Christian A. Thill

Trifluralin-mediated polyploidization of Rosa chinensis minima (Sims) Voss seedlings

Many diploid rose species and cultivars possess valuable traits that can be introgressed into modern tetraploid cultivars. Interspecific, interploidy crosses are possible, but triploid hybrids typically have limited fertility, hindering further breeding and selection. Tetraploidizing diploids before mating with tetraploids can alleviate fertility barriers. The efficiency of trifluralin was investigated for polyploidization of Rosa chinensis minima (2n = 2x = 14) seedlings. Treatments were trifluralin at 0.086% and 0.0086%, colchicine (0.5%), and distilled water and contained 2% dimethyl sulfoxide and a surfactant. Approximately 5 μl of the treatment solution was applied to the apical meristem of seedlings (N = 337, 82–85 per treatment) in the process of cotyledon expansion. Guard cell length, pollen diameter, and root tip squashes of rooted cuttings were used to detect polyploidy in meristematic layer (L)I, LII, and LIII, respectively. Trifluralin (0.086%) was the most effective treatment for polyploidization (LI 20.2%, LII 12.9%, LIII 12.9%), followed by trifluralin (0.0086%) (LI 10.6%, LII 7.1%, LIII 4.7%) and colchicine (LI 2.4%, LII 0%, LIII 0%). Polyploidization consistently occurred from LI inward. Polyploids as a group had reduced pollen stainability and a lower leaflet length to width ratio than diploids. In addition, two diploid seedlings were identified which produce 2n pollen. Considerations in selecting germplasm and generating somatically-induced polyploids from seedlings versus clones for use in breeding are discussed.

Foliar resistance to late blight in potato clones evaluated in national trials in 1997

Changes in the oomycetePhytophthora infestans in the United States and other parts of the world pose a significant threat to potato production. A continual evaluation of potato clones for resistance to late blight is necessary to identify clones with resistance and to monitor the stability of resistance in light of the emergence of new and more aggressive strains of this pathogen. Twentytwo potato clones (10 cultivars and 12 selections) were evaluated in 1997 for late blight resistance at seven U.S. locations. Seven late blight differentials (R1R2R3R4, R1R2R4, R1R3R4 R3, R8 R10, and Rmulti) were also included in the test at five of these locations. The US-8 strain of P.infestans was present at all locations. Percent infected foliage was recorded at approximately weekly intervals following the onset of disease. Area under the disease progress curve (AUDPC) was calculated. The nonparametric stability statistics mean absolute rank differences (Si(1)) and variances of the ranks (Si(2)) were used to analyze phenotypic stability. Although neither of these statistics was significant for individual clones, both of these statistics were significant when summed over clones, indicating the importance of genotype × environment interactions on the rankings of these clones across locations. The most late blight-resistant and susceptible clones were the most stable; clones in the intermediate ranges were most subject to rank changes due to genotype × environment interactions. The most late blight-resistant clones were AWN86514-2, B0692-4, B0718-3, and B0767-2. The most susceptible clones were B0811-13, B1004-8, Nor-Donna, and Krantz. AUDPC was very low for the late blight differentials R8 and Rmulti, moderately low for R10 and very high for the remaining differentials. This study is important in characterizing the reaction of potato clones to new strains of P.infestans.

Foliar resistance toPhytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South AmericanSolarium species having EBNs of 1, 2, and 4 and implications for breeding

