Epsilon Open Archive

Abstract

Treatment of cereal seed using hot, humid air, or aerated steam, was investigated as a method for control of seed-borne diseases. The influence of important treatment parameters on the vitality of the seed and of the pathogen was determined. Optimum strategies of treatment time and air humidity were proposed for effective disinfestation with maintained seed viability. The process of heat and moisture transfer between the treatment air and the seed was clarified and it was concluded that quick heating with humid air for a short time, immediately followed by rapid cooling, gives a partly selective heating of external layers of the seed where most of the important cereal seed-borne pathogens are located. By taking the discussed physical relations into account, the improved viability equation of Ellis & Roberts was modified for prediction of post-treatment germinability and infestation rate with considerably reduced error. Tolerance to high temperatures was tested for a large number of seed lots. Different species were differently influenced by high temperatures. Due to variations in growing and storage history among seed lots, individual lots differ in heat tolerance. Due to such factors, the tolerance to high temperatures varies also within seed lots. However, the optimum temperature for thermal treatment of a seed lot can be found by pre-testing procedures. The influence of seed storage on the effect of the aerated steam treatment was investigated, both for treatments performed after storage and for seed stored after the treatment. Long-term storage of seed infested with pathogens persistent to storage reduced the disinfestation rate obtained from the treatment both when the seeds were stored before and after the treatment. When long-term storage is required before or after the treatment, the seeds should be stored at low temperature and at low moisture content. The optimized treatment method was evaluated in extensive experiments in six European countries. It was concluded that the method is capable of controlling most cereal seed-borne diseases equally with chemical seed dressing, exceptions being those where the pathogen is located deeply within the seed. The method can also control many important seed-borne diseases on other crops.