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).     

Economic Optimum Nitrogen Fertilization Rates and Nitrogen Fertilization Rate Effects on Tuber Characteristics of Potato Cultivars

The objective of the research was to determine the economic optimum nitrogen (N) fertilization rates and to determine the effects of N fertilization rates on tuber characteristics and fresh mass loss after storage under cold and ambient conditions of four potato cultivars, Ágata, Asterix, Atlantic, and Monalisa. The experiments were, simultaneously, conducted in the same area and similar experimental conditions during the fall/winter period in Viçosa, Minas Gerais State, Brazil. In each experiment, five N fertilization rates (0, 50, 100, 200, 300 kg ha^?1) were evaluated in a randomized complete block design. For all cultivars, increasing N fertilization rate increased total and marketable yields and tuber dry matter yield up to a maximum following a quadratic model. Increasing N fertilization rate linearly increased the tuber protein concentration of Atlantic and Monalisa and had no effect on tuber pH. N fertilization rate effects on tuber mass, tuber titratable acidity, and fresh mass loss during storage were cultivar-dependent. N use efficiency (tuber yield divided by N fertilization rate) decreased with increase in N fertilization rate. The economic optimum N fertilization rates ranged from 147 to 201 kg ha^?1 depending upon cultivar and relative prices of N and potato tubers. Depending on the cultivar, under favorable price conditions (low N price and high tuber price), the economic optimum N fertilization rates to be applied by potato growers were 92–95% of the estimated N fertilization rate for obtaining the maximum potato yield, whereas under unfavorable conditions (high N price and low potato tuber price) the economic optimum N fertilization rates to be applied should be decreased to 86–92% of the rates for maximum yield.     

Accumulation of mineral elements in tuber periderm of potato cultivars differing in susceptibility to common scab

Summary Concentrations of Ca, P, K, Mg, Al, Fe, Mn, Cu and Zn were determined in healthy tuber peelings of cultivars less (Karin, Santé and Symfonia) and more (Agria, Désirée and Tomensa) susceptible to common scab when grown at two sites that differed in the level of scab incidence. The accumulation of some elements was significantly influenced by site, year, cultivar, maturity and the age of tuber periderm. At both sites, Ca and P in periderm tissue declined but Mg increased during the growing season. The Ca/P ratios in tuber periderm of all cultivars greatly decreased 83 days after planting. Concentrations of mineral elements measured at harvest may not reflect conditions present during the infection period, and consequently may not be related to scab incidence or severity.     

Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes

Summary Potato tuber dormancy is usually defined as lasting from tuber initiation until a sprout of 2 mm long has been formed under storage conditions optimal for sprouting. We tried to find out whether there is a period during which buds of seed tubers do not grow and whether different batches of seed take the same time to grow sprouts 2 mm long. We measured changes in number of leaf primordia and length of tuber buds of cvs Diamant and Désirée over two years. After early haulm pulling, buds did not grow for at least 60 days (‘Diamant’) or 95 days (‘Désirée’). Buds in both cultivars and two tuber weights of ‘Diamant’ took about 20 days from the estimated onset of sprouting to grow 2 mm long. We question whether this period is always similar and thus whether the moment sprouts 2 mm long have formed is a good criterion for the end of dormancy.     

Comparison of the NegFry decision suport system with routine fungicide application for the control of potato late blight in Ireland

Summary Field experiments between 1996 and 2000 compared the efficacy of fungicide programmes applied in accordance with the NegFry and Met éireann (Mé) decision support systems (DSS) for the control of late blight with 7- and 10-day routine fungicide programmes. The Mé DSS reduced fungicide use by 68% and 54% respectively while NegFry reduced fungicide use by 49% and 27% compared with the 7- and 10-day programmes. The NegFry DSS was similar to the 10-day routine programme in terms of late blight control, quality and marketable yield. A similar result was found when the NegFry DSS was compared with a 7-day routine mancozeb programme (included for two seasons only). Within the NegFry DSS the use of fluazinam resulted in improved yield, foliage blight and tuber blight control compared with mancozeb, but this benefit was significant for tuber blight only. The Mé DSS resulted in inferior disease control, yield and quality.     

