Effect of cultivar maturity period on the growth and yield of potato plants grown from microtubers and conventional seed tubers

Potato plants of early cultivars grown from microtubers have been reported to have a much lower growth vigor and produce lower yields than microtubers of late cultivars. This study intended to clarify the field performance of plants grown from directly planted microtubers of cultivars with different maturity periods, with a special attention to early cultivars. The experiments were conducted at Hokkaido University, Japan, over four years. Microtubers and conventional seed tubers of the early cultivar Kitaakari, late cultivars Konafubuki and Norin 1, and very late breeding line IWA-1 were planted, and the plant growth and tuber yields were analyzed. The microtuber plants of Kitaakari had a lower initial increase in leaf area index than conventional seed tuber plants, but at the maximum shoot growth had the same leaf area index. This pattern was also observed in the other cultivars. Tuber initiation and tuber bulking occurred on average five days later in microtuber plants than in conventional seed tuber plants of cultivar Kitaakari. At maximum shoot growth, microtuber plants had on average 65% of tuber dry weight of conventional seed tuber plants, with small variation among cultivars. Irrespective of maturity period, microtuber plants showed a higher tuber increase after maximum shoot growth, achieving around 86% of tuber dry weight of conventional seed tuber plants at harvest. From the results of this study we conclude that microtuber plants of early and late cultivars have a similar yield potential relative to conventional seed tuber plants, and microtubers of both early and late cultivars might be used as an alternative seed tuber source for potato production, if necessary.     

Impact of Agronomic Strategies (Seed Tuber Pre-sprouting,Cultivar Choice) to Control Late Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) on Tuber Growth and Yield in Organic Potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Crops

In order to optimize potato crop management in organic farming systems, knowledge of crop growth processes in relation to limitations and reductions by nitrogen (N) and disease is necessary. This paper examines the effect of different prevention measures (seed tuber pre-sprouting, choice of cultivars: resistance to Phytophthora infestans; earliness of tuber initiation) against disease-related constraints on yields, depending on the N-mediated growing conditions of organic potato crops. Under conditions of a relatively high N supply, accelerating the early development and tuber initiation of potato crops by seed tuber pre-sprouting (yield increase of c. 18–23%) or the selective choice of cultivars with an earlier tuber initiation (yield increase of c. 0–21%) are the most effective strategies in combating late blight. They bring forward the crop development c. 7–10 days, escaping the negative impact of the fungus on tuber growth. Under conditions of a relatively low N supply, these strategies do not affect final tuber yield. The reason for the differences of the effect depending on N supply of the crops is, that the lower the N supply, the shorter the period of time over which tuber growth takes place, independent of whether P. infestans becomes severe or not. Tuber growth of organic crops low in N has mostly ceased by the time late blight becomes potentially important for limiting yield, with the consequence that preventative measures against P. infestans are meaningless. Surprisingly, the level of cultivar haulm resistance to late blight did not affect tuber yields in years with an early and strong late blight development. Probably, the positive effect of a longer resistance to the fungus (c. 1 week) was counterbalanced by a later tuber initiation (also c. 1 week). In years with a moderate late blight incidence, less susceptible cultivars were able to produce higher tuber yields on fields with a lower N availability (c. 17–20%), probably due to higher N use efficiency and a better match of N mineralization and N uptake. Under conditions of a relatively high N supply, the tested cultivars with a higher haulm resistance to late blight were not able to improve tuber yields.     

Soil water stress and the growth and yield of potato plants grown from microtubers and conventional seed tubers

Tuber yields of potato plants grown from microtubers in fields are more variable than yields from conventional seed tubers (CT). One reason could be their higher susceptibility to water stress. This study clarified the effect of soil water stress from 1 month after emergence on the growth and yield of plants grown from conventional seed tubers and microtubers in fields. Microtubers (0.5–3 g) and conventional seed tubers (50 g) were grown in Hokkaido, Japan, over three field seasons. One month after emergence, poly-shelters were placed over the plots to prevent rainfall, and either irrigated (wet plot) or non-irrigated (dry plot) treatments were formed. At mid-flowering (about 50 days after emergence) leaf area index (LAI) in microtuber plants was decreased relatively more due to soil water stress than LAI in conventional seed tuber plants. However, at maximum shoot growth (about 80 days after emergence) both microtuber and conventional seed tuber plants had a similar relative decrease in LAI due to soil water stress. At mid-flowering and maximum shoot growth microtuber and conventional seed tuber plants had reduced stomatal conductance due to soil water stress, but the reduction in stomatal conductance was greater in conventional seed tuber plants than in microtuber plants. Microtuber and conventional seed tuber plants had similar root development at maximum shoot growth. Tuber production from mid-flowering until plant maturity was similarly affected by soil water stress in microtuber and conventional seed tuber plants. At harvest, plants affected by soil water stress had about 87% of the tuber dry weight of irrigated plants. We conclude, that the greater variation on tuber yield of microtuber plants cannot be attributed to soil water stress from 1 month after emergence.     

Growth and yield of potato plants grown from microtubers in fields

Despite many reports of thein vitro production of microtubers, little is known about plant growth and yield from microtubers planted in the field. This study clarified differences in growth and yields between potato plants grown in the field from microtubers and from conventional seed tubers. The experiments were performed at Hokkaido University, Japan, over four years. Conventional seed tubers of about 50 g and microtubers of two sizes (0.5–1.0 g and 1.0–3.0 g) of the latematurity cultivar Norin 1 were planted, and plant growth and tuber yields were analyzed. The microtuber plants had a lower initial increase in root and leaf area index than conventional seed tuber plants, but had the same leaf area index after about 40 days from emergence. The first tuber formation in microtuber plants was about 7 days later than in conventional seed tuber plants, while tuber bulking occurred about 14 days later in microtuber plants. Consequently, the onset of tuber weight increase was later in microtuber plants, but the rate of increase thereafter was similar between conventional seed tuber and microtuber plants. At harvest the tuber fresh weight of microtuber plants was 82% that of conventional tuber plants, suggesting a potential for using microtubers for field planting.     

