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Cucurbit Genetics Cooperative Report 17:94-96 (article 28) 1994

Effect of Gamma-Radiation on vitality and Fertilization Ability of Cucumis melo and C. metuliferus Pollen

A. Beharav and Y. Cohen

Bar-Illan University, Dept. of Life Sciences, Ramat Gan 52900, ISRAEL

The mentor pollen technique can be applied to overcome crossing barriers in certain interspecific hybridization, where pollen tube growth is arrested before the ovary (4). Oost and Den Nijs (3) reported on mentor pollen as a tool in interspecific hybridization in Cucumis. Our observations (1) show that the nature of cross incompatibility between C. melo and C. metuliferus is prefertilization barrier. The use of such double pollinations with foreign pollen and irradiated maternal mentor pollen in crosses between the two species is being investigated to introduce valuable resistance genes from C. metuliferus into the C. melo. Knowledge of the behavior of irradiated pollen may be useful for the application of the mentor pollen technique. The influence of Gamma-radiation on in vitro germination, pollen tube growth and on in vivo fertilization of C. melo, were evaluated ion the present study.

Determination of pollen tube growth after Gamma-radiation: Freshly harvested male flowers were irradiated with a caesium source. The dose rate was 0.473 Krad per min. The flowers were placed in a closed glass vial within 250 ml erlenmial icetin. Doses of 100, 150 and 200 Krad (100 Krad = IK Gray) were given. Pollen from irradiated and non-irradiated flowers was germinated in vitro on a substrate composed of 2-% sucrose, 20 ppm boric acid and 1% agar in the dark at 25+1 ˚ C, a modification of the procedure which was described by Van Den Boom and Den Nijs (6). Germination percentage and mean pollen tube length from 2 cultivars of C. melo ('Vedranrais' and 'Chartentais') and 3 accessions of C. metuliferus (PI 292 190 So/1,2 and 5) were determined under a light microscope after incubation for 120 min. A pollen grain was considered to have germinated when tube length at least equaled the grain diameter. The mean genotype effect was regarded as 'block' in the analysis of variance for pollen tube length, while the various tubes were regarded as samples.

Determination of C. melo pollen vitality in vivo after gamma-radiation: Anthers with pollen from the nonmoecious line PI 12411F were collected in the morning from fresh male flowers and irradiated with 100, 150 and 200 Krad gamma-rays. The flowers were kept overnight at 5 ˚ C. Pollination was carried out the next morning. Fruit and seed set of the genoecious line 'Gylan' E6/10 following pollination with non-irradiated or irradiated pollen were determined.

Radiation with 100 Krad did not have an effect whereas a dose of 150 Krad had only a limited, though significant, effect on the germination of the C. melo pollen. A dose of 200 Krad decreased the germination percentage by 35% (compared with the control). In contrast, the mean pollen tube length was already reduced in accordance with the dose radiation, by a radiation dose of 100 Krad. The germination of C. metuliferus appeared to be much less sensitive to gamma-rays. A 100 Krad radiation dose had no effect on the germination percentage, while a dose of 200 Krad decreased the germination percentage by only 14%. The mean tube length was not influenced by the radiation, even by a dose of 200 Krad. This is in agreement with Van Den Boom and Den Nijs (6).

Effect of gamma-radiation on the behavior of C. melo pollen in vivo: Fruit set of the genoecious line 'Gylan' E6/10 was reduced by increased radiation dose of pollen from the monoecious line PI 12411F (Table 2). After pollination with 200 Krad-irradiated pollen, only 1 out of 3 pollinated flowers set fruit, which stopped developing after a few days. This is in accordance with the high decrease of pollen vitality in vitro of this dose (Table 1) . Fruit weight was also decreased in accordance with the radiation dose (unpublished data).

All seeds obtained after pollination with irradiated pollen were flat and devoid of embryo ['pseudo-fertilization'(2)].

The competition for ovules between irradiated and non-irradiated pollen is a major problem in the mentor pollen technique (5). When simultaneously applied, the irradiated maternal pollen probably grows faster down the style than the pollen of the foreign species, and thus has the opportunity to occupy many ovules. Therefore, it is necessary to irradiate the mentor pollen at a dose that is high enough to eliminate this competition but low enough to stimulate fruit set (6). Our results about in vitro germination and pollen tube growth of C. melo and C. metuliferus and in vivo fertilization of C. melo indicate that an irradiation dose of 100-150 Krad appeared to be suitable for the C, melo pollen when used as the maternal mentor pollen, while a dose of 200 Krad could be suitable for the C. metuliferus pollen when this species is used as the maternal mentor pollen.

Table 1. Effect of gamma-radiation on the in vitro germination and pollen tube length of Cucumis melo and C. metuliferus.

Dose in Krad
C. melo
C. metuliferus
Germination percentagez
Pollen tube length ( μ m)y
Germination percentagez
Pollen tube length ( μ m)y
0
96 ax
293 aw
84 a
403 a
100
95 a
259 ab
80 ab
416 a
150
89 b
227 bc
200
62 c
192 c
72 b
413 a

zPercentage from 345 and 178 pollen grains of 2 cultivars of C. melo and 3 lines of C. metuliferus, respectively.
y Mean from 89 and 69 pollen tubes of 2 cultivars of C. melo and 3 lines of C. metuliferus, respectively.
x Percentage separation in columns by Chi square test, 5% level.
w Mean separation in columns by z

Table 2. Fruit and seed set following pollination of Cucumis melo line 'Gylan' E6/10 with non-irradiated or irradiated pollen of line PI 124111F.

Dose in Krad
Germination pollinations
Number of fruits
0
11
10
100
3
3z
150
3
2z
200
3
1y

zAll seeds were flat and empty (samples of 50 seeds per fruit).
y Stopped developing after a few days.

Literature Cited

  1. Beharav, A. and Y. Cohen. 1993. The crossability of Cucumis melo and C. metuliferus, and investigation of in vivo pollen tube growth. Cucurbit Genet. Coop. Rpt. 17:97-100.
  2. Grant, J.E., K.K. Pandey, and E.G. Williams. 1980. Pollen nuclei after ionizing irradiation for egg transformation in Nicotiana. N.Z.J. Bot. 18:339-341.
  3. Oost, E.H. and A.P.M. Den Nijs, 1979. Mentor pollen as a tool in interspecific hybridization in Cucumis. Cucurbit Genet. Coop. Rpt. 2:43-44.
  4. Stettler, R.F. 1968. Irradiated mentor pollen: in use in remote hybridization of black cottonwood. Nature 219-746-747.
  5. Stettler, R.F. and R.P. Guries. 1976. The mentor pollen phenomenon in black cottonwood. Can. J. Bot. 54:820-823.
  6. Van Den Boom, J,M,A, and A.P.M. Den Nijs. 1983. Effect of gamma-radiation on vitality and competitive ability of Cucumis pollen. Euphytica 32:677-684.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
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