Effects of shoot,root and stolon temperature on the development of the potato (Solanum tuberosum L.) plant. III. Development of tubers

Summary The cultivars Bintje and Désirée were growth with their shoots, roots and stolons at different temperatures, to study the effects on tuber development. More tuber sites were initiated in ‘Bintje’ when the air, root or stolon temperature was increased but a combined increase of air and root temperature greatly reduced the number of sites. In contrast, each temperature increase reduced the number of tuber sites in ‘Désirée’ but an increase in temperature in one compartment usually increased the number of tubers set. The relative tuber set was enhanced by a combination of high stolon temperature and low root temperature. Especially an increase in air temperature reduced tuber yield and tuber dry-matter content, but increasing stolon temperature had the largest effects on the induction of second growth. Stolon and tuber development, dry-matter partitioning and initiation of second growth responded differently to variation in temperature around different plant parts suggesting that these processes are affected by different regulation mechanisms.     

The response of potatoes to a single transient heat or drought stress imposed at different stages of tuber growth

Summary The effects of a single treatment of heat or drought stress imposed at different stages of tuber growth, were investigated in two potato cultivars, Désirée and Cara. Both stresses impaired dry matter accumulation in tubers, and tuber yields. Stress imposed at early stages of tuber growth, when tubers were less than 20 mm in diameter, had little effect on dry matter accumulation, whereas stress imposed later resulted ingnificant losses of dry matter in tubers. Stress imposed during later tuber growth increased the percentage of tubers sprouting in the soil. Tuber malformation was less affected. The adverse effects of heat on tuber yield and quality seemed to be greater than those of drought. Drought increased the content of total soluble solids (TSS) and lowered the osmotic potential in the tuber tissue of both cultivars. These effects were detectable even 55 days after stress relief. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No 984-E, 1984 Series. This investigation was sponsored by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

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.     

Der Einfluss des physiologischen Alters der Pflanzknollen auf die Ertragsbildung von Kartoffelsorten verschiedener Reifezeit

Zusammenfassung Durch kontinuierliche Untersuchungen wurden das Kraut- und Knollenwachstum bei 5 Sorten und 4 Varianten unterschiedlichen physiologischen Alters (Keimung zum Teil unter Licht) verfolgt. Das physiologische Alter beeinflusst die Ertragsbildung durch zwei entgegengesetzt wirkende Tendenzen. 1) Mit zunehmendem Alter wird die Vorauflaufentwicklung verkürzt und die Vegetationsperiode in günstigere meteorologische Bedingungen vorverlegt. 2) Durch altes Pflanzgut kann das Krautwachstum so stark gehemmt werden, dass die geringe photosynthetische Kapazit?t des Krautes verminderte Knollenwachstumsraten und damit einen geringeren Ertrag bei Abreife zur Folge hat. Bei frühen Sorten wurde durch junges Pflanzgut, bei sp?ten Sorten durch Pflanzgut mittleren Alters die günstigste Krautentwicklung erreicht. Die Zahl der oberirdischen Stengel (einschliesslich gr?sserer Verzweigungen) und Knollen der frühen Sorten nahmen mit zunehmendem Alter des Pflanzgutes ab.