The potential for production of high quality seed potatoes in Tierra del Fuego Island, Argentina

Summary In Argentina, different areas are suitable for seed potato production: however, each has particular problems, mainly related to different pest and diseases. Tierra del Fuego Island is well isolated from traditional potato growing areas. Therefore, it was tested for its potential for seed production. The cultivars Achatt. Mailén INTA. Pampeana INTA and Spunta were grown in Río Grande, San Pablo and Ushuaia from 1991–1994. Nematode presence and aphid population dynamics were recorded. Average tuber yield ranged from 20.1–37.6 t ha⁻¹. After three years PVY and PLRV remained low (0–1% for different cultivars and locations). Moreover, seed tubers obtained were physiologically young. Long days, early frosts and strong winds may limit tuber yield in some years. The island can be considered as an ecological “safe haven” and is very suitable to obtain healthy and physiologically adequate seed potatoes.     

Microtuber and minituber production and field performance compared with normal tubers

Summary Microtuber and minitubers of cv. Monalisa were produced in the laboratory and compared with normal seed tubers in a field experiment. These tubers were planted at similar plant densities (13.6 sprouts per m²) with two distances between rows (60 and 90 cm). Final ground cover was almost complete only in the plots derived from normal tubers and decreased with the size of the mother tubers. Normal seed, mini- and microtubers yielded respectively 50.8, 31.7, and 17.0 t/ha (means of two spacings). At close and wide spacing between rows, microtubers yielded respectively 27.3 and 6.7 t/ha, and minitubers 38.9 to 24.4 t/ha. Row spacing did not influence the yields from normal seed tubers. Total number of tubers per m² was also affected and, as means of the two spacings, ranged from 107.8 with microtubers, 122.1 with minitubers, to 142.9 with normal tubers. Mother tuber type also affected the yield distribution in three tuber grades (<36, 36–55, and 55–80 mm) and micro and minitubers produced many small tubers. Multiplication rates and the possible use of different propagation sources are discussed.     

Etablierung von Kartoffelsorten im Feld nach physiologischer Alterung der Pflanzknollen

Zusammenfassung Die physiologische Alterung der Pflanzknollen durch Lagerung bei überoptimalen Temperaturen (jahresunterschiedlich 16–29,5°C, 1988–90 vor dem Pflanzen abgekeimt, 1991 vorgekeimt wie Kontrolle) führte im Vergleich zur vorgekeimten Kontrolle im Mittel von 25 Sorten in allen Versuchsjahren zu einer Verminderung der Bestandesdichte und des Ertrages. Eine Gruppe von Sorten erwies sich in allen Jahren als relativ tolerant gegen die Alterung, eine andere als signifikant empfindlicher, dazwischen lag ein breites Mittelfeld mit zum Teil erheblichen Schwankungen in den Jahren. Die Reaktion der Sorten zeigte keine Beziehung zu ihrer Reifegruppe und ihrer Keimintensit?t, dagegen war die sortentypische Ertragsdepression nicht sehr eng, aber signifikant mit dem Schwund w?hrend der Lagerung korreliert.

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Summary Seed tubers were stored at above optimal temperatures. Mean temperatures varied during test years from 16 to 29.5°C (in 1988–1990 tubers desprouted before planting; in 1991 chitted tubers as in control; Table 1). This procedure of physiological ageing of seed tubers resulted in reduced plant density and lower yield compared to the chitted control in every year of the test period (average of 25 cultivars). The emergence was significantly delayed as compared to the control in all years (Table 2). Assessed for yield, the cultivars Désirée, Sanetta, Astilla and Andra showed a significantly higher degree of tolerance to warm storages (>80%, when compared to the control) than the cultivars Arkula, Dorisa, Karlena and Koretta (<25%; Table 3). Between these two extremes there was a large number of intermediate levels of tolerance, a result of fluctuating reactions of various cultivars to changing conditions in the years of the test period (Fig. 1). No correlation could be found between the cultivars' reactions and their maturity group or their sprouting behaviour. There was, however, for each cultivar a significant negative correlation between loss in weight through transpiration and respiration and plant density and yield (r=−0.55 and −0.54; Table 4). Plant density and yield were closely correlated (Table 4). The regressions between loss of plants and reductions in yields show that after seed tuber storage at higher temperatures a reduced yield must be expected even when plant density is not reduced (loss of plant 0%; Fig. 2). With complete stands, the use of physiologically aged seed tubers that were desprouted before planting (1988–1990) resulted in a reduction of yield of 17–20%; when old seeds were chitted as in control a loss in yield of 15% was calculated.

     

Effect of gibberellic acid and multiple harvests on production and reproductive value of seed potatoes produced above ground on stem cuttings

Summary Potato plants of cvs Eersteling and Bintje were grown from stem cuttings and induced to form aerial tubers for use as seed. Spraying the plants with gibberellic acid in concentrations of 10, 25 and 50 mg/l to induce stolon formation in the leaf axils led to a decrease in the number of tubers formed per plant. Multiple harvesting of the largest tubers from plants treated with gibberellic acid or not, approximately doubled the number of tubers formed but halved their individual weight compared with only one harvest at plant senescence. After a storage period of about 1 year, with their vigour declining, the aerial tubers were planted in the field. Aerial seed tubers taken from multiple harvests during the previous year produced the same number of tubers as plants grown from above-ground tubers harvested at plant senescence only, but the tuber yields declined with earlier harvesting when small (5–13 mm) aerial tubers were used, compared to larger (14–19 mm) tubers.     

