Pre-sprouting as a Tool for Early Harvest in Organic Potato (Solanum tuberosum L.) Cultivation

Earlier harvest of potatoes (Solanum tuberosum L.) can be achieved by different pretreatments of the seed tubers. In factorial field trials in 2008–2010, two different pre-sprouting methods were evaluated: conventional pre-sprouting of tubers and pre-sprouting of tubers with stimulation of adventitious root formation (PR). The results were compared with those for untreated seed tubers stored at 4 °C until planting (control). One variety was included in three trials, and two varieties were included in one trial. The new PR method was intended to give faster development and tuber initiation than conventional pre-sprouting, which can be of value when the growing season is restricted or when early harvest is important. Plant emergence, leaf necrosis (as a measure of maturity) and incidence of late blight were assessed during the growing season. After harvest, tuber fresh weight, size and density were assessed. It was found that pre-sprouting treatments gave on average 7 days earlier emergence compared with the control. Necrosis began earlier in pre-sprouted treatments in all cases except for the late variety Sarpo Mira. In 2008 and 2009 potato late blight struck late, after onset of senescence, but in 2010 it struck earlier and the pre-sprouted treatments proved more susceptible than the control. Total tuber yield was 7–24% higher on average in all pre-sprouted treatments in the different field trials. Tests on time of harvest showed that the advantage for the pre-sprouting treatments was maintained during the season, but the difference with the control decreased with time. When the different pre-sprouted treatments were compared, the new PR method proved to be not better than conventional pre-sprouting.     

Assessment of Opportunities for Burundian Small-Scale Potato Farmers to Increase Productivity and Income

From 2014 through 2016, on-farm experiments were carried out in three provinces surrounding Bujumbura town in Burundi to improve the low potato (Solanum tuberosum) yields, which currently stand at about 6 t ha^?1. It was hypothesised that in rain-fed conditions, improved varieties, healthier seed tubers, pre-sprouting in light, proper fertilisation and protection from late blight attack would improve yield and quality, such as tuber weight, tuber size and lower brown rot incidence. The treatments in the on-farm trials at five farms in each of three sites (15 replicates) were applied in two seasons, giving 30 replicates in 580 plots. The following treatments were compared with growers’ current practices: introduction of two new varieties, use of early generation seed from a rapid multiplication scheme, earlier harvesting of a seed crop, seed storage in a diffused light store, and research-based timing and dose rate of fertilisers and fungicides. Marginal rates of return on investments were calculated at farm level and current and tested alternative technologies were compared. Costs and benefits of applying such techniques were calculated. An improved variety contributed up to 20% yield increase and healthier seed 80%. Early harvesting reduced yield by 30% and reduced incidence of brown rot in the current season, but increased it (from 21 to 39%) in the following season when tubers were replanted. Diffused light storage, alternating contact and systemic fungicide application, and application of chemical fertilisers resulted in 30, 50 and 60% yield increases, respectively. It was shown that it is possible to double yields and economic returns (marginal rates of return) under the growing conditions in Burundi when growers plant healthy pre-sprouted seed of a new variety and apply chemical fertilisers and fungicides.     

Seed Potato Performance after Storage in Light at Elevated Temperatures

In regions with short growth seasons, it is of great importance to use potato (Solanum tuberosum L.) seed tubers with a high growth vigour and a short growth cycle. Such qualities may be obtained by treatments advancing the physiological age of the seed tubers. In this study, we have exposed tubers from four cultivars to various combinations of temperature and light conditions (green-sprouting) for 3–7 months in controlled climate. Subsequent sprout quality, seed tuber health and performance were studied in laboratory, greenhouse and field trials. Satisfactory short, sturdy and leafy sprouts were produced even after 7 months storage at 15 °C under light exposure. An assay of black scurf (Rhizoctonia solani) on the tuber skin showed that light exposure significantly reduced the occurrence compared with dark-stored tubers, while the average effect of storage temperatures was insignificant. In general, green-sprouting advanced emergence and plant growth by 1–2 weeks, and showed early tuber initiation and growth, compared to untreated material. Yields, 107 days after planting in the field trial, did not deviate significantly from untreated tubers. However, plant development at harvest was in accordance with general responses to physiological ageing of potato seed tubers, i.e. still tall and immature plants from untreated tubers, and short and mature plants from aged tubers. Results demonstrated the possibility of successful long-term storage of potato seed tubers in light at elevated temperatures and a potential for earlier harvests and higher early yields from such treatments.     

