Production of seed potatoes in Cyprus: the effects of roguing and planting date on the spread of potato leaf roll virus,tuber yield,and infestation by potato tuber moth

Summary Field experiments during 1984–6 tested the effects of planting date on the development of aphid infestations and the spread of potato leaf roll virus (PLRV) in rogued or unrogued plots of potatoes, cv. Spunta. Plantings were made each month from December to April, the customary time for planting being February. Aphid infestation in early-planted plots was severe throughout the growing season; plots planted in February were also severely infested early in the growing season but the populations later gradually declined to undetectable levels. Nevertheless, the incidence of PLRV in the latter plots was as high as in those planted in December-January. Late-planted crops escaped aphid infestation and PLRV infection, either in part (March planting) or completely (April planting). Such crops, however, were uneconomical due to poor yields and heavy losses from potato tuber moth infestation. Roguing significantly reduced the spread of PLRV in all years but its interaction with planting date was insignificant.     

Plants used in controlling the potato tuber moth, Phthorimaea operculella (Zeller)

A survey of literature (published from 1915 to 1993) on the plants used for the control of the potato tuber moth, Phthorimaea operculella (Zeller) has revealed that the preparations from 35 plant species are effective against the pest either in the storage (non-refrigerated) or in the laboratory. In some studies chopped and dried leaves were used, while in others leaf/seed extracts, fruit peel, bulb, root and rhizome were used. Plant preparations are effective in reducing the pest damage or killing at different stages of the pest.     

Intercellular spaces enhance potato tuber elasticity

Summary The intercellular volume within tuber tissue increases with tuber maturation. At the same time, both tuber injury after mechanical load and lentical perforation after water uptake by tubers in wet peat decreases. The degree of tuber injury is correlated with intercellular space (r=−0.667,n=16) and with water saturation of tissue (r=0.697,n=16). The tubers lose water during storage. In wet soil wilted tubers take up significantly higher amounts of water than turgid tubers, and lenticel perforation is much more frequent. Tuber maturation in autumn and low water loss during storage enhance the cushioning effect of the intercellular gas volume of tuber tissue against outside mechanical load and internal tension after water uptake.     

Somaclonal variation in tuber traits of potato

Summary About 13,000 somaclones of 17 cultivars and clones of potato were obtained from in vitro callus cultures and individually planted in a greenhouse, followed by tuber generations grown in the field. These plants were subjected to the multistage selection procedure commonly used in potato breeding. Over a period of five years and three field generations the tuber number, size, shape, eye depth, starch content, starch yield and tuber appearance of these somaclones were assessed and compared with that of the controls. These characters varied depending on donor genotype and trait. The frequency of variants was assessed and there were acceptable proportions of desirable abberrants and invariants among the somaclones. Depending on trait the average gain rate for all donor genotypes ranged between 0.2 and 2.3% for-deviants, between 12.2 and 15.5% for invariants and between 0.1–1.4% for +deviants. It is concluded that this technique should be used into potato breeding programmes to improve commercially important characteristics of specific cultivars and breeding clones.     

Studies on natural repellents against potato tuber moth (Phthorimaea operculella Zeller) in country stores

Summary The effects of the leaves of five plant species, one from each of the generaAmbrosia, Anemone, Eupatorium, Eucalyptus andLantana, on potato tuber moth were investigated under indigenous storage conditions at the Central Potato Research Station, Shillong (1800 m above sea level). Their action was compared with that of a biological insecticide (spores ofBacillus thuringiensis), a chemical insecticide (carbaryl), and an untreated control. The data collected after six months storage on tuber damage, sprout damage and the rotting indicated that the leaves ofLantana aculeata provided most protection to the tubers, reducing damage from over 70% in the check to below 5%, and sprout damage from over 45% to below 3%. Next best wasEucalyptus globulus followed byB. thuringiensis. They may be used on tubers stored for table use or for seed as they had no adverse effect on germination or on the yield of a subsequent crop.     

