Stomatal conductance and gross photosynthesis of potato (Solanum tuberosum L.) as influenced by irradiance,temperature, and growth stage

Summary Stomatal conductance (SC) and gross photosynthesis (P_G) of two potato clones were measured simultaneously with a dual-isotope porometer. Maximum P_G rates by Russet Burbank in the field were at intermediate levels early in the season, nearly doubled during mid-season, and declined during August. Maximum SC and P_G rates by Russet Burbank in the field occurred about 11h00, although leaf temperature did not reach its maximum unit¹ about 16h00. P_G rates by Russet Burbank in the glasshouse were maximum at about 24–30°C; SC was maximum by about 24°C and remained relatively constant at higher temperatures even though P_G declined. Clone A6948-4 had higher P_G rates in the field than Russet Burbank under all conditions and did not reach maximum levels until 1350 μE. The P_G response by Russet Burbank to varied irradiance in the glasshouse was similar to its response in the field.

---

Zusammenfassung Die stomatale Leitf?higkeit (SC) und die Bruttophotosynthese (P_G) von zwei Kartoffelklonen (Solanum tuberosum L. — Russet Burbank und A6948-4) wurden gleichzeitig mit einem Dual-Isotop-Porometer gemessen. Die maximalen P_G-Raten von Russet Burbank im Feld waren anfangs Saison mittleren Grades, w?hrend der Saisonmitte fast doppelt und im Lauf des Augustes nahmen sie ab (Abb. 1). Die maximalen SC- und P_G-Raten von Russet Burbank im Feld wurden um etwa 11 Uhr vormittags erreicht, obwohl die Blattemperatur ihr Maximum erst ungef?hr um 4 Uhr nachmittags erzielte (Tabelle 1). Die P_G-Raten von Russet Burbank im Glashaus waren bei ca. 24–30°C maximal; das Maximum von SC war ungef?hr bei 24°C und blieb bei h?heren Temperaturen relativ konstant, selbst wenn P_G abnahm (Abb. 2). Offenbar kann die Abnahme von P_G nicht Aenderungen in SC zugeschrieben werden, sondern muss auf eine direkte Temperaturhemmung von P_G zurückgeführt werden. Die P_G-Reaktion von Russet Burbank auf unterschiedliche Einstrahlung im Glashaus war gleich wie ihre Reaktion im Feld. Im Gegensatz zu manchen C₃-Spezies nahm die SC von Russet Burbank mit steigender Einstrahlung von 400 auf 1700 μE m² s¹ zu (Abb. 3). Vergleichende SC-Messungen mit Kartoffeln müssen offenbar bei konstanten und bekannten Lichtstufen vorgenommen werden. Die SC- und P_G-Reaktionen auf die Einstrahlungsstufen (Abb. 3) deuten darauf hin, dass Russet-Burbank-Pflanzen einen überm?ssigen stomatalen Wasserverlust haben und dass SC unter Feldbedingungen vielleicht ohne jede Reduktion in P_G reduziert werden k?nnte. Der Klon A6948-4 hatte h?here P_G-Raten im Feld als Russet Burbank unter allen Bedingungen und erreichte die maximalen Grade nicht bis 1,350 μE (Abb. 4). Diese Vergleiche illustrieren die natürliche Variabilit?t, die in Kartoffelzüchtungsprogrammen vorhanden ist, und best?tigen den Wert des Screenings, um jene auszulesen, die als Elternmaterial für Kreuzungen am nützlichsten sind.

