On the cover: Plant growth regulators (PGRs) classically comprise phytohormones, but in recent years, various inhibitors of phytohormone synthesis or translocation and blockers of their receptors have emerged as additional, equally important, growth regulators. While the application of PGRs is becoming increasingly apparent in agriculture, viticulture, and horticulture, ongoing research is focussing on uncovering the complex signalling networks and regulatory processes underlying their actions in a range of plant species. This special issue highlights the latest research in this exciting field, including steps towards enhancing crop yield and resistance to biotic and abiotic stresses (see editorial by Tripathi et al., 2022).

The cover image shows two steps of the ripening process of sweet pepper (Capsicum annuum L.) fruits, which undergo very drastic external phenotypic changes, with green-coloured immature fruits turning into red-coloured ripe fruits being the most noticeable. At the metabolic level, melatonin has been revealed as a signalling molecule that can modulate the ripening process of fruits (for more information, see Aghdam et al., 2022). Images supplied by Francisco J. Corpas [Group of Antioxidants, Free Radicals and Nitric Oxide in Biotechnology, Food, and Agriculture, Granada (Spain) and the Spanish National Research Council (CSIC)].