, ‘gastronomic author’ and founder of Feeding Good and Peter Maes, corporate marketing director Koppert Biological Systems are our guests in this very special Jungle Talk on Tuesday 26 April, 19.30 Dutch time. The central theme is the relation between healthy plants, healthy food and healthy people.
After WW II the so-called ‘Green Revolution’ improved food production, both in quantity and in quality. Prices went down, production volumes increased and now a growing part of the world population has access to affordable food.
Dealing with the future challenge of having to feed 9 billion people in 2050 large scale production still dictates the daily life of most agri- and horticultural producers. Large scale and monoculture production, often combined with pesticides and synthetic fertilizers have exhausted soils in many places. Is this the way to continue or can we find alternatives?
Healthy plants, healthy food
A healthy soil is supplying elements to the plant, making it more vital and healthy and less vulnerable to pests and diseases. Healthy plants are providing solutions to prevent malnutrition. Can we try to combine natural solutions with modern technology for a sustainable future? Can we focus on healthy food instead of calories only? Can this be done in a sustainable way? What can we learn from nature?
Our guests invite you to join the discussion on sensible solutions for food production and food technology. Join our debate on Tuesday evening April 26 at 19.30 hrs.
You can register to participate in this Jungle Talk (free of charge) via this link. The only thing you need to do is to be online and make sure your internet connection is working properly. Please note this webinar will be conducted in English.
For more information, please visit www.jungletalks.com.
Marius Mans of Mans Flowers is one of the first growers in the Dutch ornamental plant cultivation sector to firmly adhere to the guidelines of the Next Generation Growing. "You become more conscious of your energy usage and that leads to savings. But optimizing growth remains the primary objective."
Modern growers are increasingly becoming entrepreneurs who must know all about the many aspects of a modern greenhouse cultivation company. "Nowadays, regulation and control by a climate computer play an essential role in any of the larger companies", says Mans. However, despite that fact, he believes that having green fingers is still very important. "Certainly in the case of the Next Generation Growing, it is about making the right observations and using this information to choose the correct settings at the right time."
"Insight into every detail of the plant's growing process leads to many other opportunities."
In the last few years, Mans Flowers has developed the Next Generation Growing even further. He became more aware of his energy consumption, which was the first step towards making savings. However, the biggest added value is the optimal growth that he has experienced. "An optimal greenhouse climate greatly improves quality. I can now also deliver top quality products during the more difficult growing periods in the year. Insight into every detail of the plant's growing process leads to many other opportunities."
Balanced greenhouse climate
Mans has recently switched to Priva for his climate control needs. "I have made that choice because it gives me more options to achieve the ideal, balanced greenhouse climate. I get calculations in advance based upon a variety of parameters. And that helps me to take the right decision at the right time in order to achieve my goal."
"A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world."
Fighting diseases and pests also has a very high priority, says Mans. "The gerbera is a bushy plant with a lot of leaves close to each other, which makes it difficult to treat diseases and fight pests. For that reason and also because we want to demonstrate corporate social responsibility, biological control is extremely important. It has to do with having the right balance and an integrated approach. A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world. That helps us to be able to hold and improve our strong position in the future."
Royal Pride is one of the few companies in Holland that is allowed to display the Milieukeurmerk (Dutch quality mark), so the bar on food safety has been set high in Middenmeer. 'The first step in striving for the lowest possible amount of crop protection agents is to prevent diseases in the crop. A good climate computer system is essential here', says tomato grower Frank van Kleef.
Royal Pride recently switched to a different climate system and a different supplier. Co-owner Frank van Kleef explains the motivation for teaming up with Priva. 'In terms of development the Connext from Priva is much more advanced than other systems. It allows us to grow crops more energy efficiently and make advances in terms of production. This allows you to successfully recoup this type of investment. The new system also has an advantage in the field of food safety, as a good growing climate produces healthier plants with higher resistance.'
'It is, and remains, the green-fingered grower who can best decide whether or not the plant is happy.'
It is an essential aspect of the operational safety Royal Pride continuously strives for. 'We've come a long way in that field. With the current size of tomato companies like ours, that safety is very important. When we switched to the new climate system we had good reason to include a loop so that the necessary back-up was available at all times.'
Technical developments provide added value, but Frank van Kleef does not believe that automation will make expertise superfluous in the future. 'The grower's judgement will always be very important.' At the company in Middenmeer 3500 sensors have been installed to measure all kinds of things. 'But it is, and remains, the green-fingered grower who can best decide whether or not the plant is happy.'
'A development such as Next Generation Greenhouse Cultivation is promising but keeps shifting because technology keeps changing.'
However, due in part to the technological developments, that grower has regularly changed the way they work over the past 20 years. 'A development such as Next Generation Greenhouse Cultivation is promising but keeps shifting because technology keeps changing. We need to continue improving. While 20 years ago we grew 40 kg of tomatoes with 60 cubic metres of gas, today we grow 70 kg with just 35 cubic metres.'
Source/photo: Priva/The Grower Files.