Germination behaviour of Conyza bonariensis to constant and alternating temperatures across different populations

Abstract

Conyza bonariensis is one of the most problematic weed species across the world. It is considered highly noxious due to the interference with human activities, specially associated to competition with different crops. This research investigated the temperature requirements for seed germination of four different populations of C. bonariensis and the interval temperature effect in this specie. For this, different experiments were performed in growth chambers. In the first one, seeds of the four populations were maintained at constant temperatures of 5, 10, 15, 20, 25, 30 and 35ºC, and from this, we could obtain the final germination, the cardinal temperatures (base, optimum and maximum) and also the thermal time of each population. In the second experiment, we studied the influence of alternate temperatures on final germination, an important issue in annual-surface germination weeds. Seeds were exposed at different temperature regimes: 5/15, 10/20, 15/25 and 25/35ºC night/day temperature (intervals increasing 10ºC) and to 18/22, 26/24, 14/26, 12/28 and 10/30ºC night/day temperature (intervals with average of 20ºC). In general, all populations behaved similarly, with highest percentages of germination in the temperatures close to the optimum obtained (between 17.5 and 19.3ºC) both for constant and alternate temperatures. Also, germination response was accordingly with its climatic origin, where highest germination percentage at the lowest temperature assayed, were obtained from the coldest location (26.7% for Lleida). In addition, we could observe that the alternate temperatures can affect positively to total germination, especially in those ranges that are further close from the optimum temperature in its average (20ºC), with high germination percentage for all ranges and all populations . Also, the cardinal temperatures obtained shows differences across the populations. These results could help to better understand the behaviour of the specie providing valuable information to develop or improve current field emergence models.