Growing Degree Day Targets for Fruit Development of Australian Mango Cultivars II Harvest Windows

Forecasting the mango harvest window from flowering aids cultivar selection and harvest planning. This study evaluated the cross-site and cross-season generalizability of accumulated growing degree days (GDD) calculated using either a lower base temperature (Tb) alone or both lower and upper temperature thresholds (Tb and TB), relative to calendar days, for Australian mango cultivars. Operational values of Tb = 12 °C and TB = 32 °C were recommended for all assessed cultivars. The coefficient of variation across site-season populations for calendar days, GDD calculated using Tb alone, and GDD calculated using both Tb and TB was 13.5%, 2.5%, and 1.3%, respectively, confirming the robustness of the bounded GDD estimate across growing environments. Cultivar-specific GDD values associated with minimum and maximum fruit maturity were established using two complementary approaches. The first was based on ripening time (GDDr), with time-to-ripen at 20 °C durations of 12 and 6 days used to define lower and upper maturity boundaries (minGDDr and maxGDDr). The second was based on internal attributes at harvest (GDDi), including flesh color, dry matter (DM), soluble solids concentration (SSC), titratable acidity (TA), and flesh firmness. Minimum maturity was based on cultivar-specific flesh-color and DM targets and an SSC:TA criterion of 7.0. The mean firmness of cohorts at maxGDDr ranged from 2.2 to 3.6 kgf; a 3 kgf individual-fruit benchmark was therefore used for maxGDDi assessment. There was close agreement between GDDr and GDDi estimates of minimum maturity. The average of minGDDr and minGDDi for ‘B74’, ‘Honey Gold’, and ‘Keitt’ differed from previously published preliminary values by only 9–13 °C d, equivalent to approximately one calendar day, while values for ‘Nam Dok Mai’, ‘1201’, and ‘4069’ had not previously been estimated. Overall, minGDD values were established for nine cultivars, while complete harvest windows were resolved within the current study for four. For the remaining five cultivars, upper-boundary estimates were based on a single assessment approach, legacy observations, or remained unresolved.