10:15am-10:45am       
Revolutionizing Seed Potato Production System in Africa and Asia
Kalpana Sharma, International Potato Center

               Limited access to quality seed poses a significant challenge for the potato subsector in Africa and Asia. Previous efforts have focused on enhancing the quality and quantity of seed potatoes available to farmers, with a particular emphasis on addressing the bottleneck in the seed value chain—namely, the insufficient quantity of early generation seed (EGS) for field multiplication. Minitubers have traditionally served as the starting point for seed multiplication. Rapid multiplication technologies such as aeroponics and sand-hydroponics have been promoted for minitubers production. This has resulted in a remarkable increase in the supply of high-quality seed potatoes in Africa and South America. More recently, Rooted Apical Cuttings (RAC) was introduced in Africa and Asia as a revolutionary approach to EGS production. RAC are rooted transplants produced in a screenhouse from tissue culture plantlets. The three technologies, aeroponics, sand-hydroponics, and RAC, differ in multiplication rates, investment costs, profitability, required skills, infrastructure needs, and associated risks. Among the three rapid multiplication technologies, RAC stands out for significantly increasing EGS volumes in a short period (30-50% increase in EGS within the initial six months depending upon the environmental conditions). RAC seedlings eliminate concerns about seed dormancy, allowing for optimal seed production during the short window of 2-3 months between planting seasons, but it requires constant irrigation and careful management from transplanting until vegetative development. While these technologies are integral to the seed value chain, success in scaling requires careful consideration of the specific context, enabling policy and socio-economic environments. Key recommendations include raising awareness and developing effective marketing strategies to promote not only the adoption of these technologies, but also the development of value chains for certified seed and ware potatoes. Additionally, efforts should focus on ensuring the adequate multiplication of RAC into commercial seed to enhance accessibility for smallholder farmers in Africa and Asia.

10:45am-11:00am       
Potato Zebra Chip Pathogen is a Quarantine Pest for all Brazil: the IAC-Sprout/Seed-potato Technology May Contribute to Prevent the Introduction and-or Spread.
José Alberto Caram de Souza-Dias, Phytosanitary R&D Center / Agronomic Institute Campinas (IAC)/APTA/SAA-SP (Brazil)

               In Brazil, the Zebra Chip (ZC) pathogen: Candidatus Liberibacter solanacearum (CaLsol) is a quarantine pest (Ministerial Decree SDA/MAPA n.617 of 07/12/2022). Due to the traditional Brazilian dependence on annual imports of tuber/seed-potato lots (TSP), aiming high-sanitary, basically virus-free, stock renewal for local certified or home-saved production schemes, there are risks of CaLsol introduction as producing countries in South America and Europe have detected CaLsol or been phytosanitary worrying. Under Brazilian legislation (MAPA IN 32 /20-11-2012) imported TSP are internalized as generation zero (G-0); usually not reaching G3-G4 due insect-transmitted Potyvirus, Crinivirus, etc, causing fast TSP degeneration. The ZC disease name is due to depreciative dark brownish stripes and  streaks symptoms in fried processed tubers; thus seriously damaging the potato processing industry were the disease occurs. Therefore, Brazil's Ministry of Agriculture and Livestock, and the Brazilian Potato Growers Association have produced acts to prevent introduction and protect the emerging, highly competitive local potato processing industry (https://www.youtube.com/watch?v=E2HPepSO-xo ). ZC symptoms in tuber-progenies from infected mother-plant has been reported as not sprouting or if it does, weak, hair-like sprouts emerge from all or some of a tuber eyes; no guaranteeing  CaLsol is not TSP perpetuated, besides other pests.   One way to minimize CaLsol entrance in the country via TSP would be through the use of IAC-Sprout/seed-potato technology (IAC-SSPT) (Kreuze, Souza-Dias et all, 2020. P. 389-430. https://link.springer.com/book/10.1007/978-3-030-28683-5 ). The IAC-SSPT can be an effective contribution, since only imports of apical vigorous sprouts (>4,0 cm high x >0,4 cm diameter), removed from G-1 or G-2 certified TSP fields, are used as seed-potato (SSP); planted inside insect-proof screenhouse;  where  sanitary evaluation and minituber/seed-potato production  (G-0) are performed. The innovative, Brazilian imports of SSP lots were successfully demonstrated with experimental imports of SSP from Alaska, USA (2003-2007) and New Scotia, New Brunswick, Canada (2008-2011)  (Souza-Dias et all. 2014. https://carambatatasemvirus.blogspot.com/2016/05/19th-triennial-conference-of-european.html )

11:00am-11:15am
The Effect PVY Strain has on Potato Yield and Quality in Colorado.
Andrew Houser, Colorado State University/Colorado Potato Certification Service

