Penn State Potato Program
The United States produces more than 43 billion pounds of potatoes annually on around 1.1 million acres with an approximate value of $4.3 billion. Pennsylvania has a long history and tradition of growing potatoes and is one of the leading states in the production of potato chips. Penn State’s Department of Plant Pathology & Environmental Microbiology potato research program is engaged in various potato research programs including potato germplasm evaluation and selection, integrated potato disease management, and potato pathology. Our potato program is committed to developing research-based information to support Pennsylvania potato production. We work closely with Pennsylvania potato growers and industry, identify acute commercial potato production and disease problems, and conduct laboratory- and field-based experiments designed to provide critical information to solve these problems. We cooperate closely with other potato programs in the U.S. for developing disease-resistant potato germplasm and new potato varieties with improved processing quality or culinary appeal. Perhaps the most unique part of the Penn State potato program is the involvement of the Pennsylvania potato industry. There is a long history of cooperation between the University and potato industry. While Pennsylvania potato acreage has declined, growers continue to rely on variety trial research to select productive varieties.
Potato Germplasm Evaluation and New Variety Development
Potato Germplasm Evaluation
Potato cultivars currently grown in Pennsylvania present a variety of problems to growers. We conduct potato germplasm evaluation trials on potato growers’ farms and on agricultural research fields at the Russell E. Larson Agricultural Research Center in Rock Springs. The objective of this project is to find new varieties and breeding clones that have adaptation to Pennsylvania potato growing regions and have qualities that are suitable for either processing or tablestock. In 2015 a total of 286 potato varieties/breeding clones including white-skinned, red/purple-skinned, and russet-skinned cultivars from different breeding programs including USDA, University of Maine, Cornell University, Colorado State University, University of Wisconsin, Idaho, Michigan State University, and Canada were evaluated for yield, processing, and culinary characteristics in three locations in Pennsylvania. After harvest we assessed yield, tuber size and shape, internal and external defects, skin color, texture, specific gravity, overall appearance, and French fry, chip, and culinary qualities. High quality potato varieties and breeding clones for processing, fresh market, and specialty uses are selected and introduced to Pennsylvania growers and industry.
Figure 1. A 2015 potato germplasm evaluation trial in Rock Springs.
New Variety Development
We are involved in a regional potato research NE1231 program and cooperate with potato breeding programs from the northeast U.S. to develop high yielding, disease-resistant, and processing and/or specialty-type potato varieties. This research will enable farmers in the eastern U.S. to produce and market a wide range of potato varieties. This project involves eight states, four potato breeding programs, and numerous stakeholders. We evaluate breeding clones from these breeding programs from early generations to commercial trials. Data from our evaluation helps breeders determine which lines should be released as new varieties, on which lines to focus for potential release in the near future, and which lines could be used as parents for further crossing. We collaborated in 2015 with Dr. Haynes from USDA-ARS Beltsville to release a new potato variety, an early-maturing, small, round, red-skinned, light yellow-fleshed potato variety primarily adapted to the northeastern U.S. and Canada. The variety was selected from a cross of B0811-2 x Redsen and evaluated under the pedigree B2152-17.
Figure 2. A new red-skinned potato variety which is in the process of being released in 2015.
We have potato demonstration trials which are conducted on growers’ farms and on agricultural research fields in Rock Springs every year. Demonstration trials are designed to show growers and industry new potato varieties. Growers have the opportunity to look at the various varieties and share their thoughts and concerns. In 2015 we had a demonstration trial with thirty varieties in Rock Springs which was shown to visitors during Ag Progress Days, sixteen varieties in Lehigh County, and sixteen varieties in Erie County which were shown to growers during Potato Field Days.
Figure 3. A 2015 potato demonstration trial in Rock Springs which was shown to visitors during Ag Progress Days in August.
Potato Disease Management
The very best way to combat potato diseases is to grow disease-resistant varieties. Every year we have field disease test trials to evaluate new potato varieties and advanced breeding clones for resistance to late blight, early blight, common scab, and powdery scab, respectively. We also have participated in the National Late Blight Trial and the National Common Scab Trial for many years. In 2015 potato varieties/breeding clones were evaluated for resistance to late blight (978), early blight (108), common scab (153), and powdery scab (56) in Pennsylvania. The resistant varieties/breeding clones are selected and introduced to potato growers.
Figure 4. A 2014 field trial to evaluate potato varieties/breeding clones for resistance to late blight in Rock Springs.
