engleski

Germination response of common ragweed (Ambrosia artemisiifolia L.) at low temperatures

Ambrosia artemisiifolia L. (common ragweed) is widespread weed species present for more than 70 years in Croatia with high density occurrence in row crops and ruderal areas. Besides negative agricultural effects, common ragweed pollen causes significant health problems to approximately 15% of the Croatian population. Although defined as thermophile summer annual, in the last few years in the northwest part of the country, seedlings have been observed even in the fall (November) and in the middle of February in overwinter wheat. Since the timing of emergence contributes to the dynamics of further phenological stages (pollen and seed production), the laboratory experiment aims to investigate the possibility of common ragweed germination at lower temperatures than the optimum one. Five replicates of 50 seeds were sowed in Petri dishes with the addition of 2 ml of deionized water and placed in the gemination chamber. Germination was tested simultaneously at different temperatures: 25 (control), 1, 3, 6, 9 and 12 °C with photoperiod 12h:12h (day:night). Germination was recorded once a day for seeds set on 6, 9, and 12 °C and once a week for seed set on 1 and 3°C to avoid entering heat (room temperature) into the chamber. Germination was defined as 1 mm of radicle protrusion and germinated seeds were removed from the Petri dishes. Recording was conducted until no further germination occurred for 10 days. Percentage of final germination and cumulative germination at different temperature data were subjected to ANOVA in SAS with Fisher`s protected LSD (α ≤ 0.05). The germination time course was analysed using a logistic function in the Bioassay97 program. Germination time course was used to define time necessary for germination of 10 (t10), 50 (t50) and 90 % (t90) of germinated seed. Results show common ragweed germination at each studied temperature with the highest percentage of germination (67.6%), as expected at 25 °C (control). The lowest germination was found between 6 to 12 °C (49.6 - 40.4%). Between the highest (25 °C) and the lowest studied temperature (1°C) (59.6%), no significant differences were found. However, germination dynamics (t10, t50 and t90) differed considerably between the two studied temperatures. At 25 °C germination test lasted (t90) for one week while at the lowest temperature germination lasted for 165 days (d) The fastest initial germination (t10) at lower temperatures was achieved in 15 d at 12 °C, while the slowest initial germination was determined in 84 d at 1 °C. The fastest medium (t50) and final (t90) germination was at 12 °C (46 d), 9 °C (42 d) and 6 °C (46 d). The slowest medium and final germination was at 1 °C (120 - 160 d). Results of the experiment suggest that the germination of common ragweed is possible even at 1 °C when exposed to constant temperature and moisture longer period (approx. 5 months).

invasive species ; germination dynamic ; seed ; summer annual ; weed

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