The May-June 2015 issue of the American Journal of Potato Research (Vol. 92:379.) contained an article entitled “Wild Yeast Strains as Prospective Candidates to Induce Resistance against Potato Late Blight.” This wild yeast is not a plant pathogen; however, when present on the potato leaf in advance of the arrival of spores of Phytophthora infestans, the late blight pathogen, it incites an immune response in the potato that suppresses late blight symptoms.
The Northwest Potato Research Consortium commissioners, who oversee the use of grower assessments derived from potato sales, had the foresight to allocate a portion of these funds to basic bio-control research designed to see dividends in future years. This allocation is in addition to those directly aimed at determining recommendations on chemicals and management practices beneficial for current cropping.
Both consumer and grower interests are for minimization of all pesticides where possible. Alternately, growers who sell on the organic market must conform to the regulations set forth by the National Organic Program (NOP), which restricts the use of any chemically synthesized pesticide. These regulations leave organic growers few tools to protect their potatoes from late blight.
For example, even the natural anti-fungal carbohydrate polymer, chitosan—something prevalent in all soils (and consumed safely at daily doses of 500 milligrams for weight loss)—is restricted for use by the NOP as a fungicide. Commercial chitosan is derived primarily from crab shell chitin through a single chemical reaction—thus making it ineligible for NOP approval. However, it can be legally utilized against late blight as a sticker with copper compounds. Even though the safety of genetic modifications has been determined, this technology for developing late blight-resistant varieties also does not conform to NOP guidelines.
Fortunately, bio-control procedures are still unrestricted by NOP and can also be used in conjunction with conventional growers who utilize synthetic pesticides. The vital entity, the wild yeast strain, utilized in this study was obtained from a collection by Tyler Bourret and other students under the direction of Dr. Dean Glawe. It came from a vineyard in Washington State. It was screened originally as a yeast that could suppress the growth of other fungi when growing on an agar plate.
Additionally, when grown on a plate containing DNA- incorporated agar, the yeast was found to release an enzyme (DNase) capable of degrading DNA in its vicinity. DNase was found previously to be a signal that can induce immune responses in plants.
Therefore, it was not surprising to find that certain concentrations of the yeast cells when applied before late blight inoculum were able to almost completely suppress the symptoms typically generated by P. infestans.
Most pathologists will be quick to tell you that what you find working under laboratory conditions may not always function in the field. Also, just because there is protection for the 15 days of the lab experiment, for this control to work economically, the protection should cover the period of natural infections occurring in the field. As potato growers know, the conditions for late blight infections do not occur all years in all regions.
For those interested in conducting further research, Mike Hubbard has a testing program near Bonners Ferry, Idaho, in a region that typically sees conditions that can encourage late blight and where natural inoculums are often present. Dr. Dennis Johnson’s lab at Washington State University can provide inoculum if needed. The test requires about 8 gallons of yeast cells at a concentration of 20 million cells per milliliter to cover the five weekly applications needed to span the typical late blight period. The yeast cells are unusually stable and can be generated in low-cost solutions of potato by-product.
Wild yeast certainly holds potential in the fight against late blight, but there are likely many adjustments and refinements that still need to be worked out for it to satisfy the requirements for successful commercial use.