R. L. Plaisted

A technique for evaluating the ability of selections to yield consistently in different locations or seasons

SummaryVarieties differ in their ability to produce a, dependable crop. In New York experience has shown Katahdin and Cobbler to be favorable in this respect, whereas Green Mountain has a reputation of being variableYield data over locations were analysed in all possible combinations of pairs of varieties. Estimates of the variety × location component of variance were obtained for each of these analyses. The average of these components for all combinations having a variety in common was defined to be the relative contribution by that variety to the variety × location interaction. In four of five analyses, Green Mountain had the highest relative contribution to the variety × location interaction, and Cobbler and Katahdin had a low contribution.

QTL analysis of trichome-mediated insect resistance in potato

Genetic mapping of several components of a complex type of insect resistance has been undertaken as a means toward more efficient use of the valuable characteristics of a wild relative of potato. RFLP maps constructed on interspecific diploid progenies of Solanum tuberosum × S. berthaultii were used in conjunction with morphological, biochemical and biological phenotyping to identify quantitative trait loci (QTLs) contributing to trichome-mediated insect resistance. By superimposing QTL data for a wide range of phenotypes including biochemical assays, correlative and direct screens for insect resistance, and adaptation to the target environment on the genetic maps, we have addressed the organization, action and interaction of genes controlling the resistance mechanism. The outcome contributes to an understanding of the association between component traits and between desirable and undesirable features of the donor species generated in an applied breeding program. Research is proceeding toward the development of selectable markers for the introgression and transfer of this resistance among potato gene pools.

The past record and future prospects for the use of exotic potato germplasm

Potatoes had probably been introduced into North America from Europe by the end of the 17th Century. Several significant introductions since then have added to the initial germplasm. The Chilean clone “Rough Purple Chili”, introduced by Chauncey Goodrich in 1851, is in the pedigrees of almost all modern varieties. The initiation of plant exploration and establishment of germplasm centers in the 1920’s greatly expanded the germplasm base. Utilization ofS. demissum for blight resistance led to the development of many new varieties in the 1940’s. The German variety “Jubel” was widely used in breeding for scab resistance and “Villaroela” from Chile, for virus resistance. “Katahdin”, with several European introductions as well as the South American varieties “Daber” and “Rough Purple Chili”, in its pedigree, was widely used as a parent from the 1930’s to the 1960’s. More recently, the convenience of obtaining germplasm from the IR-1 project, and the genetic, cytogenetic, and adaptation studies based on this germplasm, have fostered a new wave of the use of exotic material. This research, coupled with extensive screening for valuable traits, makes the use of exotic germplasm more feasible and more productive.CompendioLa papa posiblemente fué introducida a America del Norte desde Europa al final del siglo XVII. Varias introduciones significantes han sido agregadas al germoplasma inicial. El clon chileno “Rough Purple Chili”, introducido por Chauncey Goodrich en 1851, esta en el linaje de casi todas las variedades modernas. La iniciación de expediciones para colectar variedades nativas cultivadas y silvestres y la establacimiento de centros de germoplasma en los 20’s logró una gran expansion grande del base de germoplasma. Utilización deS. demissum para resistencia aPhytopthora infestans impulsó el desarollo de muchas variedades nuevas en los 40’s. La variedad aleman “Jubel” fue usada mucho en cruces para resistencia a sarna y la variedad “Villaroela”, de Chile, para resistencia a virus. “Katahdin”, junto con diferentes introducciones europeos asi como variedades suramericanos “Daber” y “Rough Purple Chili”, en su genealogia, fueron usadas con mucha frequencia como padres desde los 30’s hasta los 60’s. Mas recientemente, la conveniencia de obtener germoplasma del Projecto IR-1, y los estudios geneticos, cytogeneticos, y de adaptación basado en este germoplasma, han impulsado una nueva ola de uso de material de papa exótica. Este tipo de investigación, ademas de ensayos extensivos buscando caracteristicas valiosas, hace mas factible y productivo el uso de germoplasma exotico.

