Type of Lab Work Performed

This project conducts plant disease diagnosis for fungal, bacterial, viral and phytoplasma diseases. We also extract plant pathogenic nematodes from soils for identification. The specific type of lab work performed depends on the diseases and pathogens and pests. Many workers in Alaska based on their diagnosis on visual observation of disease symptoms. However, this method can be highly inaccurate and misleading. For instance, symptom expression of late blight is totally different on potatoes grown under dry land or irrigated conditions. In Alaska, symptoms of diseases such as bacterial ring rot and viruses are frequently “masked”. Research results of one of my graduate students indicated that 40% of bacterial ring rot diseased plants may remain symptomless and healthy looking under certain environmental conditions in Alaska. We have found similar results with virus diseases on potatoes.

In some plant bacterial and fungal diseases, disease diagnosis often requires sophisticated analysis. Pure cultures of the causal agent, obtained under aseptic conditions, will be analyzed for their fatty acids, isozymes, and specific proteins, etc. In the case of Phytophthora infestans, the causal agent of late blight, a mating experiment is needed. Taiwan quarantines P. infestans A2 mating type but not A1 mating type.

To process massive numbers of samples for bacterial ring rot and many of the potato viruses, the Enzyme-Linked ImmunoSorbent Assay (ELISA) is used. Other immunological methods, such as immunofluorescence staining are used for further identification. Conjugates and antisera (against bacterial ring rot and various potato viruses) and reagents are commercially available.

For the diagnosis of potato witches broom phytoplasma and aster yellow phytoplasma, both of which are quarantined by China, molecular techniques will be used. Dr. Gay in my lab successfully tested for both phytoplasmas using two universal primers. Other techniques used include DNA extraction, polymerase chain reaction (PCR) amplification and DNA sequencing for identity verification. RT-PCR will be used in the identification of tobacco rattle virus which is not stable enough for ELISA.

Soils and roots are collected around potato plants and processed for the extraction of plant pathogenic nematodes. Different genera of plant pathogenic nematodes can be differentiated based on their morphological characteristics. Speciation of some plant pathogenic nematodes will also depend on analysis of specific conserved DNA sequences. The genus of Trichodorus and Ditylenchus are of special interests to Alaska. Species of Trichodorus cause stubby roots on potatoes. They also serve as a vector for the tobacco rattle virus. Furthermore, Trichodorus proximus is a pest quarantined by China. Both Ditylenchus destructor and D. dipsaci are quarantined by Taiwan.

The Plant Pathology and Biotechnology Lab at UAF is the only laboratory in Alaska with the expertise and equipment to routinely perform diagnosis of plant diseases and plant pathogenic nematodes, using biological, immunological, biochemical and molecular techniques.