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.     

The physico-chemical properties of the seed and seed oil ofJatropha gossipifolia

The physico-chemical properties of the seed and seed oil ofJatropha gossipifolia were assessed by standard methods. The seed contains 35.8% crude oil of iodine value 107.25, 13.40% protein, 9.25% fibre, 30.32% carbohydrate and 6.0 g/kg saponins. The fatty acid composition of the seed oil was determined by GC-MS. Caprylic, myristic, palmitoleic, palmitic, oleic, stearic, linoleic, vernolic, arachidic, behenic and lignoceric acids were found.     

Seed proteins ofPisum mutants and recombinants

The seed protein production of more than a hundredPisum mutants and recombinants was determined. There is a negative correlation between seed production and protein content of the seed meal in the material tested. Geneipc of thePisum genome increases the protein content of the seed flour by about 20%, but the mutant carrying this gene and the recombinants available so far produce only low amounts of protein, due to their poor seed production. The biochemical methods used allow the detection of the genetic diversity as expressed in altered gene products in closely related genotypes. Many mutants and recombinants, derived from the same mother variety, are available in our collection showing not only quantitative and qualitative differences in their seed proteins, but also other characters of agronomic interest such as higher yield or adaptation to distinct climatic conditions. They represent a suitable material for analyzing the regulatory mechanisms controlling the incorporation of proteins into seeds.     

Shortening dormancy of seed potatoes by storage temperature regimes

Summary Four experiments (three with four cultivars, one with twenty cultivars) investigated the effect of different storage temperature regimes on the duration of dormancy of seed potatoes harvested immature. Regimes included constant temperatures (18 and 28°C), hot pre-treatments (20 days at 28°C and subsequently 18°C) and cold pre-treatments (20 days at 2°C and subsequently 18°C). Compared with 18°C, storage at 28°C slightly prolonged dormancy of some cultivars with a genetically short dormancy and shortened dormancy by up to 45 days in cultivars with a long dormancy. Some tubers of one cultivar lost their ability to sprout after storage at 28°C for 90 days. A hot pre-treatment shortened dormancy by 2–3 weeks on average, for all cultivars examined. A cold pre-treatment shortened dormancy by 2 weeks on average in some cultivars with a short dormancy and in all cultivars with a long dormancy.     

Chemical changes in developing lupine seed

Developing seeds of lupine cultivars Kali, Neuland, Reuscher and Unicrop, grown under field conditions, were sampled at different stages of maturity and analysed for total nitrogen, crude fat and fatty acid composition. Nitrogen and lipid deposition occurred between 30 and 60 days after anthesis coinciding with the stage of maximal dry weight increase of the developing seed. The rate and duration of dry matter, nitrogen and crude fat accumulation was cultivar dependent. Percent of total saturated fatty acid decreased with increasing seed development.Contribution No. 636, with financial assistance from Agriculture Canada and Natural Sciences and Engineering Research Council, Canada.     

Nutritional potential ofVigna minima (Roxb.) Ohwi and Ohashi:

Quantitative variation in different fractions of seed proteins and their amino acid levels in populations ofVigna minima (Roxb.) Ohwi and Ohashi and inV. umbellata cv. IC 1568 — the rice bean — were investigated. Globulin I fraction, together with globulin II, constitutes 38 to 54 per cent of the total seed protein. The alkali soluble (glutelin) fraction is the second largest fraction. Both these fractions show broad range of variation, suggesting a broad genetic base. The profiles are population specific; the coastal population, which contains higher seed protein also possesses maximum levels of globulin I and glutelin fraction suggesting its potentiality for breeding lines with high protein content, high nutritive value, and salt tolerance. Protein content is positively correlated with globulin I and glutelin fractions, which are in turn positively correlated with each other. The amino acid profiles are specific not only to the fractions but also to the populations. The range of variation in the levels of all amino acids in different fractions is broad suggesting substantial genetic diversity. The average levels of lysine and sulphur amino acids are high in globulin I and glutelin fractions.     

