Growing Degree Day Targets for Fruit Development of Australian Mango Cultivars

Abstract

A forward estimate of mango (Mangifera indica L.) harvest timing is required for farm management (e.g., for organization of harvest labour and marketing). This forward estimate can be based on accumulated growing degree days (GDD) from an early stage of flowering to fruit harvest maturity, with fruit maturity judged on a destructive assessment of flesh colour and dry matter content. The current study was undertaken to improve GDD targets for Australian mango cultivars, to improve estimation of harvest maturity, and to document a methodology recommended for future work characterizing fruit maturation GDD for other mango cultivars. An alternate algorithm on GDD calculation involving use of a function that penalizes high temperatures as well as low temperatures was demonstrated to better predict harvest maturity in warmer climates. Across multiple locations and seasons, the required heat units (GDD, Tb = 12 °C, TB = 32 °C; where TB is upper base temperature of 32 °C and Tb is lower base temperature of 12 °C) to achieve maturity from asparagus stage of flowering was documented as 2185, 1728, and 1740 for the cultivars Keitt, Calypso and Honey Gold, respectively. GDD difference between the asparagus and two-thirds floral opening stages of flowering was 188 ± 18 for Calypso, 184 ± 12 for Honey Gold, 238 ± 21 for Keitt and 175 ± 10 for KP. Colour specifications for a colour card set suitable for maturity assessment of all cultivars was also proposed. A flesh colour harvest maturity card specification of 9 was proposed for the cultivar Honey Gold and 13 for the cultivar Keitt.

Management Information Systems for Tree Fruit–2: Design of a Mango Harvest Forecast Engine

“…Other approaches for harvest-load estimation use satellite-imagery-derived vegetation indices [15,16] and UAV-derived canopy structure attributes [8]. Our research group has reviewed each of these aspects, i.e., the forecast of harvest timing based on GDD [17] and/or DMC [18], the forecast of fruit number [3,19], and the forecast of fruit size at harvest [20].…”

“…GDD units for mango reproductive growth are typically calculated using the average of the daily minimum (Tm) and maximum (TM) temperatures, minus a minimum base temperature value (Tb). Amaral et al [17] implemented a set of equations (1 to 5) for the calculation of daily GDD, as proposed by Ometto [22], which involve a maximum base temperature value (TB). Working with Australian mango cultivars, the optimum Tb and TB was established to be 12 and 32 • C, respectively, and cumulative GDD targets were set for the fruit maturation of a suite of cultivars (Table 3).…”

“…While it is obvious that temperatures and thus GDD accumulation will vary regionally, temperatures can also vary across a given farm (Figure 1) as a function of farm geography. The development of low-cost remote monitoring technologies such as LoRa (Long Range radio) allows for multiple temperature recording stations to be maintained on a given farm [17].…”

“…where the variables represent the following: For the proposed harvest MIS, it is recommended that wireless temperature sensors be established according to Bureau of Meteorology specification (viz., enclosed in a white, slatted screen, mounted 1.5 m above grassed or mulched ground, and positioned at least 10 m from tall objects) in each geographic zone of the farm, with orchard blocks within those zones linked to the output of respective sensors in the MIS database. Data from these sensors should be collected at 15 min intervals [17] to support the measurement of Tm and TM. These records can be accumulated over the years to produce a historical record for each location.…”

“…DMC of fruit at harvest is strongly correlated to juice soluble solid content in the ripened fruit and thus, eating quality. The DMC level associated with harvest maturity will vary with growing condition but can be established via association with flesh color [17] (Figure 3).…”