Seed dormancy release and germination ecophysiology of wild Mexican sunflower (Tithonia tubaeformis)

Wild Mexican sunflower [Tithonia tubaeformis (Jacq.) Cass.] is one of the most important annual weeds for sugarcane (Saccharum spp. hybrid) and, to a lesser extent, for soybean [Glycine max (L.) Merr.] and bean (Phaseolus vulgaris L.) in the northwest of Argentina and some other countries. Currently, its management relies on chemical methods, and no information is available to develop alternative management methods. In the current study, we conducted laboratory germination assays in the presence of different conditions of light, temperature, and phytohormone (gibberellins and abscisic acid) concentrations, as well as fluridone, trinexapac-ethyl (TE), methyl viologen (MV), dry afterripening (DAR), cold stratification, and pericarp scarification. Likewise, a field experiment was carried out to assess the impact of various sugarcane crop residue amounts on seedling emergence. Darkness and constant temperatures (e.g., 20 C) reduced the germination of fresh seeds. The addition of TE, a gibberellic acid inhibitor, and abscisic acid reduced germination. In contrast, the addition of MV increased germination. Pericarp scarification and embryo excision stimulated germination, suggesting that the pericarp acts as a barrier to prevent germination. DAR did not promote germination. On the other hand, cold stratification enabled dormancy release, which in turn promoted germination when the stratified achenes germinated in light and at alternating temperatures of 20/30 C. Field experiments showed that increasing amounts of sugarcane crop residue were useful to reduce weed seedling emergence and biomass, probably by limiting the triggering effect of light and temperature alternation on seedling emergence. These findings provide information about the endogenous control of germination, which can be useful for developing a rational integrated management system for T. tubaeformis.