Tetrodotoxin concentrations in Pleurobranchaea maculata: temporal, spatial and individual variability from New Zealand populations

Tetrodotoxin (TTX) is a potent neurotoxin that has been identified in a range of phylogenetically unrelated marine and terrestrial organisms. Tetrodotoxin was recently detected in New Zealand in Pleurobranchaea maculata (the grey side-gilled sea slug). From June 2010 to June 2011 wild specimens were collected from 10 locations around New Zealand. At one site (Narrow Neck Beach, Auckland) up to 10 individuals were collected monthly for 6 months. Attempts were also made to rear P. maculata in captivity. Tetrodotoxin was detected in samples from eight of the ten sites. The highest average (368.7 mg kg⁻¹) and maximum (1414.0 mg kg⁻¹) concentrations were measured in samples from Illiomama Rock (Auckland). Of the toxic populations tested there was significant variability in TTX concentrations among individuals, with the highest difference (62 fold) measured at Illiomama Rock. Tetrodotoxin concentrations in samples from Narrow Neck Beach varied temporally, ranging from an average of 184 mg kg⁻¹ in June 2010 to 17.5 mg kg⁻¹ by December 2010. There was no correlation between TTX levels and mass. The highest levels correspond with the egg laying season (June–August) and this, in concert with the detection of high levels of TTX in eggs and early larval stages, suggests that TTX may have a defensive function in P. maculata. Only one larva was successfully reared to full maturation and no TTX was detected.     

Nutritional assessment of seed proteins in rice bean [Vigna Umbellata (Thumb.) Ohwi and Ohashi

Seeds of three rice bean accessions had 17.26 to 21.42% protein, 3.46 to 4.03% fat, 61.09 to 64.73% carbohydrates 3.99 to 4.58% ash and 5.22 to 7.43% fiber (dry weight basis).The most limiting amino acids in the seed meal, albumin and globulin fractions, were methionine and cysteine with chemical scores of these fractions being 38% to 59%. The amino acid pattern of globulin and seed meal were similar.Thein vitro protein digestibility (IVPD) ranged from 82 to 86% for the seed meal, 86 to 88.5% for the albumin and 75.9 to 83.3% for the globulin. Relative nutritive values (RNV) of raw mature seed of two accessions were 22.6% and 42.4% and increased to 55.6% to 79.4% after boiling and roasting.Part of MS thesis of the senior author.     

Production of above-ground seed tubers on stem cuttings from eight potato cultivars

Summary The formation of above-ground tubers on stem cuttings of eight potato cultivars was studied over three seasons. To promote tuber formation in the leaf axils, stems grown from single node cuttings were exposed to short day conditions. Tuber formation underground was reduced by covering the soil with a plastic sheet and by using single node cuttings planted with the leaf axils several centimetres above the soil surface. With all cultivars except Alpha, which produced mis-shapen tubers in all experiments, an average of 11 (maximum 40) tubers per cutting were harvested. Significant cultivar × year interactions were observed.     

Effects of contamination byErwinia carotovora subsp.carotovora andE. carotovora subsp.atroseptica of potato seed tubers and of cultivar resistance on blanking or nonemergence and blackleg development in Valencia,Spain

Summary High grade potato seed tubers of three cultivars were inoculated in Scotland by vacuum infiltration in suspensions ofErwinia carotovora subsp.carotovora and subsp.atroseptica in different combinations, and transported to Valencia, Spain. They were cut into two to three pieces and planted in January 1984, 1985 and 1986 in fields furrow irrigated before and after emergence. High incidences of blanking and blackleg were associated with seed inoculated with high numbers ofE.c. atroseptica alone or together withE.c. carotovora and not with high or low numbers ofE.c. carotovora alone.E.c. atroseptica predominated at emergence in March in rotting seed pieces which failed to produce a plant, regardless of the seed treatment, and in diseased stems in April but it was replaced byE.c. carotovora in May. The levels of blanking and blackleg after inoculating 16 cultivars with both erwinias were not correlated between years nor were they significantly different within years among most of the cultivars.     