---

Résumé La conductance des stomates (SC) et la photosynthèse brute (P_G) de deux clones de pommes de terre (Solanum tuberosum L. —Russet Burbank et A6948-4) ont été mesurées simultanément en utilisant un poromètre à isotope dual. Les intensités maxima de P_G pour Russet Burbank, au champ, se situaient à des niveaux intermédiaires en début de saison, étaient pratiquement doubles en milieu de saison, puis déclinaient en ao?t (fig. 1). SC et P_G atteignaient leur maxima au champ vers 11 heures du matin, alors que la température des feuilles ne parvenait à son maximum que vers 4 heures de l’après-midi (tableau 1). En serre, pour Russet Burbank, P_G était maximum vers 24–30°C; SC était maximum vers 24°C puis restait constant aux températures supérieures, tandis que P_G diminuait (fig. 2). Apparemment, la diminution de P_G ne pouvait être attribuée à des variations de SC mais devait être d?e à une inhibition directe de P_G par la température. Pour Russet Burbank, la réponse de PG en serre à une variation de l’irradiation était identique à la réponse au champ. Contrastant avec de nombreuses espèces C₃, chez Russet Burbank, SC a augmenté avec l’irradiation de 400 à 1700 μEm² sec¹ (fig. 3). Pour les pommes de terre, les mesures comparatives de SC doivent de toute évidence être effectuées à des niveaux constants et connus d’éclairement. Les réponses de SC et P_G aux différents niveaux d’irradiation (fig. 3). suggèrent que les plantes de Russet Burbank perdraient trop d’eau par les stomates et que l’on pourrait peut être réduire SC dans les conditions du champ sans réduire P_G d’aucune fa?on. Quelles que soient les conditions, le cone A6948-4 avait des niveaux de P_G plus élevés au champ que Russet Burbank et n’atteignait un maximum que pour 1,350 μE (fig. 4). Ces comparaisons illustrent la variabilité naturelle que l’on rencontre dans les programmes d’hybridation des pommes de terre, et qui établit la valeur discriminante pour choisir quels seront les matériels parentaux les plus utiles pour les croisements.

     

Agronomic performance of potato germplasm selected for high resistance to verticillium wilt

A three-year study was conducted from 1991 through 1993 to evaluate the field performance of potato clones that had been selected for resistance to wilt symptom development and stem colonization byVerticillium dahliae. The total yield, size distribution, and specific-gravity of these highly resistant clones were compared with standard cultivars and two parent clones with high Verticillium resistance and high yield, A66107-51 and A68113-4. Two groups of Verticillium resistant germplasm were selected in 1991. One group was the highly resistant progeny from a cross between A66107-51 and A68113-4. The second group consisted of hybrids between wild species accessions with high Verticillium resistance and cultivated diploid and tetraploid germplasm. Twenty-one out of 125 progeny clones from the A66107-51 × A68113-4 cross were highly resistant to Verticillium infection and were tested in yield trials for two years. Another eight selections had high Verticillium resistance but such low yield of seed tubers that they were tested only one year for yield. Eleven of the original 29 highly resistant selections were significantly lower in total yield than Russet Burbank. Only one clone was significantly higher in yield than RB, and none outyielded either of the resistant parents. Reddale and Century Russet had moderate to high Verticillium resistance, respectively. Both outyielded Russet Burbank and were comparable with the high yielding resistant parents. Of 15 interspecific hybrids tested in 1991, only four had sufficient yield to produce seed for yield trials and good wilt resistance after three successive seasons of evaluation. We concluded from this study that selecting at early stages of variety development strictly for Verticillium resistance is likely to be inefficient. Rather, selection should be for yield and other agronomic criteria in Verticillium infested fields.     

Effect of declining or interrupted irrigation on yield and quality of three potato cultivars grown on sandy soil

Many potatoes in the Northwest are grown on sandy soils with sprinkler irrigation. The low water holding capacity and restricted rooting often associated with coarse-textured soils create conditions where water stress injury is likely. Temporary water shortage due to irrigation system failure is a hazard on these soils. The Russet Burbank cultivar is often severely injured by such water stress. It is not known how the cultivars Nooksack and Lemhi respond to these conditions. A study was conducted to compare the responses of Russet Burbank, Nooksack, and Lemhi cultivars to interruptions in irrigation during tuber initiation or during bulking, and to gradually increasing water stress from declining water application rates during the last 8 to 10 weeks of the growing season. In most categories evaluated, Russet Burbank was most injured by water stress, especially in percent U.S. No. 1 tubers. Much of the decrease in U.S. No. 1 tubers was due to small size. Nooksack generally was the least affected by water stress while Lemhi was affected slightly more than Nooksack. Both Nooksack and Lemhi withstood periods of water stress and produced satisfactory yields and grades of tubers while Russet Burbank did not produce profitable levels of marketable tubers.     

