Nonhost and Insects resistance

The focus of the research in our group is on breeding for resistance to insects and fungal diseases using mainly (molecular) genetic approaches. Research covers all aspects related to resistance breeding, including the development of screening tools for the identification of qualitative and quantitative resistance in host or nonhost species and potential complications of introgression such as crossing barriers and linkage drag when related species are used in crosses. Additional steps involved are the identification, isolation and characterization of the genes involved, as well as the determination and use of allelic variation and molecular markers.

Contact: Olga Scholten

Breeding for insect resistant plants

Insects are causing increasing damage to crop production worldwide, most likely due to climate change.

Many crops suffer from insects, either directly through their feeding or indirectly through transmitted viruses. Until recently, chemical crop protection was regarded as the best way to prevent these problems, but due to environmental concerns, other solutions are increasingly preferred. The chemicals used cause damage to beneficial insects, such as predators and parasitoids of the pest insect, pollinators and harmless fauna. In addition, insects develop very quickly resistance to the insecticides used, which calls for higher doses or more toxic compounds.

The use of insect-resistant crops is an attractive way to control insect pests in agriculture (see for example our review published by Broekgaarden et al., 2011[VB1]). Plants can defend themselves in two ways: 1) directly by killing the insects or interfering with their life cycle, for example by producing trichomes or toxic secondary metabolites, or 2) indirectly by attracting parasitoids or predators that attack the pest insects. In our research group, we mainly focus on direct defence of insects. To achieve this, we evaluate germplasm for new resistances against sucking insects, mainly thrips, aphids and whiteflies, and chewing insects such as the Colorado potato beetle and caterpillars.

The development of insect-resistant crops can be strongly enhanced by knowledge on plant resistance mechanisms and the genes involved. Resistant material is therefore further characterized with respect to the resistance mechanism and the inheritance of resistance. The approaches used include genetics, genomics, metabolomics and detailed analysis of life history components of the pest insects.

The research is expected to result in the identification and characterization of genes conferring resistance to insects and means of introducing them into crop varieties.

The majority of our projects are carried out in collaboration with breeding companies, the Laboratory of Entomology of Wageningen University, and the business unit Bioscience of Wageningen Research for metabolomics analysis. Most of our projects are funded by the Topsector Horticulture and Starting Materials together with breeding companies. Additional funding bodies are the Ministry of LNV, TTW, and the EU.

Contact: Olga Scholten & Lotte Caarls Link naar artikel


In barley, we have developed barley experimental lines with susceptibility to some rust species and wheat powdery mildew, to which barley normally is a non-host. This allows identification of the genes that in regular barley cause “immunity” to these grass rusts and wheat powdery mildew.

The results of this work show that the non-host immunity is based on quantitative trait genes (QTLs) that show similarity in location with QTLs for basal resistance to the barley leaf rust P. hordei. Map based cloning of several QTLs for basal resistance to P. hordei and non-host resistance to several unadpated grass leaf rusts is in an advanced stage, and will allow identification of the molecular basis of basal resistance to both the barley leaf rust and to a rust to which barley normally behaves as a non-host. In barley-powdery mildew similar work is being carried out.

Contact: Rients Niks


In lettuce we make use of the rare opportunity that a wild non-host species, Lactuca saligna, can be crossed with the cultivated host species L. sativa.

A set of introgression lines (BILs) has been developed in the L. sativa cultivar, each containing only one chromosome introgression fragment from L. saligna. This allowed the identification of about 15 resistance QTL (in 15 BILs). Eight BILs showed lowered infection levels at the, most relevant, adult plant stage in the field, but their 30 to 50% infection reduction is not high enough for cultivation practice.

Stacking the quantitative resistances of BILs in pairs showed that most effects of stacked quantitative resistances do not simply add up. This result suggests that not a single locus, nor the combination of two QTLs, explain the absolute resistance of L. saligna to B. lactucae. We hypothesize that multi-locus interactions with additive and/or epistatic effects explain the absolute resistance. Therefore, we embark on new extreme selection strategies in gene mapping studies, using large F2 populations from multiple segregating L. saligna × L. sativa populations.

We will identify new QTL that, together, determine the immunity of the wild species to B. lactucae. These genes are valuable assets to breeders, since they would turn a susceptible lettuce cultivar into a “pseudo-nonhost” to this economically very devastating lettuce pathogen.

Contact: Marieke Jeuken

Breeding for insect resistant plants

Insect related problems are causing more and more damage to crop production worldwide.

Many crops suffer from insects, which may take the form of direct damage by feeding but more often the transmission of viruses by the insects causes the real damage. Until now chemical crop protection is seen as the major way to combat these problems. However, insects develop resistance to the insecticides very quickly and insecticides are causing damage not only to the pest insect but also to beneficial insects, such as predators and parasitoids of the pest insect, pollinators, and to harmless fauna.

Working towards insect resistant plants

The best strategy is to prevent the problems occurring. For this it would be convenient to have plant varieties that are resistant to insects. In our research group germplasm is evaluated for novel resistances primarily towards sucking insects, with an emphasis on:

  • aphids
  • thrips
  • whiteflies

Resistant material is further characterized with respect to the resistance mechanism and the inheritance of the resistance. Approaches used involve genetics, genomics, metabolomics and detailed analysis of life history components of the pest insects.

The research is expected to result in the identification and characterization genes conferring resistance to insects and means to introduce them into crop varieties.

Several of the projects within our groups are carried out in close collaboration with the Laboratory of Entomology of Wageningen University and the business unit Bioscience for metabolomics.

Contact: Ben Vosman


The aim of the Allium research group is the exploitation of genetic variation in the genus Allium to enable the breeding of cultivars for a durable Allium production chain, mainly onion and leek. The research focus in leek, mainly is on resistance to thrips.

Genetic research Allium

The Allium research focuses on the interface between molecular genetics, disease resistance and quality traits. The research will result in the development of marker based breeding programs aimed at the development of healthier crops, higher yields and sustainable production.

In addition, markers linked to resistance to the fungi causing Fusarium basal rot and Botrytis leaf spot in onion have been identified. Also research is carried out with onions to study whether the breeding for improved responsiveness to arbuscular mycorrhiza fungi (AM) and/or the rooting system will contribute to the growth of onions under low input conditions. The relationship between these traits and resistance to Fusarium basal rot will be studied.

Finally, the use of AM fungi to increase disease resistance in onion is studied.

Contact: Olga Scholten

Genomics research Allium

Onion has a huge genome (16GB). However, sequence information is extremely valuable for the identification of genes associated with important traits such as disease resistance and for understanding the underlying mechanisms. The onion genome project (Sequon) focused on a de novo assembly of the onion genome. The availability of the onion genome will speed up onion breeding and lead to several innovations.

Contact: Olga Scholten