RESUMEN
Even though exhaustively studied, dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga remains a mystery. To clarify this, we asked the following question: could dormancy alleviation in diaspores of this species be associated with ageing, GA/ABA balance and remaining structures of the panicoid spikelet? We answer this question using diaspores of U. humidicola cv. BRS Tupi as a biological model, a cultivar with a wide edaphoclimatic range in Neotropical areas and whose diaspores possess 'deep dormancy' when dispersed. We analysed both germination and early plant development using a split-plot model. Our findings demonstrate that dormancy alleviation in diaspores of U. humidicola is a synergic phenomenon driven by crosstalk between age, GA/ABA balance and remaining structures of the panicoid spikelet covering caryopses, since this interaction acts on the dynamics of germination and early plant development. We demonstrate that: (i) spreading germination time is a maternal survival mechanism of this species, which has repercussions for occupational aggressiveness of the species; (ii) remaining structures of the panicoid spikelet covering caryopses are the main modulator of embryo development. These structures control the after-ripening process, which is modulated by some molecular factor. We also highlight that it is necessary to review concepts about dormancy of dispersal units in this grass species.