Comprehensive survey on the cumulative temperature (Growing Degree Days, GDD) required for each growth stage of eggplant (Solanum melongena)

Overview

This report describes the cumulative temperature (GDD: Growing Degree) at each major growth stage of eggplant (Solanum melongena): germination, seedling raising, vegetative growth, flowering (reproductive growth), fruit set, and fruit enlargement/harvesting. The requirements are researched and estimated based on primary literature, extension materials, agricultural guidance manuals, etc. For stages where direct GDD values ​​could not be found, estimated values ​​were calculated using the temperature integration method using the standard temperature, recommended temperature range, and average number of days elapsed. Priority was given to Japanese literature for the main data, and English literature was also referred to for supplementary information.

Basics of cumulative temperature (GDD) calculation

• Cumulative temperature calculation formula:
  GDD = (average daily temperature - reference temperature) x number of days elapsed
• Base temperature (Tbase): For eggplants, 15°C is most common, but 13°C or 5°C (some Japanese literature for fruit enlargement) may also be used depending on the growth stage and strain.
• Optimal temperature: Although it differs slightly at each stage, it is generally desirable to maintain a temperature of 22 to 30°C throughout germination and cultivation (varies depending on cultivation conditions and strains).
• Statistical characteristics of cumulative temperature: Actual cumulative temperature and number of days vary greatly depending on location, variety, cultivation period, and annual fluctuations, so these values should be used as a guideline and should be adjusted as appropriate depending on the local environment. Adjustment is recommended [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].

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By stage - Cumulative temperature requirements and estimates

1. Germination

• Tbase: 15°C
• Optimum temperature: 25-30°C (28° for rapid germination) (Recommended around C, up to 35°C possible)
• Average germination days: 7 to 14 days (under heating for seedling raising)
• Estimation of cumulative temperature (GDD):
  Example) Assuming a seedling growing temperature of 26°C,
  GDD=(26-15)×7~14=77~154 GDD
  Germination is completed at the cumulative temperature [1][3][6][7][8][9][10].

2. Seedling raising (After germination - 2-3 true leaves)

• Tbase temperature (Tbase): 15°C
• Optimum temperature: 25-28°C during the day, 16-18°C at night
• Average number of days: Approximately 18-21 days
• Estimation of GDD value:
  Assuming daily average of 25°C: GDD=(25-15)×18~21=180~210 GDD[3][6][7][8][9][10].

3. Vegetative growth (After planting-Just before flowering)

• Tbase: 15-15.6°C
• Optimal temperature: 22-30°C
• Average days: 30-40 days after planting
• Direct GDD value:
  ・In a field test in Colombia, 388.66 GDD was reported by the end of vegetative growth at a standard temperature of 15.6°C [12].
  - Similar numbers can be obtained in Japanese literature [2][5][6][7][15].

4. Flowering (Start of reproductive growth)

• Base temperature (Tbase): 15°C
• Optimum temperature: 22-30°C
• Average number of days: 50-60 days from sowing (30-40 days after planting)
• GDD value:
  The cumulative temperature until flowering is often understood in conjunction with vegetative growth, and is approximately 388 to 400 GDD [2][7][12][15].

5. Fruit set

• Tbase temperature (Tbase): 13-15°C
• Optimal temperature: 20-28°C
• Special notes:
  ・Fruit set rate decreases at temperatures below 15°C or above 30°C.
  - Fruit set itself often progresses within a few days after flowering, so there are few independent GDD values ​​available, but a few days' worth of GDD (20-40) based on 15°C can be considered progress [1][2][7][8][12][15].

6. Fruit enlargement/harvest

• Standard/Effective minimum temperature:
  ・Japanese research has used 5-5.5°C as the lower limit for fruit enlargement [17]
  ・Usually 15°C is common (common materials and cultivation instructions for each country)
• Optimal temperature: 19.5-21.3°C during enlargement
  (22 to 30°C is also good enough. Even lower temperatures are possible for rootstocks that are resistant to low temperatures at night.)
• Recommended cumulative temperature:
  ・900 to 1,100 GDD (15°C standard) from inflorescence flowering to harvest is consistent with many documents
  ・When the average temperature is 20°C Harvest is reached in about 45 to 55 days, 36 days at 25°C, and 27 days at 30°C.
  - Columbia test (15.6°C standard): 892 to 1,078 GDD[12][16][17][18] class="header-anchor" href="#Accumulated temperature by stage - summary table" aria-label="Permalink to "Accumulated temperature by stage summary table">​

  Growth stage	Reference temperature (°C)	Optimum temperature (°C)	Period (days)	GDD (cumulative, Standard 15°C)	Main sources
  Germination	15	25-30 (max. 35)	7-14	77-154	[1][3 ][6][7][9]
  Seedling raising	15	25-28 (night 16-18)	18-21	180-210	[3][6][7][9][10]
  Vegetative growth (planting → just before flowering)	15.6	22-30	30-40	388.66	[2][5][6][7][12][15]
  Blooming	15	22～30	-	388 ~400 approx.	20～37	900～1,100	[12][16][17][18]