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Summary The effect of the physiological age of seed tubers on yield was studied using 4 treatments of various ages (extremes of treat ent: accumulated temperature, 300–400 day-degrees>0°C, chitting to 3 mm; 200 day-degree>0°C, light chitting to 30 mm). Five cultivars in maturity classes ‘first early’ to ‘mid-late’ were examined over a 4-year period by experimental liftings and measurements of haulm growth. Increased physiological age accelerated emergence, but the time between emergence and tuber initiation, and between emergence and senescence was not affected (Table 1; Figs 1, 2). The total stem number (above-ground stems including concealed ones, which were inserted below half the maximum plant height) and the tuber number per plant of early cultivars decreased significantly with increased age of the seed tubers in spring (Figs 3,6). In one year there were higher stem numbers, but not tuber numbers, with greatly increased physiological age, due to dying-off of the apices of light chitted material (Fig. 3). The total stem numbers and tuber numbers of the mid-late cultivars were not affected significantly by the physiological age of the seed tubers (Figs 3,6). Haulm elongation was checked by increased physiological age of the seed tubers (Table 2). The physiologically youngest seed of the early cultivars had the greatest quantity of haulm and leaf weight up to the time of tuber initiation (Tables 2, 3; Figs 1, 2a). With the mid-late cultivars, seed of more advanced physiological age gave as good or even better haulm development up to tuber set (Table 2; Fig. 2b) as the physiologically youngest treatment. The effect of physiological age on yield development stemmed from two main factors. Firstly, the acceleration of emergence with increased age brought forward the vegetative period, in general, towards better conditions with regard to light and water supply. Secondly, increased age restricted haulm development thereby giving lower photosynthetic performance of the haulms up to the time of tuber formation, leading to reduced tuber growth rates or to an extension of the exponential part of the yield curve (Figs 1, 2a). The physiologically youngest seed of the early cultivars showed by tuber set the best haulm development and with it the highest yield potential (Figs 1, 2a), but there was no such advantage of young seed over seed of intermediate age for the mid-late cultivars (Fig. 2b). The yield at the end of the vegetation period is a consequence of both factors. The yield of the very early cultivars was strongly affected by the first, while the mid-late cultivars were affected principally by the advancing of the vegetative period (Fig. 5). Allowances had to be made when interpreting harvest yields for extremely unfavourable soil moisture conditions during the second half of the vegetative period of the experimental year (Fig. 4).

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Résumé L'influence de l'age physiologique des plants sur le rendement a été examinée à l'aide de 4 variantes de plants d'ages physiologiques différents (variantes extrêmes: somme des températures: 300–400°C>0°C, germes jusqu'à 3 mm; 200 °C>0°C, germes colorés jusqu'à 30 mm), et de 5 variétés des groupes très précoces à mi-tardives, pendant 4 ans. Les examens ont porté sur des échantillonnages de récolte et des mesures de la croissance des fanes. Un age physiologique avancé a activé la levée. Les durées entre la levée et la tubérisation ainsi que levée-maturité n'ont pas été influencées (tabl. 1, fig. 1 et 2). Le nombre total de tiges (tiges axillaires situées sur la moitié inférieure des fanes comprises) et le nombre de tubercules par plante diminuait de manière significative au printemps chez les variétés précoces d'un age physiologique avancé (fig. 3 et 6). Certaines années, une augmentation du nombre de tiges mais non de celui de tubercules avec des plants d'un age physiologique avancé pouvait résulter du dessèchement apical des germes exposés à la lumière. Chez les variétés mi-tardives, le nombre total de tiges et tubercules n'a pas été influencé par les différents ages physiologiques (fig. 3 et 6). Un age physiologique avancé des plants (tabl. 2) a freiné la croissance des fanes. Les plants jeunes de variétés précoces ont produit, jusqu'au moment de la formation des tubercules, la plus grande masse de tiges et feuilles (tabl. 2 et 3, fig. 1 et 2a). Chez les variétés mi-tardives les plants d'un age plus avancé donnèrent une croissance des fanes égale ou parfois meilleure que les plants les plus jeunes (tabl. 2, fig. 2b). L'effet de l'age physiologique sur le rendement se manifeste par deux facteurs principaux. Primo, par l'accélération de la levée due à un age plus avancé, la période de végétation se situera (en général) dans la saison la plus favorable pour ce qui concerne le rayonnement et le ravitaillement en eau. Secondo, l'age avancé des plants inhibe la croissance des fanes et parlà l'activité de la photosynthèse lors de la formation et la croissance des tubercules, ce qui a pour conséquence une prolongation de la partie exponentielle de la courbe de croissance (fig. 1 et 2a). Tandis que pour les variétés précoces, c'est le plant jeune qui a donné le meilleur rendement (fig. 1 et 2a). Chez les variétés mi-tardives le plant jeune ne présente aucun avantage par rapport au plant d'age moyen (fig. 2b). Le rendement en fin de période de végétation est la résultante des deux facteurs précités. Les rendements des variétés très précoces ont été très fortement influencés par le premier facteur, tandis que pour les variétés mi-tardives, c'est l'avancement de la période de végétation qui a principalement été profitable (fig. 5). Lors de l'interprétation des rendements il s'agit également de tenir compte des conditions du sol très défavorables pendant la seconde moitié de la période de végétation (fig. 4).