Response of russet norkotah clonal selections to nitrogen fertilization

The low vine vigor and high N requirement of Russet Norkotah may lead to N loss and groundwater contamination on coarse-textured soils. Recent clonal selections from Texas have produced strains that have larger and stronger vines, which may alter N requirements. This twoyear study examined the N use efficiency (NUE), yield, and quality of Russet Norkotah strain selections fertilized with different N levels on a Hubbard loamy sand in central Minnesota. The selections, Texas Norkotah Strain (TXNS) 112, TXNS 223, and TXNS 278 were grown with standard Russet Norkotah under irrigated conditions and received total N levels of 28, 112, 224, or 336 kg ha^-1. Total, marketable, and large (>340 g) tuber yields increased linearly (P>0.05) with rate of N application in 1998 but not in 1997. The genotype main effect was not significant for any of the tuber yield parameters measured based on fresh weight. Vine, tuber, and total dry biomass yields were 116%, 5.8%, and 13.2%, respectively, higher with the selections than Russet Norkotah. Harvest index (HI), or the proportion of total dry matter partitioned to tubers, was 7% greater for Russet Norkotah than the TXNS selections, reflecting the larger vine growth of the selections. The selections accumulated significantly higher N in the vines (0.113 kg kg^-1 N) than the standard clone (0.053 kg kg^-1 N) as N rate increased from 28 to 336 kg ha^-1, and the difference between the selections and the standard clone was larger at higher N rates than at lower N rates. Russet Norkotah partitioned 10% more N to tubers than did the TXNS selections, reflecting the difference in HI between the standard cultivar and its clones. Nitrogen recovered from fertilizer N applied in addition to the 28 kg ha^-1 starter N (NUE₂₈) averaged 36% and varied little with genotype, N rate, or cropping year. Biomass accumulation from similar N additions (AUE), however, was significantly higher for the selections than Russet Norkotah at 112 kg N ha^-1 in 1997 only. At low N rate (112 kg ha^-1), the selections had higher physiological use efficiency (PUE₂₈) (mean 45.9 g g¹) than Russet Norkotah (25.9 g g¹). Results from this study demonstrate that, although N recovery was similar for the four genotypes, the Texas Norkotah strains produced greater biomass than Russet Norkotah per kg N applied at low rate in 1997 and per kg of fertilizer N absorbed by the plant in both years. However, under the conditions of this study, higher biomass of the selections did not translate into a marketable yield advantage over the standard cultivar.     

Verticillium wilt resistant potato germplasm: A66107-51 and A68113-4

Potato breeding selections A66107-51 and A68113-4 (Solanum tuberosum gptuberosum) are being released as germplasm that is highly resistant to Verticillium wilt (Verticillium dahliae Kleb.) These selections have been extensively evaluated for resistance to Verticillium as measured by symptom severity and degree of colonization byV. dahliae. They combine outstanding wilt resistance with good tuber maturity characteristics, high yield, and french fry processing tuber type. A66107-51 has long-oblong, russeted tubers, with high yield and variable processing quality. A68113-4 has long-oblong, partially russeted tubers with high yield and good processing quality. Both selections are fertile as female parents, and A66107-51 is occasionally pollen fertile. The Verticillium resistance of these two clones has been transmitted to progeny. These selections were developed by USDA-ARS in cooperation with the Idaho Agricultural Experiment Station. Seed is available from USDA-ARS, Aberdeen, Idaho.     

Tyrosine synthesis in potato tuber tissue from blackspot-susceptible and resistant genotypes

Summary Radioactively-labeled shikimic acid (¹⁴C) was incubated with potato tuber tissue disks to determine the relative rate of tyrosine synthesis in blackspot-resistant and susceptible cultivars. Tyrosine synthesis was 55% higher in the susceptible cultivar, Lemhi Russet, than the resistant clone TXA 763-5. The susceptible clone also partitioned a lower percentage of¹⁴C tyrosine into soluble protein than did the resistant genotype. The percentage of labeled free tyrosine which would be available for oxidation by polyphenyloxidase was therefore much higher in the susceptible cultivar. Hort/LA Paper No. 90-27. Project No. 0766. Washington State University, College of Agriculture and Home Economics Research Center, Pullman, WA 99164     

