Elmer E. Ewing

Heat stress and the tuberization stimulus

Heat stress may lower potato tuber yields through reduction in the net amount of photosynthate available for total plant growth and through reduced partitioning to the tubers. The latter effect is generally more serious and is the main subject of this paper. High temperatures have much the same effect on partitioning as do long days, and there are significant genetic differences in response to both factors. Both affect the total morphology of the plant. A cutting technique may be used to rapidly screen seedling populations for reaction to temperature or photoperiod. Although progress has been made in studying the nature of the hypothetical “tuberization stimulus”, more needs to be done to clarify the physiological and biochemical changes involved during tuber induction.ResumenEl stress térmico puede disminuir el rendimiento de los tubérculos de la papa, reduciendo la cantidad neta de material fotosintetizado disponible para el total desarrollo de la planta y reduciendo su distribución a los tubérculos.Este último efecto es generalmente más serio y es el principal motivo de este artículo. Altas temperaturas y días largos tìenen efectos semejantes sobre la distribución del material elaborado, existiendo además significativas diferencias genéticas en relación con la respuesta a ambos factores. Ambos factores afectan la morfología total de la planta. El método de propagación vegetativa con secciones del tallo, puede usarse para analizar la respuesta de poblaciones de plántulas a la temperatura o al fotoperíodo. Aun cuando se ha progresado en el estudio de la naturaleza del estímulo hipotético de la tuberización, se necesita todavia clarificar los cambios fisiológicos y bioquímicos que ocurren durante la indución de la tuberización.

The Role of Hormones in Potato (Solanum tuberosum L.) Tuberization

Tuber initiation in the potato plant is accompanied by extensive morphological and biochemical changes above and below ground. Plants that are capable of tuber initiation are said to be “induced” to tuberize. It has long been postulated that the changes leading to induction are mediated hormonally. Before considering the evidence, it is helpful to summarize what is known about the tuberization process, its genetic and environmental control, and the techniques that have been employed to study it. For a more comprehensive treatment of these topics and for literature citations, see the recent review article by Ewing and Struik (8).

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.

Growth analyses of eleven potato cultivars grown in the greenhouse under long photoperiods with and without heat stress

Six potato cultivars from North America were grown in two greenhouses under 18-h photoperiods. All plants were started in a greenhouse that was well ventilated and maintained as close as possible to summer ambient temperatures. One month after planting, half the plants of each cultivar were moved to a greenhouse that was kept at 30 C during the night and was allowed to reach 40 C or higher during the day. Plants from each treatment were harvested at monthly intervals for growth analyses. Concurrently, five clones considered to be heat tolerant were subjected to a similar test in a second experiment. In response to high temperatures, plants in both experiments were taller with smaller leaves, lower tuber yields, higher ratios of stem to leaf dry matter, and lower ratios of tuber to leaf and to stem dry matter. Tubers were lower in percent dry matter, maturity was delayed, and cuttings developed fewer tubers. Cultivars differed greatly in the degree to which they were affected by the heat. In the first experiment, Norchip had outstanding heat tolerance. LT-2 was the most tolerant of the clones in the second experiment. For the cooler treatment the best performance in either experiment was from two clones originally selected in the lowland tropics.ResumenSeis cultivares de papa de Norteamérica fueron cultivados en dos invernaderos con 18 horas de luz. Al inicio todas las plantas estuvieron en un invernadero “fresco” con suficiente ventilación y a temperatura ambiental. Un mes después, la mitad de las plantas de cada cultivar fueron cambiadas a un invernadero cuya temperatura nocturna se mantuvo a 30 C y durante el dia se permitio que subiera a 40 C o más. Plantas de cada tratamiento fueron cosechadas a intervalos mensuales para comparar el crecimiento. Al mismo tiempo, cinco clones considerados tolerante al calor fueron sujectos a un ensayo similar en un segundo experimento. Las temperaturas altas causaron en los dos experimentos hojas más pequeñas, plantas más altas, altos valores en la relatión tallos sobre hojas, y translocación de materia seca de los tubérculos hacia los tallos y hojas. El porcentaje de materia seca en los tubérculos fue más bajo, la madurez se retrasó, y las estacas desarrollaron menos tubérculos. Los cultivares de papa presentaron diferente tolerancia a altas temperaturas. Entre los seis cultivares de Norteamérica en el primer experimento, Norchip sobresalió por su tolerancia. En el segundo experimento con cinco cultivares diferentes, LT-2 fue el menos afectado. Para el tratamiento más frio el mejor rendimiento de los dos experimentos fueron de los dos clones seleccionados en el trópico cálido.

Evidence from Polygene Mapping for a Causal Relationship between Potato Tuber Dormancy and Abscisic Acid Content

In previous studies polygene mapping of a backcross population derived from haploid potato (Solanum tuberosum) and a diploid wild species (Solanum berthaultii) showed at least eight quantitative trait loci (QTLs) associated with tuber dormancy. The same population was mapped for abscisic acid (ABA) content in tubers so that any QTLs identified could be compared with those detected previously. At least three distinct loci on three chromosomes (2, 4, and 7) were associated with variation in ABA content. One of the QTLs was detected only as a main (single locus) effect, and two QTLs were found through two-locus interaction analysis (epistasis). Interaction between QTLs at markers TG234 (chromosome 2) and TG155 (chromosome 4) explained 20% of total phenotypic variance for this trait. The interaction closely resembled one previously detected for dormancy, suggesting an association between high ABA content and long tuber dormancy. Although relationships between ABA level and dormancy could be demonstrated through polygene mapping, there was no indication of a relationship between these traits when they were subjected to a conventional correlation test. This illustrates the usefulness of polygene mapping as a tool to identify possible associations between hormone levels and plant development.

