Cucurbit Genetics Cooperative Report 4:56-57 (article 29) 1981

Species Crosses Under Controlled Temperature Conditions

Y. O. Kho, J. Franken and A. P. M. den Nijs

Institute for Horticultural Plant Breeding, P. O. Box 16, Wageningen, The Netherlands

Pollen tube behavior and fertilization in selected crosses between species of Cucumis were studied at different temperatures in glasshouses of the I. V. T. phytotron in the summer season of 1980. This investigation follows the large scale crossability program reported earlier (1). Plants were grown in plastic containers, as this improved flowering. The following cross pollinations were carried out at 20, 23, and 26°C constant: Cucumis sativus (Gbn 1811) x respectively C. melo cv. Gulfstream, C. ficifolius (Gbn 1729) and two accessions of C. metuliferus (Gbn 0164 an Gbn 1802); and C. metuliferus (Gbn 0164 and Gbn 1802) x respectively C. melo cv. Gulfstream and C. sativus (Gbn 1811). For the crosses C. ficifolius (Gbn 1729) x respectively C. sativus (Gbn 1811) and C. melo cv. Gulfstream, pollinations were also made at 17°C constant. Pollen tube growth was examined in vivo by UV microscopy three days after pollination. Fruits were dissected and checked for possible ovule and embryo development, using a binocular microscope.

In general, the pollinations under controlled temperature conditions in the phytotron did not give better results that earlier work in the glasshouse as far as pollen tube growth is concerned. However, to some extent a temperature effect could be noted for three parental combinations which are listed in Table 1. 26°C proved beneficial for pollination and fertilization in C. metuliferus x C. melo. Four fruits were obtained, containing seeds of different size. Globular and heart shape embryos were found in one fruit only. Placed on an agar medium, some embryos developed cotyledons but no growing point. The same cross involving a different accession of C. metuliferus did not reveal any temperature dependence. It may, therefore, be rewarding to test many accessions of C. metuliferus for their crossability in crosses with C. melo.

A temperature effect also appeared to exist for the pollinations on C. ficifolius (Table 1). One fruit was obtained at 20°C following pollination with C. sativus and five and three fruits respectively at 20 and 23°C when C. melo cv. Gulfstream used as pollen parent. The fruits, harvested about five weeks after pollination, only contained seeds without an embryo. The structure of the tissues found in the embryo sacs could often not be determined. Perhaps these seeds were too old, as fruits harvested two weeks after pollination in the cross C. ficifolius x C. melo contained seeds with a small embryo (0.05 mm). These embryos did not develop further when put on an agar medium; larger scale experiments are necessary to decide whether such embryos may or may not be cultured on plantlets.

Table 1. Temperature effect on pollen tube growth and fertilization of 4 different species crosses in Cucumis L.

Cross combination	Temp (°C)	Number pollinations	No. fruit used for UV tests	Pollen tubes in	Remarks
C. metuliferus (Gbn 0164) x C. melo cv Gulfstream	20	16	4	style	no fruit set
	23	19	6	style	no fruit set
	26	21	5	ovary	fruits with small globular embryos
C. metuliferus (Gbn 1802) x C. melo cv Gulfstream	20	31	10	style	no fruit set
	23	29	9	style	no fruit set
	26	28	12	style	no fruit set
C. ficifolius (Gbn 1729) x C. sativus (Gbn 1811)	17	15	10	ovary	no fruit set
	20	57	19	ovary (micropyle)*	one fruit; not determinable tissues in seeds
	23	49	19	ovary	no fruit set
	26	29	18	style (ovary)	no fruit set
C. ficifolius (Gbn 1729) x C. melo cv Gulfstream	17	17	10	stigma (style)	no fruit set
	20	58	16	style (ovary)	fruits with determinable tissues in seeds; small embryos in seeds of 14 days old fruits
	23	40	17	micropyle	fruits with determinable tissues in seeds; small embryos in seeds of 14 days old fruits
	26	22	12	ovary	no fruit set

*(...) a few pollen tubes.

 

Literature Cited

1. Kho, Y. O., A. P. M. den Nijs and J. Franken. 1980. Interspecific hybridization in Cucumis L. II. The crossability of species, an investigation of in vivo pollen tube growth and seed set. Euphytica 29:661-672.