Short-Term exposure to low temperature in the fall affects field performance of seed tubers

Field trials were conducted in Alberta and Ontario with Norchip, Norland, Russet Burbank, Sangre and Superior potato cultivars to determine response to short-term exposure of seed tubers to below freezing temperatures in the fall. Exposure of the dormant seed tubers to ?-1 C for up to 48 hours did not affect the yield or growth characteristics of the cultivars. However exposure of seed tubers to ?-5 C temperatures for 6 or 12 hours caused marked (P < 0.05) reductions in marketable yield, marketable tuber number, maturity and vine size. Exposure to ?-5 C for periods longer than 12 hours resulted in severe freezing damage and subsequent decay of most of the tubers.     

Production of potato minitubers by repeated harvesting: Effects of crop husbandry on yield parameters

Summary Minitubers can be produced in large quantities by repeated harvesting of tubers from in vitro propagated plantlets at 4, 7 and 10 weeks after transplanting to the glasshouse at high plant densities. Yield parameters of minitubers can be manipulated by crop husbandry. By supplying nutrients or using a square plant arrangement, minituber yield increased. Effects on numbers of tubers were cultivar-dependent. Changing plant density from 50 to 800 plants per m² or the minimal diameter of harvested tubers from 5 to 12 mm did not significantly affect tuber yield per m². Higher plant densities resulted in more tubers per m² but fewer tubers per plant. Removing smaller tubers greatly increased the number of small tubers, but did not affect yield and number of tubers in larger grades. Crop husbandry techniques affected minituber yield mainly through their effects on leaf area duration, and the number of minitubers through their effects on growth of tubers to a harvestable size.     

Effect of whole seed tuber size and pre-plant storage conditions on yield and tuber size distribution of Russet Burbank

Field experiments were conducted in 1995, 1996, and 1997 at Agriculture and Agri-Food Canada’s Harrington Research Farm to assess the effect of whole seed tuber size and pre-plant seed storage conditions on processing yield (> 51 mm dia.) of potato (Solanum tuberosum L. cv Russet Burbank). Following commercial storage, seed tubers were stored at 4.4 C then subjected to one of three pre-plant treatments: (1) planted directly from storage, (2) held at 10 C for 3 wk before planting, or (3) green-sprouted for 3 wk before planting. Five sizes of whole seed were used (28, 42, 56, 70, and 84 g) with a variable size cut seed treatment added for comparison. Plots were harvested 138,134, and 131 days after planting in 1995, 1996, and 1997, respectively. Cut seed produced a higher yield of tubers > 51 mm diameter in comparison to all whole tuber seed sizes, with the exception of the 28 and 56 g sizes. In terms of total yield, the 28and 42-g whole seed tubers yielded significantly less than all other seed sizes examined. Warming or greensprouting seed tubers prior to planting did not increase tuber yield. The larger whole seed tuber sizes tended to result in greater numbers of stems and tubers per plant. To maximize marketable yield of Russet Burbank planted from whole seed tubers, it is recommended that the seed be between 28 and 42 g in size. Accepted for publication 25 May 2004.     

Influence de la durée de prégermination et de l'époque de plantation sur le rendement et la qualité technologique de la pomme de terre. 1. Effets sur le rendement en tubercules et amidon

Résumé Un essai de prégermination et de plantations différées a été effectué de 1973 à 1977 avec trois variétés de pommes de terre qui présentent une bonne aptitude pour la transformation technologique. La prégermination des plants pendant 6 et 12 semaines permet d'avancer la levée des cultures de 10–12 jours par rapport à l'utilisation de plants non prégermés. Un effet favorable de la prégermination sur le rendement a été particulièrement observé pour la variété tardive Maritta, avec 10–15% d'augmentation. L'effet a été moins marqué pour les variétés Bintje et Saturna. La prégermination a également permis d'augmenter la proportion de grands tubercules. La plantation à fin avril-début mai para?t être légèrement plus favorable au rendement que celle effectuée un mois plus t?t. Ni la prégermination, ni l'époque de plantation n'ont permis d'influencer la teneur en amidon des tubercules.

