The most sustainable way to prevent diseases and pests in vegetable cultivation is to develop varieties that are resistant. Developing a new variety used to take more than twenty years, but thanks to new technologies, such as tissue culture, marker technology and bioinformatics, we can reduce that period to just four to eight years.
All around the world, vegetable growers provide healthy and tasty products that meet the requirements of the consumer. These professionals are used to working with the possibilities and challenges that nature offers them.
An important part of their work is to prevent diseases and pests. Sometimes a pesticide is necessary to keep a crop healthy, but growers prefer to use chemicals as little as possible. Treatment often demands energy from the plant and involves costs. Moreover, there are diseases and pests for which no pesticides are available at all, like clubroot (Plasmodiophora brassicae), a soil-borne pathogen that can cause serious damage to brassicas, such as cabbage crops.
Natural resistance
Nature often provides the solution. Some plants have a natural resistance to fungal or bacterial infections and some can even defend themselves against pests. From these useful, inherited characteristics, breeders can make a selection and develop varieties that have acquired these resistance characteristics.
Bejo has already developed varieties using these techniques, such as red cabbage, pak choi, Chinese cabbage, white cabbage and cauliflower, that are resistant to certain strains (physios) of clubroot.
Traditional breeding is a process of selecting plants with the desired characteristics and cross-breeding them over many generations. It generally takes approximately twenty years before a new variety is ready to be introduced to the market using this classic method. Modern breeding companies can do this much faster thanks to 'life sciences', such as tissue culture, the use of DNA markers and bioinformatics, resulting in a reduced time frame of just four to eight years – depending on the variety.
Start in the field
How does this work in practice? Bejo begins in the field where their representatives visit vegetable growers on a daily basis. They are the first to notice an outbreak of a specific plant disease, e.g. a fungus, in a region. If a structural cultivation problem arises, this could be an opportunity for Bejo to start a disease resistance breeding programme.
Isolating pathogens
It is important when breeding for resistance to know the pathogen and the variant (physio) concerned. For example, of the previously mentioned clubroot there are at least nine known physios. These variants are often specific to certain regions or climates.
Breeding for resistance starts by identifying the cause, and Bejo's researchers do that in the Phytopathology & Content Analysis department. They isolate the pathogen which is then cultured to reproduce it. This results in a so-called isolate which is then used to carry out a ‘disease test’. In other words: they infect a population of plants. Any plants that remain healthy are selected by the breeders as the basis for a resistant variety.
Marker technology and bioinformatics
In modern breeding, plant DNA is also researched. Breeders are mainly interested in pieces of DNA that are typical of a certain characteristic, the so-called DNA markers. As soon as Bejo's Marker Technology & Genomics department is aware of the marker for the relevant resistance, a disease test is no longer required. This means they can select much faster, gaining a year in the process. Researchers only need a few plant cells to produce a DNA profile in order to determine whether a plant has the desired characteristics. This can be carried out when the plant is still very small, which also saves a lot of time.
Thanks to so-called bioinformatics, breeders can research multiple resistances simultaneously. They use selective marker tests to analyse a population of plants for resistance and then conduct further research on the strongest. The DNA tests also enable the ‘stacking’ of resistances, or breeding for resistance to three different disease pathogens at the same time, for example. By using automation and robotisation, researchers can process samples in large quantities and analyse complex connections.
Tissue culture and embryo rescue
In order to have the next generation of plants in a short period of time, Bejo uses tissue culture and embryo rescue in their Tissue Culture & Cell Biology department. Through these techniques they can propagate a selected plant or accelerate its uniformity.
Moreover, they can increase the chances of success of a unique cross-bred plant by using techniques from cell biology. Old varieties or wild varieties may have interesting resistance characteristics, but sometimes they are difficult to cross with common varieties used by vegetable growers. In many cases, it appears that the fertilisation is successful, but often the seed of such a combination is not strong enough to germinate and grow into a healthy plant. Sometimes it is possible to cultivate the seed of a unique cross-bred plant under laboratory conditions and the plant produced from this seed is then cross-bred with quality lines. After cross-breeding and selecting for a number of generations, a new variety can emerge with the unique characteristic of the wild variety and with seed that is capable of germinating. Bejo has developed new onion varieties that are resistant to downy mildew, such as Hylander and Powell, based on a cross-bred wild onion.
If, after selection, it appears that a cross-bred plant has potential, it is then extensively tested: breeders want to know how such a potential new variety copes in natural circumstances. Bejo assesses this first in its own fields, often in different places around the world. They then carry out practical tests at our customers. Only when it has become clear in practice that a new variety has added value do they start production for the introduction of the seeds as a commercial variety.
Resistance breeding never stops
The development of new vegetable varieties that are resistant to diseases and pests never stops. In the field, pathogens can adapt to resistant crops, which can eventually affect the plant. The resistance is then broken down and the breeders and researchers have to start all over again. It’s an arms race.
Furthermore, every area in the world requires different resistances. A white cabbage in early spring, for example, can perform well in Eastern Europe, while the same variety in the humid tropical climate of Asia is sensitive to the Xanthomonas bacteria.
Insects
Variable conditions in cultivation and changing regulations can also have an impact on the demand for resistant varieties. A ban on a pesticide used against insects often results in a change in disease levels. Damage caused by the cabbage fly can increase the effect of secondary bacterial or fungal infections.
The possibility of making plants resistant to insects through breeding is a new and promising development, and one which Bejo pays a lot of attention to.
Sustainable cultivation methods
At Bejo they believe that our scarce natural resources deserve protection so that we can continue to harvest, not only now but also in fifty years’ time. Therefore, the development of resistant varieties is essential. In the Research Centre in Warmenhuizen, the Netherlands, they are constantly looking for ways to further improve breeding methods. Breeders and researchers work closely together with experts at various universities and during field trials.
For more information:
Bejo Zaden
Trambaan 1
1749 CZ Warmenhuizen
Postbus 50
1749 ZH Warmenhuizen
Netherlands
T +31(0)226 - 39 61 62
F +31(0)226 - 39 35 04
www.bejo.nl