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Seed dormancy breaking in Crataegus laevigata

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Laboratory experiments were made to determine the optimum conditions for dormancy breaking in the midland hawthorn (Crataegus laevigata (Poir.) DC. = C. oxyacantha L.). Its small applelike fruits should be collected when they are fully ripe (in Poland in October). The nutlets extracted from the fruits must be dried at room temperature to the moisture content of 9–13%. The dormancy of midland hawthorn seeds can be overcome by: (1) stratification in a moist medium: 20~30°C/3°C, 16–20 weeks at 20~30°C (16+8 hrs or 24+24 hrs) followed by 16–18 weeks at 3°C, i.e. to the time when first radicles start to appear; or (2) chemical scarification in concentrated sulphuric acid for 2 or 3 hrs, followed by warm stratification at 27.5°C or 20~30°C for 4 weeks and cold stratification at 3°C, lasting 19–21 weeks, i.e. to the time when first radicles start to appear. The stratified seeds germinate vigorously (in 3–5 weeks) and at a high percentage at temperatures of 3~15°C or 3~20°C (16+8 hrs) and all seedlings emerge in such conditions about 4–6 weeks after sowing. Seed germination after stratification or scarification can be stopped by partial desiccation of seeds. Seed desiccation after stratification to the moisture content of 10–13% and sealed storage at –3°C for one year do not reduce seed germination and seedling emergence rates of the previously pretreated seeds. Storage for 20 months at –3°C of seeds dried after harvest to the moisture content of 14% does not reduce their germination and seedling emergence.
Effects of several stratification variants on seed dormancy breaking were compared in Crataegus submollis Sarg. (hairy cockspur-thorn or Quebec hawthorn). Ripe seeds were collected (in October), cleaned, and dried to a moisture content of 7–12%. Seed dormancy in this species was broken most effectively by warm-cold stratification of nutlets, in a substrate or without any substrate, at 15~25°/3°C or 20~30°/3°C, i.e. with a cyclically alternating warm stage (16+8 hrs or 24+24 hrs/cycle) lasting 16–20 weeks, followed the cold stage lasting ca. 20 weeks, i.e. till the appearance of the first germinating seeds. After stratification, emergence rate is equally high (ca 50%) at cyclically alternating temperatures of 3~15°C and 3~20°C (16+8 hrs). Chemical scarification of nutlets in 96% sulphuric acid for 3 hrs, followed by warm-cold stratification at 20~30°/3°C, with a short, 4-week warm stage, also ensures a high emergence rate (58%). Seed desiccation (in nutlets) slowly to a moisture content of 10–12%, after stratification in a substrate or without any substrate as well as after scarification, results in a reduced emergence rate, especially if seeds are dried to the lower moisture content. Seed storage (in nutlets after drying to a moisture content of 10%) for 10 years at –3°C, does not decrease the emergence rate (93%) after stratification at 20~30°/3°C in a substrate, with a cyclically alternating warm stage (24+24 h) lasting 16 weeks.
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Seed dormancy breaking in Crataegus pedicellata

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The effects of stratification and scarification on seed dormancy breaking were compared in scarlet hawthorn (Crataegus pedicellata Sarg. = C. coccinea L). Ripe fruits were collected (in October) and the extracted nutlets were cleaned, and dried to a moisture content of 9–12%. Seed dormancy in this species was broken most effectively by warm-followed-by-cold stratification of nutlets, in a substrate or without any substrate, as well as at 15~25° or 20~30°C, i.e. with a cyclically alternating warm stage (16+8 hrs or 24+24 hrs/cycle) lasting 16–20 weeks, followed by the cold stage at 3°C lasting ca. 20 weeks, i.e. till the appearance of the first germinating seeds. After stratification, emergence rate is equally high (ca 76%) at cyclically alternating temperatures of 3~15°C or 3~20°C (16+8 hrs). Chemical scarification of nutlets in 96% sulphuric acid for 2 hrs, followed by warm-cold stratification at 20~30°/3°C, with a short, 4-weeks warm stage, also ensures a high emergence rate (85–93%). Seed desiccation (in nutlets) slowly to moisture content of 12–14%, after stratification in a substrate or scarification does not reduce the seedling emergence of seeds. Emergence decreased when seeds were desiccated after stratification without any substrate. Results provide new methods of breaking of dormancy and high germination and emergence of hard-coated Crataegus seeds in controlled conditions.
The most advantageous time for collecting fruits of the common hawthorn (Crataegus monogyna Jacq.) falls on October, when they are fully ripe. The stones extracted from the fruits must be dried at room temperature to the moisture content of about 10%. The dormancy of the common hawthorn seeds can be overcome by their stratification in a moist medium in one of the three thermal regimes: - 25°/3°C (16 weeks at 25°C followed by 15-18 weeks at 3°C, i.e. to the time when the first seedlings start to appear) - 20~30°/3°C (16 weeks at 20~30°C (16+8 hrs/day) followed by 15-18 weeks at 3°C, i.e. to the time when first seedlings start to appear) - 20~30°/3°C (16 weeks at 20~30°C (24+24 hrs) followed by 15-18 weeks at 3°C, i.e. to the time when first seedlings start to appear) Having been stratified, the seeds germinate vigorously (in 3-5 weeks) and at a high percentage at temperatures of 3~10°, 3~15°, 3~20° and 3~25°C, (16+8 hrs/day) and the seedlings emerge at 3~20°C (16+8 hrs/day) in 4-6 weeks. Storage for one year at -3°C in the case of the seeds dried after harvest to the moisture content of 10% does not reduce their germination capacity. Stones scarification in concentrated sulphuric acid for 120 minutes followed by stratification at 3°C has an adverse effect on seed emergence at the temperature 3~20°C (16+8 hrs/day). It is recommended that stratified seeds should be sown into the still cool soil at the end of March or the beginning of April, as the increased temperature induces the secondary dormancy in seeds.
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