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Summary Field experiments with chitted seed planted on different dates were carried out from 1973 to 1977 (Fig. 1–3) with cvs. Bintje, Maritta and Saturna whose tubers could be used industrially. Two chitting treatments of 6 and 12 weeks duration were compared with unchitted seed stored at 4°C until planting time. The treated seed were planted on two dates with a one month interval (Table 1). The mean duration of emergence over 5 years of trials was 25–30 days for chitted seed that was planted early. Non-chitted seed stored at low temperature emerged after 37–39 days. The equivalent emergence periods for seed planted late, in early May, were 15–16 days and 25–27 days respectively (Fig. 4). Yield increases of 12–15% were obtained with chitted seed of the mid-late cv. Maritta but no significant differences in yield were found with Bintje and Saturna. Chitting also favoured an increase in the proportion of large tubers (Fig. 5). Yield was slightly higher in crops planted late than in those planted a month earlier (Fig. 5). Tuber starch content was affected neither by chitting nor by planting time (Fig. 6). In these studies, yield was more affected by growth conditions than by seed preparation.

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Zusammenfassung W?hrend den Jahren 1973–1977 (Abb. 1–3) wurde an der Station fédérale de recherches agronomiques de Changins/Nyon ein Vorkeim- und Pflanzzeitversuch mit den Kartoffelsorten Bintje, Maritta und Saturna, welche für die technologische Verarbeitung bestimmt waren, durchgeführt. Drei Lagerungsverfahren des Saatguts wurden geprüft, wobei 12 und 6 Wochen vorgekeimtes mit nicht vorgekeimtem, kühlgelagertem (4°C) Saatgut verglichen wurde. Das Saatgut der drei Verfahren wurde an zwei Terminen ausgepflanzt (Tab. 1). Im Durchschnitt der 5 Jahre ben?tigte bei der frühen Pflanzung anfangs April das vorgekeimte Saatgut 25–30 Tage zum Auflaufen, das kühlgelagerte, nicht vorgekeimte hingegen 37–39 Tage. Bei der sp?ten Pflanzung anfangs Mai waren es nur noch 15–16 und 25–27 Tage für gleich behandeltes Saatgut (Abb. 4). Die Vorkeimung erlaubte eine Ertragssteigerung von 12–15% bei der mittelsp?ten Sorte Maritta, hingegen waren die Ertragsunterschiede bei Bintje und Saturna nicht signifikant (Abb. 5). Der Anteil an grossen Knollen wurde durch die Vorkeimung ebenfalls gesteigert (Abb. 5). Die sp?te Pflanzung führte zu einer leichten Ertragserh?hung gegenüber der frühen. Der St?rkegehalt der Knollen wurde weder durch die Vorkeimung noch durch den Pflanztermin beeinflusst (Abb. 6). In diesem Versuch übte die Witterung einen gr?sseren Einfluss auf den Ertrag aus als die geprüften anbautechnischen Massnahmen.

     

Field production of potatoes from true seed and its use in a breeding programme

Summary Potato crops, grown from true potato seed (TPS) sown directly into fields, required a long growing season and the yield, tuber size and quality were inferior to tuber-propagated crops. Some plants produced excellent yields of high-quality tubers and some lines had earliness, high yield capacity, uniform tuber type and high solids. Field sowing of TPS has good potential, both as a breeding tool and for potato production in long-season, underdeveloped countries where healthy seed tubers are not readily available. Correlation analyses showed positive relationships between seedling vigour, mature plant size, and number and yield of tubers but these growth parameters were not significantly related to tuber size and they had a strong negative relationship to density (specific gravity). Mention of a trade name of a company is for specific information only and does not constitute a guarantee or warranty of a product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Effect of short- and long-term exposure of seed tubers to low temperatures on the growth and yield of five potato cultivars

