Efficacy of Brassica seed meal for management of Pythium root rot in greenhouse-grown vegetables

Abstract

Mustard seed meal is the material that remains after oil is extracted from the seeds of plants in the mustard (Brassica) family. When in the presence of water, this seed meal releases compounds that can suppress plant diseases and weeds. As a result, mustard seed meal was investigated as an alternative method for disease and weed control, in an effort to reduce synthetic pesticide usage. Further, few studies examined the use of mustard seed meal for application in the commercial greenhouse industry, which is a large consumer of synthetic chemicals. Instead, many researchers assessed the seed meal in an outdoor setting. This project bridged the gap in literature and evaluated mustard seed meal as an additive to the soilless potting medium commonly used in the greenhouse industry. In a laboratory setting, the seed meal was successful in killing two species of the plant pathogen Pythium, which commonly causes root-rotting diseases. In a greenhouse setting, the mustard seed meal prohibited Pythium from killing tomato and cucumber seedlings but also damaged the seedlings at higher application rates. These observations were investigated in another series of experiments to identify a maximum seed meal application rate. In these experiments, seed meal rates up to 0.4% (by volume) did not decrease or delay germination. When a sowing delay of one day was employed, there were no decreases or delays in germination for seeds grown in medium combined with seed meal at rates up to 2.4%. Increasing the duration of the sowing delay up to seven days did not yield any added benefits. These experiments' data suggest adding seed meal up to 2.4% (by volume) will not decrease or delay germination as long as there is a minimum of one day between combining the potting medium and seed meal and sowing the seeds. However, seedlings that were transplanted into the same potting medium and mustard seed meal combinations were more sensitive than seeds. Even with a one-day delay, these seedlings were damaged at 1.2% seed meal and above, and were killed at all seed meal rates when there was no planting delay.