Improvement of winter oilseed rape (B. napus L.) resistance towards Verticillium longisporum

The aim of this joint research project (in collaboration with the GFP and the Institute of Agronomy and Plant Breeding I, University of Gießen is to develop molecular markers for Verticillium longisporum resistance based on double haploid (DH) populations that also have a high oleic acid content. The evaluation of the B. napus resistance is performed in greenhouse and in field trials at different locations in Northern Germany and in South Sweden. The obtained data is analyzed by Quantitative Trait Loci (QTL) mapping at the Institute of Agronomy and Plant Breeding I at the University of Gießen.
Greenhouse trials are conducted by infecting the plants via root dip inoculation. This is followed by the weekly estimation of the disease severity with a 1-9 assessment key. Additionally the plant height is scored because stunting of the plant is a typical symptom caused by V. longisporum. For the classification of the tested DH-lines four reference cultivars are applied from susceptible over moderately tolerant to resistant.
In order to characterize the DH-lines concerning their resistance to V. longisporum in natural conditions diverse locations were chosen to perform field trials. In Göttingen an enhanced infestation level in the soil is reached by incorporating infested stubbles directly before sowing into the upper soil layers whereas in Northern Germany and South Sweden field trials are performed in places with a natural infection pressure. The visual disease assessment is performed shortly after harvest by scoring the presence of microsclerotia in the root, under the epidermis and in the stem pith of the stubble according to a 1-4 rating scale.
For identification of resistance factors involved in pathogen defence the ultrastructure of the vascular tissue of selected resistant plants is investigated by transmission electron microscopy. The main focus is on the formation of all known vascular occlusions which are relevant in resistance to systemic colonization, including the induction of phenolic substances, cell wall reactions by lignin and callose formation and the accumulation of gels and tyloses. Another intention is the study of the direct interaction of these defence structures with V. longisporum. Additionally the pathogen spread is examined by quantitative PCR.
Since vascular occlusions not only prevent the fungal spread but also affect the water transport agronomical important characteristics like drought stress resistance is analysed.

Further reading (Background information)

Investigators:

• Jessica Knüfer (PhD student, until 2011)
• Jutta Schaper (technician)
• Christina Eynck (PhD student, until 2008)
• Daniel Lopisso (MSc student, now PhD student, current investigator)

• Prof. Andreas von Tiedemann

• Prof. Avinash Kamble, Department of Botany, University of Pune, India
• Prof. Wolfgang Friedt, Institute of Agronomy and Plant Breeding, University Giessen
• Prof. Petr Karlovsky, Molecular Phytopathology and Mycotoxin Research, University Göttingen
• German rapeseed breeders