The recent US-8 clonal lineage ofPhytophthora infestans, the pathogen causing late blight (LB) disease, is one of the most widespread and difficult to control. Sources of foliar resistance to US-8 were evaluated in 1927 seedling genotypes by sampling 49 plant introductions (PIs) representing 13 Mexican and South AmericanSolanum species having an Endosperm Balance Number (EBN) of 1, 2, or 4, and one species with an unknown EBN. Species evaluated were 2x(1EBN)S. bulbocastanum, S. cardiophyllum, S. commersonii, S. pinnatisectum, andS. trifidum; 2x(2EBN)S. berthaultii, S. megistacrolobum, S. microdontum, andS. verrucosum; 4x(2EBN)S. fendleri andS. stoloniferum; 6x(4EBN)S. guerreroense;2x unknown EBNS. polyadenium; as well as4x S. tuberosum families as controls. Foliar resistance in the field was monitored in 1998 and 1999. Resistance differed relative to species geographic origin, EBN, species themselves, PIs within a species, and genotypes within a PI. In 1998 Mexican germplasm had a lower area under the disease progress curve (AUDPC, 1140) and greater resistance than South American germplasm (1601), while the 1EBN (1119) and unknown EBN (1075) species had greater resistance than 2EBN (1470) and 4EBN (1888) species. AUDPC ranged among species from 555 (S. cardiophyllum) to 1932 (S. megistacrolobum) and among PIs within a species most widely forS. bulbocastanum (267–1007) and least widely forS.polyadenium (1019–1179). In 1999 LB symptoms were not observed on the species before an early freeze; however, all 1999S. tuberosum families showed LB symptoms and segregated for resistance, pointing to greater resistance in the species than in cultivated germplasm. Resistance found in diploid 2EBN germplasm is more accessible due to greater crossability with cultivated germplasm; however, though more difficult to introgress, resistance found in some of the more reproductively isolated 1EBN germplasm is worth pursuing.ResumenEl nuevo linaje clonal US-8 dePhytophthora infestans causante de la enfermedad conocida como tizón tardio (LB) es uno de los más difundidos y difícil de controlar. Se evaluaron las fuentes de resistencia foliar en 1927 genotipos de plántulas, muestreando 49 introducciones de plantas (PIs) que representan 13 especies deSolanum mexicanas y sudamericanas, con un número de balance del endospermo (EBN) de 1, 2, o 4 y una especie de EBN desconocido. Las especies evaluadas fueron 2x(lEBN)S. bulbocastanum, S. cardiophyllun, S. commersonii S. pinnatisectum yS. trifldum; 2x(2EBN)S. bertaulthii, S. megistacrolobum, S. microdontum yS. verrucosum; 4x(2EBN)S. fendleri yS. stoloniferum; 6x(4EBN)S. guerreroense;S. polyadenium 2x de EBN desconocido y familias deS. tuberosum 4x, fueron también incluidas como testigo. La resistencia foliar en el campo fue monitoreada en 1998 y 1999. La resistencia fue relativamente differente en especies de origen geográfico distinto, EBN, especie, PIs dentro de la especie y genotipos dentro de un mismo PI. En 1998, el germoplasma mexicano presenté menor area bajo la curva de progreso de la enfermedad (AUDPC, 1140) y mayor resistencia que el germoplasma sudamericano (1601), mientras que el 1EBN (1119) y la especie de EBN desconocido (1075) tuvieron mayor resistencia que las especies 2EBN (1470) y 4EBN (1888). El AUDPC varié entre especies de 555 (S. cardiophyllum) a 1932 (S. megistacrolobum) y entre PIs dentro de una especie, más amplio paraS. bulbocastanum (267–1007) y más restringido paraS. polyadenium (1019–1179). En 1999, no se observaron síntomas de LB en esta especie antes de la primera helada, sin embargo, todas las familias deS. tuberosum mostraron sintomas de LB y segregaron para resistencia, indicando mayor resistencia en la especie que en el germoplasma cultivado. La resistencia encontrada en el germoplasma diploide 2EBN es más accesible debido a una mayor posibilidad de cruzamiento con el germoplasma cultivado, sin embargo, aunque es más difícil la incorporación de genes por hibridación, vale la pena hacer un seguimiento de la resistencia hallada en el germoplasma 1EBN aislado de los cruzamientos más reproductivos.

Introgression of Cold (4 C) Chipping from 2x (2 Endosperm Balance Number) Potato Species into 4x(4EBN) Cultivated Potato Using Sexual Polyploidization

Cold-chipping cultivars could reduce microbial spoilage and chemical use due to cold storage of chipping potatoes. Sexual polyploidization breeding schemes that introgress cold chipping from diploid potato species may develop improved cultivars at an accelerated rate. The research objectives were (1) to determine the breeding behavior of cold chipping introgressed from 2× 2 Endosperm Balance Number (EBN) potato species into 4×(4EBN) progeny using sexual polyploidization, and (2) to determine if differences exist between 2n gametes and n tetrasomic gametes for transmission of cold chipping. Experimental families of 4×(4EBN) progeny were synthesized using sexual polyploidization (2× × 4× and 4× × 2×) and 4× × 4× matings using cold-chippingS. phureja and cultivated potato -wild species (C -W) hybrid parents. Control families from 4× × 4× matings using as parents current industry leading germplasm were also made. Progeny were field grown and evaluated for chip color (1 light-10 dark, ≤4.0 is industry acceptable) after 3 and 6 months storage at 4 C. A larger percentage of progeny from experimental families had acceptable chip color compared to control families, likely due to introgression of cold-chipping alleles from diploid potato species. Out of experimental families, the best chip color means, highest phenotypic variance, and greatest percentage of acceptable chipping progeny resulted in 2× × 4× and 4× × 2× matings. The ability of 2n gametes to transmit dominant alleles to high frequencies of 4× progeny may contribute to the superiority of 4× -2× crosses. Breeding schemes that use sexual polyploidization in conjunction with early generation selection should rapidly develop 4× cold-chipping germplasm.

