Interdependence between seed age and aerated steam treatment intensities

Sammanfattning: Aerated steam treatment is a modern and environmental friendly method for seed borne fungus sanitation, mainly used on cereals. The method involves exposure to heat and high humidity, factors which are known to induce a fast ageing of seeds, thus resulting in reduced storability. This thesis clarifies the interdependence between seed age and the aerated steam treatment intensities. Two studies were carried out in this thesis. In the first study the storage longevity of seeds treated with aerated steam was examined. The second study investigated the shelf-life of the pre-tests used to determine the aerated steam treatment tolerance of a seed lot, by testing the treatment tolerance of seeds aged prior to the treatment. Both studies were carried out on winter wheat seed (Triticum aestivum L.) with different moisture contents. The storage longevity study showed that seeds treated with high aerated steam treatment intensities had more reduced storability than seeds treated with lower aerated steam treatment intensities. Seeds from all aerated steam treatments maintained 85% viability or above after artificial ageing comparable to 0.5 years of storage, and dry seeds treated at low intensities maintained 85% viability or above after artificial ageing comparable to 1.6 years. To determine this, the seeds were treated with a range of aerated steam treatment intensities prior to artificial ageing of the seeds. The ageing was performed by rapid ageing designed to induce changes comparable to the effects of storage for 0.5, 1.6 and 2.5 years in 10 °C. In the shelf-life of the pre-tests study it was found that the LD0.1 aerated steam treatment tolerance decreases linearly with age with 0.62-0.85 kJ/m3 during a year, which should be considered when the aerated steam intensity for a seed lot is chosen. To investigate this, the seeds were aged by rapid ageing corresponding to 0.5, 1.6 and 2.5 years in 10 °C before the aerated steam treatment pre-tests. The results from this study show that aerated steam treatment has deteriorative effects on the seed, which should be considered especially if the seed is stored more than one season before or after the aerated steam treatment. After validation by natural ageing, these results can be used to better adjust the aerated steam treatment intensity for individual seed lots based on storage time before or after the aerated steam treatment.