     

Tuber yield and tuber quality of several potato cultivars as affected by seasonal high temperatures and by water deficit in a semi-arid environment

Summary The effects of high temperatures and water deficit on potatoes were investigated under field conditions. Nine cultivars and one un-named seedling were grown in the spring and in the summer under high temperatures. In both seasons the cultivars were grown under 3 water regimes: adequate water supply, moderate water deficit, and severe water deficit that were achieved by a modification of the single line source sprinkler irrigation system. Severe drought reduced tuber yields in both seasons. Moderate tolerance to a moderate water deficit in the spring season was exhibited by Draga, Désirée, and Monalisa. Late and intermediate cultivars produced high tuber yields in the spring season, and early cultivars had relatively smaller yield losses in the summer. The extent of tuber disorders, sprouting, rotting and malformation, varied considerably. High temperatures enhanced sprouting, rotting and malformation and drought may enhance sprouting and malformation. This investigation was supported by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

The relationship between yield, mainstem number, and tuber number in five maincrop and two early-maturing cultivars

Using data from an 11-year period, total and marketable yield were related, using regression analysis, to mainstem and tuber number for five maincrop varieties (Russet Burbank, Shepody, Atlantic, Norchip, and Norland) and two early-maturing varieties (Conestoga and Carlton), at irrigated and dryland sites in western Canada. Mainstem number by itself was a poor predictor of total and marketable yield. Highly significant regressions of yield on the derived variable tuber number per mainstem were evident for all cultivars grown at the dryland sites. In general, the proportion of the total variation in yield accounted for by the regression models was much higher at the dryland than at the irrigated sites, indicating that the relationship between yield and its predictor variables was more complex for irrigated sites. While the study suggests that the use of tuber number per mainstem may be useful as an early-season predictor of tuber yield for cultivars, particularly under dryland conditions, a model using the predictor variables mainstem and tuber number will generally be superior due to the additional information it provides when competitive effects are present for light energy within the canopy or for assimilates among developing tubers. Contour plots provide a useful way to study the yield response to changes in tuber number at specific stem density levels.     

Breeding Potential of Potato Somatic Hybrids: Evaluations for Adaptability,Tuber Traits,Late Blight Resistance,Keeping Quality and Backcross (BC<Subscript>1</Subscript>) Progenies

Ten tetraploid interspecific potato somatic hybrids developed earlier through protoplast fusion between the dihaploid Solanum tuberosum L. ‘C-13’ and the diploid wild species Solanum pinnatisectum Dun. were used in this study. Somatic hybrids and standard control cultivars were evaluated for adaptability, tuber traits, late blight resistance and keeping quality attributes (dormancy, sprouting, weight loss and appearance after 75 days of storage) during two successive winter crop seasons (short-days) in the sub-tropical plains of India, where nearly 90% of India’s potatoes are grown. Somatic hybrids showed medium to good plant vigour and late to very late plant maturity. Though none of the somatic hybrids produced equal or higher tuber yield than the control cultivars, except clone P7, all other somatic hybrids produced significantly higher marketable and total tuber yield after a 90-day growth than the parent C-13. Most of the somatic hybrids possessed higher tuber dry matter concentration, resistance to late blight and better keeping quality attributes than the control cultivars. Notably, the tubers of somatic hybrids showed a tendency for colour change from white to purple on exposure to sunlight. Breeding potential of somatic hybrids was further assessed by crossing them with commonly grown local potato cultivars for the development of backcross (BC₁) progenies. In the hybridization programme, berries were formed while somatic hybrids were used either as male or female parents with common cultivars. Our results revealed that the use of bulk pollen of somatic hybrids not only resulted in higher pollination success but also helped to achieve higher numbers of true potato seeds (TPS) per berry. Despite the formation of berries, TPS was absent in 22 crosses using somatic hybrids as a female or male parent which may be due to ovule or embryo abortions. Segregating BC₁ generations were evaluated under the same sub-tropical conditions for further exploitation in potato breeding. Based on our study, the somatic hybrids P4, P8 and P10 can be utilized for the introgression of important characters such as high tuber dry matter concontration, resistance to late blight and excellent keeping quality attributes into the cultivated potato via conventional breeding methods for cultivar development in the sub-tropical plains of India.     

