Etablierung von Kartoffelsorten im Feld nach physiologischer Alterung der Pflanzknollen

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

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

     

Beziehungen zwischen morphologischen Merkmalen,Photosyntheserate und Ertrag bei Kartoffelgenotypen unterschiedlicher Reifegruppen. 2. Photosyntheserate und ihre Kombination mit morphologischen Merkmalen

Zusammenfassung überwiegend positive Korrelationskoeffizienten zwischen Photosyntheserate und Ertrag, aber stark schwankende Ergebnisse zwischen verschiedenen Sortimenten, weisen darauf hin, dass die Photosynthese nur als ein Faktor innerhalb eines gr?sseren Merkmalskomplexes die Produktivit?t beeinflusst. Ungünstige morphologische Merkmale, die die Strahlungsinterzeption negativ beeinflussen (geringe Staudenh?he, wenig Stengel, Lagern der Stengel), k?nnen bei (klimatisch oder durch den Bestandesaufbau bedingt) suboptimaler Beleuchtung nicht durch eine hohe potentielle Photosyntheserate kompensiert werden. Extrem ertragreiche Genotypen zeichneten sich durch eine Kombination günstiger morphologischer Merkmale mit einer hohen Photosyntheserate aus.

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Summary Previous and existing studies have found overall a positive correlation between rate of photosynthesis and yield of potato genotypes (Table 1). The large variation in the correlations of different collections is the result of the various combinations of rates of photosynthesis and morphological characters. High rates of photosynthesis cannot under sub-optimal conditions, produced by climate or canopy architecture, compensate for the negative effect of morphological characters such as low crop height and stem counts, and stem lodging on the interceptions of radiation (group 1, Table 2). Very high-yielding types have good morphological characters and high rates of photosynthesis (group 6, Table 2). An upper canopy which allows the penetration of light is better when combined with a high rate of photosynthesis than a dense one in which only the uppermost leaf layers are intensively lit (Table 2). Rates of photosynthesis under optimal conditions of isolated leaf discs, and intact field-grown plants of three genotype gave the same ranking order in each case (Table 3). There was no indication from the daily course of photosynthesis that the genotypes responded differently to environmental conditions (Fig. 1).

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Résumé Dans des travaux antérieurs ainsi que dans celui-ci, on a principalement obtenu des corrélations positives entre la photosynthèse et le rendement pour les génotypes de pommes de terre (tab. 1). Les fortes variations de caractères mesurées dans les assortiments sont expliquées par les différentes combinaisons entre la photosynthèse et les caractères morphologiques. Les paramètres morphologiques qui influencent l'interception du rayonnement de manière négative (p. ex. faible développement des fanes et tiges, verse des tiges), ne peuvent pas être compensés, lors de conditions de rayonnement suboptimales, (climat et peuplement) par un taux élevé de photosynthèse (groupe 1, tab. 2). Les types à rendement extrêmement, élevé se distinguaient par des caractères morphologiques favorables, et un taux de photosynthèse élevé (groupe 6, tab. 2). Un port des plantes permettant la pénétration de la lumière, combiné avec un taux élevé de photosynthèse semble plus favorable qu'un port compact en surface, où seules les feuilles supéreures sont exposées au rayonnement intensif (tab. 2). Des comparaisons du potentiel de photosynthèse, entre rondelles de feuilles isolées et de plantes au champ ‘in situ’ par des conditions optimales, ont révélé le même ordre de rang pour 3 génotypes (tab. 3). L'évolution journalière de la photosynthèse selon les génotypes, n'a pas montré de différence de réaction aux conditions de l'environnement selon les génotypes (fig. 1).

     

How widespread is resistance to invermectin among gastrointestinal nematodes in sheep in The Netherlands?

