The appearance of the induced dormancy in seeds of some umbell'iferae vegetable crops under the effect of allelopathic substances

Allelopathic effects in plants are due to a combination of many adaptive and environmental factors having evolutionary and economic importance. Currently the investigations on the effects of allelopathic substances on seed germination in order to develop new environmentally friendly approach to plant protection against weeds are in progress. The main goal of our experiments was to examine the peculiarities of the seed dormancy induced under the influence of an extract from seeds of dill ( Anethum graveolens L.) variety Kentavr and specific overcoming of the dormancy in various vegetable crops - carrot ( Daucus carrota L.) variety Rogneda, root parsley ( Petroselinum crispum (Mill.) Nyman ex A.W. Hill.) variety Lyubasha, celery root ( Apium graveolens L.) variety Kupidon, lavage ( Levisticum officinale W.D.J. Koch) variety Don Zhuan, coriander ( Coriandrum sativum L.) variety Yantar’, and parsnip ( Pastinaca sativa L.) variety Kulinar. The seeds of tested crops were treated with 15 % aqueous extract from dill seeds at 23 °C for 0 (control), 5 and 20 days in the dark. A germination of the treated seed germination was studied in dynamics at different temperature conditions - 20 °C (control); 3 °C; and 3 °C (8 hours)/20 °C (16 hours). We calculated Tip (initial period, i.e. the time prior to seed germination starts), Twagt (the weighted average germination period, i.e. the time to reach maximum germination rate) and T50 (the time to reach 50 % germination), measured the embryo length and calculated the temperature coefficient (Q10). It was shown the extract noticeably inhibited the embryo growth and seed germination in the studied crops. After exposure to allelopathic factors for 5 days the seeds of carrots, celery root, parsnip and coriander did not germinate at a standard temperature. The Twagt values exceeded the control by 229-328 %, and the T50 values were 310-379 % higher. In dill, parsley root and lovage the germinated seeds accounted for 42, 52 and 23 %, respectively. After a 20 day exposure to the allelopathic factor the seeds of celery root, carrots, parsnip and coriander did not germinate whereas in dill and lovage seeds germination delayed by 21 and 22 days. Increasing exposure time resulted in a reduced temperature coefficient (Q10) for embryo growth at different temperatures. Low temperature including constant 3 °C and variable (3/20 °C) contributed to a partial recovery of these processes in the seeds pre-exposed to allelopathic factor. In this, the Twagt and T50 increased by 11.7-35.3 days and 11.7-43.1 days, respectively, compared to control. Analysis of a combined effect of the allelopathic factor and temperature evidenced that the inhibition of seed germination influenced by the substances contained in the extract of dill seeds is due to the dormancy phenomenon.