8:00am- 8:15am
Increasing the Resilience of Potato Production to Combat Climate Change
Joseph Coombs, Michigan State University

               Potato production is sensitive to heat stress.  This sensitivity contributes to the vulnerability of US potato production to climate change, including projected increases in temperature and more frequent heatwaves. Storage, a key stage of potato production prior to marketing or processing, is also vulnerable to climate change. Maintaining tuber quality through the storage period is essential to grower profitability. Field and storage studies were conducted to benchmark elite chip-processing cultivars (Mackinaw and Snowden) under heat stress conditions during different physiological developmental stages during the 2021-23 growing seasons in Lakeview, MI. Heat stress events were applied to the field plots during four different stages of potato growth. A portable greenhouse heat stress structure was constructed to increase the plot day and night temperatures for 7-10 days during each of the four growth stages.  Yield, specific gravity, tuber size distribution as well as stress-related internal and external tuber defects were assessed after harvest. Treatment effects on tuber processing quality were evaluated monthly in a simulated commercial storage environment. Heat stress at specific times significantly reduced yield in all three years. Tuber specific gravity was also significantly reduced at specific heat stress events.  In both cases, the negative impact was greater for Snowden than Mackinaw.  Based on the 2021 and 2022 storage seasons, heat stress treatments inconclusively impacted the storability of the varieties. The Mackinaw variety was able to store further into the storage season with acceptable chip-processing than Snowden.  This research may also provide insight to how global climate change will affect other specialty crops in the mid-century and help industry leaders better prepare for the impacts that climate change will bring.

8:15am-8:30am
Status of potato cyst nematode (PCN) Globodera pallida and G. rostochiensis prevalence, distribution, and sources of host resistance in Africa
John Onditi, USDA and Kenya Agricultural and Livestock Research Organization (KALRO)              

               Potato (Solanum tuberosum L.)  is one of the major crops in Africa with the potential of improving food and nutritional security. Potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis have more recently been reported as a new pest challenging production of the crop in Africa. Knowledge of prevalence and distribution of the pest and the available sources of resistance can provide an immediate option of PCN control that can be recommended to the farmers. The aim of the study was to analyze the status of prevalence and distribution of the pest in the region and identify sources of host resistance in existing cultivars which can be used in its control. The review revealed G. rostochiensis as the most widespread PCN species reported in eight African countries as compared to G. pallida only found in four countries. G. rostochiensis Ro1/4 and G. pallida Pa/2/3 were the only PCN pathotypes that have been reported in Africa. Multiple PCN resistances to the most predominant PCN species and pathotypes were found in each of the PCN infested countries particularly among cultivars originally sourced from Europe. This review proposed identification and utilization resistant cultivars already adopted by farmers as an immediate strategy for PCN control while waiting for development of new resistant cultivars as a long-term solution to the problem.

8:30am-8:45am
Inheritance of potato processing traits in a half-diallel breeding population segregating for Columbia root-knot nematode resistance
Max Feldman    USDA-ARS        

               The Columbia root-knot nematode (Meloidogyne chitwoodi) is a destructive soil borne pest that can cause serious economic damage to potato tubers within infected, unfumigated fields. There are very few known sources of genetic resistance to root-knot nematodes and no released potato cultivars exhibit this trait. Literature indicates that nematode resistance introgressed from Solanum bulbocastanum is dominantly inherited across many genetic backgrounds. We generated a 32 family half-diallel progeny test population utilizing 3 root-knot nematode resistant clones (female) and 11 clones (male) with russet skin type (1,600 clones, between 25 – 60 clones per family). In 2023, 1,200 progeny were evaluated relative to 6 control varieties planted at high replication at the Washington State University Experiment Station in Othello, WA. A scale, RGB-D imaging conveyor, and index scoring system was used to record: total yield, the number of tubers per plant, tuber size distribution, aspect ratio, skin color, starch content, and defect severity from all samples within this trial. The distribution of phenotypic values observed from the progeny suggest that choice of parent is a highly significant factor that influences almost all traits evaluated. The phenotyping strategy utilized by our team is inexpensive, expandable, and flexible enough to be adopted by many different types of vegetable breeding programs. Data from this experiment is being used to develop potato tuber defect classification models and assess the utility of adopting genomic selection within our potato breeding program.

8:45am-9:00am
Late Blight Resistance Evaluation of S. microdontum Accessions
David Douches, Michigan State University

               Solanum microdontum is known to have resistance to late blight (Phytophthora infestans (Pi)).  We obtained the US Potato Genebank collection of 116 accessions of this species.   One plant was selected to represent each accession.  The late blight disease reactions were evaluated using whole plant and detached leaf bioassays on 100 accessions.  For the whole plant assays, three replications of each accession were inoculated with Pi US-23 genotype by spraying a solution that contained 3 x 104 zoospores onto each plant in a greenhouse humidity tent.  For the detached leaf bioassays, three replications of each accession were assayed.  Each leaflet received a 10 ul drop of 4 x 104 zoospores of Pi US23.  Reference varieties of Atlantic and Manistee were used as susceptible controls and Sarpo Mira and 3R-gene Diamant line (DIA-MSU-UB255) were used as resistant controls.  For the whole plant assay, 30% of the S. microdontum accessions had no sign of late blight lesions.  43% of the S. microdontum accessions had between 1 to 5% of the leaf surface with lesions from late blight compared with the susceptible controls which had between 48 and 80% late blight foliar lesions.  The resistant controls also did not show any late blight when checked under the microscope. For the detached leaf assay, only 11 accessions showed resistance to US-23, those plants were then tested against the P. infestans NL13316 isolate and only eight accessions showed resistance to both late blight strains.  These accessions with the most resistance to late blight have been used in crosses to MSU diploid germplasm (dihaploids and breeding lines) to transmit and identify the resistance genes.