Co-current introgression of economically important traits in a potato-breeding program

Wild potato species contain many traits of economic importance. Late blight (LB) resistance and cold chipping are traits desired in potato cultivars. These traits could be co-currently introgressed if they occurred together in wild potato species. Our research objectives were (1) to determine if variation for cold chipping exists between potato species, accessions within species, and plants within accessions all having foliar LB resistance, and (2) to identify wild potato genotypes combining LB resistance and cold chipping. Materials include 665 genotypes from 43 LB-resistant accessions of 12 potato species having Endosperm Balance Numbers (EBN) of 1, 2, and 4, and 59 LB-resistant genotypes retained from these accessions for breeding. Potato chips were made from greenhouse-grown tubers following storage at 4 C for 6 months. Chip color was scored 1–10, ≤ 4 is acceptable by industry standards. Most of the variation for chip color was due to differences between species. Species ranged in the percentage of acceptably chipping genotypes (0% – 67%) with nine of 12 species having cold-chipping genotypes. Appreciable variation was present within accessions as well. The best chipping accessions wereS. verrucosum plant introduction (PI) 161173 – 4.33 / 0.67 (mean / proportion acceptable genotypes),S. stoloniferum PI 250510 -4.36 / 0.64,S. pinnatisectum PI 347766 -4.65 / 0.35 and 275233 -4.73 / 0.44, andS. megistacrolobum PI 195210 -5.14 / 0.29. Eleven 1EBN genotypes fromS. pinnatisectum andS. trifidum and five 2EBN genotypes fromS. verrucosum, S. fendleri,S. stoloniferum, andS. microdontum were identified that combined LB resistance and cold chipping. Co-current introgression would require fewer breeding cycles than other breeding methods to identify hybrid genotypes possessing both traits.ResumenLas especies silvestres de papa contienen muchas características de importancia económica. La resistencia al tizón tardío (LB por sus siglas en inglés) y al endulzamiento por frío son características muy apreciadas en los cultivares de papa. Ambas podrían ser introgresadas conjuntamente si existieran juntas en las especies silvestres de papa. Los objetivos de nuestra investigación fueron 1) determinar si la variación de la tolerancia al endulzamiento por trío existe entre las especies de papa, entre accesiones de las especies y entre plantas de las accesiones que tienen resistencia foliar al LB, y 2) identificar genotipos de especies silvestres de papa que combinen la resistencia al LB y al endulzamiento por frío. Los materiales incluyen 665 genotipos de 43 accesiones resistentes a LB de 12 especies de papa que contienen un Número Balanceado de Endospermas (EBN en inglés) de 1, 2 y 4, y 59 genotipos resistentes al LB retenidos de esas accesiones para mejoramiento. Se hicieron hojuelas de papa con tubérculos cultivados en invernadero y almacenados a 4C durante 6 meses. El color de las hojuelas tuvo un rango de 1 – 10, ≤ 4 es aceptable para los estándares industriales. Gran parte de la variación en el color de las hojuelas se debié a las diferencias entre especies. Las especies variaron en el porcentaje de genotipos aceptables para hojuelas (0% – 67%), 9 de las 12 especies tuvieron genotipos tolerantes al endulzamiento por frio. Se presentó una variación apreciable también dentro de las accesiones. Las mejores accesiones para hojuelas fueron la introducción de planta deS. verrucosum (PI) 161173 -4.33 / 0.67 (medio / proporción aceptable de genotipos),S. stoloniferum PI 250510 -4.36 / 0.64,S. pinnatisectum PI 347766 -4.65 / 0.35 y 275233 / 4.73 / 0.44, yS. megistacrolobum PI 195210 / 5.14 / 0.29. Se identificaron once genotipos 1EBN deS. pinnatisectum yS. trifidum y 5 genotipos de 2EBN deS. verrucosum, S. fendleri, S. stoloniferum, y S. microdontum que combinaban resistencia al LB y al endulzamiento por frío. La introgresión conjunta requeriría ciclos menores de mejoramiento que los de otros métodos de mejoramiento para identificar genotipos de hibridos que posean ambas características.

