Reproductive Patterns of Three Melon Cultivars in Response to Temperature Accumulation

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Cucurbit Genetics Cooperative Report 14:61-62 (article 23) 1991

James R. Dunlap, Stephen J. Maas
Texas Agricultural Experiment Station, Weslaco, Texas; USDA-ARS, Subtropical Agricultural Research Laboratory, Weslaco, Texas

Patterns of reproductive development in plants are partially controlled by the temperature experienced during growth. The correlation is sufficient that heat-unit accumulation has been used to model the initiation and maturation of reproductive structures for major agronomic crops (3, 4). Perry and Wehner (5) recently developed a heat-unit model to predict fruit maturity for cucumber cultivars. Similar information is of great value to the melon industry where cuiltivar maturities are used as part of the production strategy. Phenotypic responses unique to individual melon cultivars have already been observed for seed germination and plant growth rates (1,2). Therefore, a study was established to obtain preliminary information of flowering and fruit maturity patterns in melojn (Cucumis melo L. reticulatus) as affected by cultivar and growing temperature.

Methods. Two field plantings of 3 commercial melon cultivars were established in February and March, respectively,. Plots were direct-seeded into 155 cm raised beds with approximately 20 cm between plants within a row. Plots were cultured according to commercial recommendations. Fully open female flowers were tagged each morning and the fruit followed to harvest. Fruit were harvested daily at full slip. Temperatures were monitored at 2-4 cm below the soil surface and at 1 m above ground using thermistors and a Campbell CR-21 data logger. The accumulated degree-days were computed by summing the differences between air or soil temperature and a base temperature of 10C.

Results. The results of this inital study are summarizedin Table 1. There was no difference in the mean flowering date for all cultivars in the early planting. Only two days separated the earliest and latest maturing cultivar. Despite warmer growing temperatures in the later planting, fruit maturity was 3 to 4 days later in all cultivars. However, the accumulated degree-days increased by more than 200 for each cultivar. The days from seeding to flowering also remained constant at approximately 50 to 56 days and appeared unrelated to increasing degree-days. The air and soil temperature were highly correlated with an R2 of 0.85. Using soil temperatures to compute accumulated degree-days did not improve the relationship with fruit maturity.

The lack of relationship between cultivar fruit maturity and temperature was unexpected. However, fruit size is generally smaller for early planted melon cultivars. The primary effect of temperature may be on fruit size rather than maturity. Our initial observations also indicate that the distribution of female flowering and fruit set may be responsive to increasing temperatures. The small sampling of cultivars and single-season data set may contribute to the absence of any clear growth relationship to temperature. Additional studies are planned for succeeding years to construct and validate a heat-unit model for predicting melon maturity by cultivar.

Table 1. The time (mean Julian day) and sum of growing degree-days. (SGDD) required for maturity of three melon cultivars established on two different dates in the Texas Lower Rio Grande Valley.

Planting Date

Cultivar

Flowering

Harvest

SGDD (0C)

Maturity (days)
February 2 Laguna 85 123 573 38
(Julian 33) Easy Rider 85 124 585 39
Durango 85 125 585 40
March 8 117 158 775 41
(Julian 67) Easy Rider 123 166 831 43
Durango 123 166 831 43

Literature Cited

  1. Dunlap, J.R. 1986. Influence of soil temperature on the early growth of three muskmelon cultivars. Scientia Horticulturae 29:221-228.
  2. Dunlap. J.R. 1988. Effects of temperature and water potential on the germination of muskmelon cultivars. Ann. Appl. Biol. 112:187-194.
  3. Maas, S.J. 1990. Combined model of plant canopy growth and reflectance for cotton. Agron. Abstr., p. 18
  4. Maas, S.J. 1991. GRAMI: A crop growth model that can use remotely sensed information. USDA Technical Bulletin (In press).
  5. Perry, K.B. and T.C. Wehner, 1990. Prediction of cucumber harvest date using a heat unit model. HortScience 25:405-406.