Variation in the duration of tuber dormancy within a seed potato lot

Summary The variation in duration of dormancy within a seed tuber lot was studied over three years by harvesting individual plants of cvs Diamant and Désirée from field plots and by storing the tubers at 18°C. The variation in dormancy within a tuber lot was large (especially for cv. Diamant) and was mainly caused by variation within plants. For cv. Diamant there was a close negative relation between dormancy and the cube root of tuber weight, whereas for cv. Désirée a relation with tuber weight was almost absent. The duration of dormancy of a seed lot comprising tubers with a narrow range in weight can be well described by two parameters. It is proposed to maintain the moment of 80% sprouting as the criterion for the end of dormancy of a tuber lot and to characterize the spread in dormancy duration by the time lapse between 10% and 90% sprouting.     

Periderm and lenticel characterization in relation to potato cultivar, soil moisture and tuber maturity

Summary Using the fluorescent lipid stain fluorol yellow 088 to detect suberin in tubers, the numbers of layers and the thickness of the suberized cells in the periderm and within the lenticels showed changes after the early stage of tuber formation. These changes as tubers matured were affected by cultivar and soil moisture conditions. Penetration of the surface tissues of tubers by the water soluble stain safranin O was confined to the lenticles. Although the zone of suberized cells in lenticels acted to some extent as a barrier to penetration, there was not a clear relationship between permeability and suberization. Stored tubers showed thicker suberin berriers in lenticels than freshly harvested tubers. When lenticels of stored tubers proliferated the suberin barrier was disrupted but a further thick suberin barrier formed after exposure to air for two weeks. The findings are discussed in relation to biological control ofErwinia by antagonistic bacteria.     

Comparison of the effect of storage environment on tuber contamination withErwinia carotovora

Summary One tonne boxes of seed potatoes cv. Désirée contaminated withErwinia carotovora were held in four different types of farm stores. In general, contamination fell rapidly immediately after harvest and rose later in the storage season. The extent of these changes varied considerably with store type. The greatest reduction was from a log count of 5.5 to 2.1 after one month storage, followed by a rise to 5.1 prior to planting. No relationship was found between store temperature, relative humidity and change in contamination. There was some evidence that reduction in contamination was related to duration of ventilation, and rise in contamination to onset of sprouting. A sample held at a constant 4°C showed little reduction in contamination, and no rise occurred later in the storage season.     

Aspects of nitrogen fertilizer rate on tuber dry-matter content of potato cv. Record

Summary Effects of three rates of fertilizer nitrogen, viz. 80, 160 and 240 kg N/ha, on tuber yield and dry-matter percentage in potato cv. Record were compared in two experiments. Crop nitrogen uptake increased with application rate but total uptake differed between experiments. Tuber yield was highest following application of 160 or 240 kg N/ha but differences between these two rates were not significant. Tuber dry-matter percentage was reduced in one experiment with increasing nitrogen rate, but in the second experiment final dry- matter percentage was highest following application of 240 kg N/ha. In all treatments, positive linear relationships were found between dry matter percentage and mean fresh weight of tubers >30 mm, but within experiments, the regression coefficients were generally reduced by increased crop nitrogen uptake.     

Seed tuber production from true potato seed (TPS) in Egypt and the influence of environmental conditions in different growing periods

Summary The effect of environmental conditions on seed tuber production from true potato seed (TPS) in nurseries was evaluated in different growing periods during two seasons in Egypt. In the autumn season, high soil and air temperatures reduced emergence and initial foliage development of early-sown seedlings, and decreased tuber yields. In late-sown seedlings low night temperatures and short daylengths caused early tuberization, poor foliage development and low tuber yields. In the spring season, low temperatures and short daylengths resulted in a slow initial foliage development and early haulm-tuber competition for assimilates in early-sown seedlings. However, tuber yields were higher than for late-sown seedlings, presumably because net assimilation and assimilate partitioning to the tubers were impaired by above optimum air and soil temperatures in May and June. Slow development of true seed-sown plants caused a high sensitivity towards adverse environmental conditions and would limit yielding ability in Egypt.     