Effect ofErwinia carotovora subsp.atroseptica on yield of potatoes from cut and uncut seed tubers in Valencia

Summary The effect on the development of blackleg symptoms and on yield of inoculating seed tubers of 15 cultivars withErwinia carotovora subsp.atroseptica (Eca) was investigated. Tubers were planted either whole or as pieces. Eca inoculation reduced the mean yield per plant by 8% for whole tubers and by 12% for cut tubers. There was no correlation between blackleg symptoms and yield loss.     

Comparison of two seed oils used in cosmetics, moringa and marula

Comparison of the seed oil of Moringa pterygosperma (moringa) and Sclerocarya birrea (marula) showed a marked difference in fatty acid composition and oxidative stability. Moringa, with 1000 ppm tocopherols, had an oil stability index (OSI) of 133 h at 110 °C while marula with 1000 ppm tocopherols yielded 37 h at 110 °C. This correlated well with the fatty acid composition of these two oils. Moringa had less than 1% polyunsaturates and marula had 6.7% of these oxidatively unstable materials. In addition, fatty acid compositions of seven species of moringa are presented. All of these species had levels of behenic acid ranging from 1 to 7% with oleic acid levels from 68 to 79%. The highest amount of polyunsatures was found in the moringa species was in Moringa drouhardii with 3.6%.     

Certain functional properties of defatted pumpkin seed flour

Defatted pumpkin (C. pepo andC. maxima) seed flour has potential food uses because of its high protein content, 61.4±2.56%. The functional and electrophoretic properties of the defatted flour were investigated. Polyacrylamide gel electrophoresis and electrofocusing indicated 14 bands of water-soluble protein subunits with isoelectric points between 3.81–8.08 and apparent molecular weights between 19,200 and 97,000 daltons. Minimum nitrogen solubility was observed at pH values between 3.0–7.0 and exceeded 90% at pH above 9.0. Solubility was a function of ionic strength. It appeared that, even at the pH of minimum solubility, the pumpkin seed proteins could be dissolved up to high concentrations by increasing NaCl molarity. The viscosity of flour-water dispersion was affected by flour and salt concentrations, and temperature. The least gelation concentration was 8% (w/v) and the water and oil absorption 24.8±2.03 and 84.4±4.05 g/100 g respectively. Sorption isotherms, BET monolayer moisture and binding energy of sorption were also calculated. Both foam capacity and stability were pH dependent.     

Contamination of pathogen-free seed potato stocks byErwinia carotovora during multiplication: Results of a six-year monitoring study

Summary Recontamination byErwinia carotovora of seed potato stocks (VT) derived from stem cuttings in the process of multiplication was monitored on four farms in the east of Scotland from 1973 to 1978. Randomly selected VT stocks of different ages from a wider range of farms were also examined. The results showed that although contamination can occur early during stock multiplication there was, in general, no stepwise increase in contamination level from one generation to the next. However, contamination tended to be greater after the third multiplication year when stocks are grown by conventional methods used for lower-grade seed stocks. It is notable that contamination was consistently high on some farms and low on others. Contamination byE. carotovora var.carotovora tended to be greater than byE. carotovora var.atroseptica. These results may be explained by the farm practices of individual growers, soil moisture status and aerial transmission of the bacteria. The results also indicate that contamination of some potato stocks derived from stem cutting could be maintained at a low level over several generations more readily on some farms than on others.