               Potato virus Y (PVY) is a major disease affecting potatoes and causes more rejections of certified seed across the United States than any other pathogen.  PVY can negatively affect a potato plant by reducing harvestable yield and quality.  There are several recombinant strains of PVY that occur in Colorado, with PVYN-Wi becoming the most dominant in recent years.  The specific effect each strain has on potato yield and quality is not yet fully known.  In addition, yield reductions caused by PVY are not always obvious to a potato farmer.  This study evaluated the effect two of the major PVY strains in Colorado have on potato yield and quality (PVYO & PVYN-Wi).  PVY infected potato plants were identified on several commercial potato fields in Colorado in 2022 and 2023.  Individual plants were staked and leaves from each plant were tested for PVY using TAS-ELISA to determine the presence of PVY and the PVY strain was detected using Immuno-Capture PCR from leaf sap.  Plants were harvested individually at the end of the growing seasons.  Results show that PVY has a negative impact on overall yield when compared with healthy plants (a yield reduction of 24% - 72% depending on the cultivar and strain).  In the cultivar Russet Norkotah sel. 278, PVYO reduced the number of tubers >10oz by roughly 60%.  In Reveille Russet, overall yield was significantly lower in plants infected with PVYO compared to PVYN-Wi (132 cwt/A vs 359 cwt/A for PVYN-Wi).  This study shows that strains of PVY can affect yield and grade at different severities and both PVYO and PVYN-Wi significantly reduce yields when compared with healthy plants.  This study further indicates that efforts to reduce PVY levels in seed by certification agencies and certified seed growers are justified and doing so will benefit the entire potato industry.

11:15am-11:30am       
Assessing the risk of seedborne Potato mop-top virus         
Kylie Swisher Grimm, USDA - Agricultural Research Service   

Potato mop-top virus (PMTV) is vectored to potato by Spongospora subterranea and can cause internal tuber necrosis, or spraing, in many potato cultivars, rendering tubers unmarketable. PMTV presence in asymptomatic tubers can also have a negative impact on tuber marketability, particularly in international markets when testing occurs by methods other than visual assessment. Since 2016, seed lots entering Washington State have been monitored for the presence of PMTV, with as high as 6% of the lots testing positive for the virus each year. To assess the risk of planting PMTV-infected seed on plant emergence and daughter tuber yield and quality, a small plot study was conducted in 2022 and 2023 at two different S. subterranea-free field locations at the USDA-ARS research station in Prosser, WA. In each year of the study, three susceptible cultivars were planted as two seed treatments (PMTV-infected or un-infected) in a randomized complete block design. Differences in emergence rates were not consistent, with treatment, cultivar, and year-dependent effects. Yield of daughter tubers harvested from PMTV-infected seed was significantly reduced in 2022, but only numerically lower in 2023. The percentage of daughter tubers with internal spraing symptoms and the percentage with PMTV detected were both significantly greater from PMTV-infected seed compared to un-infected seed. In both years of the study, internal tuber symptoms were recorded for 7% of the daughter tubers, compared to just 1.5% of the daughter tubers from un-infected seed. Results from this two year study indicate that seedborne PMTV can pose a risk to tuber quality, even when planted in S. subterranea-free soil.

11:30am-11:45am                      
Characterization of Microbiome associated with host resistance to Corky Ringspot disease in potato.        
Holly Golightly, Oregon State University

Stubby root nematodes (SRNs) (Paratrichodorus and Trichodorus spp.) threaten potato crops by vectoring tobacco rattle virus (TRV) which causes corky ringspot disease (CRS). Corky ringspot disease in potato is characterized by necrotic, ring-like lesions in the tubers. Potato crops which have even 6% of CRS-symptomatic tubers may be either downgraded or even rejected for their processing quality. The goal of this project is to identify fungal and bacterial communities associated with potato genotypes that are resistant and susceptible to CRS. Resistant variety ‘Castle Russet’ and susceptible variety ‘Russet Burbank’ were grown in two fields, one fumigated and other infested with SRNs vectoring TRV at the USDA-ARS. Characterization of rhizosphere, bulk soil, root tissue, and tuber tissue microbiomes associated with resistant and susceptible variety across different growth stages are underway. This study will improve our knowledge on influence of microbiome on host genetic resistance for soil borne pathogens. Preliminary results suggest that there is no significant difference in microbiomes between TRV-susceptible and resistant potato varieties.

11:45am-12:00am
Broad and strain-specific sources of resistance to potato virus Y in potato
Alexander Karasev, University of Idaho

               Potato cultivars Payette Russet, Dark Red Norland, and Chieftain were challenged with four strains of potato virus Y (PVY), PVYO, PVYEu-N, PVYN-Wi, and PVYNTN under greenhouse conditions. Cultivars Dark Red Norland and Chieftain were found to exhibit strain-specific, hypersensitive resistance to PVYO and PVYNTN strains. The same two cultivars, Dark Red Norland and Chieftain appeared to have an additional resistance source in their genomes providing partial resistance against PVYN-Wi but were found fully susceptible to the non-recombinant PVYEu-N strain. Payette Russet was found immune to these four strains of PVY: PVYO, PVYEu-N, PVYN-Wi, and PVYNTN. Payette Russet was additionally challenged with the total of 18 isolates of PVY representing 12 strains and genetic variants of the virus from potato and non-potato solanaceous hosts. None of the 18 isolates of the virus was found able to replicate in the inoculated or upper non-inoculated leaves of Payette Russet, confirming the broad specificity of the Rysto gene present in the Payette Russet genome.