Penetration of potato tuber lenticels by bacteria in relation to biological control of blackleg disease

Summary In a glasshouse experiment three potato cultivars were grown to maturity in wet or dry compost. The number of lenticels per tuber was greater with larger tubers but was unaffected by the cultivar or soil moisture regime. The frequency of lenticel penetration by a water soluble stain, safranin O, remained high as tubers developed to maturity in wet soil. In dry soil penetration declined markedly as the tubers matured. When tubers, harvested just before the onset of haulm senescence, were inoculated withErwinia carotovora ssp.atroseptica, the frequency of lenticel rotting was less than the rate of stain penetration, indicating that additional factors were involved in the bacterial infection process. Inoculating mature tubers with bacteria and incubating them in anaerobic conditions frequently resulted in rotting of the lenticels. Comparable tubers incubated in aerobic conditions showed no rotting or invasion by bacteria. The results are discussed in relation to the biological control of blackleg.     

Leaf effects of wild species ofSolanum and interspecific hybrids on growth and behaviour of the potato tuber moth,Phthorimaea operculella Zeller

Summary Four introductions ofSolanum berthaultii wild species and sevenS. tuberosumxS. berthaultii hybrids were evaluated by antibiosis and antixenosis laboratory tests with potato tuber moth. Some morphological and chemical traits related to the trichomes were analysed. Two clones of the wild speciesS. sparsipilum and five ofS. pinnatisectum, characterised by high tuber resistance, were tested for leaf resistance, both by antibiosis and antixenosis assays. The genotypes with high density of trichomes A and with high exudate PPO activity, showed a moderate negative effect on pupal weight and fecundity in the antibiosis tests. Trichomes B exudate showed a strong repulsive effect on oviposition of adult in the antixenosis tests. TheS. pinnatisectum clones revealed a good leaf resistance level, whereas theS. sparsipilum clones showed lower levels of antibiosis and antixenosis.     

Integrated pest management in faba bean

Successful production of faba bean crops in the presence of a wide range of disease-causing fungi, parasitic weeds, nematodes, insects, mites and other pests depends on the integration of genetic resistance, hygienic management, monitoring of the target organisms and timely application of appropriate chemical and biological treatments. This paper reviews the progress in this area.     

Integrated pest management in field vegetable crops in northern Europe — with focus on two key pests

Improvements in (1) insecticide application, (2) supervised control, and (3) pest forecasting systems have each helped to reduce considerably the amounts of insecticides required to control fly, caterpillar and aphid infestations in vegetable crops in northern Europe. By growing plants that are partially resistant to certain major pests, it is now possible to apply even less insecticide than the dose recommended for the crop. In crops where only small amounts of insecticides are applied, natural predators should prevent large increases in pest insect populations and natural parasitoids should reduce the numbers of pest insects entering subsequent generations. The possible impact of introducing transgenic plants and the use of physical (crop covers), cultural (crop rotation, undersowing) and microbial (e.g. fungi, bacteria and nematodes) methods of control are also discussed. The withdrawal of certain insecticides, as a result of environmental and commercial pressures, means that some crops may soon be without appropriate insecticides for controlling one or more of the major pest species. Whether such systems will be sustainable, remains to be seen.     

The effect of potato seed tuber age and soil temperature on the phenomenon of non-emergence

Summary In three experiments seed tubers of cvs Jaerla, Bintje and Alpha, stored at 12 °C in the dark, were planted in glasshouses on various dates at soil temperatures varying from 8 °C to 28 °C to study the phenomenon of ‘non-emergence’ with ageing seed tubers. In general the tubers were desprouted before planting. At all plantings cv. Alpha produced normal plants. The cvs Jaerla and Bintje, however, showed high proportions of the ‘little potato’ phenomenon when planted in cold soil, and high proportions of decayed tubers more frequently in warm soil. When using physiologically older seed at later planting dates, both the range of soil temperatures became wider and the proportions of seed tubers experiencing both ‘little potato’ and decay increased.     

