G. C. C. Tai

Relationship between resistance to late blight in potato foliage and tubers of cultivars and breeding selections with different resistance levels

Due to changes in the pathogen population, late blight of potatoes caused byPhytophthora infestans has become a more difficult disease to manage and there is a need for new potato cultivars with greater and more stable disease resistance. Field studies are required to identify and characterize host resistance to late blight in both foliage and tubers but, as epidemics vary from year to year, combining multi-year results can be difficult. Residual maximum likelihood (REML) was successfully used to analyze data which demonstrated good correlations between foliar and tuber responses to late blight (US-1 genotype). In addition, studies on post-harvest inoculated tubers provided more reliable disease responses than field studies, and the disease resistance with this method correlated well with foliar disease responses. This tuber test would be a useful method of pre-screening selections for disease response prior to testing in the field.

Effects of nitrogen application and seedpiece spacing on yield and tuber size distribution in eight potato cultivars

The responses of eight cultivars to nitrogen fertilizer and spacing treatments were examined from 1992 to 1996. Experiments were carried out at the Agriculture and Agri-Food Canada Research Farm in Harrington, Prince Edward Island. Four nitrogen rates and three seedpiece spacings were compared. Total and Canada #1 yields were investigated for patterns of responses of the individual cultivars to both treatments, and possible interactions between the treatments. Response surfaces were presented for all cultivars. Nitrogen application increased both total and Canada #1 yields for all cultivars. Increasing rates of nitrogen showed linear and/or quadratic trends for both total and Canada #1 yields in all cultivars, whereas responses to spacing treatments showed linear patterns for total yield, but little change for Canada #1 yields in seven of the eight cultivars. No interactions were detected between fertilizer and spacing treatments for total or Canada #1 yields. Generalized regression equations representing the responses of the cultivars to fertilizer and spacing treatments for both total and Canada #1 yields were also derived. These equations should be useful as a guideline for determining appropriate nitrogen rates and seedpiece spacing for the eight cultivars tested. Ratios of Canada #1 to total yield were higher after initial application of nitrogen (0 to low rate) in all but one cultivar. However, only two cultivars showed higher ratios as nitrogen rate was further increased. Wider seedpiece spacing yielded higher ratios of Canada #1 in five of the eight cultivars tested.ResumenEntre 1992 y 1996, se examinaron las respuestas de ocho cultivares al tratamiento de espaciamiento y fertilización con nitrógeno. Los experimentes se realizaron en el Campo de Investigación de Agriculture and Agri Food de Canadá, en Harrington, P.E.I. Se compararon cuatro niveles de nitrógeno y tres espaciamientos de semilla. Como patrones de respuesta de los cultivares individuales a ambos tratamientos y la posible interacción entre tratamientos se investigaron los rendimientos totales y de Canadá N° 1. Todos los cultivares presentaron respuestas superficiales. La aplicación de nitrógeno acrecentó los rendimientos totales y de Canadá N° 1 en todos los cultivares. El incremento en los niveles de nitrógeno mostró tendencias lineales y/o cuadráticas en el rendimiento total y de Canadá N° 1 en todos los cultivares, mientras que las respuestas al tratamiento de espaciamiento mostraron patrones lineales para el rendimiento total y un pequeño cambio en el rendimiento con relación a Canadá N° 1 en siete de los ocho cultivares. No se detectaron interacciones entre los tratamientos de fertilización y espaciamiento sobre el rendimiento total o de Canadá N° 1. También se establecieron ecuaciones de regresión generalizada representando las respuestas de los cultivares a los tratamientos de fertilización y espaciamiento, tanto para rendimientos totales como para Canadá N° 1. Esas ecuaciones deberían servir como una pauta para la determinatión de los niveles adecuados de nitrógeno y del espaciamiento de semillas de los ocho cultivares examinados. La relación de Canadá N° 1 con los rendimientos totales fueron mayores después de una aplicación inicial de nitrógeno (0 a niveles bajos) en todos los cultivares menos uno. Sin embargo, solamente dos cultivares mostraron alta relación a medida que el nivel de nitrógeno fue adicionalmente incrementado. Espaciamientos más amplios de semillas produjeron relaciones más altas con Canadá N° 1 en cinco de los ocho cultivares examinados.

Transmission of resistance to common scab from the diploid to the tetraploid level via 4x-2x crosses in potatoes

SummaryDiploid potato clones selected for their reaction to common scab and their ability to produce 2n male gametes were used in a series of crosses to a susceptible tetraploid female parent (cv. Shepody). In addition, two tetraploid clones were also selected for their reaction to common scab and crossed with Shepody as a female parent. Results indicated that resistance to common scab can be effectively transmitted from the diploid to the tetraploid level via 4x-2x crosses. Diploid parents producing 2n pollen via either first division or second division restitution can be used to transmit scab resistance. A relatively small proportion of resistant individuals could be recovered from susceptible x susceptible crosses in both 4x-2x and 4x-4x combinations. The data support a previously developed hypothesis that scab resistance is relatively simply inherited.

Potential for improvement by selection for reducing sugar content after cold storage for three potato populations.