The effect of water stress on the yielding capacity of potato crops and subsequent performance of seed tubers

Summary The effect of water stress on yielding capacity of potatoes was studied in 3 years using four different levels of soil water potential (0.7, 1.9, 3.4 and 7.8 atm.) in experiments in specially adapted structures that excluded uncontrolled water supply. Seed tubers from these crops were planted in the following years to investigate effects of water stress on their subsequent performance. Limited soil moisture availability decreased yield and the number and size of tubers. The growing period was shortened by 1–4 weeks and dormancy period by 2–8 weeks. In the following year, seed produced under conditions of moisture stress gave plants with 20% fewer stems. 24–33% less yield, 18–22% fewer tubers and 19–22% fewer large tubers than plants from seed produced under abundant water supply. It is concluded that the yield potential of seed tubers can be improved by careful attention to the availability of soil moisture during their production.     

Innovative propagation methods in seed tuber multiplication programmes

Summary The production of large volumes of vitroplantlets and greenhouse tubers for increasing the rate of multiplication at the start of seed programmes provides the opportunity of reducing the total number of field generations grown before the seed moves into commerce. This implementation is especially useful for countries where high quality potato seed tubers cannot be produced because there are no vector-free production areas. This review covers the following steps: a) laboratory production of microplantlets and microtubers; b) minituber production in the glasshouse; c) storage and dormancy of micro- and minitubers; d) field performance of micro- and minitubers compared with conventional seed tubers; e) incorporation of the mentioned propagules in seed production systems. Many optimized protocols are already available for propagating plantlets, inducing microtubers and obtaining minitubers in the glasshouse at all periods of the year. Advanced molecular approaches techniques (RFLP and RAPD) to detect genetic variation in the progeny of these propagules have been described. Investigations carried out in this field have shown genetic stability, with the propagules usually reproducing plants true-to-type and tubers without deviants. By contrast, variations were demonstrated in DNA extracted from old suspension cell culture. Field trials assessed a lower yield potential crops from in vitro propagules compared with conventional seed tubers., mainly due to slow early crop development and the failure of plants caused by early stress after emergence. This may cause problems when the growing season is short because of the necessity for planting late to avoid night frosts and the mandatory haulm killing dates, common in many seed producing areas. Strategies for improving the field performance of micro- and minitubers are discussed. The most promising crop husbandry techniques appear to be: a) using tubers of a suitable physiological age, properly presprouted and encapsulated; b) optimizing the time application of fertilizer and irrigation, and c) using floating films. Outside the classical seed tuber areas of Northern Europe where the length of the growing period for pre-basic seed is usually not more than 80 days, the growing season is long enough to obtain reasonable yields even from micro- and minitubers.     

PARS-70: An interspecific potato hybrid suitable for long storage and autumn-to-autumn seed multiplication

Summary Potato production in Pakistan has been largely based on imported cultivars. Efforts have been made to breed indigenous cultivars adapted to local seed multiplication and production practices. An indigenously bred hybrid(Solarium chacoense xSolatium acaule), named PARS-70 has been approved and released for cultivation in Pakistan. In yield trials, this hybrid was found superior to cultivars Diamant, Patroness, Ultimus, Cardinal and indigenous cultivars/selections Sialkot Sufaid and FB-9555-28. It produces white-yellow tubers, roundoval in shape with an average dry matter content of 21.8%. PARS-70 has the ability to store for up to 13 months in commercial storage (10–14 °C) and also can be stored in improvised unrefrigerated storage as a seed for next crop. Yields were reduced in crops grown from seed tubers stored under improvised unrefrigerated conditions. The long storage characteristic permits use of PARS-70 in autumn-to-autumn seed multiplication cycle without any loss of yield after several cycles of seed multiplication.     

Field performance of potato minitubers with different fresh weights and conventional seed tubers: Crop establishment and yield formation

Summary Field performance of five fresh weight classes of minitubers ranging from 0.13–0.25 g to 2.00–3.99 g and conventional seed tubers was studied in a short growing season (79 or 82 days) in two years. The heavier minitubers gave a more regular emergence, faster ground cover soon after emergence, higher dry-matter yields, and higher fresh tuber yields. Radiation conversion coefficient (RCC) did not differ. Higher tuber yields resulted from more radiation intercepted due to a faster ground cover, and a higher harvest index. All minitubers produced plants with one primary stem. In one experiment when heavier minitubers had long sprouts, time to 50% emergence decreased with tuber weight, whereas dry-matter concentration of progeny tubers increased. Conventional tubers appeared superior to minitubers in all characteristics mentioned except RCC, which was similar. Differences in performance between minitubers and conventional tubers were attributed to weight and age of seed tubers, presprouting method and crop husbandry.     

Field performance of potato minitubers with different fresh weights and conventional seed tubers: Multiplication factors and progeny yield variation

Summary Multiplication factors and progeny yield variation in crops from minitubers of five weight classes (ranging from 0.13–0.25 g to 2.00–3.99 g) and conventional seed tubers were studied in field experiments in three years. Multiplication factors were calculated as the number and weight of progeny tubers produced per planted tuber or per unit planted tuber weight. They were lower for the lighter minitubers when calculated per tuber and higher when calculated per weight. Yield variation was described by coefficients of variation for the number and weight of progeny tubers produced. Variation over individual plants of a crop was higher in stands from the lighter minitubers. Variation over plots within a field was sometimes higher for the lighter minitubers, but variation over years was similar for all minituber classes. Variation over plots in progeny tuber weight was higher for minitubers than for conventional tubers.     