Selection for cold chipping genotypes from three early generations in a potato breeding program

Chipping potatoes are an important market for the processing industry. Of the traits influencing chip quality,chip color is market limiting since other traits have diminished value without light chip color. Cold (4 °C) storage can reduce storage losses and cultivars producing light colored chips directly from cold storage are needed for this reason. Selection for cold chipping cultivars is traditionally practiced by visual evaluation of progeny the first few years in the field, followed by selection for cold chipping in years 4–5. Early generation selection for cold chipping may reduce cultivar development time by identifying good chipping progeny, families and parents earlier in the breeding cycle. Progeny from 175 4x × 4x families were evaluated from three early generations. They were greenhouse grown tubers (GGT) evaluated after6 mo. storage using randomly selected progeny, and field grown single hills propagated from either seedling transplants (FTR), or from greenhouse grown tubers (FGT). Progeny from field grown generations were selected first by visual evaluation, and then by random selection and chipped after6 mo. (visual selections) or 3 and 6 mo. storage (random selections). Cold chipping progenies were found in all three early generations. The earliest generations for selection are GGT or FTR, but may be less efficient than FGT. Correlations suggest that reliable parent and family selection is possible using GGT data. Visual selection eliminated 4/5 of the good chipping progeny, while identifying 8 of 11,714 genotypes combining visual merit and cold chipping potential. Increased genetic variation and sexual polyploidization are possible strategies for increasing the number of desirable genotypes.

Variation for 2n pollen production and male fertility in wildSolanum germplasm resistant toPhytophthora infestans (Mont.) de Bary (US-8)

Wild potato species possess genetic variability for valuable traits including resistance toPhytophthora infestans, the causal agent for potato late blight disease. Breeding schemes using 2n gametes are a powerful tool for introgressing these traits. Forty-five plant introductions (PIs) across 12Solanum species representing various Endosperm Balance Numbers (EBN) and having resistance toP. infestans (US-8, isolate ND 95-2) were screened for 2n pollen production and male fertility. Species evaluated were 2x(lEBN)S. bulbocastanum, S. cardiophyllum, S. pinnatisectum, andS. trifidum; 2x(2EBN)S. berthaultii, S. megistacrolobum, S. microdontum, andS. verrucosum; 4x(2EBN)S. fendleri andS. stoloniferum; 6x(4EBN)S. guerreroense; and 2x(unknown EBN)S. polyadenium. Acetocarmine staining and cytological analyses were used to determine 2n pollen production and pollen stainability from genotypes grown across three locations. Based on frequency, genotypes were assigned to 2n pollen production categories (0≤1%, Low=1%–10%, Medium=11%–60%, and High≥60%) and pollen stainability categories (0≤1%, 1=196–5%, 2=6%–10%, 3=11%–20%, 4=21%–50%, and 5≥50%). Eleven of the 12 species and 37 of the 45 PIs examined contained genotypes producing ≥1% 2n pollen with ranges of 0%–63.6% and 0%–81.8%, respectively. Dependence was found between location and pollen stainability, EBN and pollen stainability, but not for location and frequency of genotypes with 2n pollen. Stability for 2n pollen production was observed across environments. Among the 1EBN germplasm, dependence was found between 2n pollen and pollen stainability. Resistance toP. infestans was found to be independent of 2n pollen production; therefore, identifying genotypes combining 2n pollen production, fertility, and resistance toP. infestans was possible.

White Pearl—A chipping potato variety with high level of resistance to cold sweetening

White Pearl is a chipping cultivar with high level of resistance to cold sweetening. The cold-chipping capacity of White Pearl is better than the current chipping cultivars, including Atlantic, Snowden and NorValley. White Pearl has low glucose content and good chip color when processed directly after a 7-month storage period at 3.3 to 5.5 C. White Pearl tubers are similar to Snowden with a round oval shape, light netting, shallow eyes, white flesh, small to medium size, uniform shape, and are practically free of external and internal defects. The yield and specific gravity of White Pearl are medium. White Pearl is similar to Snowden in susceptibility to early blight, pink rot and soft rot, but it is slightly more resistant to common scab. White Pearl vines are susceptible to late blight, but can be managed effectively with fungicides. White Pearl is more sensitive to blackspot bruise than Atlantic or Snowden at 7.2 C, but is more resistant at higher temperatures. White Pearl is sensitive to metribuzin (Sencor), but not rimsulfuron (Matrix) or sulfentrazone (Spartan).ResumenWhite Pearl es una variedad para fritura en hojuelas con nivel alto de resistencia al endulzamiento por efecto del frío. La capacidad de fritura después de almacenado en frío de White Pearl es mejor que las variedades que comúnmente se usan para hojuelas incluyendo Atlantic, Snowden y NorValley. White Pearl tiene bajo contenido de glucosa y buen color de hojuelas cuando se procesa directamente después de siete meses de almacenamiento a 3.3 a 5.5 C. Los tubérculos de White Pearl son similares a los de Snowden, tienen forma redonda ovalada, ligeramente reticulados, ojos poco profundos, pulpa blanca, de tamaño pequeño a mediano, uniformes y están prácticamente libres de defectos internos y externos. White Pearl es de rendimiento y gravedad específica media. Es similar a Snowden en susceptibilidad al tizón temprano, pudrición rosada y pudrición blanda, pero es ligeramente más resistente a la sarna común. El follaje de White Pearl es susceptible al tizón tardío, pero esta enfermedad se puede manejar en forma efectiva con fungicidas. White Pearl es más sensible a la mancha negra causada por magulladura que Atlantic o Snowden a 7.2 C, pero es más resistente a temperaturas mayores. White Pearl es sensible al metribuzin (Sencor) pero no al rimsulfuron (Matrix) o a sulfentrazona (Spartan).