Reaction of potato clones and accessions ofSolanum spp. toVerticillium dahliae Kleb. and its toxin

Summary The reaction of 40 potato clones and six accessions ofSolanum spp. to wilt caused byVerticillium dahliae and to the acetone precipitate (AP) of the toxin produced by the pathogen in vitro was studied. There was a highly significant correlation between the wilt reaction of the clones in the glasshouse, the incidence and progress of wilt and severe wilt in the field, and the degree of colonization of stem apices byV. dahliae. Of the clones and accessions evaluated, NDA8694-3, Norgold Russet, BelRus, Superior, Russet Norkotah, Norland andS. demissum were the most susceptible, while A66107-51, A68113-4, Targhee, NDA843-3, Alpha, A7805-8, A7816-14, Russet Nugget,S. chacoense, S. sparsipilum, andS. tarijense were the most resistant to wilt. The reaction of genotypes to the AP ofV. dahliae toxin in an excised leaf bioassay was not correlated with their reaction to Verticillium wilt in the field or glasshouse. Idaho Agricultural Experiment Station Article No. 89741.     

Yield and relationships among tuber size,sucrose and chip color in six potato cultivars on various harvest dates

Cultivars were harvested biweekly for yield, weekly for sucrose determinations, and stored for chipping. At the last harvest Crystal was highest in total and marketable yield. Specific gravity was higher in Lemhi, Russet Burbank, and Norchip than in Kennebec, Crystal and Dakchip. Storage tests showed Norchip had superior chipping color to other cultivars. Dakchip had better color after short rather than after long-term storage, while the opposite was true for Kennebec and Russet Burbank. Lemhi and Crystal were marginal in color throughout storage. Sucrose (mg sucrose/g fresh tuber) expressed as a sucrose rating (SR) ranged from 1.2 to 11.9 among the various cultivars and harvest dates. Correlation between SR’s and tuber size within cultivars ranged from ?.91 to ?.97. Variability in sucrose content of immature tubers explained 70% of the variability in chip color among cultivars after storage from four to six months. Sucrose levels may be used to predict relative chipping quality of various cultivars after moderate to long-term storage if measured during early tuber development when differences in sucrose concentration are greatest among cultivars.     

Lesion nematode suppression with the butte potato and relationships to verticillium wilt

Field studies conducted over a 5 yr period to compare the effect of continuous cropping of several potato clones (Butte, Russet Burbank, Targhee, A66107-51, and A68113-4) showed Butte to be highly resistant toPratylenchus neglectus while being highly susceptible toVerticillium dahliae. This was further evidenced during the 6th yr when Russet Burbank was cropped over all plot-locations. Populations ofP. neglectus were shown to be significantly less (0.05 P) in both soil and roots when Russet Burbank was grown over sites previously cropped with the Butte potato than over site-locations cropped by either Russet Burbank, Targhee, A66107–51, or A68113–4. Additional field and greenhouse studies corroborated the high degree of resistance of Butte toPratylenchus spp. In addition toP. neglectus resistance, a greenhouse investigation also showed resistance to P. penetrans. A field study designed to compare the effects of Butte with nematicides showed that Butte reducedP. neglectus populations in both soil and roots when compared with Russet Burbank. This degree of reduction was equivalent to the effects of either of two systemic nematicides (aldicarb and isofenphos) at 3.4 to 4.0 kg a.i./ha, respectively. Results demonstrate biological control with the Butte potato clone forP. neglectus suppression. Although populations ofP. neglectus were reduced by either nematicides or Butte, wilt severity was higher with Butte than Russet Burbank. Results showed wilt suppression andP. neglectus reduction with treatments of either nematicide, while having no significant effect on the colonization of potato stems byV. dahliae.     

The effects of foliar application of cytokinins on potato yields in southeastern Idaho

The “Cytex” product, a commercial seaweed extract containing natural cytokinins, was tested as a foliar spray for seven years, using several potato clones and several rates and dates of application. Throughout seven years, the Russet Burbank cultivar showed no measurable response to the “Cytex” product. Application of kinetin in a single season also produced no response. Throughout five years of testing, the Lemhi Russet showed a substantial yield response in one year, a moderate response in a second year, and a possible small response to 1 of 6 treatments in a third year. The best time for application is during the 2-week period directly following tuber initiation.     