Quelques aspects de l’influence du tubercule de semence et du nombre des tiges sur la croissance de la plante de Pomme de terre

Résumé La croissance des plantes de Pommes de terre estétudiée ici en fonction de l’age et de la taille du tubercule qui est à leur origine. L’influence de la taille est envisagée en considérant d’une part des plantes unitiges issues de tubercules de taille différente, d’autre part des plantes ayant un nombre variable de tiges pour une même taille du tubercule de semence. Schématiquement, on peut dire que les plantes ont un cycle végétatif d’autant plus court et un développement final d’autant plus faible que le tubercule de semence est plus agé ou que la quantité de réserves disponible par tige est plus petite. L’étude de plantes unitiges issues de tubercules entiers et de plantes provenant de bourgeons isolés permet d’attribuer une plus grande importance aux réserves qu’au capital méristématique.

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Summary The growth of potato plants was examined in relation to the age and size of the seed tuber. The influence of size is regarded as being involved in considering on the one hand plants originating from tubers of different sizes and on the other hand plants from tubers of the same size but having a variable number of stems; briefly, in varying the quantity of reserves available per stem. In order to distinguish the influence of these reserves from that of the bud meristem, 1-stemmed plants were grown from both whole tubers and detached buds. The plants were placed in pots filled with soil; some experiments were made in sand incorporating Hoagland’s medium or in half-strength Hoagland’s solution. One-stemmed plants were grown from tubers having only the apical bud, or, failing this, a bud at the rose end; during growth, lateral branching of the stems was prevented. Only significant results at the ‘end of the vegetative period’ (prior to yellowing of 25% of the plants) are discussed here.Influence of the size of the seed tuber: a. plants developing from whole tubers (P=30–40 g; G=100–130 g), grown in the glasshouse (Fig. 1), in the open air (Fig. 2) and in a controlled environment room (Fig. 3, 4). It was established that at the final stage of development, plants of series G were larger than those of series P: the diameter of the stems and final number of nodes are more important, the weight of tubers harvested was greater. The vegetative cycle of plants P was shorter than that of plants G; the growth of the stems finished earlier and yellowing started sooner. b. plants grown from buds detached from tubers of different sizes (Fig. 5,6): at the ‘end of the vegetative period’ the differences noted above were slight or non-existent, particularly in respect of the aerial part of the plants. Influence of the age of the seed tuber: a. plants developing from whole tubers (V, I, J 16, 7 and 3,5 months old, respectively) grown in a controlled environment room (Fig. 3,4). Final development of the aerial part of plants J was better than that of plants V: the diameter of the stems and the final number of nodes was greater. Tuberisation was earlier in plants V. Plants I were intermediate between plants V and J. The duration of the vegetative cycle diminished with increasing age of the seed tuber. b. plants grown from buds detached from tubers of different ages (Fig. 6): at the ‘end of the vegetative period’ differences in the aerial parts of the plants were less marked than in the case of plants grown from whole tubers. Influence of the number of stems (Fig. 7, 8): where the seed tuber is small, the number of nodes is greater on single than on 2-stemmed plants. The number of nodes on the principal stem of plants grown from large tubers falls as the number of stems increases (5 to 7). Yield per stem is more important in the case of 1-stemmed plants. In conclusion: The vegetative cycle of the plants is shorter and final development poorer the smaller the reserves available per stem or the greater the age of the seed tuber is. It would appear that more importance should be placed on the tuber reserves than on the meristematic tissues.