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Zusammenfassung Von 1977 bis 1978 wurde auf vier Betrieben im Osten Schottlands im Laufe der Vermehrung von Pflanzkartoffelposten (SC), die von Stengelschnitten stammten, eine erneute Verseuchung durchErwinia carotovora beobachtet. Zudem wurden Stichproben von SC-Posten unterschiedlichen Alters aus einer gr?sseren Zahl von Betrieben untersucht. Die Zusammenfassung aller Ergebnisse der vier Betriebe zeigte, dass die ersten drie Generationen der Best?nde (Vermehrungsjahre 1 bis 3) zu weniger Ansteckung neigten als jene in den Jahren 4 und 5, wenn die Posten zur Erzielung von Saatgut tieferer Anbaustufen (Tabelle 1) mit konventionellen Handelsmethoden behandelt wurden. H?here Verseuchungsgrade wurden auch in den Jahren 4 und 5 in den Stichprobenposten erreicht (Tabelle 5). Wenn die Daten Betrieb für Betrieb analysiert wurden, fand man auf einigen Betrieben durchwegs hohe und auf anderen niedrige Verseuchungsgrade (Tabelle 2). Obwohl die Gesamtzusammenfassung der Daten (Tabelle 1) darauf hinwies, dass sowohlE. carotovora var.carotovora als auchE. carotovora var.atroseptica in ungef?hr gleichem Ausmass vorhanden waren, war der erste Organismus auf drei von vier Betrieben und der letztere auf dem vierten Betrieb vorherrschend (Tabelle 3). Obwohl die Ansteckung früh w?hrend der Bestandesvermehrung auftreten kann, gab es im allgemeinen keinen Entwicklung im Verseuchungsgrad. Statt dessen fiel der Verseuchungsgrad manchmal von einer Generation zur n?chsten (Tabelle 4). Diese Ergebnisse wurden versuchsweise mit dem Aufwand an Sorgfalt durch den einzelnen Pflanzen, durch den Zustand der Bodenfeuchtigkeit und durch den Lufttransport der Bakterien erkl?rt. Auf einigen Betrieben konnten die Kartoffelbest?nde nicht nur über einige Generationen relativ frei von Ansteckung durchE. carotovora erhalten werden, sondern weisen auch darauf hin, dass seit 1973 eine deutliche Verbesserung eintrat, selbst wenn einige Jahre n?sser und damit für die Bestandesverseuchung günstiger waren als andere (Tabelle 6). Parallel mit dieser Abnahme der Verseuchung verl?uft ein schw?cheres Auftreten der Schwarzbeinigkeit in Pflanzbest?nden, die seit 1973 zur Feldbesichtigung angemeldet wurden, als ein stets h?herer Anteil von Best?nden von Stengelschnitten stammte (Tabelle 7).

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Résumé La recontamination parErwinia carotovora de lignées de pommes de terre de semences (SC)_ provenant de bouturage dans le procédé de multiplication a été contr?lée dans quatre exploitations agricoles dans l'est de l'Ecosse de 1977 à 1978. Des lignées de bouture, sélectionnées au hasard, de différents ages, provenant d'une plus grande gamme d'exploitations, furent aussi examinées. Le résumé des résultats obtenus dans les quatre exploitations montraient que les trois premières générations de récolte (années de multiplication 1 à 3) avaient tendance à être moins contaminées que celles des années 4 et 5 quand les lignées avaient été traitées par des méthodes commerciales conventionnelles utilisées pour des clones de qualité inférieure (tableau 1). De hauts niveaux de contamination furent aussi obtenus dans les années 4 et 5 des lignées sélectionnées au hasard (tableau 5). Quand les données furent analysées ferme par ferme, les niveaux de contamination montrèrent qu'ils étaient significativement hauts dans certaines exploitations et bas dans d'autres (tableau 2). De la même manière, quoique le résumé des résultats (tableau 1) suggère queErwinia carotovora var.carotovora etErwinia carotovora var.atroseptica étaient présents en même quantité, le premier pathogène prédominait dans 3 exploitations sur quatre, et le dernier dans la quatrième exploitation (tableau 3). Bien que la contamination puisse avoir lieu au début de la multiplication de la lignée, il n'y a pas eu, en général, de niveau de contamination avancée. Le niveau de contamination tombait même quelquefois d'une génération à l'autre (tableau 4). Les résultats s'expliquaient par l'importance des précautions prises par les agriculteurs, le niveau d'humidité dans le sol et la transmission aérienne des bactéries. Non seulement on a pu maintenir dans quelques exploitations des lignées de pommes de terre relativement indemnes de contamination parErwinia carotovora pendant plusieurs générations, mais encore les résultats suggèrent qu'une amélioration notable a eu lieu depuis 1973 pendant certaines années plus humides, et par conséquent plus favorables à la contamination de la récolte que d'autres (tableau 6). Parallèlement à cette réduction de contamination, la jambe noire a eu moins d'importance dans les cultures de semence soumises au contr?le depuis 1973, tandis qu'une proportion de plus en plus élevée provenait de bouture (tableau 7).