Tuber initiation and development in irrigated and non-irrigated potatoes

Tuber initiation and development are processes basic to potato production and are particularly critical in areas with short growing seasons. It is important to know how and to what extent management decisions affect these processes in order to maximize the yield of marketable tubers. A two-year field study, conducted in southcentral Alaska, examined top growth, tuber initiation, and tuber development in eight potato cultivars grown with and without irrigation. Plants of the cultivars Allagash Russet, Bake-King, Green Mountain, Kennebec, Lemhi Russet, Russet Burbank, Shepody, and Superior were harvested weekly throughout the growing season, and top dry weight, numbers of tubers, and individual tuber fresh weights were recorded. Top dry weight was reduced by moisture stress shortly after emergence in 1993, and about one month following emergence in 1994, when early-season soil moisture was greater. The weight of tubers was similarly affected within approximately 5 wk of emergence in 1993 and 6 weeks in 1994. Tuber weight at harvest was increased two-to three-fold by irrigation in all cultivars. The number of tubers each plant set was affected by irrigation in most, but not all, cultivars. Some varieties (Lemhi Russet in 1994, Allagash Russet both years) set more tubers than were maintained through the growing season. Tuber remnants found during sample collection indicated that tuber reabsorption had occurred. Irrigated Green Mountain had more than one tuber initiation period during the season, whereas other varieties such as Shepody maintained a relatively constant number of tubers following initial tuber set. Tuber size distribution at the end of the growing season showed that larger tubers were favored by irrigation.     

Nitrogen fertilization and irrigation affects tuber characteristics of two potato cultivars

Nitrogen fertilization, irrigation, and cultivars affect tuber characteristics such as tuber size, specific gravity, and N concentration. Few studies, however, have investigated the interaction of irrigation and N fertilization on the tuber characteristics of potato cultivars, particularly in Atlantic Canada. The objective of this on-farm study, conducted at four sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and six rates of N fertilization (0-250 kg N ha^-1) on the number of tubers per plant, the average fresh tuber weight, tuber N concentration, nitrate (NO₃-N) concentration, and specific gravity of the cultivars Shepody and Russet Burbank. Nitrogen fertilization increased the average fresh tuber weight, tuber N and N0₃-N concentrations, and decreased specific gravity. Effects of increasing N fertilization on tuber characteristics were often more pronounced for Shepody than for Russet Burbank, and for irrigated than for non-irrigated conditions. Shepody had greater average fresh tuber weight and tuber N concentration, lower specific gravity, and fewer tubers per plant than Russet Burbank. Supplemental irrigation increased the average fresh tuber weight and the number of tubers per plant, but it had a limited effect on specific gravity and tuber N and NO₃-N concentrations. Tuber NO₃-N con centration and specific gravity were strongly related to tuber N concentration, which in turn depended primarily on N fertilization. Incidents of lowest specific gravity and highest NO₃-N concentration occurred with a relative yield close to or equal to 1.0. We conclude that the risks of low specific gravity and high tuber NO₃-N concentration are greater when fertilization exceeds the N requirements to reach maximum tuber yield.     

Effect of cold storage on proteinase and chorismate mutase activities inSolanum tuberosum L. Genotypes differing in blackspot susceptibility

Potato tubers (Solanum tuberosum) from genotypes differing in chemical susceptibility to the physiological disorder blackspot bruise (TXA 763-5, Atlantic, Ranger Russet, Russet Burbank, and Lemhi Russet) were stored for eight months at 3 C. Protein extracts from each cultivar were assayed for proteinase and chorismate mutase (CM) activities. During cold storage, three of five genotypes tested increased in their ability to develop melanintype pigments responsible for blackspot. Concurrent with this were increases in either endopeptidase, aminopeptidase, or CM activities or combinations of enzyme activities specific to genotypes. These increases in enzyme activity may be responsible for the increase in levels of the melanin precursor tyrosine, associated with cold storage of potato tubers.     