We have research projects aimed to understand the genetic basis of disease resistance in potatoes. One example of this research is the late blight resistance in diploid potatoes. Dr. Haynes from USDA-ARS Beltsville cultivated a diploid hybrid Solanum phureja× S. stenotomum (phu-stn) potato population. The population has been under recurrent selection first for tuberization and recently for late blight and early blight resistance. Two clones from the late blight cycle one population were crossed to develop a mapping population. This mapping population was mapped for both late blight resistance and early blight resistance. Recurrent selection for late blight resistance has moved onto the fourth cycle of selection in 2015. Late blight resistant clones will be crossed with late blight susceptible clones from the fourth cycle population to generate a diploid mapping population in 2016. This mapping population will be evaluated for late blight resistance in 2017 and 2018 in Rock Springs. SNPs will be mapped and linkage groups will be generated. Phenotyping and genotyping data will be combined to produce gene/QTL maps. The locations of late blight resistance genes/QTLs and the SNP markers linked to these genes/QTLs will be identified. The SNP markers linked to these resistance genes/QTLs will be used to select late blight resistant clones in future crossing populations. The overall long term goal of this project is to introduce genes/QTLs responsible for late blight resistance in diploid potatoes into commercial tetraploid potato varieties.
Figure 5. Functional map for the mapping population of Solanum phureja- S. stenotomum showing QTL regions for foliage late blight resistance, resistance to tuber late blight, resistance to early blight and late maturity.
Biocontrol is an attractive and potentially sustainable option for control of potato soil-borne diseases. Many streptomycetes found in lenticels of potato tubers grown in scab-suppressive soil are nonpathogenic, produce antibiotics, and inhibit the growth of pathogenic Streptomyces scabies strains, which cause common scab on tubers. Biological control using suppressive strains of Streptomyces has given promising results for the control of several diseases. We had biocontrol trials to use non-pathogenic Streptomyces strains to suppress potato common scab in a field with a common scab history in Rock Springs. Several non-pathogenic Streptomyces strains showed potential to reduce common scab incidence and severity on two important potato chipping cultivars in the field. These results can be further applied to reduce common scab disease severity in potatoes.
Late blight and early blight have been occurring more often in recent years in the U.S. Currently, no potato varieties are immune to late and early blight, and these diseases are mainly managed with fungicides. In response to the potato industry, we have developed a testing program to test efficacy of foliar fungicides for the control of late and early blight. We cooperate with companies such as Syngenta, DuPont, Gowan, USA Certis, etc. to evaluate their new chemical products every year. We had a late blight fungicide trial in 2015 with twelve chemical treatments. Foliar fungicides can be highly effective if used properly.
There are several soil-borne diseases, such as silver scurf, black dot, Rhizoctonia, and common scab that appear to be increasing in frequency and severity in Pennsylvania, and there are no effective methods to control these diseases. Plant extracts and crop residues have been considered to have a potential role in controlling soil-borne diseases. A special focus has been made on members of the Brassicaceae family. Brassica cover crops mown down at maturity and incorporated into soils as green manures might reduce the populations of soil-borne pathogens. We conducted field trials to investigate the effect of cover cropping with green manure incorporation on the control of soil-borne potato diseases. A field known to have a history of common scab, black dot, silver scurf, and black scurf is located in Rock Springs. A three-year rotation of potato, corn, and wheat has been practiced in this field. After harvesting of wheat, mustard ‘Caliente 199’ was grown in the field. This green manure crop was immediately incorporated into the soil. Potatoes were then grown in the field. After harvest, incidences and severities of common scab, black dot, silver scurf, and black scurf were scored. Tuber quality and yield were measured. We are in the process of data analyses to determine the effects of green manure on potato yield and soil-borne diseases.
Soil-borne fungus Verticillium dahliae or Verticillium albo-atrum causes early death of potato vines and results in up to 50 percent losses in yields. The fungus persists in soil for long periods in the absence of potatoes. Soil fumigation plays an integral role in the management of soil-borne diseases. We cooperated in 2015 with TriEst Ag Group, Inc. to use the soil fumigant chloropicrin to control potato Verticillium wilt. The experiment with eight treatments and five replications was conducted in a grower’s farm in Schuylkill County. Chloropicrin was injected into the soil before potatoes were planted. The trial was harvested, and we are in the process of data analyses. The experiment will be repeated in 2016.
Plant Disease Detection
Soil-borne pathogens are well adapted to soil conditions and once established are very difficult to eliminate by any known method of control. Soil-borne pathogens may survive for many years in fields. The accurate identification and quantification of pathogens in field soils is essential for effective disease controls. It enables more informed decisions to be made about variety choice and how and when chemicals can be used most effectively to control disease epidemics. We have developed real-time PCR assays for Spongospora subterranea (powdery scab pathogen), pathogenic Streptomyces spp. (common scab pathogen), Helminthosporium solani (silver scurf pathogen), Colletotrichum coccodes (black dot pathogen), and Rhizoctonia solani (black scurf pathogen). These PCR assays have been used successfully for the detection and quantification of pathogens in soils. We also use these PCR assays to detect pathogens on seed tubers. Pathogen detection is important for preventing the spread of diseases by seed tubers.
