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Cucurbit Genetics Cooperative Report 19:47-48? (article 17) 1996

Phenylurea Cytokinin (CPPU) More Effective than 6-Penzyladenine in Promoting Fruit Set and Inducing Parthenocarpy in Melon

J. Brent Loy and Peter C. Allen

Department of Plant Biology, University of New Hampshire, Durham, NH 03824

The cytokinin N6 -benzyladenine (BA) promotes fruit set in hand-pollinated melons (3). Because fruit set in hand-pollinated melons is often low, many breeders have adopted the use of BA to enhance fruit set. In our program 200 ppm BA is conveniently applied in a lanolin-water paste (7:3) to the base of ovaries with a disposable syringe (minus needle). Hayata et al. (3) reported that 200 ppm of the synthetic cytokinin, 1-(2-chloro-4-pyridyl)-3phenylurea (CPPU), increased fruit set in watermelon from 26.9%to 95%. the same concentration of CPPU also induced parthenocarpy in 89.5% of treated fruit. Likewise, in an earlier report, Hayata et al. (2) found that CPPU enhanced fruit set in melon. In the present study we compared the effects of CPPU and BA on fruit set and parthenocarpy in melon, cv. Delicious 51.

Delicious 51 seeds were sown in Jiffy mix in 50 plug trays in Jan 1995. Seedlings were transplanted into 21.6 x 21.6 cm (dia./ht.) pots (#6000 XL nursery pots, Nursery Supply, Inc.) on 10 Feb and grown in groundbeds in a greenhouse 27 C day and 17 C night). Plants were vertically trellised, pruned to one central leader, and lower laterals were removed. For the first experiment there were 18 replications of the following treatments: (1) control (pollination + lanolin), (2) pollination + BA (200 ppm), (3) pollination + CPPU (200 ppm), (4) no pollination + BA, (5) no pollination + CPPU. For all hand pollinations, anthers were carefully emasculated just prior to applying pollen.

Growth regulators were applied in a lanolin water paste (7:3). BA (10 mg) was dissolved in 2 ml 0.1 N KOH and then bought up to 15 ml distilled water. CPPU (10 mg) was solubilized in 1.5 ml dimethylsulfoxide (DMSO) and brought up to 15 ml distilled water. The 15 ml aliquots were each added to 35 ml lanolin paste and stirred vigorously to form uniform lanolin paste emulsions. The emulsions were loaded into 3 ml disposable syringes (minus needles) for treatment applications to the base of ovaries of pollinated flowers. A ring of approximately 0.05 ml was applied to each ovary. Treatments began on 6 April and were completed on 19 April. During most pollination days, complete sets of treatments were made. Following fruit harvest, seeds were removed, and if less than 100 viable (well filled) seeds per fruit was indicated, seeds were counted. Seed viability was confirmed directly by germination tests.

In spite of the seemingly favorable growth conditions and weather during pollination, no fruits set with the control treatment. Both cytokinin enhanced fruit set with 14 out of 18 (77.7%) set with BA+ pollination and all fruits set with CPPU + pollination. Without pollination, 44% of the BA-treated flowers set fruit. Although both hormones markedly stimulated fruit set, seed set or fill was low in many of the pollinated fruits (Table 1), presumably reflecting the apparently unfavorable conditions for fruit set and/or pollen viability. Because of the small sample size, it is not possible to ascertain if seed set was significantly different between the BA and CPPU treatments.

One concern that BA was solubilized in KOH, whereas CPPU was solubilized in dimethylsulfoxide (DMSO), a solvent known to increase the absorption of chemicals through biological membranes (4). Therefore, we cannot rule out that the greater effectiveness of CPPU was due to increased absorption. Secondly, it is possible that higher concentrations of BA would elicit the same response as 200 ppm of CPPU. Previous studies (Zack and Loy, unpublished) with higher concentrations of BA suggest that this is not the case, but in view of our current findings, this aspect needs to be reinvestigated. In a second experiment we compared fruit set with pollination and with or without lanolin application. With lanolin, 6 of 15 flowers set fruit; without lanolin, 7 of 15 flowers set fruit, indicating that lanolin neither stimulated nor inhibited fruit set.

Because of its strong propensity to induce parthenocarpy in melons, we cannot wholeheartedly endorse CPPU treatment in a breeding program without further seed set data. Overall, however, we have been more satisfied with out pollination results with CPPU than with BA, especially in lines that exhibit poor fruit set with hand pollination.

Table 1. Counts of filled seed in pollinated and unpollinated (NP) melon fruits.

Treatments
Fruit examinedz
No. seed
1-20 seed
20-100 seed
100+ seed
Control
0
-
-
-
-
BA
4
-
2
2
-
CPPU
13
3
2
3
5
BA-NP
7
7
-
-
-
CPPU-NP
18
17
1 (3 seed)
-
-

zSeed data for 10 fruit from BA+ pollination treatment and 5 fruit from CPPU + pollination treatment were not recorded, but fruit appeared to have mostly well-filled seed.

Literature Cited

  1. Hayata, Y., Y. Niimi, R. Isoda, and K. Makita. 1990. Effect of cytokinin on the fruit setting and sugar accumulation of melon fruit. Abstr. Jpn. Soc. Hort. Sci. Spring Meeting 59:178-179.
  2. Hayata, Y., Y. Niimi, and N. Iwasaki. 1995. Synthetic cytokinin--1- (2-chloro-4-pyridyl)-3-phenylurea (CPPU)--promotes fruit set and induces parthenocarpy in watermelon. J. Amer. Soc. Hort. Sci. 120-997-1000.
  3. Jones. C.M. 1965. Effects of benzyladenine on fruit set in muskmelon. Amer. Soc. Hort. Sci. 87-335-340.
  4. Norris, L.A. and V.H. Freed. 1963. dimethyl sulfoxide as an absorption and translocation aid. Western Weed Control Conf., Res. Prog. Rpt., pp. 85-86.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 15 December, 2009