Daminozide applied to the foliage of three potato cultivars increased tuber eye number

The plant growth regulator, daminozide, was applied to the foliage of Ranger Russet, Shepody and Nooksack potato (Solarium tuberosum L.) plants at 0, 0.62, 1.25, 2.5 and 5 g product·liter^?1 to determine its effectiveness in increasing eye number and reducing average tuber weight. Total tuber yields were not affected. Daminozide treatment increased tuber eye number of each cultivar and did not alter the distribution of eyes between the stem and bud ends. After 5 g daminozide·liter^?1 treatment, average eye number of the stem end and bud ends of Nooksack increased up to 1.0 eye, by 27% for Shepody and by 31% for Ranger Russet. The largest increases in eye number occurred in Ranger Russet. However, increasing daminozide concentration caused increased tuber elongation in Ranger Russet. Average tuber weight decreased significantly in response to daminozide treatment only in Shepody. As a seed tuber production aid, daminozide can be used to increase eye number, and in some cultivars, to reduce average tuber weight.     

Differential ozone susceptibility of Centennial Russet and White Rose potato as demonstrated by fumigation and antioxidant treatments

Because quantitative field estimates of potato (Solarium tuberosum L.) yield losses attributable to ozone (O₃) air pollution damage in California need to be assessed, the antioxidant compound N-[-2-(2-oxo-l-imidazolidiny l)ethyl]-N′-phenylurea (EDU or DPX-4891) was evaluated for suitability in estimating these yield losses and in differentiating O₃-susceptible from O₃-resistant cultivars. Differential susceptibility of two cultivars, ‘Centennial Russet’ (O₃sensitive) and ‘White Rose’ (O₃-resistant), to O₃ was confirmed in greenhouse experiments. Five weekly 5-hour treatments with 25 parts per hundred million O₃ reduced tuber yield of Centennial Russet by 32% but did not reduce the yield of White Rose. In the absence of O₃ under greenhouse conditions, EDU had no observable effect on shoot dry weight, tuber number, or tuber yield of either cultivar, suggesting that EDU does not materially affect plant growth in the absence of O₃ at the treatment levels used and under the conditions herein. In field experiments conducted at the University of California at Riverside (UCR) and in commercial fields of Kern County (KC), untreated Centennial Russet and White Rose plants produced total tuber yields of 174 and 512 q/ha, respectively at UCR and 268 and 498 q/ha, respectively, at KC. At UCR, EDU applied at the highest rate—17.8 kg/ha—increased marketable and total tuber yields of Centennial Russet by 208 and 188 q/ha, respectively, and increased specific gravity by 0.013. White Rose was not affected by EDU. Averaged over four KC experiments, EDU application at 8.9 kg/ha increased Centennial Russet marketable and total tuber yields by 40 (from 214) and 45 (from 268) q/ha, respectively, whereas White Rose was not affected and averaged 398 (marketable) and 491 (total) q/ha.     

Summit Russet: A new russet potato variety with good fresh market and frozen processing qualities

Summit Russet (A84118-3), the result of the cross A77236-6 x TND329-1Russ, was released in 2003 by the USDA/ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington. The vines of Summit Russet are erect, with very thick stems, large yellowish-green leaves and abundant white flowers. The tubers are tan, with medium russet skin, long-flattened shape, a slightly prominent eyebrow, white flesh, and moderately prominent pith. Tuber dormancy is very long. Summit Russet was compared with Russet Burbank in trials across the Pacific Northwest for yield, quality, and disease response. In general, Summit Russet produced similar or lower total yields than did Russet Burbank, but higher U.S. No. 1 yields. In Idaho variety trials, Summit Russet exhibited resistance to second growth, growth cracks, blackspot bruise, and stem-end discoloration, and moderate susceptibility to hollow heart and shatter bruise. In comprehensive product quality evaluations, Summit Russet was rated superior to Russet Burbank for french fry quality and similar for baked potato quality. French fry quality was retained after long-term storage. In replicated disease trials, Summit Russet was found to have good resistance to common scab, early blight tuber rot, and Verticillium wilt, and moderate resistance to Fusarium dry rot and tuber net necrosis caused by PLRV. It demonstrated susceptibility to late blight, foliar PLRV, PVX, PVY^o, and bacterial soft rot. Biochemical analysis of Summit Russet tubers showed them to be higher in total solids and sucrose, and lower in dextrose than those of Russet Burbank. Tuber glycoalkaloid concentration as measured from tubers produced in 1994–1996 trials was 6.7 mg 100 g¹.     