Trials were conducted in Alberta with Norchip, Norland, and Russet Burbank and in Ontario with Kennebec, Russet Burbank, Norchip, and Superior tubers to determine their response to short-term exposure to air temperatures of 0, ?1, and ?5 C and to long-term exposure to ?1, 0, 1,2, and 3 C. Exposure of seed tubers to ?1 C from 6 hours to 5 days did not affect growth characteristics or tuber yield of any of the five cultivars studied. Long-term (October–May) exposure to ?1 C in one study severely reduced emergence and tuber yield of Norchip (P<0.05). While the marketable yield of Russet Burbank was also reduced (P<0.05) by this treatment, Norland was not affected. Tubers of all cultivars exposed to air temperatures of ?3 or ?5 C for longer than 24 hours were severely injured and were not planted in the field trials at either location. In Alberta exposure of seed tubers of Norchip, Norland, and Russet Burbank to ?5 C for 6 and 12 hours caused a reduction (not significant) in yield. In Ontario, long-term storage at 1, 2, and 3 C and in combination with short-term (2 weeks) exposure to 0 or 10 C had no effect on growth or marketable yield of Norchip, Russet Burbank, Superior, and Kennebec seed tubers.     

Contribution a l'etude de la tuberisation chez la pomme de terre

Resume L'étude de la tubérisation exposée ci-dessus résulte de deux années d'expérimentation sur 8 variétés de l'Assortiment officiel suisse, examinées en procédant à 5 arrachages successifs de 30 plantes chacun. Au moment de ces arrachages, effectués plante par plante, nous dénombrons les tiges principales et axillaires, les tubercules ébauchés et formés; nous déterminons aussi le rendement en tubercules et la répartition de ceux-ci en 3 catégories de calibre. Les résultats confrontés avec les observations sur la prégermination et les conditions de culture, différentes d'une année à l'autre, révèlent l'existence d'une relation entre le stade de germination atteint à la plantation (en particulier la différenciation sur les germes des futurs organes de la plante), la structure de l'appareil végétatif, le nombre de tubercules formés et la répartition de ceux-ci d'après le calibre. Cette répartition dépend en outre de la précocité de formation et de croissance des tubercules qui varie selon le mode de préparation des plants et les conditions de culture. L'étude de ces relations a une portée pratique pour les différents types de production de pommes de terre (primeurs, plants, consommation, tout-venant), compte tenu des caractéristiques variétales également importantes.

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Summary During 1956 and 1957, studies were made of the development of plants and tubers of 8 varieties growing in a split plot layout in the Cery Lausanne Experimental Farm. Before planting, the percentage of sprouted eyes was determined and, on 5 dates during the growing period (Table 1), the stage of development (number of main and side-shoots, newly formed and developing tubers) and yield (in 3 size grades) was recorded for each of 30 plants of each variety. Comparison of the results with observations made on sprout development and weather conditions in the spring of both 1956 and 1957 showed that, in addition to the influence of the weather, the method of pre-sprouting had a marked effect on the subsequent growth of the plants, the number of tubers formed and the rate of increase of yield. Varieties differed little in the total number of eyes per tuber but the number of sprouted eyes and the number of main shoots per plant were typical of the variety and bore no relation to its time of maturation (Table 2). In 1956, after a 5 weeks pre-sprouting period, there was a decrease in the number of main shoots and tubers per plant in all varieties but an increase in the number of side-shoots. The favourable weather conditions during and after emergence favoured the growth of plants and tubers with the result that, by the last harvesting date, most tubers measured >50 (55) mm. A 19 day pre-sprouting period in 1957 promoted sprouting of side-eyes. The resultant plants had many main shoots, few side-shoots and bore a large number of tubers. The dry, cold spring retarded growth, with the result that the greater part of the tubers harvested measured 35–50 (55) mm. Fig. I shows the average daily increment in yield which, about 30–50 days after the first tubers are formed, may be in excess of 800 kg day hectare in the case of early and medium varieties. The daily increment in yield of late varieties is generally lower but it is uniform and continues until the tubers are mature. For practical purposes the investigation has shown that there are 3 production types, represented inFig. 4 bySirtema, Bintje andAckersegen. Thefirst is definitely an early potato with comparatively few, large tubers and a high daily increment in yield. When it is desired to produce large numbers of seed tubers the pre-sprouting period should be short.Bintje is a variety of interest to seed producers; it has a high daily increment in yield and tends to produce a large number of tubers per plant. A pre-sprouting period of 3–4 weeks results in an early and high yield of seed sized tubers.Ackersegen also produces a large number of tubers per plant but these develop late. With this variety it is often difficult to obtain a satisfactory yield of seed tubers early and growers often cannot decide whether to lift the crop early or not, particularly in low lying districts where the crop should be lifted comparatively early.

