Douglas C. Scheuring

Selection, evaluation, and identification of improved Russet Norkotah strains

Strain (sub-clonal, line, or intraclonal) selection for certain characteristics within some potato varieties has been very successful e.g. improved skin type (Russet Burbank from Burbank), improved skin color (Red LaSoda from LaSoda; Red Norland and Dark Red Norland from Norland), and improved vine vigor and yield (Norgold Russet M from Norgold Russet). In 1989, strain selection with Russet Norkotah was initiated by the Texas Potato Variety Development Program. Some 192 giant hill and/or tall type plants were selected from seedsmen and/or commercial Russet Norkotah fields in Colorado, while 183 were selected from commercial fields in Texas. Replicated yield trials with the final 13 of the original strain selections and Russet Norkotah were conducted in 1992, 1993, and 1994 in both Colorado and Texas. A mixed model analysis of variance was performed followed by disjoint cluster analysis in order to group strains into high, medium, and low yielding classes or clusters. Canonical discriminant analysis was performed to confirm the three clusters and to determine the extent to which various yield attributes are related and can be used to separate the three clusters. Several strains including TXNS (Texas Norkotah Strain) 112, TXNS 134, and TXNS 278 were identified as superior in Colorado, while TXNS 223, TXNS 249, and TXNS 296 were similarly identified for Texas growing conditions. These strains usually outyielded Russet Norkotah by 20–30%.

Population structure analysis and association mapping of seed antioxidant content in USDA cowpea (Vigna unguiculata L. Walp.) core collection using SNPs

Abstract: Cowpea (Vigna unguiculata L. Walp.) is an important legume, and the antioxidant content in cowpea seeds has been recognized as a health-promoting compound for humans. The objectives of this study were to analyze the population structure of cowpea collections and to identify single nucleotide polymorphism (SNP) markers associated with the seed antioxidant content and seed coat colour. A set of 1047 SNPs were used to analyze a 369 cowpea core collection from 47 countries. Results indicated that: (1) there were three clusters in the 369 entries; and the germplasm collected from India, South Africa, and the US showed broader genetic diversity; (2) Scaffold7139_14363 and Scaffold29110_4657 were strongly associated with antioxidant content, and C35063613_1497, Scaffold81493_886, and Scaffold84620_6785 were strongly associated with seed coat colour across three models; (3) significant correlations were detected between the seed antioxidant content and black seed colour (r = 0.45) and between seed antioxidant content and red seed coat colour (r = 0.50); and (4) Scaffold42008_191 and C35082838_2258 were associated with both seed antioxidant content and seed coat colour. The SNP markers identified could potentially be used in marker-assisted breeding to accelerate genetic improvement of cowpea for higher seed antioxidant content.

Investigations on Putative Zebra Chip Tolerant Potato Selections

Abstract‘Candidatus Liberibacter solanacearum’ (Lso) has emerged as a devastating pathogen of solanaceous and other vegetable crops. In potato, Lso is the causative agent of zebra chip (ZC) disease, which threatens production in North and Central America and New Zealand. Lso has caused significant economic losses to the potato industry in Texas since the emergence of the disease in 2000. Presently, disease control relies on pesticide applications, but efforts are under way to identify plant resistance. The objective of this work was to validate the most promising cultivars identified as potentially resistant or tolerant to ZC from previous field trials in different Texas locations and in multiple years. An important component of the study was the development of protocols to effectively evaluate resistance or tolerance. Results show that, while none of the tested cultivars displayed resistance against ZC, differences in susceptibility among them were confirmed. Results also demonstrated the importance of performing cage trials in which vector and disease pressure can be controlled.Resumen“Candidatus Liberibacter solanacearum” (Lso) ha emergido como un patógeno devastador en cultivos de solanáceas y otras hortalizas. En papa, Lso es el agente causal de la zebra chip (ZC) o papa rayada, que amenaza la producción en Norte y Centroamérica, y Nueva Zelanda. Lso ha causado pérdidas económicas significativas a la industria de la papa en Texas desde que surgió la enfermedad en 2000. En la actualidad, el control de la enfermedad se respalda en aplicaciones de plaguicidas, pero hay esfuerzos en proceso para identificar resistencia en la planta. El objetivo de este trabajo fue validar las variedades más prometedoras, identificadas como potencialmente resistentes o tolerantes a ZC, de ensayos de campo previos en diferentes localidades texanas y en múltiples años. Un componente importante del estudio fue el desarrollo de protocolos para evaluar efectivamente la resistencia o tolerancia. Los resultados muestran que, mientras que ninguna de las variedades probadas mostró resistencia contra ZC, se confirmaron diferencias en la susceptibilidad entre ellas. Los resultados también demostraron la importancia de hacer ensayos en jaulas en los que se puede controlar la presión del vector y de la enfermedad.