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Zusammenfassung Das Wachstum von Kartoffelpflanzen wurde in Abh?ngigkeit von Alter und Gr?sse der Saatknolle untersucht. Der Einfluss der Gr?sse wurde geprüft, indem einerseits Pflanzen mit verschieden grosser Mutterknolle und anderseits Pflanzen, die bei gleich grosser Mutterknolle eine unterschiedliche Zahl von Trieben aufwiesen, in Betracht gezogen wurden, d.h. indem man also die Menge der verfügbaren Reserven pro Trieb variierte. Um den Einfluss der Reserven von jenem des meristemischen Gewebes der Triebe zu unterscheiden, wurden eintriebige Pflanzen, sei es von ganzen Knollen, sei es von isolierten Keimen, kultiviert. Die Pflanzen wurden in mit Erde gefüllte T?pfe gepflanzt; einige Versuche wurden auf mit Hoagland-N?hrboden impr?gniertem Sand oder in einer zur H?lfte verdünnten Hoagland-N?hrl?sung angestellt. Die eintriebigen Pflanzen entwickelten sich aus Knollen, die nur den apikalen Trieb oder, wo dieser fehlte, einen Kronentrieb aufwiesen; man verhinderte die eventuellen seitlichen Verzweigungen der Stengel. Es stehen hier nur die signifikanten Ergebnisse am Ende der Vegetationszeit (bevor 25% der Pflanzen gelb wurden) zur Diskussion. Einfluss der Gr?sse der Saatknolle: a. Pflanzen, hervorgegangen aus ganzen Knollen (P=30–40 g; G=100–130 g). Die Kulturen befanden sich teils im Glashaus (Abb. 1), teils im Freien (Abb. 2) oder in der Klimakammer (Abb. 3 und 4). Man stellte fest, dass die Endentwicklung der Pflanzen in der Serie G gr?sser ist als in Serie P. Durchmesser und Endzahl der Stengelknoten sind gr?sser, das Gewicht der geernteten Knollen ist h?her. Der vegetative Zyklus der P-Pflanzen ist kürzer als jener der G-Pflanzen: das Wachstum der Stengel ist früher abgeschlossen, und die Bl?tter werden früher gelb. b. Pflanzen, hervorgegangen aus Keimen, die Knollen verschiedener Gr?sse entnommen wurden (Abb. 5,6): am ‘Ende der Vegetationszeit’ waren die früher beobachteten Unterschiede schwach oder gleich Null, besonders im oberirdischen Teil der Pflanzen. Einfluss des Alters der Saatknolle: a. Pflanzen, hervorgegangen aus ganzen Knollen (Alter: V= 16, I=7 und J=3,5 Monate). Die Kultur wurde in der Klimakammer durchgeführt (Abb. 3 und 4). Die Endentwicklung des oberirdischen Teils der Pflanzen J war besser als bei den V-Pflanzen. Durchmesser und Endzahl der Internodien waren gr?sser. Die Knollenbildung war deutlich früher bei den V-Pflanzen. Das Verhalten der I-Pflanzen lag zwischen jenem der V- und der J-Pflanzen. Die Dauer des vegetativen Zyklus nimmt mit zunehmendem Alter der Saatknolle ab. b. Pflanzen, hervorgegangen aus isolierten Keimen von Knollen verschiedenen Alters (Abb. 6): am ‘Ende der Vegetationszeit’ waren die Unterschiede in bezug auf den oberirdischen Teil der Pflanzen geringer als bei den Pflanzen aus ganzen Knollen. Einfluss der Anzahl Stengel (Abb. 7 und 8). Die Knotenzahl der Pflanzen mit einem Stengel war gr?sser als bei Pflanzen mit zwei Stengeln, wenn die Saatknolle klein war. Die Knotenzahl des Haupttriebes von Pflanzen aus grossen Knollen nahm bei erh?hter Stengelzahl (5–7) ab. Der Ertrag pro Stengel war bei den einstengeligen Pflanzen h?her. Schlussfolgerungen: Die Pflanzen haben einen um so kürzeren vegetativen Zyklus und eine um so schw?chere Endentwicklung, je kleiner die verfügbare Reservemenge pro Stengel oder je ?lter die Saatknolle ist. Es scheint, dass man den Reserven eine gr?ssere Bedeutung zuschreiben muss als den Eigenschaften des meristemischen Gewebes.

     

Potato Plants Grown from Minitubers are Delayed in Maturity and Lower in Yield,but are not at a Higher Risk of <Emphasis Type="Italic">Potato virus Y</Emphasis> Infection than Plants Grown from Conventional Seed

Potato virus Y (PVY) is the most important virus in North American seed potato (Solanum tuberosum L.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type.     

Trials to grow certified seed potatoes in the Golan Heights

Summary A trial to grow seed potatoes in summer 1968 in the Golan Heights indicated that hardly any aphid transmission of potato virus Y (PVY) could be noticed. Normal plant growth and tuber formation were observed. The incidence of seed borne virus diseases in fields grown from local seed produced in the Golan Heights in 1970 was: PVY 0.1–0.3% in 2 out of 33 inspected fields, potato leaf roll virus (PLRV) 0.3–2% in 19 fields. In 1972 30 fields were inspected, PVY was observed in 3 fields at a level of 0.1–0.2% PLRV at a level of 1–4% in 28 fields. Alfalfa mosaic visus (AMV) and Stolbur were not observed. The result of post-harvest control in field plots planted with seed potatoes produced in the Golan Heights in 1969, 1970 and 1971 were: PVY very low infection, 0.2–0.7%, for the three years; PLRV, low percentage, 0.3–0.7%, in 1970 and 1971, while it increased in 1972 to 1.3–6%. AMV and Stolbur were not observed.