Stability Analysis of Agronomic Traits in Potato Cultivars of Different Origin

Potato (Solanum tuberosum ssp. tuberosum) cultivars are expected to express a stable level for traits important for growers and consumers. To investigate how this expectation was met by a set of 21 cultivars bred in Hungary, Poland and Spain, 2-year field experiments were carried out in these countries for the evaluation of tuber yield, starch content and yield, and occurrence of secondary growth of tubers. Stability in an agronomic sense was evaluated by the analysis of genotype by environment interaction (GE) using the Scheffé-Caliński mixed model. Unstable trait expression was indicated by the statistically significant share of GE in the variability contributed by a specific cultivar. This instability could lead to either complete or partial unpredictability. Stable trait expression was observed for 6–11 cultivars, depending on the trait. A significant genetic factor, which indicates broad adaptation, was rarely found. Stable expression of tuber yield occurred together with stable or predictable expression of both starch content and yield. Unstable expressions of tuber and starch yield were also associated. The stability or instability of secondary growth was not associated with stability or instability of the other measured traits. Analysis of GE interaction was useful for identifying stable or unstable responses and revealed the presence of incomplete stability or partial unpredictability as intermediate types of reaction.     

The Effect of Long Term Storage on Bacterial Soft Rot Resistance in Potato

Bacterial soft rot is a serious disease in potato (Solanum tuberosum L.), causing rapid tuber tissue maceration and, consequently, marketable yield loss. Soft rot bacteria, including Pectobacterium carotovorum subsp. carotovorum (Pbc), are favored by moist conditions, which are prevalent in large potato storage facilities. However, although most potatoes in North America are stored before use, there are no published surveys of soft rot resistance in cultivars exposed to long-term storage conditions. Thus, we tested 65 cultivars and 13 breeding lines for soft rot resistance after 6 months of storage. There was a significant effect of cultivar and production environment on soft rot resistance score. During 6 months of storage, tuber soft rot resistance in resistant clones did not change, while it changed in susceptible clones. The three most resistant cultivars to soft rot were Freedom Russet, Anett, and Alaska Red Eye.     

Assessing six Austrian potato cultivars for resistance toErwinia carotovora subsp.atroseptica

Summary The susceptibility of six new Austrian cultivars to soft rot, stem rot and blackleg caused byErwinia carotovora subsp.atroseptica was assessed over 2 years in two locations. Soft rot susceptibility was assessed by whole tuber and half tuber tests, stem rot by stem inoculation and blackleg by planting inoculated tubers in the glasshouse. The susceptibility of the cultivars tested with the tuber and blackleg test methods were in general agreement. The half tuber test was more precise in differentiating intermediate levels of susceptibility than the whole tuber test. The reaction of the cultivars to soft rot could be classified as susceptible (Gina and Romina), moderately susceptible (Ditta, Sonja and Bintje), or slightly susceptible (Treff, Komet and Désirée). Results from the stem rot test did not agree with this classification and also depended upon the physiological state of plants as influenced by growing season and glasshouse conditions.     