Influence of heat stress on dry matter production and photo-assimilate partitioning by four potato clones

Partitioning patterns of¹⁴C labeled assimilates were studied to determine their relationship to dry matter accumulation and distribution in four potato clones (Desiree, DTO-28, LT-1 and Russet Burbank). Plants placed in growth chambers at 35/25 C day/night temperature and 12-hour photo-period two weeks after tuber initiation were compared with plants grown continuously at 25/12 C. Two weeks after temperature treatments were begun, the most recently expanded leaf was labeled with¹⁴CO₂ for 30 minutes, and plants were harvested 20 hours or 15 days later. High temperature reduced total dry matter production and altered dry matter distribution in favor of vines at the expense of tubers. Partitioning of¹⁴C assimilates generally followed the pattern of dry matter distribution. Potato clones exhibited variation in¹⁴C assimilate export from labeled leaves and in partitioning to vines and tubers. Assimilate partitioning to tubers was not consistently higher in clones considered heat tolerant.     

Tuber growth and biomass partitioning of two potato cultivars grown under different n fertilization rates with and without irrigation

Nitrogen and water deficiencies are known to affect potato yield, but much less is known of their effect on tuber growth and biomass partitioning. The objective of this on-farm study conducted at two sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and N fertilization rates on tuber growth and biomass partitioning of the cultivars Shepody and Russet Burbank. The N fertilization rates were 0,100, and 250 kg N ha^-1in 1995, and 0, 50,100, and 250 kg N ha_?1 in 1996 and 1997. The highest bulking rate observed in our study (7.3 g fresh tubers m^-2 °C^-1) can be considered near the potential bulking rate in New Brunswick. The water deficit in the absence of supplemental irrigation reduced this potential bulking rate by as much as 40%, but this reduction was much less at five of six sites and negligible at two of six sites. Nitrogen deficiency reduced the bulking rate at two of six sites. This negative effect of N deficiency on bulking rate was greater with irrigation than without irrigation at two of six sites; the tuber bulking rate with irrigation was reduced by as much as 50% with no N applied at one site. Shepody had a greater bulking rate than Russet Burbank. The tuber bulking of Russet Burbank, however, started earlier and lasted longer than that of Shepody. Water and N deficiencies increased biomass partitioning to tubers and large roots. Shepody partitioned a greater proportion of its biomass to large roots and had a greater root biomass than Russet Burbank. Our results demonstrate the ability of potatoes to modify biomass partitioning when grown under water and/or N stresses. As a result of this compensation, the reduction in tuber yield due to limited N and water stresses is minimized.     

Western russet: A new potato variety with excellent fresh market and frozen-fried processing quality and field resistance to common scab and PVYo

Western Russet, designated experimentally as A7961-1, and resulting from the cross A68113-4 x Bel-Rus, was released in 2004 by the USDA/ARS and the agricultural experiment stations of Idaho, Oregon, and Washington. The foliage of Western Russet is spreading, with medium-sized olive-green leaves and abundant white flowers. The tubers are tan, with medium russet skin, oblong shape, a slightly prominent eyebrow, white flesh, and distinctly visible pith. Western Russet was compared with Russet Burbank in trials across the Pacific Northwest for yield, quality, and disease response. In general, Western Russet produced lower total yields than Russet Burbank, but on average and depending on location, similar U.S. No. 1 yields. When observed for defect problems, Western Russet exhibited resistance to second growth, growth cracks, shatter bruise, stem-end discoloration, and heat necrosis, moderate resistance to hollow heart, and moderate susceptibility to blackspot bruise. In product quality tests, Western Russet was rated similar to Russet Burbank for french fry and dehydrated potato flake quality and slightly inferior for baked potato quality. In replicated evaluations, Western Russet was found to have good field resistance to common scab and PVY^o, and moderate resistance to verticillium wilt and tuber net necrosis caused by PLRV. It demonstrated susceptibility to late blight, foliar PLRV, dry rot, soft rot, and tuber early blight. Biochemical analysis of Western Russet tubers showed markedly higher vitamin C content than those of Russet Burbank. Tuber glycoalkaloid concentration in tubers produced in a 1988 trial was 1.0 mg 100 g^?1.     