     

Physico-chemical composition and characterisation of the seed and seed oil ofSclerocarya birrea

The physicochemical composition ofSclerocarya birrea was assessed by standard methods and was found to contain 11.0% Crude oil, 17.2% Carbohydrate, 36.70% Crude protein 3.4% fibre and 0.9% crude saponins. The fatty acid distribution in the seed oil was obtained by fractionating the volatised fatty acid by GC-MS. The oil is made up of nine fatty acids of which palmitic, stearic and arachidonic acids are the most dominant.     

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.     

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.

     

Influence of seed tuber infestation,chemical seed treatment,and pre-harvest climate on incidence of gangrene and dry rot of potato (Solanum tuberosum L.)

Summary In each of the five years 1978 to 1982, seed lots of cv. Bintje, variously infested byPhoma foveata Foister andFusarium solani var.coeruleum (Sacc.) Booth, as found by wound and cut tests, respectively, were planted in a series of field experiments at six sites in Sweden. A statistically significant relationship between seed and progeny infestation was found forP. foveata each year, and in three years forF. solani. Benomyl and thiabendazole mist treatments of seed tubers at grading in spring controlled the development of gangrene and dry rot in treated seed tubers, but did not consistently reduce the levels ofP. foveata andF. solani infestation in progeny from treated seed tubers. The site of cultivation markedly influenced mean levels ofP. foveata infestation, which were found to be related to temperature and rainfall during a 40 day pre-harvest period at the trail sites; however, mean levels ofF. solani infestation were not so related.     

Aspects of insecticide resistance and reproductive biology ofAphis gossypii glover on seed potatoes

Summary For several years the aphid population patterns and the incidence of the main potato virus diseases have been monitored in Italian potato-growing areas. Starting from 1992, an increase inAphis gossypii, as compared toMyzus persicae, Macrosiphum euphorbiae andAphis fabae, was observed on seed potato fields in the north of Italy. Laboratory tests revealed thatA. gossypii was insensitive to the pesticide pirimicarb, even at the maximum dose tested (2400 μg/ml). Moreover, in the presence of pirimicarb the reproductive capacity increased up to 30% as compared with the control, and the new-born aphids began to appear 2 days earlier in the treated group. By contrast,M. persicae was controlled at a lower dose (300 μg/ml). Lambda-cyhalothrin and imidacloprid were very effective against both aphids.     

The feasibility of predicting the number of stems per tuber produced by potato seed stocks from measurements made before planting

Summary The number of stems per seed tuber produced by 17 seed stocks of cv. Record was determined in glasshouse and field experiments to assess the feasibility of predicting the number of stems produced in the field. Multiple regression analysis showed that seed tuber weight alone gave the most satisfactory fit to stems produced in the field, which was not improved by adding terms involving the number of stems produced in the glasshouse. Quadratic relationships between the number of above-ground stems per tuber and tuber weight were most appropriate for each stock, with the fitted curves for individual stocks differing only in the constant term. However, there were significant rank correlation coefficients between the constant terms for relationships between field stems and tuber weight and glasshouse stems and tuber weight, suggesting that in other cultivars and seed stocks a predictive glasshouse test might still be useful.