QTL analysis of potato tuberization

Quantitative trait loci (QTLs) affecting tuberization were detected in reciprocal backcrosses between Solanum tuberosum and S. berthaultii. Linkage analyses were performed between traits and RFLP alleles segregating from both the hybrid and the recurrent parent using a set of framework markers from the potato map. Eleven distinct loci on seven chromosomes were associated with variation in tuberization. Most of the loci had small effects, but a QTL explaining 27% of the variance was found on chromosome 5. More QTLs were detected while following alleles segregating from the recurrent S. tuberosum parent used to make the backcross than were detected by following alleles segregating from the hybrid parent. More than half of the alleles favoring tuberization were at least partly dominant. Tuberization was favored by an allele from S. berthaultii at 3 of the 5 QTLs detected by segregation from the hybrid parent. The additive effects of the QTLs for tuberization explained up to 53% of the phenotypic variance, and inclusion of epistatic effects increased this figure to 60%. The most common form of epistasis was that in which presence of an allele at each of 2 loci favoring tuberization was no more effective than the presence of a favorable allele at 1 of the 2 loci. The QTLs detected for tuberization traits are discussed in relationship to those previously detected for trichome-mediated insect resistance derived from the unadapted wild species.

Spindle tuber virus in seeds and pollen of infected potato plants

The presence of potato spindle tuber virus (PSTV) in seed and pollen of diseased plants was demonstrated. Transmission through the seed from open-pollinated female parents to the seedlings occurred frequently (average 31%) but varied in individual collections from zero to 100%. The amount of transmission did not appear to be correlated with variety or with age of the seed. All PSTV infections encountered appeared to be caused by mild strains. It is suggested that only healthy parents should be used for breeding purposes.ResumenLa presencia del virus que causa tubérculos ahusados (PSTV) ha sido demonstrada en semillas y polen de plantas infectadas. Transmisión del virus por semilla obtenida de padres femininos libremente polinizados a las plantulas sucedió con frecuencia (promedio 31%) pero varió en colecciones individuales desde zero a 100%. La magnitud de la infección parece no correlacionarse con la variedad o con la edad de la semilla. Todas las infecciones con PSTV encontradas parecen haber sido causadas por cepas no muy virulentas. Se sugiere que solamente padres sanos sean usados para propagación.

Specific and general combining ability for yield in potatoes

SummaryForty-five lines were crossed to six testers to evaluate their general combining ability. These lines did not clearly represent a random selection of lines with respect to this character, though they had not undergone any formal selection in this respect. In these lines, the variance in specific combining ability exceeded the variance in general combining ability. Six or more testers are required to evaluate general combining ability in lines of this nature. The interaction of general combining ability and locations was less than the variation in SCA and locations.The variation in specific combining ability of a line was not related to the magnitude of its GCA effect.The general combining ability effects of 32 of the lines are given. Four of the better lines were B2368-4, La1859, I-1015-2 and I-1077W28-5.

A test of the maximum heterozygosity hypothesis using molecular markers in tetraploid potatoes

It has been theorized that in cross-pollinated polyploid species hybrid vigor is maximized by the frequent occurrence of more than two alleles per chromosomal locus. In polyploid crops this condition of maximum heterozygosity has been reported to be associated with increased yield and optimum field performance. We report herein the first direct test of the maximum heterozygosity hypothesis. Molecular markers were used to examine the association between maximum heterozygosity and several components of yield in three different populations of tetraploid potatoes. The results indicate that the value of maximum heterozygosity is not universal but dependent on the genetic background of the material under evaluation. In a cross between adapted breeding lines, homozygosity was negatively correlated with tuber yield, and maximum heterozygosity was positively correlated with the proportion of tuber yield in the large-size fraction. In contrast, in crosses between adapted and unadapted parents, maximum heterozygosity had no detectable effect on any character. Quantitative trait locus (QTL) analysis of the three populations reveals that, regardless of the genetic background, additive genetic effects are more strongly correlated with the components of yield than are any measures of heterozygosity and that some common QTLs may be influencing yield in all three populations.

The germplasm release of NYL 235–4, a clone with resistance to the Colorado potato beetle

Clones selected from the wild diploid species,Solanum berthaultii, have been shown to possess valuable levels of resistance to the Colorado potato beetle (Leptinotarsa decemlineata), as well as to insects such as aphids, flea beetles, leafhoppers and the potato tuber moth. Resistance is associated with the presence of glandular trichomes on the foliage ofS. berthaultii (2). Six generations after producing a hybrid between the diploid species and a tetraploid variety, a clone with good beetle and leafhopper resistance, as well as reasonable agronomic characteristics has been produced.