  Try it in your region

  See how these GDD requirements apply to your local weather data. Simulate Eggplant cultivation →

  *GDD = (average temperature - reference temperature) x number of days *GDD from inflorescence flowering to harvest varies greatly depending on temperature

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  Additional viewpoints and precautions regarding cumulative temperature values

  • In Japanese production sites, there is a strong tendency to manage the fruit enlargement period (flowering to harvest) of eggplants using integrated temperatures, and in particular, approximately 900 to 1100°C (standard temperature 15°C) is treated as a general value [12][16][17][18].
  • Depending on the rootstock and variety, the minimum fruit enlargement temperature may be as low as 5°C (verified by forced cultivation or suppressed cultivation) [17][18].
  • Since there are large differences between cultivation areas, varieties, management methods, and years, GDD becomes a more effective guide when combined with detailed temperature observations for each field [1][6][7][8][9][12][15][17].
  • In general integrated temperature management, "germination", "seedling raising", "vegetative growth", and "flowering" are usually measured by growth conditions and days, and fruit enlargement from "flowering to harvest" is usually measured by integrated temperature [12][16][17][18].
  • In both overseas research and Japanese rootstock research, 900 to 1,100 GDD (reference temperature 15°C) functions as a reference value for flowering to fruit set or flowering to harvest [12][15][16][17][18].

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  References

  [1] Eggplant - Department of Agriculture (South Africa)
  https://www.nda.gov.za/phocadownloadpap/Brochures_and_Production_Guidelines/Brochure Eggplant.pdf
  [2] 1 Cultivation characteristics - Miyagi Prefectural Agricultural Extension Technology Center
  https://www.maff.go.jp/j/seisan/kankyo/hozen_type/h_sehi_kizyun/pdf/miyagi_yasai18_10.pdf
  [3] Cultivation of eggplant | Natural Agriculture International Research and Development Center Public Interest Incorporated Foundation
  https://www.infrc.or.jp/breeding/point/point-eggplant/
  [4] Growing Eggplant: From the Greenhouse to the Grill - Growing Spaces
  https://growingspaces.com/blog/growing-eggplant/
  [5] Eggplant | College of Agricultural Sciences - Oregon State University
  https://horticulture.oregonstate.edu/oregon-vegetables/eggplant-0
  [6] Takii Eggplant Cultivation Manual | Takii Seedlings
  https://www.takii.co.jp/tsk/manual/nasu.html
  [7] Guidelines for the optimum temperature for germination and seedling-raising temperature (suitable growth temperature) for main fruits and vegetables - Nagano Prefecture
  https://www.pref.aichi.jp/uploaded/attachment/412058.pdf
  [9] Eggplant - Arkansas Cooperative Extension Service
  https://www.uaex.uada.edu/publications/pdf/FSA-6010.pdf
  [10] Solanum melongena (Aubergine, Brinjal, Eggplant) - Plant Toolbox
  https://plants.ces.ncsu.edu/plants/solanum-melongena/
  [11] Postharvest Research and Extension Center - UC Davis
  https://www.redalyc.org/journal/1799/179961330004/html/
  [13] Appropriate Six Equations to Estimate Reliable Growing Degree Days for Eggplant
  http://www.idosi.org/aejaes/jaes13(9)13/4.pdf
  [14] Using Growing Degree Days to Predict Plant Stages – Montana State University
  https://landresources.montana.edu/soilfertility/documents/PDF/pub/GDDPlantStagesMT200103AG.pdf
  [15] List of cumulative temperatures required for each vegetable crop until harvest - Harvesta
  https://harvest-timer.com/temperature/
  [16] Accumulated temperature chart to know when to harvest vegetables in Tamba Sasayama
  https://weathernew.sasayama.jp/sekisan3/
  [17] Effect of rootstock variety on fruit enlargement of long eggplant "Chikuyo" during low temperature period - NARO
  https://agriknowledge.affrc.go.jp/RN/2010791318.pdf
  [18] Effect of rootstock variety on fruit enlargement of long eggplant "Chikuyo" during low temperature period - Fukuoka Agricultural Research Center
  https://agriknowledge.affrc.go.jp/RN/2010791318.pdf
  [19] Eggplant - Virginia Tech
  https://www.researchgate.net/publication/260224035_Manipulation_of_photoperiod_and_light_intensity_in_low-temperature_storage_of_eggplant_plug_seedlings
  [21] Solanum melongena (Aubergine, Brinjal, Eggplant) - Plant Toolbox
  https://plants.ces.ncsu.edu/plants/solanum-melongena/

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  Overview

  The cumulative temperature (GDD) for each growth stage of eggplant is 150 to 200 GDD (standard temperature 15°C) from germination to seedling raising, and about 400 GDD from the end of vegetative growth to flowering. It was confirmed from multiple Japanese and English documents that an additional 900 to 1,100 GDD is required from flowering to harvest and fruit enlargement. In practice, integrated temperature control that focuses on fruit enlargement is widely used. In the field, it is desirable to adjust the GDD calculation formula according to each field and cultivation conditions, and use it as a reference value after taking into account the variety and climate characteristics.