Some observations of patterns of tuber formation and growth in the potato

Summary Patterns of tuber formation and growth were studied with the varieties Désirée Maris Piper and Peniland Crown. The varieties formed similar numbers of stolons but different numbers of tubers. More tubers were formed at the first node than at any other but Pentland Crown formed fewer tubers over nodes 2–8 than the other varieties. The range of nodes over which tubers formed and competition for photosynthate within a node appeared to be factors controlling the tuber size distribution. The time over which tuber formation occurred was not important. Measurements of individual tuber growth suggested that some tubers followed an approximately sigmoid curve, some grew linearly and some showed periods of tuber growth interrupted by periods when the tubers grew slowly if at all. Estimation of the fresh and dry weights of growing tubers using a relationship between the product of tuber axis lengths and the weights of harvested tubers proved most satisfactory.

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Zusammenfassung In einer Reihe von Versuchen, bei denen die Sorten Désirée, Maris Piper und Pentland Crown verwendet wurden, wurden die Muster der Knollenbildung und das Knollenwachstum untersucht. Diese 3 Sorten haben bei gleichem Pflanzenabstand eine unterschiedliche Verteilung der Knollengr?sse; Pentland Crown neigt zur Produktion grosser Knollen, Maris Piper bringt viele kleinere Knollen und Désirée liegt dazwischen. Um die Knollenbildung zu verfolgen, wurden dreimal in der Woche Proben der wachsenden Pflanzen genommen und die Zahl der Stolonen und Knollen pro Nodium gez?hlt (Tabelle 1). Um das Wachstum der Einzelknollen in Kisten (Fig. 1) und im Feld unter Polythenfolie (Fig. 2) zu verfolgen, wurden die drei Hauptachsen gemessen und daraus das Volumen (in der Annahme, dass die Knolle ein Ellipsoid ist) oder das Gewicht errechnet (wobei das lineare Verh?ltnis zwischen dem Produkt der Knollenachsen und dem Frisch- und Trockengewicht von Knollen verwendet wurde, die unter gleichen Bedingungen gewachsen waren und jede Woche geerntet wurden, wenn die Messungen gemacht wurden). Diese Technik erwies sich als befriedigend und in Tabelle 2 sind die Werte der Parameter für die erste und letzte Messung in jedem Jahr zusammen mit den entsprechenden Bestimmtheitsmassen angegeben. Die Sorten bildeten die gleiche Anzahl von Stolonen aber unterschiedliche Knollenzahlen. Am ersten Knoten wurden mehr Knollen als an irgend einem anderen gebildet, aber Pentland Crown bildete an den Nodien 2–8 weniger Knollen als die anderen Sorten. Das Verh?ltnis der Gesamtzahl der Knollen pro Nodium und der Knollenzahl pro Nodium ausgedrückt in Prozent der Stolonenzahl (Fig. 3) unterschied sich zwischen den Sorten betr?chtlich und ist vielleicht für die unterschiedliche Verteilung der Knollengr?ssen verantwortlich. Die Zeit der Knollenbildung war bei allen Sorten gleich. In den Versuchen über das Knollenwachstum wurden mehr als 500 Knollen gemessen und einige sind in Fig. 4–6 dargestellt. Es sieht so aus, als ob einige Knollen einer ungef?hr S-f?rmigen Kurve folgten, einige wuchsen linear und einige zeigten Perioden des Wachstums, die durch Perioden unterbrochen waren, in denen die Knollen wenn überhaupt nur langsam wuchsen.