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Zusammenfassung W?hrend den Jahren 1956 und 1957 wurden an 8 Kartoffelsorten, welche im Versuchsfeld Cery Lausanne im Split-plot-Verfahren ausgepflanzt waren, genaue Erhebungen über den Verlauf der Stauden- und Knollenentwick lung durchgeführt. Vor dem Auslegen der Knollen wurden der Prozentsatz an gekeimte Augen ermittelt und w?hrend der Vegetationsperiode zu 5 verschiedenen Daten (siehetabelle 1) der Entwicklungszustand (Anzahl der Haupt- und Nebentriebe, der wachsenden und in Bildung begriffenen Knollen) sowie der Ertrag und dessen Verteilung in drei verschiedene Sortierungsgr?ssen, von je 30 Pflanzen pro Sorte durch Einzeluntersuchung jeder Pflanze festgestellt. Vergleicht man die Versuchsergebnisse mit den Beobachtungen über die Keimentwicklung und den Witterungsbedingungen der Frühjahre 1956 und 1957, so zeigt sich nebst letztern deutlich der Einfluss der Art des Vorkeimens auf den Bau der Pflanzen, die Anzahl der gebildeten Knollen und den Ertragszuwachs. In Bezug der Augenzahl bestehen nur geringfügige Unterschiede zwischen den Sorten; hingegen ist die Zahl der ausgekeimten Augen und der gebildeten Haupttriebe pro Pflanze eine Sorteneigenschaft, welche in keinem Zusammenhang mit der Reifezeit der Sorte steht (tabelle 2). Im Jahre 1956 führte die 5 Wochen dauernde Vorkeimung bei allen Sorten zu einer Abnahme der Zahl der Haupttriebe und der Knollen, highegen zu einer Zunahme die Nebentriebe. Die günstige Witterung w?hrend und nach dem Auflaufen der Pflanzen waren der Entwicklung der Pflanzen und dem Knollenwachstum f?rderlich, weshalb aus all diesen Gründen anl?sslich der Schlussernte der Hauptanteil der Knollen in die Gr?ssensortierung >50 (55) mm fiel. Die im Jahre 1957 19 Tage dauernde Vorkeimung war dem Austreiben der seitlichen Augen f?rderlich. Es entstanden Pflanzen mit vielen Haupttrieben und wenig Nebentrieben, welche aber eine grosse Anzahl Knollen trugen. Das trockene kalte Frühjahr verz?gerte das Auflaufen und das Knollenwachstum, sodass der Hauptanteil der Ernte in die Sortierungsgr?sse 35–50 (55) mm anfiel. Abb. I illustriert den durchschnittlichen t?glichen Gewichtszuwachs an Knollen, welcher bei den frühen und mittelfrühen Sorten ca. 30–50 Tage nach dem Auflaufen, Ausmasse von 800kg und mehr pro Tag und Hektare einnehmen kann. Bei den sp?ten Sorten ist die t?gliche Gewichtszunahme im allgemeinen kleiner, hingegen ziemlich gleichm?ssig und andauernd bis zur Reife. Als praktische Schlussfolgerung sch?len sich aus diesen Sortenuntersuchungen drei Produktionstypen heraus, welche in derAbb. 4 durch Sirtema, Bintje und Ackersegen dargestellt sind. Erstere ist eine ausgesprochene Frühkartoffel, mit verh?ltnism?ssig wenig, aber grossanfallenden Knollen, mit hoher t?glicher Gewichtszunahme. Will man viel Saatknollen erzeugen, so ist das Pflanzgut nur kurze Zeit vorzukeimen. Bintje vertritt den für den Saatgutproduzenten interessanten Typ mit hoher t?glicher Gewichtszunahme und einer angemessenen Knollenzhl. Durch eine 3–4 Wochen dauernde Vorkeimung kann anl?sslich der Frühernte ein relativ hoher Ertrag mit Hauptanteil an Saatknollen erzielt werden. Bei Ackersegen, welche viele, aber sich sp?t entwickelnde Knollen bildet, ist es vielfach schwierig einen befriedigenden Anteil an Saatgut schon anl?sslich der Frühernte zu erreichen, weshalb vielfach die Saatgutproduzenten sich nicht entschliessen k?nnen die Frührodung durchzuführen, insbesonders in tiefern Lagen wo der Früherntetermin verh?ltnism?ssig früh angesetzt werden muss.