In Autumn 2009, a faecal egg count reduction test (FERCT) was carried out on three sheep farms. Groups of 8-11 lambs were treated with ivermectin or moxidectin, with a 14-day interval between treatment and sampling. Ivermectin resistance was present on all three farms. Treatment with ivermectin resulted in a reduction in faecal egg numbers of 94.6%, 63%, and 59%. On two farms, 14 days after treatment pooled faecal samples yielded predominantly larvae of Hamonchus contortus (100% and 98%, respectively). On the third farm, H. contortus and (probably) Teladorsagia circumcincta were resistant to ivermectin (64% and 36% of the larvae, respectively). Treatment with moxidectin resulted in a 100% reduction in egg output in sheep on all three farms. More sensitive culture techniques failed to detect any larvae in samples taken from two farms, but a few Ostertagia-type larvae, probably of T. circumcincta, were detected in samples from the third farm. It can be concluded that gastrointestinal nematodes in sheep from these three farms were resistant to ivermectin, whereas resistance to moxidectin was not detected.     

Pear decline resistance in progenies of <Emphasis Type="Italic">Pyrus</Emphasis> taxa used as rootstocks

Progenies of 39 open-pollinated genotypes belonging to 26 Pyrus taxa were examined for pear decline resistance and pomological traits when used as rootstocks. Following graft inoculation and observation over 18 years, considerable differences in pear decline resistance between and within the progenies were observed. Not affected or little affected and moderately to severely affected trees were observed in all progenies. However, great quantitative differences among them were observed. In the progenies of about one third of the pollinated trees most of the individuals showed a high level of resistance to grafted trees. Significantly different from this group was another third of the progenies that mostly showed high susceptibility in grafted trees. Between these two groups there were progenies that statistically neither differed from the resistant nor from the susceptible group. These progenies were defined as moderately resistant. Significant differences in resistance were also observed between progenies of genotypes of the same species that originated from different locations. These data indicate segregation of the resistance trait and show that seedling progenies are unsuitable as rootstocks in commercial pear growing. Instead, careful selection of suitable genotypes for propagation is required. Great differences between and within the progenies examined were also observed in vigour and yield efficiency.     

Apple proliferation resistance in apomictic rootstocks and its relationship to phytoplasma concentration and simple sequence repeat genotypes

In an effort to select and characterize apple rootstock resistant to apple proliferation (AP), progenies from seven apomictic rootstock selections and their parental apomictic species, Malus sieboldii and M. sargentii, were compared to standard stocks M 9 and M 11. Seedlings derived from open pollinated mother plants were grafted with cv. Golden Delicious and grown under natural infection conditions. The progenies differed greatly in resistance to the AP agent 'Candidatus Phytoplasma mali'. Progenies of M. sieboldii and its descendent rootstock selections D2212, 4608, 4551, and D1131 showed a high level of resistance, whereas progenies of M. sargentii and its descendent selections D1111 and C1828 proved susceptible. M 9 and M 11 showed an intermediate level of resistance. Phytoplasma titer in roots of the M. sieboldii and M. sargentii progeny groups was similarly low, whereas the concentration in the standard stocks was 100 to 5,000 times higher. In trees on most of the resistant stocks, only a minority was colonized in the scion, while in trees on susceptible and standard stocks, infection rate was often higher. Also, the titer in the top of trees on resistant stocks was usually lower than in trees on susceptible and standard stocks. Four progenies derived from open pollinated M. sieboldii and M. sieboldii descendents were subjected to DNA typing using simple sequence repeat (SSR) markers. This study revealed that the selected groups consisted mainly of mother-like plants (apomicts) and type I hybrids (unreduced mother genotype plus one male allele at each locus). Type II hybrids (full recombinants) and autopollinated offspring were rare. In the 4608 progeny, trees grown on type I hybrid rootstocks were significantly less affected than trees on mother-like stocks. In other progenies with fewer or no type I hybrids, trees on type II hybrids and autopollinated offspring suffered considerably more from disease than trees on mother-like stocks.     

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Structure and mechanism of the lantibiotic cyclase involved in nisin biosynthesis

Nisin is a posttranslationally modified antimicrobial peptide that is widely used as a food preservative. It contains five cyclic thioethers of varying sizes that are installed by a single enzyme, NisC. Reported here are the in vitro reconstitution of the cyclization process and the x-ray crystal structure of the NisC enzyme. The structure reveals similarities in fold and substrate activation with mammalian farnesyl transferases, suggesting that human homologs of NisC posttranslationally modify a cysteine of a protein substrate.