Lignin As a Potential Defense Against Plant Parasitic Nematodes.

Lignin as a Potential Defense against Plant Parasitic Nematodes

Alison Thompson¹, Kim Garland-Campbell^2, Tim Paulitz³, Axel Elling^4, Richard Smiley⁵

¹Department of Crop and Soils, Washington State University

²USDA-ARS, Wheat Genetics, Quality and Physiology, Disease Research Unit

³USDA-ARS Root Disease and Biological Control Research Unit

⁴Department of Plant Pathology, Washington State University

⁵Department of Plant Pathology, Oregon State University

Root lesion nematodes (RLN) (Pratylenchus thornei and P. neglectus) are a characterized soil borne pathogen of wheat.  Pratylenchus nematodes damage plants by invading root cells using a stylet and feed on the cytoplasm, causing the cells to collapse and die.  Common signs of Pratylenchus nematode damage are lesions on the roots, root girdling and lack of lateral root branching.  In the Pacific Northwest (PNW) these species of nematode were found in 95% of sampled fields.  Nematicide tolerance trials of PNW spring wheat cultivars estimates RLN cause between 37% and 50% yield loss.  Resistance to these pathogens has been found in wheat landraces from Iran.  One of these sources, AUS28451, is resistant to both nematode species and has been crossed to local cultivars and a mapping population has been developed.  The mechanism of resistance to P. thornei and P. neglectus in wheat is poorly understood; understanding how resistance works can increase the efficiency of resistance breeding.  Early observational studies show that, Louise a susceptible PNW-adapted spring wheat cultivar is readily penetrated by RLN but that AUS28451 has little to no root penetration.  Overtime Louise roots in culture develop multiple lesions and few lateral roots while AUS28451 does not appear affected.   AUS28451 has been found to have increased amounts of lignin, a cell wall fortifying compound.  This trait is being examined as a potential cause for the nematodes inability to penetrate the roots.  Lignin stained root cross sections show more intense staining in AUS28451 than Louise, particularly in the epidermal cell layers.  Lignin extractions using a thioglycolic acid (TGA) precipitation method have also shown that AUS28451 has more root lignin than Louise.  This data indicates that lignin amounts might be associated with P. thornei and P. neglectus resistance in AUS28451.  Lignin is continuing to be investigated in a recombinant inbred mapping population derived from Louise and AUS28451 as the potential source of resistance.