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Zusammenfassung Die Felder auf den Golan-H?hen liegen 900 m ü. M. Die Temperatur ist tiefer als in den Ostgalil?ischen Bergen w?hrend des Sommers. Am 20. Mai 1968 wurden irische Pflanzkartoffeln der SorteUp-to-Date (anerkannt in Klasse A) in Merom Golan ausgepflanzt. In den Jahren 1969–1971 wurden im Mai Basispflanzen und Pflanzgut der Klasse A der SorteUp-to-Date an zwei verschiedenen Orten, Meron Golan und Ein Zivan, angebaut (Tabelle 2). In den Ergebnissen der Feldbesichtigungen, die 1969–71 2–3 mal in Juni/Juli durchge führt wurden, widerspiegelte sich ein offensichtliches Fehlen der Virus-Vektoren. Es wurde kaum eine Uebertragung des Kartoffelvirus Y (PVY) durch Blattl?use festgestellt mit einer Ausn?hme, n?mlich im September 1970, als eine verbreitete PVY-Infektion beobachtet wurde. Diese Parzellen unterstanden dem Seed Inspection Service, und der Ertrag wurde als zertifiziertes Pflanzgut verwendet. In den Jahren 1971–1972 wurden Muster von 100–200 Knollen in Pflanzgutgr?sse (40–100 g) zu verschiedenen Erntedaten entnommen und zu Untersuchungszwecken in einem insektensicheren Glashaus ausgepflanzt. Der durchschnittliche Virusbefall betrug 1971: PVY 1,3–2,6%, Kartoffel-Blattrollvirus (PLRV) 1,5–5,3%, Luzerne-Mosaikvirus (AMV) 6–12%, Stolbur 0–2% (Tabelle 2); 1972: PVY 1,3–2,5%. PLRV 0,5–4,6%, Stolbur war nicht vorhanden, AMV 2,5–4% (Tabelle 3). Pflanzgutmuster von den Golan-H?hen wurden 1970–72 in Versuchsparzellen angebaut. Der Virusbefall war wie folgt: PVY 0–0,7%, PLRV 0,3–6%, AMV 0–1% und Stolbur 0–0,5% (Tabelle 1). Vom Ertrag im Jahre 1970 wurden die Knollen in Pflanzgutgr?sse 1971 auf verschiedenen Feldern angebaut. Gem?ss dem Seed Inspection Service betrugen die Viruskheiten im Mittel: PVY 0,1–0,3% nur in 2 von 33 besichtigten Feldern; PLRV 0,3–2% in 19 Feldern, w?hrend das Virus in den andern 14 besichtigten Feldern nicht festgestellt wurde. 1972 wurden 30 Felder besichtigt, deren Pflanzgut im Sommer 1971 auf den Golan-H?hen erzeugt wurde. Befall mit Viruskrankheiten: PVY 0,1–0,2% in drei Feldern und keine Spur von PVY in den andern Feldern; PLRV 1–4% in 28 Feldern, und nur in 2 Feldern wurde kein sekund?res PLRV entdeckt. Die PLRV-Infektion ist also zunehmend h?ufiger aufgetreten und der Prozentsatz war h?her. Gelbscheckigkeit oder Calico infolge AMV oder Stolbur wurden in diesen 1971–1972 besichtigten Feldern nicht beobachtet. Die Ursache für diesen bedeutend geringeren Virusbefall auf den Feldern und den Kontrollparzellen, verglichen mit den Laboruntersuchungen, liegt in der Tatsache, dass eine betr?chtliche Zahl der AMV-infizierten Knollen nicht keimten oder unter Feldbedingungen nicht aufgingen. Pflanzen von PVY-infizierten Knollen neigen dazu, so früh aufzulaufen wie Pflanzen von gesunden Knollen; sie werden von ihren kr?ftigeren Nachbarn gedeckt und k?nnen daher den Augen des Anerkennungsexperten entgehen. Beurteilung von Pflanzkartoffeln von den Golan-H?hen. Im Frühling 1971 wurden Pflanzkartoffeln der SorteUp-to-Date von den Golan-H?hen im Vergleich met irischenUp-to-Date an neun verschiedenen Orten angebaut. An einem Ort war der Ertrag gleich, an vier Orten war er geringer und an den andern vier Orten h?her (Tabelle 6); w?hrend 1972 der Ertrag des Pflanzgutes von den Golan-H?hen gr?sser war mit dem gleichen Prozentsatz von grossen Knollen (über 60 g) (Tabelle 5). Die Pflanzkartoffeln von den Golan-H?hen verhalten sich wie Pflanzgut jüngerer Anbaustufen in bezug auf Auflaufen, Stengelzahl (Tabelle 4), Blühen und Knollenbildung.

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Résumé Les hauteurs de Golan se trouvent à 900 m audessus du niveau de la mer. Durant l'été la température y est plus basse que dans les montagnes de l'est de la Galilée. Le 20 mai 1968, on a planté à Meron Golan des plants irlandais certifiés A de la variétéUp-to-Date. Au cours des années 1969–1971, on a planté en mai des plants de base et des plants de classe AUp-to-Date dans deux localités différentes: Meron Golan et Ein Zivan (tableau 2). L'absence saisonnière apparente de vecteurs se reflète dans les résultats d'inspection des champs, exécutées 2–3 fois en juin-juillet 1969–71, ce qui explique qu'on n'a pu obsevver réellement aucune transmission par aphides de virus Y (PVY) sauf une fois où l'on observé, en septembre 1970, une infection réalisée en cours de saison. Les parcelles étaient soumises au contr?le du Service d'inspection des plants, et la production utilisée comme plants de pomme de terre certifiés. Au cours des années 1971–72, on a planté, en vue de tests, des échantillons de 100–200 tubercules de calibre ‘plants” (40–100 g), dans un abri toilé à l'abri des pucerons, et récoltés à différentes dates. En 1971, on a observé les viroses suivantes: PVY 1,3–2,6%, enroulement (PLRV) 1,5–5,3%, alfalfa (AMV) 6–12%, stolbur 0–2% (tableau 2). En 1972, les manifestations de viroses ont été les suivantes: PVY 1,3–2,5%, PLRV 0,5–4,6%, le stolbur étant absent, AMV 2,5–4% (tableau 3). On a planté des échantillons de plants provenant des hauteurs de Golan dans des parcelles expérimentales au cours des années 1970 et 1971. On a noté les viroses suivantes: PVY 0–0,7%, PLRV 0,3–6%, AMV 0–1% et stolbur 0–0,5% (tableau 1). En 1971, on a planté dans différents champs des tubercules de calibre ‘plants’ provenant de la production totale de 1970, les moyennes des maladies virologiques, selon le service d'inspection des plants, furent les suivantes: PVY 0,1–0,3% dans deux champs seulement des 33 champs inspectés, PLRV 0,3–2% dans 19 champs tandis qu'on a identifié aucune virose dans les 14 champs restants. En 1972, on a inspecté trente champs plantés avec des plants produits sur les hauteurs de Golan au cours de l'été 1971. Les manifestations virologiques ont été les suivantes: PVY 0,1–2% dans trois champs et aucune trace de PVY dans les autres; PLRV 1–4% dans vingt-huit champs et aucune manifestation de PLRV issu des plants dans deux champs seulement. L'infection de PLRV est donc devenue plus fréquente et le pourcentage d'infections plus élevé. On n'a pas observé de ‘Yellow mosa?c’ ou ‘Calico’ d? au AMV, ni de stolbur dans ces champs inspectés en 1971–1972. La raison de l'incidence remarquablement basse de virus dans les champs et parcelles de contr?le, comparativement aux tests de laboratoire, tient au fait qu'un nombre considérable de tubercules infectés de AMV ne germent pas ou ne lèvent pas dans les conditions des champs. Les plantes provenant de tubercules infectés de PVY ont tendance à lever aussi t?t que les plantes saines mais sont recouvertes par les plantes voisines vigoureuses. Elles peuvent par conséquent échapper aux yeux des contr?leurs. Appréciation des plants de pomme de terre des hauteurs de Golan. Au printemps 1971, on a planté, dans neuf localités différentes, des plants provenant des hauteurs de Golan, en comparaison avec des plantsUp-to-Date de provenance irlandaise. Dans une localité, la production fut identique, dans quatre localités elle était inférieur et elle fut supérieure dans les quatre autres (tableau 6); par contre en 1972 la production des plants des hauteurs de Golan était plus élevée avec le même pourcentage de gros tubercules supérieurs à 60 g (tableau 5). Les plants des hauteurs de Golan se comportent comme des plants plus jeunes eu égard à la levée, le nombre de tiges (tableau 4), la floraison et la tubérisation.

