Suitable rootstocks for organically grown tomato and cucumber in relation to Meloidogyne SPP.

In organic greenhouse vegetable production, significant yield loss occurs due to root-knot nematodes (Meloidogyne spp.). Soil steaming is effective; however, it is not preferred, since beneficial soil micro organisms are eliminated. An inclusion of resistant hosts within the crop rotation is complicated by the broad host range of the nematode and the high level of specialization of companies towards production of fruit vegetables. Nearly all species of fruit vegetables are susceptible to a varying degree and complete resistance is absent. Even when rootstocks show partial resistance, this is broken down at high temperatures and with an increase in nematode densities. In addition, a lack of compatibility between the rootstock and graft is reported. The objective of the research was to find a rootstock with a high resistance against the most important Meloidogyne species in greenhouses in the Netherlands, M. incognita and M. hapla. Secondly, rootstocks should combine resistance with high yield and quality. In five experiments, 16 to 28 rootstocks per vegetable crop were tested for susceptibility, based on the number and size of root-knots and degree of nematode reproduction. In tomato (Solanum lycopersicum L.), one of the best performing rootstocks was ‘PG76’; in cucumber (Cucumis sativus L.) ‘RZ64-10’ and ‘Harry’ performed well. In general, tomato rootstocks have a higher level of resistance against M. incognita compared with M. hapla. However, cucumber rootstocks seem to be more susceptible to M. incognita than to M. hapla

Natuurlijke ziekteonderdrukking in grondteelten : model, weerbaar telen en nieuwe substraten

Wageningen UR Glasuinbouw toont aan dat bodemweerbaarheid in de glastuinbouw bestaat. In een onderzoek onder veertien glastuinbouwbedrijven en een proefveld werden, met behulp van biotoetsen, verschillen zichtbaar gemaakt in de mate van bodemweerbaarheid tegen het wortelknobbelaaltje en de bodemschimmels Pythium en Verticillium. De resultaten van een vervolgproef laten zien dat er gestuurd kan worden op weerbaarheid tegen het wortelknobbelaaltje. Analyse van de databank van Wageningen UR Glastuinbouw van meer dan zestig metingen aan diverse kastuinbouwgronden leidde tot een model dat de bodemweerbaarheid tegen het wortelknobbelaaltje en Pythium voorspelt. De waarde van het model moet in vervolgonderzoek beproefd worden

Een integrale parameter voor ziektewerendheid

Wageningen UR Glastuinbouw onderzoekt op dit moment met diverse partners de oorzaak van verschil in ziektewering tussen bedrijven van biologische groenten. Onze hypothese is dat ziektewering ontstaat uit een geëvolueerde interactie tussen diverse micro-organismen

Two distinct AFLP types in three populations of marram grass (Ammophila arenaria in Wales)

The genetic structure of marram grass populations at coastal and inland locations, 200 m apart, was investigated at three sites by means of amplified fragment length polymorphism (AFLP) DNA markers. We expected a genetic differentiation between coastal and inland populations and more genetic variation in the coastal areas as a result of different events of colonization by different plant materials. An assignment test showed that the sampled Ammophila arenaria could be assigned to two groups based on AFLP data. The spatial distribution of the two AFLP types of A. arenaria varied with sampling location. In two of the three locations, mainly one type (1) was found in the newly formed dunes. This type did also occur further landward, but the second type (2) was preferentially found in inland populations. Genetic diversity was very low and of similar value in both coastal and inland populations. For each site, outlier loci with respect to FST value were identified, which may be indicative of different selection pressures in coastal compared with inland clusters. However, no identical outlier loci were found at all three sites. Possible explanations for the observed difference in distribution of type 1 and 2 populations between coastal and inland sites are discusse

Large anomalous magnetic moment in three-dimensional Dirac and Weyl semimetals

We investigate the effect of Coulomb interactions on the electromagnetic response of three-dimensional Dirac and Weyl semimetals. In a calculation reminiscent of Schwinger's seminal work on quantum electrodynamics, we find three physically distinct effects for the anomalous magnetic moment of the relativisticlike quasiparticles in the semimetal. In the case of nonzero doping, the anomalous magnetic moment is finite at long wavelengths and typically orders of magnitude larger than Schwinger's result. We also find interesting effects of one of the three new Hamiltonian terms on the topological surface states at the interface between vacuum and a Weyl semimetal. We conclude that observation of these effects should be within experimental reach.Comment: 6 pages, 3 figures; second version contains discussion of Rashba spin orbit coupling due to inversion symmetry breaking at the surfac

Antagonisten tegen knobbelaaltjes en natuurlijke ontsmetting

Het langdurig betelen van de grond met hetzelfde gewas of gewastype leidt tot opbouw van plantpathogenen die uiteindelijk schade aan het gewas veroorzaken. Een combinatie van preventieve en curatieve maatregelen zijn noodzakelijk om de schade te beperken. Het onderzoek binnen biologische glastuinbouw is deels gericht op het beheersen van grondgebonden ziekten & plagen. Creatief vruchtwisselen, en gebruik van resistente of antagonistische gewassen en onderstammen vormen een wapen tegen wortelknobbelaaltjes