Assessment of Dormancy and Sprouting Behavior of CIP Elite and Advanced Clones Under Different Storage Conditions in Uzbekistan

In potato breeding and selection, storability should be regarded as equally important as yield, disease resistance, and quality. A study documenting the dormancy period, sprouting behavior, and weight loss of 17 International Potato Center potato elite and advanced clones was carried out in Tashkent, Uzbekistan, under cellar and cold store conditions, during 2008 and 2009. Ninety tubers of each of 17 clones were allocated to experimental units of 30 tubers each placed in trays and randomized in three replications following a random complete block design. Therefore, there were three replications of 30 seed tubers each per entry. The dormancy period ranged from 77 to 115 days and from 100 to 186 days under cellar and cold storage, respectively. There was a relatively high positive correlation (0.69) for dormancy period between storage systems, indicating that clones demonstrating longer and shorter dormancy periods under one system will also behave similarly under the other system. A negative correlation (−0.53 and −0.88) was found between dormancy period and length of the longest sprout in cellar and cold store, respectively, meaning that clones with shorter dormancy often showed a greater length of their longest sprout. The weight loss percentage per tuber was similar in both storage systems, from 5.0% to 8.0% in the cellar and from 5.0% to 9.8% in the cold store, although for different storage periods (an average of 110 and 166 days under cellar and cold storage conditions, respectively). The study indicated that under cellar conditions, clones with a longer dormancy period and slower rate of sprout growth have less weight loss during storage and therefore better keeping quality.     

Influence of Source and Time of Potassium Application on Potato Growth,Yield, Economics and Crisp Quality

Field studies were conducted at the Central Potato Research Institute Campus, Modipuram (India), during two seasons (2003–2004 and 2004–2005), with two processing cultivars (cvs Kufri Chipsona-1 and Kufri Chipsona-2) and nine combinations of potassium source (K-chloride, K-sulphate and K-nitrate) and time of K application (basal dressing, split application and split application + foliar spray) to investigate their effect on tuber yield and processing attributes for crisp production under subtropical conditions. Yearly variations were observed for most of the variables studied. Between cultivars, the tuber and biomass yield was higher in cv. Kufri Chipsona-1, whereas specific gravity, tuber dry-matter percentage and crisp recovery were higher in cv. Kufri Chipsona-2. Stem number, plant height and compound leaf number were not influenced by sources of K fertilizer or application time. Processing-grade tuber yield, total tuber yield and biomass yield were statistically similar for K-chloride and K-sulphate and lower for K-nitrate. K sources affected both specific gravity and tuber dry-matter percentage significantly; K-sulphate and K-nitrate gave significantly higher values than K-chloride. The application time had no significant effect on processing grade and total tuber yield or on tuber specific gravity and dry-matter percentage. Values for crisp colour and reducing sugars were within the acceptable range for all treatments. Crisp yields were calculated to be highest and oil percentage of the crisps to be lowest when K-sulphate was applied as K fertilizer. Net income and benefit:cost ratio were highest for K-chloride followed by K-sulphate and lowest for K-nitrate. The study suggests that for crisping potatoes, K-sulphate is more suited than K-chloride, as it not only increased tuber dry-matter percentage and crisp yield, but also decreased crisp oil percentage.     

Evaluation of Potato Cultivars for Resistance Against Water Deficit Stress Under In Vivo Conditions

Water deficit is the most important abiotic stress factor in crop production. Evaluation of the response of different potato cultivars to water deficit stress is necessary to release cultivars for regions with water deficit. A split-plot experiment with three replications was carried out during 2005 and 2006. The main factor consisted of three levels of irrigation (irrigation after 25%, 35% and 50% discharge of the available water, i.e. normal conditions, mild stress and severe stress, respectively), and the split factor included seven potato cultivars (Agria, Savalan, Satina, Caesar, Kennebec, Marfona and Santé). Cultivars Savalan, Caesar and Kennebec had higher total and marketable tuber yield, water use efficiency, and values for stress tolerance indices than the other cultivars, both under mild and severe stress conditions. Cultivars Caesar and Kennebec were selected as tolerant cultivars; cultivars Savalan and Satina were identified as moderately tolerant cultivars whereas cultivars Agria, Marfona and Santé proved to be susceptible to water deficit.     