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Part of this paper was read at a session of the Virology Section at the 5th Triennial Conference of the EAPR (Norwich, September 1972).     

Effects of irrigation and seed tuber size on yield and infection of potatoes from commercial and healthier seed stocks

Summary Small and large seed tubers (cv. King Edward) produced from commercial and stem cutting (healthier) seed stocks were planted in field experiments at Rothamsted in 1972 and 1973. Plots were irrigated from shoot emergence (early) or from tuber marble stage (normal) or not irrigated. Large healthier seed produced plants with more stems and tubers and 6–9% more yield in September than large commercial seed but seed health did not affect yields from small seed. Early and normal irrigation decreased the number of tubers initiated in 1972 but had no effect on tuber numbers in 1973. Normal irrigation increased tuber yields more than early irrigation, especially in plots grown from healthier seed.Polyscytalum pustulans was most prevalent on tubers from commercial seed and was increased by irrigation. Tubers from healthier seed had most infections ofHelminthosporium solani which were decreased by irrigation.

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Zusammenfassung Kleine (22–25 g) und grosse (118–126 g) gekeimte Knollen aus kommerziellen Pflanzgutherkünften und aus Stecklingsvermehrungen (besonders gesund) wurden für die Versuche in den Jahren 1972 und 1973 in Rothamsted ausgepflanzt. Die Parzellen wurden bew?ssert (1) früh, vom Auflaufen bis zum Murmelstadium (‘marble stage’) der Knollen, um den Boden in 10 cm Tiefe auf Feldkapazit?t zu halten und bis September, um das Defizit an Bodenfeuchtigkeit auf weniger als 38 mm zu halten, (2) normal, vom Murmelstadium, um das Defizit auf weniger als 38 mm zu halten, (3) sp?t (nur 1972), von Mitte August bis Mitte September (Abb. 1). Aus den grossen gesünderen Pflanzknollen wurden Pflanzen mit mehr Stengeln, mehr Knollen und im September mit 6–9% Mehrertrag erzeugt als aus den grossen Pflanzknollen kommerzieller Herkunft (Tab. 1). Die Knollenertr?ge aus den kleinen Pflanzknollen wurden nicht vom Gesundheitszustand des Pflanzgutes beeinflusst, obwohl die Pflanzen aus dem gesünderen Pflanzgut mehr Knollen bildeten als diejenigen aus dem kommerziellen Pflanzgut. Im September war die Verteilung der Knollengr?ssen aus dem Pflanzgut beider Herkünfte ?hnlich, mit dem gesünderen Pflanzgut wurden jedoch geringfügig mehr Knollen >4 cm erzeugt (Abb. 2). Im Juni waren Knollenanzahl und-gewicht pro Stengel vom gesunderen Pflanzgut h?her als vom kommerziellen (Tab. 1); im September war die Knollenanzahl ?hnlich, die Ertr?ge waren aber vom kommerziellen Pflanzgut h?her als vom gesünderen. Die Ertr?ge pro Stengel waren auch bei den kleinen Pflanzknollen h?her als bei den grossen. Das Knollengewicht pro Stengel verringerte sich mit zunehmender Stengelzahl pro Pflanze, beim gesünderen Pflanzgut war dies jedoch weniger ausgepr?gt als beim kommerziellen (Abb. 4). Die gr?ssere Knollenzahl an Pflanzen aus gesundem Pflanzgut war deshalb auf die erh?hte Stengelzahl und, bei grossen Pflanzknollen, auf die erh?hte Knollenanzahl pro Stengel zurückzuführen. Die frühe Bew?sserung führte 1972, jedoch nicht 1973, zu einer Verringerung der Knollenanzahl (Tab. 2). Die Knollenertr?ge im September waren eher bei normaler Bew?sserung erh?ht (34%, 1972; 18%, 1973) als bei früher Bew?sserung (23%, 1972; 12%, 1973), die Anzahl der Knollen >4 cm (Abb. 3) und die durchschnittliche Knollengr?sse waren auch bei normaler Bew?sserung h?her (Tab. 3). Im Jahre 1972 waren vom gesünderen Pflanzgut die Knollenertr?ge um 5% h?her als vom kommerziellen wenn die Parzellen nicht oder früh bew?ssert wurden und um 12% h?her bei normaler Bew?sserung (Tab. 2), und 1973 waren die Ertr?ge vom gesünderen Pflanzgut bei den beiden Bew?sserungsmassnahmen um 6–7% h?her. Infektionen mitPolyscytalum pustulans waren an Knollen aus kommerziellem Pflanzgut h?ufiger als aus gesünderem Pflanzgut (Tab. 5), und sie nahmen bei Bew?sserung zu. Dagegen waren Infektionen mitHelminthosporium solani am h?ufigsten an Knollen aus gesünderem Pflanzgut, und sie nahmen bei Bew?sserung ab. Das Auftreten vonRhicotonia solani wurde nicht deutlich vom Gesundheitszustand des Pflanzgutes oder durch die Bew?sserung beeinflusst.

