Potato: Molecular Plant-Pathogen Interactions and Germplasm Enhancement.
Potato is susceptible to many diseases and this relatively poor disease resistance can require intensive management and considerable expense to counter. Thus, our major focus is directed towards gaining a better understanding of the molecular basis of potato disease resistance to provide gene discovery, targets for molecular manipulation, molecular markers for selection and optimal use of induced defenses. Development of plants with superior disease resistance will lead to increased yields and greater economic benefits for American agriculture. Reducing the reliance on pesticides will diminish concerns and controversy over the effect of pesticides on health and the environment.
Inducible defenses in Potato
The vast majority of research into the molecular basis of disease resistance, including induced resistance, use Arabidopsis or tobacco model systems. Consequently, far less is known about potato defense mechanisms. Systemic Acquired Resistance (SAR) is a phenomenon in plants whereby plants that are challenged by a pathogen become highly resistant to subsequent infection not only by the original pathogen, but a wide range of pathogens, and this protection can last for weeks to months. Salicylic acid (SA) is a key signal molecule that regulates SAR and is capable of inducing SAR in the absence of a pathogen, when sprayed on plants. After decades of basic research, SAR is now being utilized for crop protection, with over a dozen companies marketing products purported to mobilize SAR. SAR strategies in the field have had mixed results, effective in some crops against certain pathogens, ineffective in other crops or against other pathogens. Compounds that elicit SAR are very different from conventional pesticides and it is probable that their usage must be optimized for each crop. We are studying SAR in potato by looking at SA signaling, using different compounds to activate SAR. We have found that many potato varieties widely planted in the United States have a constitutive level of PR gene expression in the absence of exogenous stimulation. Furthermore, other substantial differences appear to exist in potato SA signaling compared to what occurs in the Arabidopsis and tobacco model systems.
Resistant varieties being developed by Chuck Brown and others in the Tri-State Breeding Program likely use some of these same defense mechanisms (i.e. salicylic acid or jasmonate mediated resistance). We are attempting to characterize the molecular basis of resistance exhibited by Columbia root-knot nematode resistant germplasm. Characterization of the molecular basis of nematode resistance in plants is less advanced than that of viral, bacterial or fungal pathogens, probably because of greater technical difficulties associated with nematode-plant model systems. Increased knowledge of the molecular and biochemical basis of resistance to M. chitwoodi will help in the development of superior disease control methods.
Crop enhancement programs have traditionally focused on improving traits such as yield, quality, taste and disease resistance, but an area likely to receive increasing attention is improving the nutritional quality of foods. Potato is one of the most nutritious foods, having a good mixture of complex carbohydrates and high quality protein. With Chuck Brown we are looking at some of the anti-oxidants, such as carotenoids, in wild-type germplasm using HPLC, in an effort to generate domesticated varieties with even higher nutritional value.
A current issue in food science is the discovery by Swedish scientists in 2002 that a wide range of foods has acrylamide present after baking or frying. Subsequent research by multiple groups strongly suggests that a combination of high heat, sugars and asparagine results in acrylamide formation. We are studying the regulation of asparagine metabolism in potato, where asparagine can account for 40% of the free amino acids.