     

Effects of soil applications of gibberellic acid on the yield and quality of tubers ofSolanum tuberosum L. cv. Bintje

Summary In two outdoor pot experiments with potato (cv. Bintje) gibberellic acid (GA) was applied to the soil on different dates at 25 (Exp. 1) or 12.5 (Exp. 2) mg/pot. Dry-matter yields were reduced by early treatments in Exp. 1. In both experiments fresh yields were increased by an application about 40 days or later after planting (DAP). GA increased the number of tubers, especially when applied 38 or 40 DAP, treatments which also induced the largest shift in size distribution towards the smaller grades. GA reduced the dry-matter content of the tubers, especially when applied 60 (Exp. 1) or 48 (Exp. 2) DAP. Because the development over time of sensitivity to GA was not similar for all yield and quality variables, GA can be used to alter tuber-size distribution without greatly affecting other quality characteristies or yield.     

Impact of Seed Cutting and Seed-Borne Inoculum on Daughter Tuber Common Scab and Plant Growth

Common scab (CS), caused primarily by the filamentous, soilborne bacterium Streptomyces scabies, creates significant challenges in the production of quality potato tubers in global growing regions. Over the past several decades, numerous studies been conducted to improve our understanding of the impact of cultural and pesticide treatments for managing the health of progeny daughter tubers. None of the previous studies, however, have addressed differences between the impacts of CS from whole seed vs. cut seed pieces on resulting disease on daughter tubers. A greenhouse trial was conducted during 2013–2014 to assess the impact of seed type and CS severity on plant health and CS on daughter tubers. Cut and suberized ‘Snowden’ seed pieces (~2 oz.) exhibiting 0, 5, and ≥50% CS severity were sown in 3-gal pots containing a 50:50 mix of sterilized sand and field soil. Whole ‘Snowden’ seed tubers (~2 oz.) with the same three levels of CS severity were sown under the same conditions. At harvest, approximately 20% of daughter tubers from asymptomatic seed pieces (both cut and whole) exhibited symptoms of CS. Disease incidence and severity significantly increased for pieces that had 5 and ≥50% CS across both experiments. Plants grown from whole seed had significantly higher yield, on average, when compared to cut seed. Daughter tubers produced from whole seed resulted in higher CS incidence than those from cut seed in one of our two experimental trials. Our results indicated a clear advantage to plant common scab-free seed potatoes with the aim of producing healthier daughter tubers.     

Advancing growth vigor of seed potatoes by a haulm application of gibberellic acid and storage temperature regimes

Seed tubers that are planted soon after their harvest give low yields because of dormancy and low growth vigor. In the research reported in this paper, we investigated the advancing effect of a haulm application of gibberellic acid (750 g GA/ha) 6 days before haulm pulling and its interaction with storage temperature regimes on the growth vigor of immaturely harvested seed tubers of three cultivars. The effects on tuber yield were also examined in one experiment. The storage regimes were: 18 C continuously, hot pre-treatments of different duration (different periods at 28 C and subsequently 18 C) and a cold pre-treatment (20 days at 2 C and subsequently 18 C). Both a foliar spray with GA and storage at 28 C enhanced physiological aging of the tubers and greatly advanced the growth vigor, without negative effects on the morphology of the plants. There was a clear interaction between the GA treatment and the storage temperature regime. At early planting, the effect of the treatments on tuber yield were small for Diamant (short dormancy), but strongly positive for Désirée and Draga (long dormancy).     