9:00am-9:15am
Genome-wide Association Study of Late Blight Resistance loci in Potato Using Genotyping-by-Sequencing in a Bi-Parental Population
Vidyasagar Sathuvalli, Oregon State University

               The cultivated potato (Solanum tuberosum L.) is the world's most important vegetable crop. Late blight (LB), caused by Phytophthora infestans, is a major disease that affect world’s potato production. Host genetic resistance is viewed as the economical means of controlling the pathogens. Clone LBR-8 (PI599265) is found to be resistant to both LB and PVX. The objective of this study was to identify genomic regions associated with LB. A full-sib population of 152 seedlings from the cross LBR-8 × ‘Ranger Russet’ was screened for LB in field trials inoculated with US-8 strain.  A frequency distribution of the phenotypes among 152 clones suggests that resistance is quantitatively inherited. Ninety-three siblings and the parents were genotyped by using Genotyping by Sequencing (GBS). Initial alignment and filtering generated 90,102 single nucleotide polymorphisms (SNPs). The SNP tags were further trimmed with Minor Allele Frequency (MAF) ˂ 0.10, ˂ 0.15, ˂ 0.20, ˂ 0.25 and ˂ 0.30. Filtering SNP markers with MAF greater than 15% will remove alleles associated with late blight resistance. After filtering with (MAF) ˂ 0.15 a total of 63,149 SNPs were used for GWAS. GWAS was made by using General Linear Model (GLM) and Mixed Linear Model (MLM). We have found a total of 22 loci associated with late blight resistance by using GLM after adjusted Bonferroni probability (P˂7.9E-7) and by using MLM at P˂ 3.2E-05 fourteen loci were identified.  The strongest association signals were detected for late blight on chromosome 5, with the peak SNP loci (Site: 4228.385KB and 4233.135KB) the two adjacent SNP markers were found to be putative late blight resistant homologs and another peak SNP markers were located on chromosome 4. We are in progress to clone the putative late blight gene for further study and develop breeder friendly genetic markers.

9:15am-9:30amThe molecular evolution and interplay of fertility factors in the self-incompatibility system of wild potatoes
Mercede Ames Sevillano, USDA-ARS

               Gametophytic self-incompatibility is a reproductive strategy to prevent inbreeding and promote outcrossing in the Solanaceae family. Studies to understand the molecular and evolutionary aspects of the self-incompatibility/self-compatibility system have been conducted in several Solanaceae family members including Petunia, Nicotiana, and Solanum. The desire to transform potato into a diploid (2x) inbred-hybrid crop has brought up the need to better understand the self-incompatibility system in wild species relatives of potatoes, most of which are diploid and self-incompatible. It is well known that S-RNAses are the pistil determinant of gametophytic self-incompatibility and multiple sequences of S-RNAse alleles have been identified in a few potato species. In this study, we used genomic and transcriptomic sequencing in combination with experimental crosses to gain insights into the variability of S-RNAse sequences in wild potato species, their evolutionary history, their gene structure and their likely interactions with the known pollen components of the self-incompatibility system such as SLFs and Sli genes. We found new S-RNAse alleles not previously reported in potatoes. We also found two types of self-compatible S. verrucosum genotypes, one that expresses S-RNases and one that lacks expression of S-RNases. Also, we found that self-compatible S. brevicaule, S. chacoense and S. kurtzianum express two S-RNAse alleles and none of the genotypes carry a Sli self-compatibility-donor allele that carries the 533 bp insertion. These results support at least two different mechanisms of self-compatibility in wild potatoes. These findings contribute to a more complete view of the incompatibility system in potato and may be useful for developing molecular breeding approaches for potato and interpreting population dynamics in wild potato relatives.

9:30am-9:45am
Dihaploid production from open pollinated Red Norland seedlings.
James Busse, USDA-ARS Vegetable Crop Research Unit and Department of Plant and Agroecosystem Science

               The production of dihaploids from cultivated tetraploid potatoes is an inefficient process that impedes the acquisiton of diploid breeding stocks. Partial inbreeding was tested for increasing the efficiency of dihaploid generation from tetraploids. Red Norland and seven seedlings from an open pollinated Red Norland population were utilized. Seedlings were self-fertile with red periderm. Seed tubers were increased for each line and planted into the field during two seasons.  Shoots with flower buds were collected, brought into the greenhouse, and put into bottles. Flowers were emasculated and pollinated with Solanum tuberosum Phureja Group IVP 101 (IVP 101). Fruits were harvested 28 days after pollination and putative dihaploid seeds lacking a seed spot marker were sown in a greenhouse.  Ploidy of seedlings was determined using flow cytometry. We observed that total dihaploid generation efficiency varied between years, 63 dihaploids from 5675 pollinations in year one and 426 dihaploids from 7223 pollinations in year two. Two of the seven lines, S1-35 and S1-39,  produced dihaploids with greater efficiency than Red Norland in both years. Our findings indicate that partial inbreeding may be an effective tool for increasing dihaploid production efficiency relative to starting material.  This may offer a path forward for generating dihaploid material from recalcitrant material.