Spinach growers face increasing problems of damping off in the production of fresh market (baby-leaf) spinach due to increasing restrictions on chemical treatments. Damping-off tolerant cultivars are increasingly important, requiring proper evaluation methods. From three locations in the Netherlands with a history of spinach cultivation and from one location in France, potential damping-off pathogens were isolated from the soil, identified to species or genus, and tested for their pathogenicity. Pythium ultimum was the most prevalent pathogen in those fields, causing spinach pre- and post-emergence damping off. Eight spinach cultivars with two or three seed lots each, were evaluated at the same field locations and in a greenhouse with soil sampled from one of the Dutch field sites. Pre-emergence damping off was more discriminating for differences among the cultivars than post-emergence damping off. Variation in levels of infection among trials, replicates, and seed lots of same cultivars, emphasized the need for a more standardized phenotyping assay. For such an assay, a cornmeal/sand-based inoculum with a pathogenic P. ultimum isolate was added to a substrate mixture of sand, perlite, and vermiculite, moistened until 50% water holding capacity, in which spinach seeds were incubated for ten days in a dark climate cabinet at 15°C, including a control treatment without P. ultimum inoculum. The assay showed reproducible results for discriminating differences in pre-emergence damping-off tolerance levels among seed lots. However, cultivar differences in pre-emergence damping-off tolerance levels could not be confirmed due to a large variation among seed lots that needs further investigation.
Effects of piperidine and piperideine alkaloids from the venom of red imported fire ants, Solenopsis invicta
Buren, on Pythium ultimum
Trow growth in vitro
and the application of piperideine alkaloids to control cucumber damping-off in the greenhouse