Cucurbit Genetics Cooperative Report 6:20-22 (article 10) 1983
A.P.M. den Nijs
Institute for Horticultural Plant Breeding, P. O. Box 16, Wageningen, The Netherlands
Competition of two types of pollen for the available ovules impedes the success of mentor pollen aiding interspecific crosses in cucumber (2). Mixed pollinations such as those involving mentor pollen are only feasible if pollen can be collected from the anthers in reasonable quantity in order to be mixed. The very sticky pollen of cucumber does not permit this. Therefore, we simulate mixed pollination by applying pollen from a staminate flower of each of the two pollen parents to the same pistillate flower. We realize that we can hardly control the relative amounts of pollen in this way. Moreover, the order in which the two types of pollen are applied influences the outcome of the competition as was shown by differences in segregation for marker genes following double pollinations involving seedling marker lines in apple and cucumber (4, 1).
Application of different pollen types on separate lobes of the stigma could possibly substitute for our poor simulation of the mixed pollination technique for intraspecific pollen competition studies. The small experiment described here was prompted by Robinson’s (3) suggestion that pollen tubes of cucumber do not always grow straight downwards, but exhibit some lateral growth, fertilizing ovules in locules not directly below the pollinated stigmatic lobe.
Eleven pistillate flowers of a glabrous breeding line (gl gl) were pollinated with both self pollen (gl) and that from a gynoecious standard line G6 (Gl) (following silver thiosulfate treatment). Each of the three stigmatic lobes of every flower was pollinated separately by one staminate flower of either of the two lines, mainly on the apical tip and outer side of the lobe. A small marking on the ovary with a felt-tip pen ensured later identification of the lobes. The mark expanded with growth but remained clearly visible and it apparently did not harm the fruit. Of six flowers, two lobes of each received Gl pollen and one lobe received gl pollen (A-type). For five additional flowers this was reversed (B-type). Three fruits of each type of cross set well. At harvest, the three locules of each fruit were separated and transversely cut into three segments of equal length for seed processing. The resulting nine seed lots per fruit were sown and seedlings scored for glabrousness. Results given in Table 1 are combined for all three fruits per type of cross.
This type of double pollination resulted in normal fruit and seed set. The numbers of seeds per locule were also approximately equal. The percentage of glabrous offspring per type of cross reflected fairly closely the relative amounts of pollen applied: 21% following 2:1 treatment in type B (33% expected); 57% following 1:2 treatment in type B (67% expected). Between locules there were no differences in percentage of glabrous offspring. This is also true for separate locule segments in the B-type of cross. In the A-type the variation between locule segments is larger, but it is inconsistent. The partly aberrant frequencies in the third segments are based on very small seed numbers and are not considered.
These preliminary data indicate that pollen tubes of either type grew in equal frequency into each of the three locules irrespective of the lobe on which the pollen was deposited. This implies much more lateral growth of pollen tubes than Robinson (3) concluded earlier. I conclude that this type of double pollination has potential use in pollen competition studies.
Table 1. Percentage of glabrous offspring per locule segment (number of seedlings measured) following double pollinations.
A. glgl x (2 Gl + 1 gl) |
Fruit locule / pollinated with |
||
Fruit segment |
I / Gl |
II / Gl |
III / gl |
| Blossom end | 18 (69) | 27 (83) | 23 (103) |
| Middle | 16 (74) | 17 (105) | 25 (84) |
| Peduncle end | 22 ( 9) | 0 ( 9) | 9 (21) |
| Mean (total) | 19 (152) | 20 (197) | 19 (208) |
B. glgl x (2 gl + 1 Gl) |
I / gl |
II/ gl |
III/ Gl |
| Blossom end | 53 (86) | 58 (88) | 59 (86) |
| Middle | 56 (78) | 57 (88) | 55 (93) |
| Peduncle end | 83 ( 6) | 85 (13) | 64 (11) |
| Mean (total) | 55 (170) | 59 (189) | 57 (190) |
Literature Cited
- Boom, A. v.d., 1982. Mentor pollen and pollen competition in cucumber. Student report. Agricultural University, Wageningen.
- Nijs, A.P.M. den and E. H. Oost. 1980. Effect of mentor pollen on pistil-pollen incongruities among species of Cucumis L. Euphytica 29:267–271.
- Robinson, R. W. and D. F. Heffernan. 1980. Pollen receptivity of different areas of the stigma in cucumber. Cucurbit Genetics Coop. Rpt. 3:25.
- Visser, T. and J. J. Verhaegh. 1980. Pollen and pollination experiments. II. The influence of the first pollination on the effectiveness of the second one in apple. Euphytica 29:385–390.