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Résumé Des types de tubérisation et de croissance ont été étudiés au cours d'une expérimentation de variétés portant sur Désirée, Maris Piper et Pentland Crown. Plantées à la même densité, ces variétés donnent différentes répartitions de calibre. Pentland Crown tend à produire de gros tubercules; Maris Piper produit un grand nombre de petits tubercules et Désirée est intermédiaire. La tubérisation a été suivie en prélevant des échantillons en cours de végétation 3 fois par semaine et en enregistrant le nombre de stolons et de tubercules formés à chaque noeud (tableau 1). Le grossissement de chaque tubercule, en caisses de bois (fig. 1), et au champ sous polyéthylène (fig. 2), a été suivi en mesurant les trois axes principaux et en transformant ces mesures en volume (on suppose que le tubercule est un ellipso?de), ou en poids (en utilisant la relation linéaire entre produit des axes et poids frais et sec des tubercules cultivés dans des conditions identiques et récoltés chaque semaine). Cette technique donne satisfaction et les valeurs des paramètres pour les premières et dernières mesures de chaque année sont indiquées dans le tableau 2 avec les coefficients de détermination appropriés. Les variétés forment un nombre de stolons similaire mais un nombre de tubercules différents. Des tubercules plus nombreux se sont formés au premier noeud, mais Pentland Crown présentait moins de tubercules aux noeuds, 2–8 que les autres variétés. Le rapport du nombre de tubercules par noeud et du nombre de tubercules formés à chaque noeud, exprimé en pourcentage du nombre de stolons (fig. 3) différait considérablement d'une variété à l'autre. La répartition des calibres de ces variétés a probablement été influencé. L'époque de tubérisation était la même pour chacune d'entre elles. Au cours de cette expérimentation, plus de 500 tubercules ont été mesurés (fig. 4–6). Pour certains tubercules, il appara?t que la courbe tubérisation s'apparente à une sigmo?de. Pour d'autres, la croissance est linéaire, parfois interrompue par des périodes de croissance ralentie.

     

Studies onFusarium wilt of potatoes. 1. Plant wilt and tuber infection in naturally infected fields

Summary Field surveys of 2600 plants during growth of the autumn crop and of 1700 plants of the spring crop showed that 6.5% and 4.0% respectively were attacked byFusarium wilt; on average, 40% of the tubers from wilted plants were infected. Similar results were obtained in an artificially infested field. Examination of 6105 planting positions in the field during growth of the autumn crop showed that 28.7% of seed tuber rots were caused byFusarium oxysporum f.sp.tuberosi, while in spring crop this percentage was much lower. The yield in an artificially inoculated field was reduced from 10 to 53% compared to controls, depending on the cultivar.

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Zusammenfassung In Felduntersuchungen wurden mitFusarium infizierte Pflanzen und Knollen nach dem Zufallsprinzip erfasst, und zwar an verschiedenen Orten in mehreren Feldern an jeweils mindestens 100 Pflanzstellen. Von den 2600 Pflanzen aus dem Herbstanbau und 1700 aus dem Frühjahrsanbau, waren 6,5% bzw. 4,0% von derFusarium-welke befallen (Tab. 5). Von 30 Pflanzen mit Welkesymptomen starben 6 vor dem Knollenansatz ab, die übrigen 24 hatten 119 Knollen, von denen 48 mitFusarium infiziert waren. Nach 3 Monaten waren von denselben Knollen noch 34% mitFusarium befallen (Tab. 6). Die Untersuchung des Knollenauflaufs an 6105 Pflanzstellen ergab im Herbst eine Auflaufrate von nur 81,7%. Von den restlichen 18,3% der nicht gekeimten Knollen wurden 29,7% nicht wiedergefunden, 23,3% hatten Nassf?ule und in nur 2,3% fauler Knollen wurdenRhizoctonia undSklerotium gefunden. 44,7% der F?ulen waren vonFusarium-Trockenf?ulen verursacht worden. Isolierungen von 106 dieser Knollen ergaben in 68 F?llen Befall mitFusarium oxysporum, das entspricht 5,2% von der gesamten Probe (Tab. 4). Die Ergebnisse aus dem Frühjahrsanbau waren ?hnlich, die Verluste jedoch viel geringer. In der experimentellen Arbeit wurden Knollen verschiedener Sorten aus Pflanzkartoffelgebieten verwendet sowie einF. oxysporum f.sp.tuberosi-Isolat von einer griechischen Kartoffelpflanze mit Welkesymptomen. Der Krankheitsindex erstreckte sich von 0,20 bis 1,07, so dass der mittlere Ertrag nicht reduziert war. Die neuen Knollen zeigten im Lager eine Gesamtinfektion mitFusarium von 5–42% (Tab. 7), was gut mit den Felduntersuchungen übereinstimmt. Die lineare Regression des Ertrages in Bezug auf den Krankheitsindex ergab eine Ertragsreduktion von 10 bis 53%.