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.

Morphology and [14C]Gibberellin A12 Metabolism in WildType and Dwarf Solanum tuberosum ssp. Andigena Grown under Long and Short Photoperiods

Summary Potato tuberization is promoted by short days and inhibited by applications of gibberellin (GA). Wildtype Solanum tuberosum ssp. andigena required short days for tuberization, whereas their dwarf siblings tuberized under long days. Nevertheless, shortening the photoperiod also enhanced tuberization of dwarf plants and caused an increase in leaf angle and a reduction in internode length of both genotypes. The potential role of GA metabolism in tuberization as influenced by dwarfing and photoperiod was investigated by studying the metabolism of [ 14 C]GA 12 in shoots of wild-type and dwarf potato plants. Measurement of metabolite levels was by radiocounting after HPLC. The data indicated a reduced conversion of GA 12 to GA 53 in dwarf plants, a difference which may be responsible for the dwarf morphology, although other explanations cannot be ruled out. Dwarf plants contained much less GA 1 , as measured by GC-MS. We did not detect differences in [ 14 C]GA 12 metabolism between plants grown under 10-h versus 16-h photoperiods, in either wild-type or dwarf plants, even though other wild-type plants contained less GA 1 , under short photoperiods than under long photoperiods.

Critical photoperiods for tuberization: A screening technique with potato cuttings

Seedling populations segregating for the critical photoperiod that controls tuberization may be screened by a cutting technique. Plants are grown under daily photoperiods which are at first long (e.g., 20 hours) and which are shortened at two-week intervals. Apical cuttings and single-node, sub-apical cuttings are taken at the end of each two-week period. The cuttings are maintained in a mist chamber under a 20-hour photoperiod for 10–14 days. The photoperiod that first promotes tuberization on cuttings may be considered as the critical photoperiod.ResumenPoblaciones de plantas segregando para fotoperíodo crítico que controla tuberización pueden ser seleccionadas usando la técnica de propagación vegetativa. Las plantas son expuestas inicialmente a fotoperíodos largos (e.g. 20 horas) que posteriormente son acortados en forma gradual cada dos semanas. Secciones apicales del tallo y secciones subapicales con un solo nudo y hoja son cortadas al finalizar las dos semanas de tratamiento. Las partes vegetativas son mantenidas en una cama de propagación bajo un fotoperiodo de 20 horas durante 10 o 14 dias. El fotoperiodo que primeramente induzca tuberización de las secciones vegetativas puede ser considerado como el photoperíodo crítico.

Jasmonates and their role in plant growth and development, with special reference to the control of potato tuberization: A review

Jasmonic acid and closely related compounds show growth regulating properties in plants. They have been found in more than 30 plant species. In this paper we review what is known about the jasmonate biosynthetic pathway, biological activities, and mode of action. We also discuss the possible role of jasmonates in potato tuberization.CompendioÁcido jasmonic y compuestos emparentados muestran tener propiedades como reguladores de crecimiento en plantas. Ellos han sido encontrados en más de 30 especies de plantas. En este reporte nosotros revisamos lo que es conocido acerca del camino biosintético del jasmonate, sus actividades biológicas y su modo de acción. Nosotros tambien discutimos el posible aporte de los jasmonates en la indución de los tubérculos de la papa.

Effects of short periods of chilling and warming on potato sugar content and chipping quality

Two days of chilling (exposure to 1 C) had no detectable effect on chip color or sugar content of potato (Solanum tuberosum L.) tubers. Four days of chilling led to increases in sugars if potatoes were stored at 10 C or 19 C for 3 to 4 days after chilling ended. Longer chilling gave increases in sugars by the end of the chilling period, and returning tubers to 10 C or 19 C magnified the response. Glucose and fructose gave similar increases from chilling treatments, except that glucose levels were consistently greater. Sucrose was increased by chilling, but the response pattern did not always resemble that of the reducing sugars. Twenty-seven days of storage at 19 C after chilling lowered levels of reducing sugars late in the storage season but not in December. Cultivars differed in response to chilling. Kennebec tubers accumulated far more reducing sugars but much less sucrose than did Norchip tubers. Storage at 19 C after chilling lowered the sucrose content of Kennebec and Monona while raising that of Norchip.ResumenTubérculos de papa (Solanum tuberosum L.), expuestos a períodos de frío (1°C) por dos días no sufrieron detectables efectos en cuanto al color que presentan rodajas de papa al freírse ni en el contenido de azúcar. Tratamiento de frío por un periodo de cuatro dias causaron un incremento en el contenido de azúcares cuando los tubérculos fueron almacenados a temperaturas de 10 o 19°C por espacio de 3 a 4 días después que el tratamiento de frio hubo finalizado. Períodos de frío más prolongados incrementaron el contenido de azúcares al final del período. Esta respuesta se magnifica si los tubérculos son almacenados a temperaturas de 10 o 19°C. Los contenidos de glucosa y fructosa respondieron similarmente al tratamiento de frío, exceptuando que los niveles de glucosa fueron consistentemente mayores. El tratamiento de frio incrementó el contenido de sacarosa, pero ésta respuesta no siempre se asemeja a la presentada por los azúcares reductores. El almacenaje a 19°C por espacio de 27 dias después del tratamiento de frío causo bajas en los niveles de azúcares reductores durante el último período de la época de almacenamiento, pero no en el mes de diciembre. Los cultivares responden diferentemente al tratamiento de frio. Tubérculos de la Variedad Kennebec acumularon mucho más azúcares reductores pero mucho menos sacarosa que los tubérculos de la Variedad Norchip. El almacenamiento a 19°C después del tratamiento de frío redujo el contenido de sacarosa de las Variedades Kennebec y Monona mientras que lo incremento en la Variedad Norchip.