Physical treatments of seeds to eradicate pathogens have the risk of reducing vitality of the seeds. Seed lots may differ in sensitivity to these treatments, therefore factors influencing this sensitivity, including the physiological condition of the seeds, should be identified. In this study priming was used to mimic the effect of pre-harvest onset of germination on the sensitivity to these treatments. The effect of humidification, by incubation for one day at 100% RH, followed by drying back, on the sensitivity was also analysed. Primed, humidified and control seeds were subjected to hot water, aerated steam or electron beam treatments at various levels. Two seed lots from Daucus carota (carrot), two seed lots from Brassica oleracea (kohlrabi) and one seed lot from Allium cepa (onion) were used in the tests. Primed seeds from all seed lots were more sensitive to the aerated steam treatment and the B. oleracea and A. cepa seed lots were also more sensitive to the hot water treatment after priming. Priming had no effect on the sensitivity towards the electron beam treatment. Humidification had no effect on the sensitivity towards the physical seed treatments, with the exception of the humidified onion seeds, which were clearly more tolerant towards the aerated steam treatment. It is concluded that seed companies should be aware that the onset seed germination processes prior to harvest may increase the sensitivity of the seeds towards aerated steam and hot water treatments.

Various essential oils, organic acids, Biosept, (grapefruit extract), Tillecur and extracts of stinging nettle and golden rod were tested for their antimicrobial properties in order to disinfect vegetable seed. In in vitro assays, thyme oil, oregano oil, cinnamon oil, clove oil and Biosept had the highest activity against the seed borne pathogens Xanthomonas campestris pv. campestris, Clavibacter michiganensis subsp. michiganensis, Alternaria dauci and Botrytis aclada. Low antimicrobial activity was found for the organic acids against the fungal pathogens. Seed treatment for 0.5 h with selected essential oils or Biosept in concentrations between 0.1 and 1% eliminated > 99% of total bacteria associated with cabbage seed. It also reduced the percentage of seeds contaminated with fungi in blotter tests from 70% to less than 10%. Extended periods of treatment did not significantly improve results. Cinnamon oil and Biosept used in concentrations exceeding 1% had a negative effect on seed germination. Antimicrobial effects with organic acids were variable, but in general, the organic acids ascorbic acids, propionic acid, acetic acid and lactic acid at concentrations of 2.5% or higher, reduced seed-associated bacteria. Of the organic acids, only propionic acid reduced seed germination at a concentration higher than 1%. Thyme oil was considered the most promising natural compound for reducing seed borne pathogens in seed. Various essential oils, organic acids, Biosept, (grapefruit extract), Tillecur and extracts of stinging nettle and golden rod were tested for their antimicrobial properties in order to disinfect vegetable seed. In in vitro assays, thyme oil, oregano oil, cinnamon oil, clove oil and Biosept had the highest activity against the seed borne pathogens Xanthomonas campestris pv. campestris, Clavibacter michiganensis subsp. michiganensis, Alternaria dauci and Botrytis aclada. Low antimicrobial activity was found for the organic acids against the fungal pathogens. Seed treatment for 0.5 h with selected essential oils or Biosept in concentrations between 0.1 and 1% eliminated > 99% of total bacteria associated with cabbage seed. It also reduced the percentage of seeds contaminated with fungi in blotter tests from 70% to less than 10%. Extended periods of treatment did not significantly improve results. Cinnamon oil and Biosept used in concentrations exceeding 1% had a negative effect on seed germination. Antimicrobial effects with organic acids were variable, but in general, the organic acids ascorbic acids, propionic acid, acetic acid and lactic acid at concentrations of 2.5% or higher, reduced seed-associated bacteria. Of the organic acids, only propionic acid reduced seed germination at a concentration higher than 1%. Thyme oil was considered the most promising natural compound for reducing seed borne pathogens in seed.

Physical sanitation methods are used by the seed industry to prevent transmission of seed-borne diseases, but sensitivity varies between seed lots. The effect of seed maturity on the sensitivity to hot water, aerated steam and electron treatments was studied. Two Brassica oleracea L. and two Daucus carota L. seed lots from commercial production were selected for containing relatively large amounts of less mature seeds. Each seed lot was sorted into three maturity fractions based on the levels of chlorophyll fluorescence of individual seeds. Less mature B. oleracea and D. carota seeds were more susceptible to hot water treatments and less mature B. oleracea seeds to the aerated steam treatment. Seed maturity did not influence the sensitivity to the applied electron seed treatments. Seed lots were not selected for infections with seed-borne pathogens, however the less mature seeds were observed to be more frequently infected. It would be advisable to harvest seeds as mature as possible and to remove less mature seeds during seed processing. Sorting seeds by their level of chlorophyll fluorescence provides a useful method of sorting B. oleracea and D. carota seed lots. This would result in more efficient physical sanitation of seed lots

PPO en PRI onderzochten in de afgelopen jaren de voordelen van het gebruik van geprimed zaad in de teelt van suikerbieten, penen en uien. Priming (voorkiemen en weer terugdrogen) leidt tot een snellere en meer uniforme kieming en een betere beworteling. De groeivoorsprong van de planten levert voordelen op wat betreft onkruidonderdrukking en vatbaarheid voor ziekten en plagen. In de proeven werd gekeken naar het effect van primen op de plant- en wortelontwikkeling en de gewasopbrengst