Preharvest use of γ-aminobutyric acid (GABA) as an innovative treatment to enhance yield and maintain quality in lemon fruit

γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid with different functions in plant metabolism, such as signalling, modulation of growth and development, pH regulation and induction of stress tolerance. GABA is currently acquiring increasing interest, applied in preharvest or postharvest, for its effects in delaying senescence and increasing tolerance to oxidative stress or chilling injury in many fruits. In this experiment, lemon trees (Citrus lemon L.) of the ‘Fino’ cultivar were treated, by foliar spray, with GABA (at concentrations of 10, 50 and 100 mM) during 2 consecutive seasons (2019-2020 and 2020-2021). Treatments were applied monthly, the first treatment being applied in August and the last one in November (4 days before harvest). ‘Fino’ lemons were harvested at green maturity stage in November and yellow stage in February. Fruit growth (diameter), crop yield (kg tree^‑1 and number of fruits tree^‑1) and quality traits were evaluated at harvest. Results showed that treatments were effective on increasing lemon size and crop yield, especially for GABA at 100 mM, for the two assayed seasons. With respect to quality traits, GABA treatments did not impact any negative effects on quality attributes, since total soluble solids, total acidity and fruit firmness were similar in fruit from control and treated trees. This study shows that GABA could be an effective tool to increase farmer economic profits, rendering increased crop yield and fruit size, which would be very interesting, since it is a natural compound with no harmful effects on the environment or human beings.