We have research projects to study the biology of potato pathogens. Powdery scab pathogen is a pathogen we are focusing on. Powdery scab of potato, caused by Spongospora subterranea, has occurred across the country especially in cool, moist growing conditions. Although there have been increased research efforts on S. subterranea, there are still gaps in our knowledge of genetic variability, life cycle, epidemiology, and control across the U.S. Our lab has developed a sensitive real-time PCR assay that allows us to detect and quantify S. subterranea in host plants and in soils. We have studied the host range and have knowledge of some hosts that can support the entire life cycle of the pathogen while there are others that cannot support the entire life cycle of the pathogen and may be considered as trap crops. Eastern black nightshade was identified as the most susceptible host. We have developed a method to produce single spore ball isolates using a hydroponic system and nightshade seedlings. We have developed several S. subterranea-specific restriction fragment length polymorphism (RFLP) markers that can be used to detect genetic variation. Different genotypes were identified across the U.S. So far we know that the western population is genetically different from the eastern U.S. population, but we do not know what this means in terms of the epidemiology of this disease. We have field trials to evaluate host resistance. A few potato varieties/breeding clones showed consistent moderate resistance to powdery scab.
Figure 6. Spongospora subterranea zoosporangia in root hairs of an eastern black nightshade.
New Research Projects
Par-Frying Potato Variety
We collaborate with Roger Springer and Bob Leiby from Pennsylvania Cooperative Potato Growers, Inc. to conduct field and laboratory experiments to evaluate and select potato varieties for par-frying for Pennsylvania growers and industry. While par-fry processing is common in Europe, virtually no par-fry potato processing is done in North America. Par-fried potato products provide a new opportunity for Pennsylvania potato growers. Keystone Potato Products, Inc. has the capacity to produce these par-fried potato products to meet market demand. We have identified several potato varieties that have promising par-fry qualities after two years’ evaluation of potato varieties in 2014 and 2015. We will look for optimum production parameters to produce high quality par-fry potatoes under Pennsylvania conditions and introduce these par-frying potato varieties to Pennsylvania potato growers and industry in 2016.
Potato Soft Rot
There was an outbreak in the U.S. in 2015 of potato soft rot in several states including Pennsylvania. Potato growers in these states are very concerned about this disease. Soft rot of stems and tubers of potato is caused by bacteria Pectobacterium species and Dickeya species. The disease can cause poor emergence in the field and rot tubers in the field and during storage, reducing yield and quality. There are no chemicals to manage soft rot once infection has occurred. Development of resistant cultivars is the most effective long-term way to control soft rot. The levels of resistance in tetraploid potato cultivars vary and are generally low. Numerous sources of resistance have been reported in diploid potato varieties. Dr. Haynes from USDA-ARS Potato Breeding Program has maintained approximately 290 clones of a hybrid population of the cultivated diploid species Solanum phureja-S. stenotomum and 50 accessions of wild Solanum species. We hypothesize that 1) soft rot resistance exists in some diploid potato germplasm, 2) higher levels of resistance exist in wild species germplasm, 3) genes/QTLs can be identified for resistance, and 4) resistance can be incorporated into commercial germplasm. We will evaluate these clones/accessions for resistance to stem rot and tuber rot in 2016 and make crosses to incorporate soft rot resistance into the commercial potato germplasm base.
Genes Involved in Late Blight Resistance
We are involved in a research project to identify late blight resistant genes in a tetraploid crossing population. The USDA-ARS Potato Breeding Program has a tetraploid clone that has served as a late blight resistant standard for fourteen years in the National Late Blight Trials, maintaining its status as one of the most late blight resistant clones evaluated all fourteen years. Resistance in this clone was derived from clones obtained from India, but the genetic basis of this resistance is still unknown. Further research is needed to understand the genetic basis of late blight resistance in this clone. The ARS Potato Breeding Program also developed the variety “Harley Blackwell,” a chipping selection with resistance to internal heat necrosis for processing directly from the field. The crossing between the late blight resistant clone and Harley Blackwell was made in 2015 by Dr. Haynes. We will evaluate this tetraploid crossing population in 2016 and 2017 for resistance to late blight. The processing traits of this population will be evaluated by the University of Florida and North Carolina State University. We will genotype each individual clone using the SolCAP SNP array. Genes/QTLs responsible for late blight resistance and processing quality in this population and SNP markers for marker-assistant selection will be identified. The purpose of this research is to develop potato varieties to combine resistance to late blight with processing quality.
