Sprouting and shoot development of Sonchus arvensis in relation to initial root size

To assess the effects of initial root size of Sonchus arvensis on sprouting and shoot development, an outdoor box experiment was performed in Sweden in 2008. Shoot emergence time, shoot numbers, rosette size and flower production were quantified as functions of root length and weight. Emergence of the first shoot per root and of later cohorts was delayed with decreasing root length and weight. Number of shoots per root increased with root length and weight, but per unit root length and weight, short roots produced more shoots. The first emerging rosettes were, for rosettes of a given age, larger for longer roots. Total rosette area per root 5 weeks after planting increased with increasing root length and weight. The number of flowers and production of mature seeds were positively related to root length and weight, because of delayed sprouting of short and light roots. The proportion of flowers leading to mature seeds declined with shoot emergence time. By clarifying relationships between root size and growth parameters, this study showed that fragmenting of S. arvensis roots delays phenological development and hampers reproduction by seeds. The information may be used to refine mechanical weed control strategies for S. arvensis.