Non host and insect resistance

Research focus is on breeding for resistance against a number of different pathogens using mainly (molecular) genetic approaches. Research covers all aspects related to resistance breeding including major resistance genes, quantitative resistances (QTL) and non host resistance. Identification, isolation and characterization of genes involved, as well as determining and using allelic variation and molecular markers are issues studied. Target areas are insect resistance and fungal resistance.

Non-host resistance

A commonplace observation is, that most plant species are completely resistant to almost all potential pathogen species. This is due to the narrow specialization of most plant pathogens: by far most pathogens have only a limited host range. Recent advances in molecular biology of plant pathogen interactions suggest that adapted pathogens are able to suppress the basal defence of their host plants, but not in, sometimes related, non-host plant species. The basal defense is also known as PAMP triggered immunity (PTI). It is not known which plant genetic factors are responsible for allowing a potential pathogen to succeed (or not) in suppression of this basal defence. For plant breeding it is useful to understand the molecular basis of (non) host status of plants to potential pathogens. When understood, it might be possible to mimic non-host resistance in a host plant species somehow, creating a pseudo-non-host resistance in a host species. Such a resistance would be complete and hard to overcome by the pathogen.

In our group, we have developed three research systems to investigate the inheritance underlying (non)host status to biotrophic specialized pathogens: barley/Puccinia rusts and powdery mildews and Lettuce/Bremia lactucae.

Barley

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

Lettuce

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

Allium

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



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