Response of soil microfauna to organic fertilisation in sandy virgin soils of coastal dunes

In young white-dune soils with a very low content of organic matter, the influence of organic fertilisation on microfauna, ciliates and nematodes, was investigated. Three fertilisers - straw, rabbit dung, and wheat bran - were added to the soil in order to mimic natural conditions in older dunes. Abundances of nematodes and ciliates were significantly increased with respect to controls, where only about 3 individuals g^-1 dry matter could be counted. The numbers of nematodes and ciliates reached 103 and 77 ind g^-1 in the bran treatment, respectively. Stimulation of microfaunal production from straw and dung fertilisation was less pronounced but also significant. The results show that nematodes and ciliates react quickly to favourable conditions with excystment and production up to the abundance values of dune soils with natural organic matter accumulation. Considering the species composition of ciliates, it becomes clear that, in spite of the fast development of ciliate species, the community does not develop into natural communities of higher organic matter soils within 3 months. The increase in abundance is mainly due to rapid development of a few bacterial feeding species so that dominance concentration is much more pronounced. Organic matter concentration is an important factor for microfaunal abundance, but the quality of organic matter and the age of its accumulation seem to determine ciliate community composition. It is concluded that, due to the fertilisation, the habitat character for ciliates has evolved from an adverse habitat to a higher favourableness but lower predictability and thus has changed from A- to r-selection, whereas in natural development of the dunes it develops from A- to K-selection.     

Quality control in bioassays used in screening for plant viruses

Test plants are often used for broad screening for plant viruses. Mechanical inoculation of a series of test plants enables generic detection of mechanically transmitted viruses in only 1 assay. Moreover, such an assay is suitable for known as well as unknown viruses and their variants. However, in comparison to serological and molecular methods, quality control in bioassays is almost never addressed. The system of positive and negative controls, blind samples and proficiency tests is applicable, provided that a broader interpretation of positive and negative controls is used. For validation, performance criteria can only be determined for individual viruses. However, results can often be extrapolated. Sensitivity is addressed by dilution and expressed as a relative value. Specificity has to consider the virus species and the plant species to be tested. Selectivity mostly depends on the plant species tested, because some hosts contain components that inhibit transmission. Repeatability and reproducibility, determined for a limited number of samples, appears high, as also substantiated by the authors' experience. This paper details how EPPO Standards on quality control were implemented by the National Plant Protection Organization of the Netherlands (NPPO‐NL). This information will be of use for other laboratories that wish to introduce quality control in bioassays for virus testing.     

Mechanical transmission of <Emphasis Type="Italic">Potato spindle tuber viroid</Emphasis> between plants of <Emphasis Type="Italic">Brugmansia suaveoles,Solanum jasminoides</Emphasis> and potatoes and tomatoes

Potato spindle tuber viroid (PSTVd) has been recently found in many solanaceous ornamental plant species. This study reports on the effectiveness of mechanical transmission between Brugmansia suaveolens, Solanum jasminoides, potato and tomato. Inoculation with ‘infected’ plant sap diluted in water, rubbing with contaminated finger tips and cutting with contaminated razor blades all resulted in transmission of PSTVd. Temperature, plant species and source of inoculum were found to be critical factors. An average temperature of 15°C only resulted in a few infections, whereas transmission at 20 and 25°C was more successful. Tomatoes were more susceptible to PSTVd than B. suaveolens, S. jasminoides and potatoes. Furthermore, S. jasminoides was a better source of inoculum than B. suaveolens. No transmission was obtained after repeated addition of inocula to tomato roots. These results indicate that PSTVd can be transmitted between plant species in practice by crop handling.     

Check-list for scientific names of common parasitic fungi. Series 2d: Fungi on field crops: Vegetables and cruciferous crops

This list is a continuation of Series 2a, b, and c [Nath. J. Pl. Path. 82 (1976) 193–214, 83 (1977) 165–204 and 85 (1979) 151–185], an account of the nomenclature of common parasitic fungi on field crops as used in official publications of the Netherlands Society of Plant Pathology and the Netherlands Ministry of Agriculture and Fisheries.