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Résumé Des tubercules germés de petit (22–25 g) et gros (118–126 g) calibres produits à partir de semences commerciales et de boutures (semences les plus saines) sont plantés dans des essais à Rothamsted en 1972 et 1973. Les parcelles sont irriguées: (1) t?t à partir de la levée jusqu'au stade tubérisation pour garder sur 10 cm de profondeur le niveau de sa capacité de rétention en eau et ensuite jusqu'en Septembre en maintenant le niveau d'humidité sur 38 mm, (2) normalement, à partir du stade tubérisation en maintenant le niveau d'humidité sur 38 mm, (3) tardivement (1972, seulement) de la mi-ao?t à la mi-septembre (Fig. 1). La semence la plus saine produit des plantes avec davantage de tiges, de tubercules et un rendement 6 à 9% supérieur en septembre que les gros tubercules de semence commerciale (Tableau 1). L'état sanitaire de la semence n'affecte pas les rendements des tubercules de petit calibre bien que les plantes issues des semences les plus saines produisent davantage de tubercules que les semences commerciales. En septembre, la distribution des tubercules selon leur taille est identique pour les semences des deux origines mais les semences issues de boutures produisent beaucoup plus de tubercules supérieurs à 4 cm (Fig. 2). En juin, le nombre et le poids des tubercules par tige sont plus élevés dans les semences les plus saines que dans les semences commerciales (Tableau 1); à partir de septembre, les nombres de tubercules sont identiques mais les rendements sont plus importants à partir de semences commerciales. De même, les rendements par tige sont plus élevés à partir des petits calibres que des gros calibres. Le poids de tubercules par tige diminue avec l'augmentation du nombre de tiges par plante mais de fa?on moindre à partir des semences les plus saines (Fig. 4). Le plus grand nombre de tubercules sur les plantes issues des semences les plus saines est donc attribué à l'augmentation du nombre des tiges et pour les semences de gros calibres à l'augmentation du nombre de tubercules par tige. Une irrigation précoce diminue le nombre de tubercules formés en 1972 (Tableau 2) mais n'a pas d'effect en 1973. Les rendements en tubercules en septembre sont davantage augmentés par une irrigation normale (34%, 1972; 18%, 1973) que précoce (23%, 1972; 12%, 1973), de même que le nombre des tubercules >4 cm (Fig. 3); le calibre moyen des tubercules est plus grand que dans le cas d'une irrigation normale (Tableau 3). En 1972, les rendements de septembre en tubercules sont 5% plus élevés à partir des semences les plus saines qu'à partir des semences commerciales quand les parcelles ne sont pas irriguées ou quand l'irrigation est précoce et 12% plus élevés dans le cas d'une irrigation normale (Tableau 2); en 1972, les rendements sont 6–7% plus élevés à partir des semences les plus saines et ce avec les deux types d'irrigation. L'infection parPolyscytalum pustulans est plus fréquente à partir des tubercules de semences commerciales qu'à partir des semences les plus saines (Tableau 5) et est accrue par l'irrigation. A l'inverse, l'infection parHelminthosporium solani est plus commune sur tubercules issus des semences les plus saines et est réduite par l'irrigation. L'incidence deRhizoctonia solani n'est pas affectée significativement par l'état sanitaire des semences ou par l'irrigation.

     

Inductive and noninductive conditions on in vitro tuberisation and microtuber dormancy in potato (Solanum tuberosum subspeciestuberosum and subspeciesandigena)

Summary The effect of growth conditions (medium and photoperiod) on in vitro tuberisation and microtuber dormancy of the cv. Désirée (Solanum tuberosum subspeciestuberosum) and Imilla Negra (Solanum tuberosum subspeciesandigena) was evaluated. The short photoperiod and presence of CCC in the medium reduced the dry matter of plants as well as the size of microtubers. The two cultivars showed a difference, in favour of Désirée, in the percentage of plants having more than one tuber and in the average time of sprouting after storage. The average time of sprouting was more rapidly obtained under long days and in a medium without CCC. The CCC and short days caused the same dormancy conditions and the same K⁺ quantity in the microtubers. The microtubers mineral composition is involved in the dormancy status.     

The infection pressure of potato leafroll virus and potato virus Y in relation to aphid populations in Cyprus

Summary The infection pressure of two viruses, potato leafroll (PLRV) and potato virus Y (PVY), both common in seed potatoes grown in Cyprus, was determined in three experiments in 1982–83. Virus-free bait plants, of potato and four other species, were exposed weekly to field infection during the growing season (March–June), and then returned to an aphid-free glasshouse for symptom expression. Only tobacco plants produced clear symptoms enabling reliable assessment of PVY infection pressure. When assessed with ELISA or by tuber indexing, the potato plants were efficient baits for both viruses whose infection period commenced at emergence (mid March to early April) and ended within 6–7 weeks. The seasonal trend of aphid populations, determined with Moericke traps or 100-leaf counts, correspond to that of virus spread. Correlation and regression analysis of aphid and virus data implicated the alate form ofMyzus persicae as the principal vector of both viruses.     

Screening potato cultivars for common scab of potato in a naturally infested field

Summary Twenty seven cultivars of potato were screened for common scab grown in a commercial field in two successive years (1996–97 and 1997–98). Eight cultivars were least susceptible and the others ranged from medium susceptible to very highly susceptible. None of the cultivars was resistant. Most showed a stable resistance reaction in both years.