QTL analysis of potato tuber dormancy

The potential loss of chemical sprout inhibitors because of public concern over the use of pesticides underscores the desirability of breeding for long dormancy of potato (Solanum tuberosum L.) tubers. Quantitative trait locus (QTL) analyses were performed in reciprocal backcrosses between S. tuberosum and S. berthaultii toward defining the complexity of dormancy. S. berthaultii is a wild Bolivian species characterized by a short-day requirement for tuberization, long tuber dormancy, and resistance to several insect pests. RFLP alleles segregating from the recurrent parents as well as from the interspecific hybrid were monitored in two segregating progenies. We detected QTLs on nine chromosomes that affected tuber dormancy, either alone or through epistatic interactions. Alleles from the wild parent promoted dormancy, with the largest effect at a QTL on chromosome 2. Long dormancy appeared to be recessive in the backcross to S. berthaultii (BCB). In BCB the additive effects of dormancy QTLs accounted for 48% of the measured phenotypic variance, and adding epistatic effects to the model explained only 4% more. In contrast, additive effects explained only 16% of the variance in the backcross to S. tuberosum (BCT), and an additional 24% was explained by the inclusion of epistatic effects. In BCB variation at all QTLs detected was associated with RFLP alleles segregating from the hybrid parent; in BCT all QTLs except for two found through epistasis were detected through RFLP alleles segregating from the recurrent parent. At least three dormancy QTLs mapped to markers previously found to be associated with tuberization in these crosses.

Resistance to potato virus Y inSolanum tuberosum spp.andigena

Tests were made on lines ofSolanum tuberosum spp.andigena to determine 1) whether resistance to potato virus Y exists in the Andigena germplasm, 2) the nature of its inheritance, and 3) the type of resistance.Results of the isolation and identification studies indicated that the pathogen involved was a common strain of potato virus Y.Under field conditions susceptible plants frequently escaped infection. However, field exposures over two seasons resulted in the same ratios as tests in which the same progenies were mechanically inoculated.Mechanical inoculation at the seedling stage proved to be a reliable means of transmission and resulted in accurate screening for resistance. Of 641 tub × tub clones tested, all were susceptible to the virus. Of 366 tub × adg clones tested, 170 were resistant and 196 were susceptible. This fits a 13:15 ratio, assuming random chromatid segregation and a single dominant gene conferring resistance.Plants that were resistant following mechanical transmission were also resistant when inoculated by aphids, indicating the reliability of mechanical transmission as a means of screening for resistance.To determine the type of resistance, top-graft and approach-graft tests were made. Failure to recover the virus from resistant plants inoculated by either grafting method suggests that immunity is the type of resistance involved.ResúmenLos ensayos se hicieron usando líneas deSolanum tuberosum spp.andigena para determinar: 1) Si existe resistencia a virus Y en el germoplasma andigeno. 2) La naturaleza de su herencia y: 3) Tipo de resistencia. Resultados del aislamiento y los estudios de identificación indican que el patöeno involucrado fue un “strain” común del virus Y. Las plantas susceptibles frecuentemente escapan a la infección en condiciones de campo. Sin embargo, los resultados de exposición en el campo durante dos estaciones fueron iguales en proporción a los experimentos en los cuales las mismas progenies fueron mecánicamente inoculadas La inoculatión mecánica en el estado de plántula demostró de signification para transmitir el virus y resultó ser un método preciso para búsqueda de resistencia. Se probaron 641 clones de tub. × tub. y todos fueron susceptibles al virus. Se probaron 366 clones de tub. × adg. y resultaron 170 clones resistentes y 196 susceptibles. Esto encuadra en una proporción de 13:15, asumiendo segregación cromatida randomizada confiriendo resistencia un simple gen dominante. Las plantas que fueron resistentes a la transmisión por inoculación mecánica, también fueron resistentes cuando se inocularon con áfidos, indicando esto la seguridad de la transmisión mecánica como medio de búsqueda para resistencia. Se hicieron injertos apicales y de aproximación para determinar el tipo de resistencia. No se recuperó el virus de las plantas mencionados, sugiriendo estos resultados que el tipo de resistencia es inmunidad.