Genome-Wide Association Study (GWAS)
Genome-wide association studies (GWAS), originally developed to study genetic disorders in humans, is an emerging tool for the detection of genes underlying complex traits in plants. With the recent completion of potato genome sequences and the development of high-density potato SNP arrays, we plan to use GWAS to identify genes responsible for quantitative variation of complex traits, such as disease resistance and other agronomic traits in tetraploid potatoes. We will first collect about 240 common tetraploid potato varieties in 2016 and evaluate them for late and early blight resistance and genotype each individual using SNP arrays. We will evaluate these varieties for resistance to other diseases and for other agronomic traits in future years. Genes responsible for these traits will be identified using GWAS. The result will accelerate new potato variety development via genomics-assisted breeding.
For many years potato breeders and researchers have been developing new varieties with a focus on high-yield and big-size tubers. Recently, customers and potato growers have shown increasing interest in small potatoes, baby potatoes, and color-fleshed potatoes. Color-fleshed potatoes have higher amounts of carotenoids and anthocyanins. These antioxidants have been shown to promote human health. To respond to the opportunities for these added-value products and the changing needs of society, we will set trials to evaluate and select small B-sized and yellow/red/blue/purple-fleshed specialty potatoes.
We collaborate closely with Dr. Kathy Haynes (USDA-ARS, Beltsville), Dr. Gregory Porter (University of Maine) and Dr. Walter De Jong (Cornell University) to develop disease-resistant potato germplasm and new potato varieties. We cooperate with the project leaders of other potato breeding programs from North Carolina State University, Colorado State University, University of Wisconsin, Michigan State University, North Dakota State University, USDA-ARS (Idaho), Real Potatoes, Sunrain, HZPC, and Solanum International by evaluating their potato germplasm. We work closely with board members of Pennsylvania Potato Research Program, Roger Springer and Bob Leiby from Pennsylvania Cooperative Potato Growers, Inc., and Keystone Potato Products, LLC to evaluate and select potato varieties for Pennsylvania growers and industry.
All Pennsylvania potato growers and industry are benefiting from our program. The results of our field potato germplasm and disease evaluation trials provide growers information on potato varieties and advanced breeding clones. We annually print a summarized report of the results of all field trials. The Pennsylvania Potato Research Reports are mailed to Pennsylvania potato growers and industry. We also make presentations to grower groups and share information to individual growers and groups through a range of activities. As a result, growers learn about new potato management information and promising new varieties in the program. Based on our information, growers can choose appropriate varieties to grow under Pennsylvania conditions with optimal cultural practices for different purposes, such as table stock, chipping, or French fries. We work with growers to facilitate commercial-scale trials. Commercial-scale trials help identify production problems that might occur on commercial potato farms. After harvest, we meet with growers to share results of the trials. Management recommendations are developed for these advanced clones entering commercial trials.
We have annual demonstration trials with new potato varieties, which are shown to growers during Potato Field Days and Ag Progress Days. Many growers come to these demonstration trials. About 1,000 visitors annually attend our potato demonstration trial in Rock Springs during Ag Progress Days. These events are opportunities for growers to view new potato varieties and receive updates from potato specialists. This helps them to select potato varieties to grow in the future. Some non-potato growers show interest in growing potatoes.
The Penn State potato program plays an important role in the Northeastern NE1231 Potato Program, which includes the University of Maine, Cornell University, North Carolina State University, The Ohio State University, the University of Florida, Virginia Polytechnic and State University, and The Pennsylvania State University. As part of the NE1231 Program, we evaluate potato germplasm for disease resistance and qualities for processing and table stock. The data from our trials helps potato breeders from the NE1231 program to develop disease-resistant germplasm, release new potato varieties, and select suitable parents for crossing. Several potato varieties released from breeders from the NE1231 program have gained popularity in Pennsylvania. For example, “Lehigh,” a widely-adapted yellow-fleshed variety co-released by Cornell University and Penn State in 2007 and named after Pennsylvania's Lehigh Valley, has become a popular variety in Pennsylvania. “Easton,” released in 2014 due to its outstanding fry processing, has shown great potential for Pennsylvania potato industry.
The data from our fungicide trials helps potato growers to develop effective fungicide spray programs to manage late blight and early blight. We have provided the industry with experimental data supporting their registration for the use of the fungicides and the EPA approval of new fungicides.
External funders of our program include the USDA, Pennsylvania Department of Agriculture and Pennsylvania Potato Research Program. We have donations from private companies, such as Syngenta, DuPont, Gowan, Certis USA, Simplot, Frito Lay, BASF Corporation, HZPC Americas Corp, etc. to support our research on potato and potato diseases. Potato growers’, industry’s, and researchers’ support to the Jim Watts Endowment Fund has added resources to our potato research operations which benefit Pennsylvania potato growers.