Effects of substituted nitroguanidine seed treatments on the potato variety Superior

In earlier reports, foliar applications of AC 243,654, a substituted benzyl nitroguanidine with cytokinin-like activity, increased yields of larger tubers and altered plant morphology of potatoes (Solanum tuberosum L.) in greenhouse tests. AC 243,654 was applied as seed tuber treatments to the potato variety Superior. Applications were 0.2 to 10% active ingredient (ai) dusts and 0.04 to 5% ai dips. All seed treatments increased the number of sprouts per tuber. The higher concentrations of seed treatments decreased stem height, and increased stem/branch number, plant dry weight and the number of tubers. Dust and dip treatments of 0.2 and 1% increased the yield (11 to 33%) of tubers < 38 mm in greenhouse tests. Higher rates decreased yields. In field trials, dust applications of AC 243,654 and its analog AC 89,470, the unsubstituted benzyl nitroguanidine, at 0.1 and 0.4% ai increased total and US #1 (< 47 mm diameter) yields between 10 and 18%; and 8 to 18%, respectively. The high rate of 10% ai of either compound decreased yield. AC 239,604, a substituted phenyl nitroguanidine, as a 0.1 % ai dust increased yields 21% while higher rates decreased them. Based on combined greenhouse and field data, AC 243,654 dust applications > 2% ai increased yields while greater application rates decreased yields.     

A method to assess cultivar differences in rate of physiological ageing of seed tubers

Inter-cultivar differences in rate of physiological ageing of potato tubers were assessed in a laboratory test and field tests. The physiological status of the seed tubers was varied by storing them at 4°C and a range of higher temperatures for 28 weeks (= excluding curing and pre-sprouting periods), after which tubers were desprouted. In a laboratory test, growth vigor was assessed by determining number and weight of sprouts after 28 days of incubation. In a field test, percentage emergence, total plant height, haulm and tuber weights were determined and a stand score was allocated 4 weeks after emergence of the 4°C storage treatment. Ageing indices were calculated by dividing the values for the warm-stored treatments by values for the tubers stored at 4°C. Using the tests the cultivars were scored from 0–10 and ranked accordingly. The indices were more evenly distributed over the range of 0–10 in the field test than in the laboratory test. Fresh haulm yield proved very suitable for calculating ageing indices but it could be replaced by a visual score of the haulm development without a great loss in accuracy     

Tillage and seed-sprouting strategies to improve potato yield and quality in short season climates

Management practices that accelerate crop development and allow earlier harvest would be beneficial in short-season potato (Solanum tuberosum L.) production areas. Yield and quality of the potato cultivar ‘Russet Burbank’ were evaluated in a 2-yr study in northern Maine to determine effects of soil tillage and seedsprouting treatments designed to dry soil early in the spring and hasten seed emergence. The tillage treatments, consisting of fall raised bed (RB), fall ridge till (RT), and spring chisel plow (CH), were tested in combination with green-sprouted and non-sprouted seed tubers on a Caribou gravelly loam (coarse-loamy, mixed, frigid,Typic Haplorthod). Plants from green-sprouted seed emerged earlier than from non-sprouted seed tubers (87%-96% vs 21%-37%, respectively, at 18 days after planting [DAP] in 2000; and 73%-88% vs 18%-23%, respectively, at 20 DAP in 2001). Green-sprouted seed tubers in RB yielded 4.6 to 5.9 T ha^-1 more than nonsprouted seed tubers in RB. However, non-sprouted seed tubers yielded higher than green-sprouted seed tubers in RT by 2.9 to 4.2 T ha^-1 and in CH by 1.1 to 4.1 T ha^-1. Similarly, green-sprouted seed tubers in RB and nonsprouted seed tubers in RT and CH produced higher marketable yield, greater tuber length, and greater tuber diameter than the corresponding seed-sprouting treatment. In the comparatively wetter year (2000), the use of green-sprouted seed tubers in RB significantly increased total and marketable yields, and produced longer and larger tubers than all other treatments. However, in 2001 (relatively dry year), yield and quality from green-sprouted seed tubers in RB did not differ from non-sprouted seed in RT or CH. Green-sprouted seed produced fewer sunburned and rotten tubers, but more misshapen tubers than non-sprouted seed in RB tillage. The technique of producing Russet Burbank potatoes in raised beds is a promising system in regions with short growing seasons for enhancing early soil drainage during spring and improving soil water retention during critical periods of crop growth and development.     