Evidence of potato virus Y asymptomatic clones in diploid and tetraploid potato-breeding populations

Potato virus Y (PVY) is a potyvirus affecting potato productivity by reducing yield and quality. To reduce the amount of PVY in potato production systems, state seed certification agencies have established threshold criteria, which simultaneously increase quality. Research has documented several commercial cultivars lacking symptom expression of PVY despite infection. The presence of PVY asymptomatic clones in production and breeding populations is particularly important because it may provide an inoculum source in breeders’ seed and this reduces the efficiency of selection. The objectives of this research were to determine to what extent PVY asymptomatic clones are present in potato-breeding populations, and if PVY expression is influenced by the environment. After exposure to PVY, genotypes from different 2x and 4x populations were evaluated for the presence of PVY both visually and by ELISA assay. PVY asymptomatic genotypes were identified in both 2x and 4x populations. Chi square indicated dependency between PVY symptom expression and (1) ploidy, (2) genetically distinct 4x germplasm enhancement populations, and (3) expression in a north temperatevs. tropical environment using 4x progeny from five half-sib families. Dependency was not found between two 4x genetically related sub-populations and PVY asymptomatic expression. Analysis of variance (ANOVA) indicated that clones within family, families, location, and the interaction of location by clone were significant sources of variation for PVY symptom expression, ELISA, and visual evaluation. PVY asymptomatic clones were present in both 2x and 4x populations with higher frequencies in a north temperate compared to a tropical environment, suggesting that PVY symptom expression may be influenced by the environment.ResumenEl virus Y de la papa (PVY) es un potivirus que afecta la productividad reduciendo el rendimiento y la calidad. Con el objeto de disminuir la presencia de PVY en los sistemas de producción de papa, las agencias de certificación de los estados han establecido un criterio límite, según el cual se incrementa simultáneamente la calidad. La investigación ha documentado varios cultivares comerciales que no presentan síntomas de PVY a pesar de estar infectados. La presencia de clones asintomáticos en la producción y en las poblaciones en mejoramiento es particularmente importante porque pueden llevar consigo una fuente de inóculo en la semilla de los mejoradores, lo cual reduce la eficiencia de la selección. El objetivo de esta investigación ha sido determinar hasta que punto los clones asintomáticos afectados de PVY están presente en las poblaciones de mejoramiento, y si la expresión del PVY es influenciada por el medio ambiente. Después de exponer los genotipos de poblaciones 2x y 4x al PVY, fueron evaluados para presencia de PVY, tanto visualmente como por la prueba de ELISA. Los genotipos asintomáticos fueron identificados en ambas poblaciones 2x y 4x. La prueba de Chi cuadrado indicó dependencia entre la expresión de síntomas de PVY y (1) ploidía, (2) incremento del germoplasma 4x genéticamente differente y (3) la expresión en un ambiente nórdico templadovs. uno tropical, utilizando progenie 4x de 5 familias semi-emparentadas. No se encontró dependencia entre dos sub-poblaciones 4x genéticamente relacionadas y la expresión asintomática de PVY. El análisis de variancia (ANOVA) indicó que los clones dentro de una familia, familias, localidades, y la interacción de localidad por clon, son una fuente significativa de variación para la expresión de los síntomas, ELISA, y evaluación visual. Los clones asintomáticos de PVY estuvieron presentes en ambas poblaciones 2x y 4x, con altas frecuencias en clima nórdico templado comparado con un ambiente tropical, lo que sugiere que la expresión de los síntomas de PVY puede estar influenciada por el medio ambiente.