Strategies for Machine Harvesting of Mature Coffee (Coffea Arabica L.) Fruits

Abstract

Greenhouse and field grown coffee plants were used to study the synchronization of flowering and fruiting. The purpose of these studies was to develop methods of improving the selective harvesting of mature coffee fruits by machine. The studies were divided into 4 parts: 1) Synchronization of flowering, 2) Synchronization of fruiting, 3) Determination of fruit detachment and fruit removal force (FRF), and 4) Alteration of the FRF of ripe fruits. Either mist irrigation or water deficit stress followed by sufficient watering were effective in inducing flowering. Gibberellic acid treatment was less effective. Gibberellic acid applied to field grown coffee plants with fruit at different ages up to 40 days after anthesis advanced fruit maturity but did not synchronize fruit maturation. Ethephon sprayed on fruits at 230 days after anthesis resulted in uniform ripening of fruit on greenhouse grown coffee plants. The mechanism of abscission of green and ripe fruits was studied. No abscission layer was found at the sites of detachment in either green or ripe fruits. The detachment of ripe fruits occurred at random, by the breaking of parenchymatous pericarp tissue immediately above the pedicel. In contrast, the detachment of green fruits occurred at random along the pedicel. The FRF of green fruits was greater than the FRF of ripe fruits. The FRF decreased as fruits matured in both the ethephon and control treatments. Indices of fruit maturation were correlated with FRF. Exocarp color change, expressed quantitatively as the degree of lightness (L) and hue angle (0), was correlated with the FRF. The soluble solids content of the pericarp tissue decreased as fruit matured. There was a strong inverse correlation between FRF and soluble solids content of the pericarp. Further reduction in the FRF of ripe fruits was achieved by mist irrigation. The FRF of green fruits was not affected by the mist irrigation treatment. These studies provide strong evidence for the selective harvesting of mature coffee fruits by machine by integration of synchronized flowering and fruiting, and the reduction in FRF of ripe fruits.