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Cape Peninsula University of Technology (2021)

Breaking the dormancy of selected asteraceae annuals in the winter-rainfall region of South Africa

Oliver, Roger Clive

Titre : Breaking the dormancy of selected asteraceae annuals in the winter-rainfall region of South Africa

Auteur : Oliver, Roger Clive

Université de soutenance : Cape Peninsula University of Technology

Grade : Master of Horticultural Science 2021

Résumé partiel
The aim with study was to investigate whether the germination of Arctotis hirsuta, Cotula duckittiae and Oncosiphon suffruticosum are three Asteraceae annuals can be improved by determining its individual temperature- and light-condition requirements and subjecting the achenes to pre-germination treatment such as scarification, GA₃ and after-ripening at high temperatures. Experiments were conducted between 2019 and 2020. The first experiments evaluated the temperature and light required per species. Treatments consisted of inducing germination at 5 different temperatures namely 7 °C, 12 °C, 17 °C, 22 °C, 27 °C and alternate temperatures at 12 °C/22 °C and 17 °C/27 °C in conditions of light, darkness and alternate lightning (12 hours each of light and darkness). In the second experiment, pre-germination treatments consisted of scarification (pericarp-pricking) and the soaking of seed over 4 periods in 4 different gibberellic-acid (GAɜ) concentrations. Seeds of all species were then subjected to pre-determined light and temperature conditions as follows : A. hirsuta (collection year 2016) [22 °C in light], C. duckittiae (collection year 2017) [22 °C in light], O. suffruticosum (collection year 2016) [12 °C in light] and O. suffruticosum (collection year 2017) [22 °C in dark] to ensure optimum germination. The third experiment, after-ripening, consisted of two different treatments over two periods (30 °C & 45 °C for 4 and 8 weeks). Seeds of all species were then subjected to pre-determined light and temperature conditions as follows : A. hirsuta (collection year 2016) [22 °C in light], C. duckittiae (collection year 2017) [22 °C in light], O. suffruticosum (collection year 2016) [12 °C in light] and O. suffruticosum (collection year 2017) [22 °C in dark] to ensure optimum germination. Chapter 2 reviewed the importance to alleviate the germination-challenges for the three species when grown from seed of wild plants. It was found that when incubated at specific temperature- and light-requirements, some winter-growing annuals can improve their germination. The utilization of these pre-determined light- and temperature-requirements, in conjunction with other pre-germination treatments such as scarification, soakings in GA₃ and after-ripening at elevated temperatures have been deemed very effective to counter challenges with germination for some species of Asteraceae-annuals. Chapter 3 indicated that germination of A. hirsuta achenes is the result of a temperature and light interaction for temperatures between the 22 °C and 27 °C in the light.

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Page publiée le 18 mai 2022