Der Einfluss von 2-Chloräthylphosphonsäure auf die Knollenzahl und den Ertrag von Kartoffelsorten unterschiedlicher Reifezeit

Zusammenfassung In 4-j?hrigen Feldversuchen wurde die Wirkung von 2-Chlor?thylphosphons?ure auf die Vermehrungsrate und den Ertrag bei Sorten unterschiedlicher Reifegruppen geprüft. Bei Sorten mit einer l?ngeren Periode der Knollenbildung und einer langsamen Reduzierung der Knollenanlagen führte die Behandlung zu einer Knollenzahlerh?hung und zu einer Verschiebung des Verteilungsmusters zugunsten der kleineren Knollenfraktionen. Die Knollenzahl und der Ertrag der kleinen Pflanzgutfraktion wurde signifikant erh?ht. Der Gesamtertrag wurde im Mittel der Jahre und Sorten signifikant gesenkt, der St?rkegehalt dagegen erh?ht.

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Summary 2-chlorethylphosphonic acid (as the commercial preparation Camposan) was tested on glasshouse and field-grown plants. Resultant graphs of tuberization show that Camposan stimulated the formation of additional sites for tuberization (Figs 1 and 3). Camposan can be applied from bud extension to flowering (Table 1), the beginning of flowering being convenient. A foliar application of Camposan (150 ml ha¹) in three of the four experimental years resulted in a higher tuber number only with Type II cultivars, which have a long tuberization period during which the number of potential sites of tuber initiation decreases only slowly (Table 2). The increase in tuber numbers resulted in an increase in the proportions in the smaller size grades (Fig. 4). When averaged overall cultivars and years. Camposan significantly increased tuber yield and the number of small (30–45 mm) seed tubers, but reduced the numbers of very large (>60 mm) tubers. In the large-tubered cultivars which have short tuberization periods and show pronounced dominance by fewer tubers (Type I, Fig. 2), Camposan did not increase tuber numbers at harvest. When averaged over all cultivars and years, Camposan significantly reduced tuber yield in these cultivars (Table 2) from 3 to 7%, but the starch content of the tubers was increased by 3 to 4% (Table 3).

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Résumé L'effet de l'acide 2-chloroéthyl-phosphonique (sous forme du produit commercial Camposan) a été testé sur plantes en serre et en pleine terre. Les courbes de formation des tubercules établies démontrent que le Camposan augmente le nombre de tubercules (fig. 1 et 3). Le Camposan peut être appliqué dès l'apparition des bourgeons jusqu'à fin floraison (tabl. 1). Le début de la floraison s'est avéré l'époque la plus favorable. Le traitement foliaire au Camposan (150 ml ha¹) n'a eu d'effet favorable durant les 3, voire les 4 années d'essais que sur les variétés de type II (fig. 2). Ces variétés sont caractérisées par une longue période de formation des tubercules et par une lente diminution du nombre des ébauches de tubercules. Par le traitement, on a observé une augmentation du petit calibre (fig. 4). Avec l'application du Camposan, le rendement et le nombre de tubercules plants de petit calibre, 30–45 mm ont augmenté de manière significative en moyenne des variétés et des années (1978–1980); par contre, le surcalibre (>60 mm) a diminué significativement. Pour les variétés qui forment peu mais de gros tubercules, avec une période d'initiation plus courte, le traitement n'a pas permis d'augmenter le nombre de pommes de terre à la récolte (type I, fig. 2 et 3). Les variantes traitées au Camposan présentaient sur la moyenne des années une diminution significative du rendement de 3 à 7% selon les variétés (tabl. 2). La teneur en amidon a été augmentée de 4–10% en valeurs relatives (tabl. 3).

     

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.