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Résumé Au cours d'observations au champ réalisées dans différents endroits,Fusarium contamine les plantes et les tubercules dans pas moins de 100 cas par endroit. Un flétrissement provoqué parFusarium a été observé sur 2600 plantes en culture d'automne et sur 1700 plantes en culture de printemps, avec respectivement un taux de 6,5% et 4,0% (tabl. 5). Sur 30 plantes flétries, 6 sont détruites avant formation des tubercules. Les 24 plantes restantes produisent 119 tubercules dont 48 sont infectés parFusarium. Les mêmes tubercules, trois mois après, présentent 34% deFusarium (tabl. 6). L'examen de tubercules formés pendant l'automne dans 6105 endroits montre que 81,7% de tubercules ont germé et sur le reste non germé, 29,7% ont disparu, 23,3% sont pourris alors queRhizoctonia etSclerotium sont responsables de seulement 2,3% de tubercules pourris. Les 44,7% des tubercules restants sont atteints de pourritures sèches provoquées parFusarium. Les isolements réalisés à partir de 106 de ces tubercules metent en évidence la présence deF. oxysporum dans 68 cas ce qui représente 5,2% de l'ensemble des échantillons (tabl. 4). Les résultats concernant les cultures de printemps sont similaires mais les pertes sont plus faibles. Dans un travail expérimental sont utilisés des tubercules provenant de régions de production de différentes variétés de semences et un isolat deF. oxysporum f.sp.tuberosi provenant de plantes de pomme de terre flétries de Grèce. L'indice de maladie étant entre 0,20 et 1,07 ce qui ne réduit pas le rendement moyen. Les nouveaux tubercules stockés ont présenté un degré d'infection totale parFusarium de 5 à 42% (tabl. 7) ce qui est en complet accord avec les observations au champ. Une régression linéaire entre rendement et indice de la maladie montre des réductions de rendement de 10 à 53%.

     

Members of the Kunitz-type protease inhibitor gene family of potato inhibit soluble tuber invertase in vitro

Summary A soluble proteinaceous invertase inhibitor was purified from tubers of cv. Provita. N-terminal amino acid sequencing of the purified protein indicated that the invertase inhibitor was a member of a family of small tuber proteins known as Kunitz-type protease inhibitors. The purified protein was completely inhibitory to soluble tuber invertase at quantities that did not inhibit trypsin. Based on amino acid sequence information of invertase inhibitor protein, seven candidate cDNA clones were identified in libraries of Provita and Saturna tubers. The candidate cDNA sequences differed from each other between 2% and 5%, having several non-conservative amino acid substitutions when compared with sequence related protease inhibitors. The results suggest invertase as an alternative target of tuber “protease” inhibitors.     

Model calculations for the effects of nitrogen,phosphorus, and potassium nutrition on the behaviour of potato tubers in storage

Summary Empirical mathematical models are described for calculating the effects of varying supplies of nitrogen, phosphorus and potassium on pot and field grown tubers. Through optimization and simulation, potato tuber fresh and dry weight losses and chemical composition changes (ascorbic acid, citric acid, glucose, fructose, sucrose, nitrate) are calculated over a 6-month period of storage at 4°C. The effects of variation in single nutrients as well as of increasing N fertilization on storage are calculated. Calculations giving the maximum vitamin C content at harvest and after storage indicate the nutrient supply required.     

Differential resistance to tuber late blight in potato cultivars without R-genes

Summary In 1983 and 1984 there were reports in Norway of more severe late blight infection than usual on tubers of cv. Pimpernel, a cultivar without R-genes known to be somewhat resistant to both haulm and tuber infection. Results from routine tests confirmed earlier experience that cv. Pimpernel shows stable resistance to tuber late blight, although the ranking of cultivars may vary between years. In experiments during three harvest seasons tubers of different cultivars were inoculated with isolates ofP. infestans obtained from stocks of cv. Pimpernel with severe tuber late blight and with other isolates. In these experiments the isolates from cv. Pimpernel caused more rot on tubers of Pimpernel than did other isolates.