Plant Growth Regulators and Short-Term Irrigation for Berry Maturation Homogeneity and Increased Coffea arabica Bean Quality

Gibberellic acid (GA3) may help to synchronize coffee flowering, whilst ethylene (in the form of Ethephon) may assist in advancing coffee berry maturation even when applied in the pre-flowering stage of phenophase. Functional–structural plant modeling (FSPM) can be used to help understand whole-plant responses, such as plant-scale photosynthesis. FSPM has never been used to investigate the response of coffee plants to external plant growth regulator (PGR) applications. We hypothesized that treatment with PGRs at the beginning of berry maturation (BM) during phenophase could (1) influence plant leaf area and plant photosynthesis at the end of BM and (2) assist in the uniformity of the berry maturation of seven-year-old coffee plants. Additionally, we assumed that (3) the distribution of berries over the vertical plant profile could be related to the coffee beans’ chemical quality, and that irrigated plants would have delayed maturation, but a higher yield than non-irrigated (NI) plants. To test these hypotheses, a short sustainable period of irrigation was applied six weeks before harvest. Irrigated plants were treated with GA3 or Ethephon. A combination of field measurements (leaf gas exchanges, berry collection and bean chemical analyses in relation to vertical plant strata) and computer modeling were used. At the beginning or the end of BM, coffee trees were coded using the VPlants modeling platform and reconstructed using CoffePlant3D software to compute the plant leaf area and plant photosynthesis. The greatest number of second-order red berries were found in the upper stratum, S3 (>160 cm), while slightly fewer were found in S2 (80–160 cm) belonging to the third-order axes, and the lowest number was found in S1 (<80 cm). Green berries were more representative in S2, with the greatest number belonging to the third-order axes. The participation of third-order axes in berry yield was up to approximately 37% for red berries and 25% for green berries. The greatest separation between PGRs could be seen in S2, where more berries in the Ethephon-treated plants were found than in the GA3 treated ones, while the dry mass (DM) percentage was higher in GA3 than in the Ethephon treatment. The percentage of DM in fresh mass was 17–28% in the green berries and 28–36% in the red berries. PGRs were important for homogenous berry maturity, especially GA3, which also showed the lowest total chlorogenic acid content. The NI plants showed reduced red and total berry production when compared to irrigated ones, indicating this horticultural measure is important, even during a sustainably reduced six-week period, due to preserved leaf area and plant photosynthesis, and it also increased the lipid and kahweol contents of irrigated plants when compared to NI plants, despite the maturation delay.