Association mapping revealed SNP markers for adaptation to low phosphorus conditions and rock phosphate response in USDA cowpea ( Vigna unguiculata (L.) Walp.) germplasm

Cowpea (Vigna unguiculata (L.) Walp) is a legume of economic importance world-wide, especially in Western Africa, where it is an important part of the population’s diet. The rapidly increasing population growth in Africa requires substantial increase in cowpea production, which can be achieved by expanding land areas for agricultural purposes. In addition, prevalence of soil acidity in Africa constrains such an alternative since phosphorus availability, a key element for plant growth and development, is limited, thus resulting in poor cowpea production. The objectives of this study were to conduct an association analysis for adaptation to low phosphorus conditions and rock phosphate response in cowpea, and to identify SNP markers associated with these two traits. A total of 357 cowpea accessions, collected worldwide, was evaluated for phosphorus stress and response to addition of rock phosphate. Association analysis was conducted using 1018 SNPs obtained using genotyping-by-sequencing (GBS). TASSEL 5 and R were used for association mapping studies based on six different models. The results indicated that: (1) substantial variability in adaptation to low phosphorus conditions and rock phosphate response exists in the USDA cowpea accession panel; (2) ten SNP markers, C35006753_110, C35028233_482, C35072764_1384, C35084634_455, Scaffold21750_4938, Scaffold26894_5408, Scaffold41885_14420, Scaffold45170_4650, Scaffold50732_679; and Scaffold88448_741 were found to be associated with tolerance to low phosphorus conditions in cowpea, and (3) eight SNP markers, C35028233_482, C35058535_121, Scaffold26894_5408, Scaffold45170_4650, Scaffold51609_507, Scaffold53730_7339, Scaffold74389_5733, and Scaffold87916_4921 were highly associated with rock phosphate response. These SNP markers can be used in a marker-assisted breeding (MAS) program to improve cowpea tolerance to phosphorus stress.

Population structure analysis and association mapping for iron deficiency chlorosis in worldwide cowpea (Vigna unguiculata (L.) Walp) germplasm

Cowpea (Vigna unguiculata L. Walp) is a legume consumed for its high protein content. It provides nutrient-dense food opportunities for human consumption. Iron deficiency chlorosis (IDC) manifests as yellowing of the leaves and reduced plant growth, resulting in reduced yield potential. Use of IDC tolerant cowpea cultivars is an efficient method to address this problem. The objectives of this study were to conduct a population structure analysis, to carry out an association mapping study, and to identify SNP markers associated with IDC tolerance in cowpea. A total of 353 cowpea accessions were evaluated for tolerance/susceptibly to low soluble iron conditions on higher pH soils. A total of 1006 SNP markers postulated from genotyping-by-sequencing were used after filtering for population structure and association analysis studies. Results revealed that: (1) a substantial variability in degree of tolerance to low soluble iron conditions was found among the cowpea accessions; (2) delta K peak was identified at K equal to 2, indicating two subpopulations within the cowpea accessions tested for adaptation to IDC, a second delta peak corresponding to K equal to 3 was also found; and (3) nine SNP markers, C35081162_3130, Scaffold16136_2033, Scaffold1764_4741, Scaffold18262_4480, Scaffold30165_15499, Scaffold47194_5530, Scaffold73235_6677, Scaffold77932_9959, and Scaffold86559_7193, were significantly associated with IDC tolerance in cowpea. These results can be used as tools to select cowpea genotypes tolerant to IDC under low soluble iron conditions.