Effect of pre-planting temperature and light treatments of seed tubers on potato yield and tuber size distribution

Summary From 1985 to 1987 field experiments were caried out to test the influence of different pre-planting storage treatments on yield and size distribution of potato crops. The storage treatments included 4, 8 and 12°C in the light and in the dark, for different periods before planting. Subjecting the seed tubers to light at low temperatures induced crops to produce a larger proportion of smaller sized tubers while storing seed tubers at higher temperatures in the dark led to an increase of tubers >55 mm. These observations were confirmed in five field experiments with two cultivars at two sites and in three growing seasons.     

Comparative effects of cut and treated seed tubers vs untreated whole seed tubers on seed decay, Rhizoctonia stem canker, growth, and yield of Russet Burbank Potatoes

Whole seed tubers have been reported to have performance advantages over seed tubers that have been cut, even if the cut tuber pieces are treated with a fungicide dust. For this study, whole seed tubers were compared to cut seedpieces and to cut seedpieces treated with four different commercial fungicide dusts for five consecutive seasons. A new field generation 3 Russet Burbank seed lot was used for each of the five years of this study. Both whole tubers and cut seedpieces were inoculated withFusarium spp., and the seedpieces were then treated with a fungicide dust. Inoculated and uninoculated untreated controls were also included. Emergence,Fusarium seed decay,Rhizoctonia stem canker, stem numbers, and vigor, as well as yield and grade data were obtained.Rhizoctonia stem canker in stems grown from whole seed tubers was significantly higher than in stems from seedpieces receiving fungicide treatment in several of the study years. Predicting whole seed tuber performance is difficult because performance varies more from year to year than performance of cut and treated seedpieces. Yield performance of whole seed tubers was not significantly better than cut and fungicide-treated seedpieces in any experimental year, and yield of large (over 280 g) tubers was significantly less than that recorded for two of the treatments when data from all five years were combined. This study demonstrated that untreated whole seed did not outperform cut and treated seedpieces for vigor, stem numbers, disease ratings, or yield in small plot comparisons for five consecutive seasons.     

Field performance of potato microtubers as propagation material

Summary In five field trials with the cultivars Gloria (early), Bintje (mid-early) Désirée (mid-late) and Morene (late), crops grown from conventional 28–35 or 35–45 mm seed were compared with crops grown from microtubers, of various sizes and from various sources, that had been producedin vitro. The following means to quicken initial crop development from the micropropagated material were tested: large microtubers, plastic soil cover, and transplanting of plantlets grown from microtubers pre-planted in a glasshouse. Crops grown from microtubers weighing less than half a gram yielded much less than crops grown from conventional seed crops but their yields were increased by each treatment. With the later-maturing cultivars, which generally produce few tubers per plant, the yields within seed grades from plants grown from transplanted microtuber plants were comparable with those of conventional crops. Reasons are given, why direct planting of microtubers, with or without plastic foil, is not a practical option.     

Influencing seed tuber yield of Ranger Russet and Shepody potatoes with gibberellic acid

Freshly-cut seed pieces of the potato cultivars Ranger Russet and Shepody were dipped in 0, 0.5, 1 or 2 mg/1 Gibberellic Acid (GA₃) prior to planting. GA₃ treatments increased stem and tuber numbers per hill of both cultivars and shifted tuber size profile toward the production of more seed-sized (up to 226 g) tubers and fewer large (greater than 340 g) tubers. The effect of GA₃ on reducing average tuber size was similar for the two cultivars. Total tuber yields were not affected. A 2 mg GA₃/1 seed piece dip decreased the yield of US#1 tubers in Ranger Russet primarily due to a significant increase in yield of tubers less than 226 g. Also, yields of culls were greater after a 1 mg GA₃/1 seed piece treatment, suggesting Ranger Russet is sensitive to this concentration of GA₃. One and 2 mg GA₃/1 seed piece dips to Shepody increased yields of tubers less than 113 g by 93% and reduced the yield of tubers greater than 340 g by 25% to 50%. GA₃ at 1 to 2 mg/1 may be useful in the production of seed potatoes with the cultivar Shepody which tends to produce many large tubers.