Infection of aerial parts of potato plants byColletotrichum coccodes and its effects on premature vine death and yield

Collectotrichum coccodes, the pathogen causing black dot disease of potato, was investigated to determine its potential for causing symptoms on the aerial parts of potato plant, premature vine death, and reduction in yield under greenhouse and field conditions. Spray inoculations with conidial suspensions (10⁶ colony forming units/ml) ofC. coccodes caused sunken, dark, necrotic lesions on stems, leaves and petioles, vein and leaf necrosis, dieback and premature vine death under growth chamber and greenhouse conditions. Field inoculations in 1986 and 1987 provided evidence for an increased incidence of premature vine death in seven potato genotypes (Russet Burbank, Norgold Russet, Superior, Butte, NDA 8694-3, A68113-4 and A66107-51). Late season application of metribuzin at 0.84 kg/ha significantly increased the incidence of stems with black dot symptoms in cv. Russet Burbank at one location. Field inoculations in 1987 at two locations resulted in yield reduction in the late-maturing cv. Russet Burbank (6.3 and 6.5 t/ha) and clone A68113-4 (5.0 t/ha), but not in the early maturing cv. Norgold Russet. Similar results were obtained in greenhouse studies following soil inoculations withC. coccodes: yield reduction was observed in cv. Russet Burbank but not in cvs. Norgold Russet, Superior and Katahdin. Colonization of stem ends of tubers byC. coccodes from spray inoculated field plots was higher than in tubers from uninoculated plots at one of the two locations. These results point to a much broader potential ofC. coccodes as a potato pathogen, than hitherto documented. Colletotrichum coccodes (Wallr.) Hughes (syn.C. atramentarium (Berk. & Br. Taub.) was described in 1825 (21) and has a wide host range (5). Potato and tomato are the more economically important hosts. This fungus has been variously referred to as an unspecialized, minor pathogen or secondary invader (18), weak pathogen (22), specialized parasite (5), or superficial colonizer and widespread epiphyte (19). The symptoms produced by this pathogen on potato have been described as black dot (10, 14) on stems, stolons, tubers and roots, sometimes associated with leaf scorch or wilt (24), rubbery tuber wilt (1), and tuber skin necrosis (17). The fungus is commonly associated with senescent, decaying root and stem tissue, especially at the end of the season. In Idaho, instances of premature death of potato without typical symptoms of Verticillium wilt, but accompanied by a high incidence of stems with black dot symptoms, have been observed in potato crops grown on fields fumigated with metam sodium. Additional observations by growers have also implicated the possible interaction of the herbicide metribuzin with the incidence of black dot. Although it was observed by some workers to accelerate leaf senescence (12, 22), Schmiedeknecht (21) concluded thatC. coccodes was unable to infect the green leaves of potato plant. Even thoughVerticillium dahliae is generally considered the major factor in potato early dying (20), several workers (7, 11, 13, 19, 22) have investigated the possible role ofC. coccodes in causing premature death of potato (8). However, these studies examinedC. coccodes only as a soilborne, root and tuber pathogen of potato; its effects on shoot portions (aerial parts) of the plant were not considered. In addition to causing anthracnose of fruits of tomato, pepper and squash (18), recent reports indicate thatC. coccodes causes foliage blights on eastern black nightshade (2) and velvetleaf (25). The objectives of this study were: (1) to examine the potential ofC. coccodes to cause symptoms on aerial parts of potato plant, (2) to investigate the effect of spray inoculation in the field withC. coccodes on incidence of premature vine death, tuber colonization and yield of potato, and (3) to document the effect of soil inoculation withC. coccodes alone or in combination withV. dahliae on potato varieties under greenhouse conditions.