The Importance of Cultural Practices in Materializing Yield Potential in a Tetraploid Watermelon Cultivar

admin

Cucurbit Genetics Cooperative Report 6:59-61 (article 30) 1983

Z. Karchi, H. Nerson, H. S. Paris, M. Edelstein and A. Govers
Division of Vegetable Crops, Agricultural Research Organization, Newe Ya’ar Experiment Station, P. O. Haifa, Israel

Breeding programs in watermelons are undertaken to improve one or more characteristics. Sometimes the process results in genotypes that differ dramatically from existing cultivars. However, new developments are usually tested under prevailing cultural practices. The net result of this procedure is often to the detriment of the new genotype. The more revolutionary the genotype, the less likely it will manifest its full potential under existing cultural practices. One way of solving the problem would be to develop cultural practices better suited to the newly developed genotype.

A prime example would be the case of the polyploids. The use of triploids has been emphasized (3, 6, 7, 8) because of their seedlessness, high quality, higher yields as compared with tetraploids, and protection of the product. Despite all their merits, triploids are still regarded as a novelty crop grown mostly in home gardens. Inherent difficulties in seed production, resulting in a high cost of seeds, and in cultural practices prevented the widespread distribution of triploid watermelons. Although tetraploids tend to have smaller fruits than their corresponding diploids (3), they in some cases excel in fruit quality as compared with diploids (1, 4) and have better germination than triploids (6). Seed yields and adaptation of tetraploids can be improved over time (1, 2). Needless to say, the cost of tetraploid seed production is lower than that of triploids, and allows consideration of a large scale commercial crop.

The tetraploid cultivar ‘Alena’, which was developed from the diploid ‘Sugar Baby’ (4), was released after several years of testing under various cultural practices (5). When grown using traditional practices, ‘Alena’ exhibited underdeveloped vegetative growth, resulting in low yields of small fruits. A study was undertaken to compare some vegetative characteristics of ‘Sugar Baby’ and ‘Alena’. Five plants of each cultivar were grown at Newe Ya’ar from a late April seeding with spacing 1.0 m in the row and 2.0 m between rows; plants were grown under traditional cultural practices. Number of side branches, total number of nodes on the main stem and side branches, and length of branches were observed and recorded. The study terminated at the date of opening of the first female flower. ‘Alena’ flowered 20 days later than ‘Sugar Baby’. At the time of flowering, ‘Alena’ plants were appreciably smaller than those of ‘Sugar Baby’, having half the number of side branches, 65% the number of nodes, and half the total lengths of main stem plus side branches. This indicates that ‘Alena’ needs a stimulating treatment to increase the rate and volume of vegetative development prior to flowering.

Accordingly, two experiments were conducted at Newe Ya’ar in spring 1981 to compare the performance of ‘Alena’ and ‘Sugar Baby’ under two cultural regimes, the first using traditional watermelon cultural practices (“Sugar Baby Regime”) and the second using practices which were expected to enhance the vegetative development of ‘Alena’ (“Alena Regime”). The experiments were planted side-by-side and received at the time of seedbed preparation a basic dressing of 61.75 kg P/ha placed under the rows, and 158 kg N/ha incorporated into the beds. The Sugar Baby Regime received no additional top-dressing, whereas the Alena Regime consisted of a top-dressing of 49.4 kg/ha of 20-20-20 plus trace elements applied at the 4-leaf stage and 29.64 kg N/ha applied at the onset of fruit set. Irrigation was by the drip method at weekly intervals according to evaporation from pans, from the onset of fruit development to the first signs of fruit maturity. In accordance with the late ripening of ‘Alena’, the Alena Regime included two more weekly irrigations than the Sugar Baby Regime. The experiments were laid out on elevated beds in adjacent plots in a randomized block design with four replicates using a population of 24,700 plants/ha, spaced in pairs at 40 cm in the row and 2.0 m between the rows.

The results presented in Table 1 demonstrate that ‘Alena’ can give satisfactory yields, equal to those of ‘Sugar Baby’, on the condition that it is provided with an intensive fertilization and irrigation regime. The Alena Regime was recommended to farmers as a guide for growing ‘Alena’ in Israel (5), and yields of high quality fruits ranging from 49–79 tons/ha were obtained with this regime. Thus, designing cultural practices according to the characteristics and mode of development of ‘Alena’ brought about the commercial utilization of this cultivar in Israel.

Table 1. Effect of the two fertilization and irrigation regimes on yield and yield components of Alena and Sugar Baby.
Regime Yield/100 m2 (kg) Fruits/plant Fruit weight (g)
Sugar Baby Regime
     Sugar Baby 641** 1.07** 2240**
     Alena 386 0.91 1640
Alena Regime
     Sugar Baby 581 0.98 2120
     Alena 585 ns 1.02 ns 2137 ns
**Significant at 1% level; ns = not significant.

Literature Cited

  1. Andrus, C. F., V. S. Seshadri, and P. C. Grimball. 1971. Production of seedless watermelons. U.S.D.A. Tech. Bull. 1425. 12 pp.
  2. Eigsti, O. J. 1978. Reproducing a colchi-autotetraploid through twenty generations. Genetics 88 supplement: s24 (Abstr.).
  3. Henderson, W. R. 1977. Effect of cultivar, polyploidy and “reciprocal” hybridization on characters important in breeding triploid seedless watermelon hybrids. J. Am. Soc. Hort. Sci. 102:293–297.
  4. Karchi, Z., A. Govers and H. Nerson. 1981. ‘Alena’ watermelon. HortScience 16:573.
  5. Karchi, Z., H. Nerson, A. Govers, and Y. Neubauer. 1981. Hanhayyot le-giddul ha-avtiah Alena. [Instructions for growing ‘Alena’ watermelon.] Hassadeh 61:1126–1128, 1132 (in Hebrew).
  6. Kirhara, H. 1951. Triploid watermelons. Proc. Am. Soc. Hort. Sci. 58:217–230.
  7. Shimotsuma, M. 1961. A survey of seedless watermelon breeding in Japan. Seiken Ziho 12:75–84.
  8. Wall, J. R. 1960. Use of marker genes in producing triploid watermelon. Proc. Am. Soc. Hort. Sci. 76:577–581.

Contribution No. 652-E, 1983 series, from the Agricultural Research Organization, Bet Dagan, Israel.