Pre-harvest growth and development, measured as accumulated degree days, determine the post-harvest green life of banana fruit

We aimed to define a more robust indicator for banana harvest date that ensures an optimal fruit green life (GL). Our hypothesis was that development rather than growth would account for GL more accurately. To this end, five indicators were compared: one related to fruit size (i.e., growth, expressed as the diameter of fruit); two related to fruit age [i.e., development, expressed as the age of fruit measured in the number of days or in degree days (°Cd) from inflorescence emergence]; and two related to metabolism during maturation (i.e., the concentrations of malate and citrate in the pulp). Different treatments (e.g., fruit removal, leaf shading, bunch bagging, defoliation, water deficit, and flooding) were applied to modify the fruit growth rate. On different dates between the emergence of the inflorescence and harvest, fruit GL and the five indicators were measured. The results showed that there was a decreasing exponential relationship between GL and accumulated °Cd from inflorescence emergence (r² = 0.77). This was more reliable than the relationships between GL and fruit diameter (r² = 0.39), or between GL and fruit age, expressed in days (r² = 0.39). Relationships were also established between GL and malate or citrate concentrations, but they were not sufficiently reliable to estimate GL. The results illustrate that GL is related to fruit development, and that °Cd is a more reliable criterion for harvest date than the number of days, or fruit diameter, because it is less sensitive to different fruit growth rates. Banana growers in the French West Indies usually use fruit diameter and age in days to determine harvest date. However, they face problems of fruit ripening during transportation. The use of °Cd as an indicator may help to determine the optimum harvest date more accurately.