The objectives of this study were to examine the expected response to selection for reducing-sugar content after cold storage in three hybrid populations, to determine whether these populations included clones low in reducing sugars, and to investigate the effectiveness of indirect selection for chip colour based on selection of sugar content after cold storage. The three hybrid populations included: a random sample of 39 clones of Population 1, which was derived from crossing ND860-2 (a clone low in reducing sugars) with F58089 (a clone intermediate in reducing sugars); 40 clones of Population 2, which was obtained from crossing ND860-2 with Russette (a clone high in reducing sugars); and 40 clones of Population 3, which was derived from crossing Russette with F58089. Sugar content and chip colour were assessed in tubers stored for 2 months at 4 °C at Cambridge, Ontario, and at 3 °C at Benton Ridge, New Brunswick. Population 1 had a slightly greater predicted response to selection for reduction in glucose and total reducing sugars than the other two populations. This could be attributed to higher heritability estimates for Population 1, which was a reflection of smaller clone × environment interaction mean squares. The greater potential advance by selection for fructose, glucose, and total reducing sugars, was a direct consequence of its lower means for these traits. Low reducing-sugar clones were found in all three populations, indicating their potential use for the selection of low reducing sugars. Populations 2 and 3, however, would require stronger selection pressures and, therefore, large population sizes. Expected correlated responses for chip colour by selection for fructose and glucose were similar to, and sometimes exceeded, the expected direct responses in all three populations. Indirect responses for chip colour by selection for sucrose, however, were lower than direct selection responses. These results indicate that indirect selection for chip colour, by selection for either fructose or glucose content after cold storage, is as effective as direct selection for chip colour.

Path analysis of genotype-environment interactions of potatoes exposed to increasing warm-climate constraints

SummaryTwenty potato cultivars were tested in replicated trials in three seasons. The weather gradually changed from relatively high humidity and cold air temperatures in February to dry and hot in July. Fresh and dry weights, sucrose, reducing sugar and starch contents were recorded on tubers sequentially harvested over four stages during the growing period of each of the three trials. The data were analyzed for genotype-environment interactions by a path regression model which is composed of a main effect and four multiplicative effects. The model fitted well to the observed data for all traits but reducing sugar. Results of dry tuber weight were used to calculate a heat susceptibility index for each of the cultivars. Four components of the index were identified based on the path model. Comparison of sizes of the components provided information on the degree of response to the environmental stress of each of the cultivars during successive stages of growth. High yielding and heat tolerant cultivars were identified based on the experimental results.

The effect of maleic hydrazide (potassium salt) on potato yield, sugar content and chip color of Kennebec and Norchip cultivars

A new formulation of maleic hydrazide (MH), a potassium salt formulation, was field tested for 3 years in Ontario to evaluate effects on yield performance, and on the sprouting and processing quality of cvs. Norchip and Kennebec potatoes. Foliar applied MH had no apparent effect on yield of potatoes, was effective in suppressing sprout growth, and had no effect on the sugar content (i.e., fructose, glucose and sucrose) of potatoes newly harvested and after 6 months storage. Although chip color varied from yearto-year, no consistent difference was found between the color of chips made from potatoes from untreated and MH-treated plants.

Segregation for somatic embryogenesis on stem-internode explants from potato seedlings

Differences in productivity for somatic embryos (SEs) in vitro among 18 potato cultivars and three wild Solanum species in an earlier study led to the hypothesis that regeneration of SEs may be under genetic control. To examine this possibility, three test crosses were initiated; Coastal Russet×AF 186-2; Costal Russet×Lenape; AF 186-2×Lenape. True potato seedlings from these crosses were germinated in vitro. Five stem internode explants from each seedling were excised and cultured on two successive media to promote the formation of SEs. Seedling explants Costal Russet×AF 186-2 cross produced more SE than the other two crosses, and explants from the AF 186-2×Lenape cross generally only produced <10 SEs per explant. SEs were produced on the stem-internode explants from the three crosses at different rates. Data for the number of explants producing SEs and numbers of SEs per explant were highly significant. Regeneration of SEs is probably under nuclear control and the inheritance for regeneration may be quite straightforward.

Discriminating Russet Norkotah intraclonal selections using canonical and cluster analysis