Transcriptome of Russet Norkotah and its clonal selection, TXNS278

ObjectivesPotato has a large genetic diversity. This diversity is in part due to somaclonal variability that appears within potato selections for which tubers are used as seeds. However, the potato tetraploid genome, as well as the use of tubers for crop propagation, does not allow for easy genetic studies. The objective is to gain knowledge at the genomic level from standard Russet Norkotah and a subclonal Russet Norkotah selection TXNS278.Data descriptionIn this report, we used RNA-seq, which allows genome-wide gene expression analysis to sequence the transcriptomes of the subclonal Russet Norkotah selection TXNS278 with standard Russet Norkotah grown in commercial fields. Among the selections, TXNS278 appeared in a multi-year analysis in Texas as a top No 1 yielding variety. Russet Norkotah and TXNS278 leaf and root transcriptomes were sequenced at two time points during growing season.

TX1523-1Ru/Y a.k.a Sierra Gold™: An early maturing, yellow-fleshed ruseet cultivar for the specialty/gourmet market

TX1523-1Ru/Y, a unique specialty cultivar with deep-yellow flesh color and an attractive russet skin, was released in 2003 by the Texas Agricultural Experiment Station. The smaller, immature tubers are round, but take on an oval shape as they mature. Eyes are shallow and the tuber surface is smooth. Tuber size tends to be medium (113.4–283.5 g; 4–10 oz). Total and marketable yield varies with year and location, but tends to be comparable to ‘Yukon Gold’, with percent marketable yield slightly higher. Vines are semi-prostrate, with medium vigor and size, and relatively early maturity. Specific gravity is about the same or slightly less than Yukon Gold, but generally greater than ‘Russet Norkotah’. TX1523-1Ru/Y has good culinary qualities, with resistance to after-cooking-darkening, and can be chipped, boiled, baked, or microwaved. It has been reported to be excellent to superior as a microwave product. Unlike Yukon Gold, TX1523-1Ru/Y is resistant to hollow heart, brown centers, and internal discoloration. It tends to be less susceptible to tuber infection by late blight (Phytopthora infestans) than Yukon Gold, has greater resistance to common scab (Streptomyces scabies), and is less susceptible to black scurf (Rhizoctonia solani). TX1523-1Ru/Y is believed to be the first yellow-fleshed resset-skin cultivar released in the United States.ResumenTX1523-1Ru/Y, es un cultivar especial y único con pulpa de color amarillo intenso y una atractiva piel rojiza, que ha sido liberada el año 2003 por la Estación Experimental Agrícola de Texas. Los tubérculos más pequeños son redondos cuando están inmaduros, pero a medida que maduran toman la forma ovalada. Los ojos son superficiales y la superficie del tubérculo es lisa. El tamaño del tubérculo tiende a ser mediano (113.4 a 283.5 g; 4 a 10 onz). El total de rendimiento comerical varía con el año y la localidad, pero tiende a ser comparable con Yukon Gold que tiene un rendimiento comercial ligeramente mayor. Las plantas son semipostradas de vigor y tamaño mediano y son relativamente de madurez temprana. La gravedad específica es la misma o ligeramente menor que Yukon Gold pero generalmente mayor que Russet Norkotah. El TX1523-1Ru/Y tiene buenas cualidades culinarias con resistencia al oscurecimiento después de la cocción y puede ser picado, cocido, horneado o usado en el microondas. Se ha reportado que es excelente a superior como producto del microondas. A diferencia de Yukon Gold TX1523-1Ru/Y es resistente al corazón vacío, oscurecimiento medular y decoloración interna. Tiende a ser menos susceptible a la infección del tubérculo causada por tizón tardío (Phytopthora infestans) que Yukon Gold, tiene mayor resistencia a la sarna común (Streptomyces scabies) y es menos susceptible a la caspa negra (Rhizoctonia solani). Se cree que TX1523-1Ru/Y es el primer cultivar de pulpa amarilla y piel rojiza que ha sido liberado en los Estados Unidos.