Intraclonal selection has been used to develop improved versions of existing popular potato cultivars. The approach is usually undertaken to overcome trait deficiencies that limit production/acceptance of the cultivar. Because of close genetic relationships, discriminating between strains and the original cultivar is more difficult than discriminating between conventionally derived hybrid cultivars. The objective of this investigation was to determine the genetic relationship between several Russet Norkotah intraclonal selections (strains) using statistical analysis. Russet Norkotah and seven Russet Norkotah strains (TXNS102, TXNS112, TXNS223, TXNS278, TXNS296, CORN3 and CORN8) were grown in 2000 and 2001 in New Brunswick, Canada, and several plant and tuber traits were measured. Hierarchical cluster analysis and canonical discriminant analysis demonstrated that the Russet Norkotah strains differ in a significant manner from the original cultivar and are therefore distinct and unique cultivars.ResumenPara desarrollar versiones mejoradas de los cultivares populares existentes se ha utilizado la selección intraclonal. Este enfoque se adopta habitualmente para superar las diferencias que limitan la producción/ aceptación del cultivar. Debido a las relaciones genéticas estrechas, las diferencias entre los strains y el cultivar original son más difíciles de distinguir que las diferencias entre los cultivares híbridos derivados convencionalmente. El objetivo de esta investigación fue el de determinar la relación genética entre varias selecciones intraclonales (strains) de Russet Norkotah utilizando análisis estadísticos. Russet Norkotah y siete strains del mismo cultivar (TXNS102, TXNS112, TXNS223, TXNS278, TXNS296, CORN3 y CORN8) se cultivaron el 2000 y 2001 en New Brunswick, Canadá y se evaluaron varios caracteres de la planta y del tubérculo. Los análisis Jerárquico Cluster y el Discriminante Canónico demostraron que los strains de Russet Norkotah fueron significativamente diferentes del cultivar original y por lo tanto son cultivares diferentes y únicos.

Photoperiodin vitro affects subsequent yield of Greenhouse-grown potato tubers

In vitro potato plantlets of cultivar (cv.) Shepody (Solatium tuberosum L.) were exposed to 12-or 16-hr photoperiods for 8 weeks. Plantlets were acclimatized to the greenhouse and grown under 14-hr photoperiods until they senesced, and minitubers were harvested. Greenhouse-grown potato plants developed from tissue-culture plantlets exposed to a 16-hr photoperiod were taller and had more nodes than plants developed from plantlets exposed to 12-hr photoperiods. However, yield data of minitubers from greenhousegrown plants indicated that the 12-hr photoperiodic treatment increased the numbers, dry weight and specific gravity of minitubers. A further advantage of the 12-hr photoperiodic treatment was the greater numbers of minitubers in the 15–40 g size class compared with tubers in the <15 g and >40 g size classes. Thus, for the cv. Shepody, plant height and node number of greenhouse-grown plants were not good indicators of minituber yield from that crop. Seed potato nuclear stock facilities producing minitubers should investigate the possibility of optimizing minituber production by exposing multiplication cultures to shorter daylengths.CompendioPlantitas in vitro de papa del cultivar (cv.) Shepody (Solatium tuberosum L.) fueron expuestas a fotoperiodos de 12 o 16 hr, por ocho (8) semanas. Las Plantitas fueron aclimatadas al invernadero y crecieron bajo fotoperiodos de 14 hr hasta su senescencia, cosechándose sus tuberculillos. Las plantas que crecieron en el invernadero, desarrolladas de plantitas procedentes de cultivos de tejidos expuestos a fotoperiodos de 16 hr, fueron mas altas y tuvieron más nudos que las plantas desarrolladas de plantitas expuestas a fotoperiodos de 12 hr. Sin embargo, la información sobre el rendimiento en tuberculillos de las plantas que crecieron en el invernadero indicó que el tratamiento fotoperiódo de 12 hr incrementó el número, el peso seco y la gravedad específica de los tuberculillos. Una ventaja adicional del tratamiento fotoperiódico de 12 hr fue el mayor número de tuberculillos en la clase del tamaño de 15–40 g, en comparación con los tubérculos en la clase de los tamanos <15 y >40 g. Por lo tanto, para el cv. Shepody, la altura de planta y el número de nudos de las plantas mantenidas en invernadero no fueron buenos indicadores del rendimiento en tuberculillos de ese cultivo. Las instalaciones de existencias nucleares de semilla de papa produciendo tuberculillos deben investigar la posibilidad de optimizar la producción de tuberculillos exponiendo los cultivos de multiplicación a longitudes de día más cortas.

Screening diploidSolarium genotypes responsive to different Anther culture conditions and ploidy assessment of Anther-derived roots and plantlets

Twenty-three diploid (2n=2x=24) potato clones were screened for response to four different anther culture media. Anther derived tissues (calli/embryos) were obtained from seven of the clones in liquid culture media. Anther culture response of these seven clones was further quantified on five additional media. Since clonal responses are specific to culture conditions (Tiainen, 1992), the seven genotypes somewhat differed from each other in the magnitude of the response to each of the media. In agreement with Heberle-Bors (1985) a more realistic assessment of the responsiveness was possible when pollen counts per anther were used to express the yield of anther-derived material. A relatively higher level of exogenous cytokinin (6-benzyladenine) to that of auxin (3-indoleacetic acid) proved to be favourable for the inducton of calli/embryos. Use of a semi-solid medium saved space and was convenient for culture observations therefore it was found more conducive for the genotypic screening. Anther derived tissues that regenerated to produce root tissue and/or plantlets were further multiplied on a root culture medium and a plantlet medium. Liquid culture conditions on orbital shakers were conducive for the growth of root explants. Anther derived material (roots and plantlets) originating from clone 9507–04 revealed differences in growth vigor. Flow cytometric estimation of ploidy in regenerated roots and plantlets, revealed that clone 9507–04 produced 44% monoploid roots and 77% monoploid plantlets. Seventy-three percent anther-derived plantlets from clone 6028–02 were monoploids.